U.S. patent application number 14/064981 was filed with the patent office on 2014-05-01 for scintillation crystal including a rare earth halide, and a radiation detection apparatus including the scintillation crystal.
The applicant listed for this patent is Pieter Dorenbos, Karl W. Kramer, Peter R. Menge, Vladimir Ouspenski. Invention is credited to Pieter Dorenbos, Karl W. Kramer, Peter R. Menge, Vladimir Ouspenski.
Application Number | 20140117242 14/064981 |
Document ID | / |
Family ID | 50545396 |
Filed Date | 2014-05-01 |
United States Patent
Application |
20140117242 |
Kind Code |
A1 |
Dorenbos; Pieter ; et
al. |
May 1, 2014 |
SCINTILLATION CRYSTAL INCLUDING A RARE EARTH HALIDE, AND A
RADIATION DETECTION APPARATUS INCLUDING THE SCINTILLATION
CRYSTAL
Abstract
A scintillation crystal can include Ln.sub.(1-y)RE.sub.yX.sub.3,
wherein Ln represents a rare earth element, RE represents a
different rare earth element, y has a value in a range of 0 to 1,
and X represents a halogen. In an embodiment, the scintillation
crystal is doped with a Group 1 element, a Group 2 element, or a
mixture thereof, and the scintillation crystal is formed from a
melt having a concentration of such elements or mixture thereof of
at least approximately 0.02 wt. %. In another embodiment, the
scintillation crystal can have unexpectedly improved
proportionality and unexpectedly improved energy resolution
properties. In a further embodiment, a radiation detection
apparatus can include the scintillation crystal, a photosensor, and
an electronics device. Such a radiation detection apparatus can be
useful in a variety of applications.
Inventors: |
Dorenbos; Pieter; (GM
Rijswijk, NL) ; Menge; Peter R.; (Novelty, OH)
; Ouspenski; Vladimir; (Saint-Pierre les Nemours, FR)
; Kramer; Karl W.; (Berne, CH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Dorenbos; Pieter
Menge; Peter R.
Ouspenski; Vladimir
Kramer; Karl W. |
GM Rijswijk
Novelty
Saint-Pierre les Nemours
Berne |
OH |
NL
US
FR
CH |
|
|
Family ID: |
50545396 |
Appl. No.: |
14/064981 |
Filed: |
October 28, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61719405 |
Oct 28, 2012 |
|
|
|
Current U.S.
Class: |
250/361R ;
252/301.4H |
Current CPC
Class: |
C09K 11/7773 20130101;
G01T 1/2023 20130101; G21K 4/00 20130101; C09K 11/7772 20130101;
G21K 2004/06 20130101; G01T 1/2006 20130101 |
Class at
Publication: |
250/361.R ;
252/301.4H |
International
Class: |
G01T 1/202 20060101
G01T001/202; G01T 1/20 20060101 G01T001/20 |
Claims
1. A scintillation crystal comprising:
Ln.sub.(1-y)RE.sub.yX.sub.3:Me, wherein: Ln represents a rare earth
element; RE represents a different rare earth element; y has a
value in a range of 0 to 1; X represents a halogen; Me represents a
Group 1 element, a Group 2 element, or any mixture thereof; and the
scintillation crystal is formed from a melt having a Me
concentration of at least approximately 0.02 wt. %.
2. A radiation detection apparatus comprising: a scintillation
crystal including Ln.sub.(1-y)RE.sub.yX.sub.3:Me, wherein: Ln
represents a rare earth element; RE represents a different rare
earth element; y has a value in a range of 0 to 1; X represents a
halogen; Me represents a Group 1 element, a Group 2 element, or any
mixture thereof; and the scintillation crystal is formed from a
melt having a Me concentration of at least approximately 0.02 wt.
%; and a photosensor optically coupled to the scintillation
crystal.
3. A scintillation crystal comprising: a rare earth halide,
wherein: for a radiation energy range of 11 keV to 30 keV, the
scintillation crystal has an nPR.sub.dev average of no greater than
approximately 8.0%; or for a radiation energy range of 30 keV to 60
keV, the scintillation crystal has the nPR.sub.dev average of no
greater than approximately 3.6%.
4. The scintillation crystal of claim 1, wherein Me is Ca.
5. The scintillation crystal of claim 1, wherein Me is Li.
6. The scintillation crystal of claim 1, wherein the melt has the
Me concentration of at least approximately 0.08 wt. %, at least
approximately 0.2 wt. %, or no greater than approximately 1.0 wt.
%.
7. The scintillation crystal of claim 1, wherein y is no greater
than approximately 0.5 and at least approximately 0.005.
8. The scintillation crystal of claim 1, wherein y is in a range of
approximately 0.01 to approximately 0.09.
9. The scintillation crystal of claim 1, wherein Ln is La, RE is
Ce, and X is Br.
10. The scintillation crystal of claim 1, wherein y is
approximately 1.0 f.u.
11. The scintillation crystal of claim 10, wherein for a radiation
energy range of 13 keV to 30 keV, the scintillation crystal has a
PR.sub.dev average of no greater than approximately 14%, or for a
radiation energy range of 30 keV to 60 keV, the scintillation
crystal has a PR.sub.dev average of no greater than approximately
8.0%
12. The scintillation crystal of claim 1, wherein: for a radiation
energy range of 11 keV to 30 keV, the scintillation crystal has a
PR.sub.dev average of no greater than approximately 8.0%; or for a
radiation energy range of 30 keV to 60 keV, the scintillation
crystal has the PR.sub.dev average of no greater than approximately
3.6%.
13. The scintillation crystal of claim 1, wherein an energy
resolution ratio is an energy resolution of the scintillation
crystal divided by a different energy resolution of a different
scintillation crystal of a different composition, wherein the
energy resolution ratio is: no greater than approximately 0.95 for
an energy of 8 keV; no greater than approximately 0.95 for an
energy of 13 keV; no greater than approximately 0.95 for an energy
of 17 keV; no greater than approximately 0.95 for an energy of 22
keV; no greater than approximately 0.95 for an energy of 26 keV; no
greater than approximately 0.95 for an energy of 32 keV; or no
greater than approximately 0.97 for an energy of 44 keV.
14. The scintillation crystal of claim 13, wherein the energy
resolution ratio is no greater than approximately 0.95 for the
energy of 8 keV.
15. The scintillation crystal of claim 1, wherein the energy
resolution ratio is no greater than approximately 0.95 for the
energy of 13 keV.
16. The scintillation crystal of claim 1 wherein the energy
resolution ratio is no greater than approximately 0.95 for the
energy of 17 keV.
17. The scintillation crystal of claim 1, wherein the energy
resolution ratio is no greater than approximately 0.95 for the
energy of 22 keV.
18. The scintillation crystal of claim 1, wherein the energy
resolution ratio is no greater than approximately 0.95 for the
energy of 26 keV.
19. The scintillation crystal of claim 1, wherein an energy
resolution ratio is no greater than approximately 0.95 for the
energy of 32 keV.
20. The radiation detection apparatus of claim 2, wherein the
radiation detection apparatus is a medical imaging system or a well
logging apparatus.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority under 35 U.S.C.
.sctn.119(e) to U.S. Patent Application No. 61/719,405 entitled
"Scintillation Crystal Including a Rare Earth Halide, and a
Radiation Detection Apparatus Including the Scintillation Crystal,"
by Dorenbos et al., filed Oct. 28, 2012, which is incorporated
herein by reference in its entirety.
FIELD OF THE DISCLOSURE
[0002] The present disclosure is directed to scintillation crystals
including rare earth halides and radiation detection apparatuses
including such scintillation crystals.
BACKGROUND
[0003] Radiation detection apparatuses are used in a variety of
applications. For example, scintillators can be used for medical
imaging and for well logging in the oil and gas industry as well
for the environment monitoring, security applications, and for
nuclear physics analysis and applications. Scintillation crystals
used for radiation detection apparatuses can include rare earth
halides. Further improvement of scintillation crystals is
desired.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] Embodiments are illustrated by way of example and are not
limited in the accompanying figures.
[0005] FIG. 1 includes an illustration of a radiation detection
apparatus in accordance with an embodiment.
[0006] FIG. 2 includes a plot of energy resolution as a function of
energy for different compositions of LaBr.sub.3:Ce scintillation
crystals at gamma ray energies in a range of approximately 8 keV to
approximately 90 keV.
[0007] FIG. 3 includes a plot of energy resolution ratio as a
function of energy for different compositions of LaBr.sub.3:Ce
scintillation crystals at gamma ray energies in a range of
approximately 276 keV to approximately 662 keV.
[0008] FIG. 4 includes a plot of energy resolution as a function of
energy for different compositions of CeBr.sub.3 scintillation
crystals at gamma ray energies in a range of approximately 8 keV to
approximately 90 keV.
[0009] FIG. 5 includes a plot of energy resolution ratio as a
function of energy for different compositions of CeBr.sub.3
scintillation crystals at gamma ray energies in a range of
approximately 276 keV to approximately 662 keV.
[0010] FIG. 6 includes a plot of non-proportionality for different
compositions of LaBr.sub.3:Ce scintillation crystals at gamma ray
energies in a range of approximately 8 keV to approximately 1332
keV.
[0011] FIG. 7 includes a plot of non-proportionality for different
compositions of LaBr.sub.3:Ce scintillation crystals at gamma ray
energies in a range of approximately 9 keV to approximately 100
keV.
[0012] FIG. 8 includes a plot of non-proportionality for different
compositions of CeBr.sub.3 scintillation crystals at gamma ray
energies in a range of approximately 8 keV to approximately 1332
keV.
[0013] FIG. 9 includes a plot of non-proportionality for different
compositions of CeBr.sub.3 scintillation crystals at gamma ray
energies in a range of approximately 11 keV to approximately 100
keV.
[0014] FIG. 10 includes a plot of relative light output for
different compositions of LaBr.sub.3 scintillation crystals over a
range of temperatures.
[0015] Skilled artisans appreciate that elements in the figures are
illustrated for simplicity and clarity and have not necessarily
been drawn to scale. For example, the dimensions of some of the
elements in the figures may be exaggerated relative to other
elements to help to improve understanding of embodiments of the
invention.
DETAILED DESCRIPTION
[0016] The following description in combination with the figures is
provided to assist in understanding the teachings disclosed herein.
The following discussion will focus on specific implementations and
embodiments of the teachings. This focus is provided to assist in
describing the teachings and should not be interpreted as a
limitation on the scope or applicability of the teachings.
[0017] The term "averaged," when referring to a value, is intended
to mean an average, a geometric mean, or a median value.
[0018] As used herein, the terms "comprises," "comprising,"
"includes," "including," "has," "having," or any other variation
thereof, are intended to cover a non-exclusive inclusion. For
example, a process, method, article, or apparatus that comprises a
list of features is not necessarily limited only to those features
but may include other features not expressly listed or inherent to
such process, method, article, or apparatus. Further, unless
expressly stated to the contrary, "or" refers to an inclusive- or
and not to an exclusive- or. For example, a condition A or B is
satisfied by any one of the following: A is true (or present) and B
is false (or not present), A is false (or not present) and B is
true (or present), and both A and B are true (or present).
[0019] The use of "a" or "an" is employed to describe elements and
components described herein. This is done merely for convenience
and to give a general sense of the scope of the invention. This
description should be read to include one or at least one and the
singular also includes the plural, or vice versa, unless it is
clear that it is meant otherwise.
[0020] Unless otherwise defined, all technical and scientific terms
used herein have the same meaning as commonly understood by one of
ordinary skill in the art to which this invention belongs. The
materials, methods, and examples are illustrative only and not
intended to be limiting. To the extent not described herein, many
details regarding specific materials and processing acts are
conventional and may be found in textbooks and other sources within
the scintillation and radiation detection arts.
[0021] FIG. 1 illustrates an embodiment of a radiation detection
apparatus system 100. The radiation detection apparatus system can
be a medical imaging apparatus, a well logging apparatus, a
security inspection apparatus, nuclear physics applications, or the
like. In a particular embodiment, the radiation detection apparatus
can be used for gamma ray analysis, such as a Single Positron
Emission Computer Tomography (SPECT) or Positron Emission
Tomography (PET) analysis.
[0022] In the embodiment illustrated, the radiation detection
apparatus 100 includes a photosensor 101, an optical interface 103,
and a scintillation device 105. Although the photosensor 101, the
optical interface 103, and the scintillation device 105 are
illustrated separate from each other, skilled artisans will
appreciate that photosensor 101 and the scintillation device 105
can be coupled to the optical interface 103, with the optical
interface 103 disposed between the photosensor 101 and the
scintillation device 105. The scintillation device 105 and the
photosensor 101 can be optically coupled to the optical interface
103 with other known coupling methods, such as the use of an
optical gel or bonding agent, or directly through molecular
adhesion of optically coupled elements.
[0023] The photosensor 101 may be a photomultiplier tube (PMT), a
semiconductor-based photomultiplier, or a hybrid photosensor. The
photosensor 101 can receive photons emitted by the scintillation
device 105, via an input window 116, and produce electrical pulses
based on numbers of photons that it receives. The photosensor 101
is electrically coupled to an electronics module 130. The
electrical pulses can be shaped, digitized, analyzed, or any
combination thereof by the electronics module 130 to provide a
count of the photons received at the photosensor 101 or other
information. The electronics module 130 can include an amplifier, a
pre-amplifier, a discriminator, an analog-to-digital signal
converter, a photon counter, another electronic component, or any
combination thereof. The photosensor 101 can be housed within a
tube or housing made of a material capable of protecting the
photosensor 101, the electronics module 130, or a combination
thereof, such as a metal, metal alloy, other material, or any
combination thereof.
[0024] The scintillation device 105 includes a scintillation
crystal 107. The composition of the scintillation crystal 107 will
be described in more detail later in this specification. The
scintillation crystal 107 is substantially surrounded by a
reflector 109. In one embodiment, the reflector 109 can include
polytetrafluoroethylene (PTFE), another material adapted to reflect
light emitted by the scintillation crystal 107, or a combination
thereof. In an illustrative embodiment, the reflector 109 can be
substantially surrounded by a shock absorbing member 111. The
scintillation crystal 107, the reflector 109, and the shock
absorbing member 111 can be housed within a casing 113.
[0025] The scintillation device 105 includes at least one
stabilization mechanism adapted to reduce relative movement between
the scintillation crystal 107 and other elements of the radiation
detection apparatus 100, such as the optical interface 103, the
casing 113, the shock absorbing member 111, the reflector 109, or
any combination thereof. The stabilization mechanism may include a
spring 119, an elastomer, another suitable stabilization mechanism,
or a combination thereof. The stabilization mechanism can be
adapted to apply lateral forces, horizontal forces, or a
combination thereof, to the scintillation crystal 107 to stabilize
its position relative to one or more other elements of the
radiation detection apparatus 100.
[0026] As illustrated, the optical interface 103 is adapted to be
coupled between the photosensor 101 and the scintillation device
105. The optical interface 103 is also adapted to facilitate
optical coupling between the photosensor 101 and the scintillation
device 105. The optical interface 103 can include a polymer, such
as a silicone rubber, that is polarized to align the reflective
indices of the scintillation crystal 107 and the input window 116.
In other embodiments, the optical interface 103 can include gels or
colloids that include polymers and additional elements.
[0027] The scintillation crystal 107 can include a rare earth
halide. As used herein, rare earth elements include Y, Sc, and the
Lanthanide series elements. In an embodiment, the scintillation
crystal 107 can include one or more other rare earth elements.
Thus, the scintillation crystal 107 can have chemical formula as
set forth below.
[0028] Ln.sub.(1-y)RE.sub.yX.sub.3, wherein:
[0029] Ln represents a rare earth element;
[0030] RE represents a different rare earth element;
[0031] y has a value in a range of 0 to 1 formula unit ("f.u.");
and
[0032] X represents a halogen.
[0033] In particular embodiment, Ln can include La, Gd, Lu, or any
mixture thereof; and RE can include Ce, Eu, Pr, Tb, Nd, or any
mixture thereof. In a particular embodiment, the scintillation
crystal 107 can be La.sub.(1-y)Ce.sub.yBr.sub.3. In particular
embodiments, LaBr.sub.3 and CeBr.sub.3 are within the scope of
compositions described.
[0034] In another a further embodiment y can be 0 f.u., at least
approximately 0.0001 f.u., at least 0.001 f.u., or at least
approximately 0.05 f.u. In a further embodiment, y may be 1 f.u.,
no greater than approximately 0.2 f.u., no greater than
approximately 0.1 f.u., no greater than approximately 0.05 f.u, or
no greater than approximately 0.01 f.u. In a particular embodiment,
y is in a range of approximately 0.01 f.u. to approximately 0.1
f.u. In a further embodiment, y is no greater than approximately
0.99 f.u., no greater than approximately 0.9 f.u., or no greater
than approximately 0.8 f.u. X can include a single halogen or any
mixture of halogens. For example, X can include Br, I, or any
mixture thereof.
[0035] The rare earth halide can further include a co-dopant or a
dopant including a Group 1, a Group 2 element, or any mixture
thereof. Group 1 elements can include Li, Na, Rb, Cs, or any
mixture thereon. In a particular embodiment, the Group 1 element is
Na. Group 2 elements can include Mg, Ca, Sr, Ba, or any mixture
thereon. In a particular embodiment, the Group 2 element is Ca or
Sr. A crystal that includes LaBr.sub.3 co-doped with Ce and Sr has
a peak emission that is at a longer wavelength as compared to a
crystal that includes LaBr.sub.3 doped with Ce. Further, when
La.sub.(1-y)Ce.sub.yBr.sub.3 is doped with Sr, the light output can
be more constant than La.sub.(1-y)Ce.sub.yBr.sub.3 over the range
of -40.degree. C. to 175.degree. C., and is brighter than
La.sub.(1-y)Ce.sub.yBr.sub.3 at temperatures higher than 50.degree.
C. Thus, La.sub.(1-y) Ce.sub.yBr.sub.3 is doped with Sr may be
useful for applications that involve extreme temperature
excursions, such as oil well logging and space applications.
Similar to La.sub.(1-y)Ce.sub.yBr.sub.3, CeBr.sub.3 doped with Sr
is brighter than CeBr.sub.3 at temperatures higher than 50.degree.
C. When La.sub.(1-y)Ce.sub.yBr.sub.3 is doped with Ba, the light
output may be higher than the light output of
La.sub.(1-y)Ce.sub.yBr.sub.3 over the range of room temperature
(approximately 22.degree. C.) to about 70.degree. C.
La.sub.(1-y)Ce.sub.yBr.sub.3 is doped with Ba may be useful for
outdoor applications, for example for port-of-entry detectors that
can be used for vehicles and cargo.
[0036] In a further embodiment, the co-dopant or dopant can include
at least two different Group 1 elements, at least two different
Group 2 elements, or at least one Group 1 element and at least one
Group 2 element. In an embodiment, the content of the co-dopant or
dopant can be measured as the amount of co-dopant or dopant in a
melt used to form the rare earth halide. The co-dopant or dopant
concentration in the melt can be at least approximately 0.02 wt. %,
or in particular at least approximately 0.08 wt. %, at least
approximately 0.2 wt. %, or more particularly at least
approximately 0.3 wt. %, or even more particularly 0.4 wt. %. In
another embodiment, the co-dopant or dopant concentration in the
melt may be no greater than approximately 1.0 wt. %, or in
particular no greater than approximately 0.9 wt. %, or more
particularly no greater than approximately 0.7 wt. %. In a
particular embodiment, the co-dopant or dopant concentration in the
melt can be in a range approximately 0.2 wt. % to approximately 0.9
wt. % or more particularly, in a range of approximately 0.3 wt. %
to 0.7 wt. %.
[0037] The starting materials can include metal halides of the same
halogen or different halogens. For example, a rare earth bromide
and SrBr.sub.2 or NaBr can be used. In another embodiment, some of
the bromide-containing compounds may be replaced with
iodide-containing compounds. The scintillation crystal can be
formed using a conventional technique from a melt. The method can
include the Bridgman method, Czochralski crystal growth method, or
Kyropolis growth method.
[0038] Scintillation crystals that include a Group 1 element-doped
or a Group 2 element-doped rare earth halide having concentrations
as previously described provide good scintillating properties,
including energy resolution at energies in a range of 10 keV to
2000 keV. In another embodiment, co-doped or doped rare earth
halides can provide unexpected results as compared to other rare
earth halide scintillation crystals, particularly at low energies.
In a particular embodiment, the lower energies can be in a range of
approximately 10 keV to approximately 60 keV. More particularly,
the Group 2 element-doped scintillation crystals have unusually
good proportionality at lower energies, and the Group 1
element-doped and Group 2 element-doped scintillation crystals have
good energy resolution over a wide range of energies. The range of
10 keV to 356 keV can be further divided into ranges of
approximately 10 keV to 30 keV, 30 keV to 60 keV, 60 keV to 356
keV. The range of 356 keV to 1332 keV is also examined. While
improved performance occurs within each of the ranges, the relative
improvement may be more significant for the range of 10 to 60 keV,
as compared to the range of 356 keV to 1332 keV or even higher
energies. The better performance at lower energies is particularly
significant for medical imaging applications. The scintillation
crystals can be used in other applications, such as well logging in
the oil and gas industry as well for the environment monitoring,
security applications, and for nuclear physics analysis and
applications.
[0039] Energy resolution is the energy range at full-width of half
maximum ("FWHM") divided by the energy corresponding to the peak,
expressed as a percent. A lower number for energy resolution means
that the peak can be resolved more readily. Values for energy
resolution may depend on the metrology equipment and the
measurement techniques.
[0040] In an embodiment, measurements for energy resolution may be
performed on scintillation crystals that varied in size from
approximately 0.01 cm.sup.3 to approximately 0.2 cm.sup.3. The
crystals can be wrapped with a reflector on the sides and one end.
Alternatively, the crystals may be placed on a window of a PMT and
covered with the reflector. In a particular embodiment, the
reflector may be a specular reflector or a diffuse reflector. For
example, the reflector may include an aluminum foil, aluminized
polyester (e.g. aluminized Mylar.TM.-brand polyester), or a
polytetrafluoroethylene ("PTFE") sheet reflector. The scintillation
crystal can be placed in a housing where scintillating light passes
through a sapphire or quartz window.
[0041] The housed scintillation crystal can be interfaced to a PMT.
In an embodiment, the PMT can be a non-saturated photomultiplier.
By non-saturated, the photomultiplier operates in a mode in which
significantly more electrons may be generated with a significantly
higher rate of photons striking the photocathode of the
photomultiplier. An exemplary PMT can be a Hamamatsu Model R1791
PMT (available from Hamamatsu Photonics Deutschland GmbH of
Herrsching am Ammersee, Del.) run at 400 V. One or more desired
isotopes that emit radiation can be placed one at a time at a
predetermined distance, for example, approximately 150 mm (6
inches), from the sample. The energy spectra of each isotope and
each crystal can be obtained from an ORTEC Model 672 spectroscopic
amplifier (available from AMETEK GmbH of Meerbusch, Del.) with a 10
.mu.s shaping time.
[0042] In another embodiment, different equipment may be used. For
example, a PMT can be Model 9305 from ET Enterprises Ltd. of
Uxbridge, U.K., run at 900 V. The energy spectra of each isotope
and each crystal can be obtained from a multi-channel analyzer that
performs bi-polar shaping at a 0.25 micro-s shaping time. An
exemplary multichannel analyzer can be obtained from Can berra
Industries Inc. of Meriden Conn., model Aptec 55008 that has
bi-polar shaping, 0.25 micro-s shaping time, and 11-bit
digitization. After reading this specification, skilled artisans
will be able to select metrology equipment for their particular
applications.
[0043] After reading this specification, skilled artisans will
appreciate that the energy resolution values that they obtain may
change if the metrology equipment and the measurement techniques
are changed. The energy resolution values described below can be
obtained using the previously described metrology equipment and the
measurement conditions to provide a more accurate comparison of
energy resolution values between different samples.
[0044] Energy resolution ratio ("ER Ratio") may be used to compare
the energy resolutions of different compositions of materials for a
particular energy or range of energies. ER Ratio can allow for a
better comparison as opposed to energy resolution because ER Ratios
can be obtained using substantially the same metrology equipment
and techniques. Thus, variations based on metrology equipment and
techniques can be substantially eliminated.
[0045] In an embodiment, the ER Ratio is the energy resolution of a
particular crystal at a particular energy or range of energies
divided by the energy resolution of another crystal at
substantially the same energy or range of energies, wherein the
energy spectra for the crystals are obtained using the same or
substantially identical metrology equipment and techniques. In an
embodiment, LaBr.sub.3:Ce crystals having a co-dopant may be
compared to LaBr.sub.3:Ce crystals without a co-dopant. In another
embodiment, a doped CeBr.sub.3 crystal can be compared to a
substantially undoped CeBr.sub.3 crystal.
[0046] When comparing a particular scintillation crystal having a
composition described herein to a different scintillation crystal
having a different composition, a lower ER Ratio allows for more
accurate detection of energy peaks. When comparing the
scintillation crystals for particular energies, the ER Ratio may be
no greater than approximately 0.95 for an energy of 8 keV. In
another embodiment, the ER Ratio may be no greater than
approximately 0.88, or more particularly, no greater than 0.80 for
an energy of 8 keV. In a further embodiment, the ER Ratio may be in
a range of approximately 0.79 to approximately 0.95 or more
particularly, in a range of approximately 0.79 to approximately
0.86 for an energy of 8 keV. At an energy of 13 keV, the ER Ratio
may be no greater than approximately 0.95. In another embodiment,
the ER Ratio may be no greater than approximately 0.88, or more
particularly, no greater than 0.80 for an energy of 13 keV. In a
further embodiment, the ER Ratio may be in a range of approximately
0.78 to approximately 0.95 or more particularly, in a range of
approximately 0.79 to approximately 0.88 for an energy of 13
keV.
[0047] At an energy of 17 keV, the ER Ratio may be no greater than
approximately 0.95. In another embodiment, the ER Ratio may be no
greater than approximately 0.90, or more particularly, no greater
than 0.80 for an energy of 17 keV. In a further embodiment, the ER
Ratio may be in a range of approximately 0.76 to approximately 0.95
or more particularly, in a range of approximately 0.78 to
approximately 0.90 for an energy of 17 keV. At an energy of 22 keV,
the ER Ratio may be no greater than approximately 0.95. In another
embodiment, the ER Ratio may be no greater than approximately 0.90,
or more particularly, no greater than 0.87 for an energy of 22 keV.
In a further embodiment, the ER Ratio may be in a range of
approximately 0.84 to approximately 0.95 or more particularly, in a
range of approximately 0.85 to approximately 0.90 for an energy of
22 keV.
[0048] At an energy of 26 keV, the ER Ratio may be no greater than
approximately 0.95. In another embodiment, the ER Ratio may be no
greater than approximately 0.86, or more particularly, no greater
than 0.80 for an energy of 26 keV. In a further embodiment, the ER
Ratio may be in a range of approximately 0.75 to approximately 0.95
or more particularly, in a range of approximately 0.77 to
approximately 0.90 for an energy of 26 keV. At an energy of 32 keV,
the ER Ratio may be no greater than approximately 0.95. In another
embodiment, the ER Ratio may be no greater than approximately 0.90,
or more particularly, no greater than 0.80 for an energy of 32 keV.
In a further embodiment, the ER Ratio may be in a range of
approximately 0.75 to approximately 0.95 or more particularly, in a
range of approximately 0.76 to approximately 0.90 for an energy of
32 keV.
[0049] At an energy of 44 keV, the ER Ratio may be no greater than
approximately 0.97. In another embodiment, the ER Ratio may be no
greater than approximately 0.88, or more particularly, no greater
than 0.80 for an energy of 44 keV. In a further embodiment, the ER
Ratio may be in a range of approximately 0.70 to approximately 0.97
or more particularly, in a range of approximately 0.73 to
approximately 0.85 for an energy of 44 keV. At an energy of 60 keV,
the ER Ratio may be no greater than approximately 0.95. In another
embodiment, the ER Ratio may be no greater than approximately 0.90,
or more particularly, no greater than 0.80 for an energy of 60 keV.
In a further embodiment, the ER Ratio may be in a range of
approximately 0.70 to approximately 0.95 or more particularly, in a
range of approximately 0.76 to approximately 0.91 for an energy of
60 keV.
[0050] At an energy of 81 keV, the ER Ratio may be no greater than
approximately 0.95. In another embodiment, the ER Ratio may be no
greater than approximately 0.90, or more particularly, no greater
than 0.81 for an energy of 81 keV. In a further embodiment, the ER
Ratio may be in a range of approximately 0.75 to approximately 0.95
or more particularly, in a range of approximately 0.79 to
approximately 0.90 for an energy of 81 keV. At an energy of 276
keV, the ER Ratio may be no greater than approximately 0.95. In
another embodiment, the ER Ratio may be no greater than
approximately 0.85, or more particularly, no greater than 0.75 for
an energy of 276 keV. In a further embodiment, the ER Ratio may be
in a range of approximately 0.70 to approximately 0.95 or more
particularly, in a range of approximately 0.73 to approximately
0.85 for an energy of 276 keV.
[0051] At an energy of 303 keV, the ER Ratio may be no greater than
approximately 0.95. In another embodiment, the ER Ratio may be no
greater than approximately 0.88, or more particularly, no greater
than 0.83 for an energy of 303 keV. In a further embodiment, the ER
Ratio may be in a range of approximately 0.80 to approximately 0.95
or more particularly, in a range of approximately 0.81 to
approximately 0.90 for an energy of 303 keV. At an energy of 356
keV, the ER Ratio may be no greater than approximately 0.95. In
another embodiment, the ER Ratio may be no greater than
approximately 0.90, or more particularly, no greater than 0.85 for
an energy of 356 keV. In a further embodiment, the ER Ratio may be
in a range of approximately 0.80 to approximately 0.95 or more
particularly, in a range of approximately 0.81 to approximately
0.86 for an energy of 356 keV.
[0052] At an energy of 384 keV, the ER Ratio may be no greater than
approximately .sub.--0.95. In another embodiment, the ER Ratio may
be no greater than approximately 0.90, or more particularly, no
greater than 0.85 for an energy of 384 keV. In a further
embodiment, the ER Ratio may be in a range of approximately 0.80 to
approximately 0.95 or more particularly, in a range of
approximately 0.81 to approximately 0.88 for an energy of 384 keV.
At an energy of 511 keV, the ER Ratio may be no greater than
approximately 0.95. In another embodiment, the ER Ratio may be no
greater than approximately 0.88, or more particularly, no greater
than 0.83 for an energy of 511 keV. In a further embodiment, the ER
Ratio may be in a range of approximately 0.78 to approximately 0.95
or more particularly, in a range of approximately 0.80 to
approximately 0.80 for an energy of 511 keV.
[0053] At an energy of 662 keV, the ER Ratio may be no greater than
approximately 0.95. In another embodiment, the ER Ratio may be no
greater than approximately 0.88, or more particularly, no greater
than 0.80 for an energy of 662 keV. In a further embodiment, the ER
Ratio may be in a range of approximately 0.74 to approximately 0.95
or more particularly, in a range of approximately 0.76 to
approximately 0.85 for an energy of 662 keV. At an energy of 1173
keV, the ER Ratio may be no greater than approximately 0.95. In
another embodiment, the ER Ratio may be no greater than
approximately 0.90, or more particularly, no greater than 0.80 for
an energy of 1173 keV. In a further embodiment, the ER Ratio may be
in a range of approximately 0.70 to approximately 0.95 or more
particularly, in a range of approximately 0.74 to approximately
0.90 for an energy of 1173 keV.
[0054] At an energy of 1274 keV, the ER Ratio may be no greater
than approximately 0.95. In another embodiment, the ER Ratio may be
no greater than approximately 0.83, or more particularly, no
greater than 0.80 for an energy of 1274 keV. In a further
embodiment, the ER Ratio may be in a range of approximately 0.60 to
approximately 0.95 or more particularly, in a range of
approximately 0.64 to approximately 0.85 for an energy of 1274 keV.
At an energy of 1332 keV, the ER Ratio may be no greater than
approximately 0.95. In another embodiment, the ER Ratio may be no
greater than approximately 0.90, or more particularly, no greater
than 0.86 for an energy of 1332 keV. In a further embodiment, the
ER Ratio may be in a range of approximately 0.60 to approximately
0.95 or more particularly, in a range of approximately 0.67 to
approximately 0.90 for an energy of 1332 keV.
[0055] For a Group 2 element, the improvement in ER Ratio can occur
at all energies. For a Group 1 element, the improvement in ER
Ratio, can be more readily seen at higher energies. In particular,
for a scintillator crystal doped with a Group 1 element, the ER
Ratio may become more significant at energies at 60 keV and higher,
as compared to energies lower than 60 keV. Further, the improvement
with ER Ratio with Group 1 elements can be lower than the ER Ratio
with a Group 2 element at energies of 356 keV and higher. In
particular, the ER Ratio with a Group 1 element can be lower than
0.70. The actual ER Ratios may depend on the concentration of the
Group 1 element within the crystal. For example, at energies
between 44 keV and 60 keV, a scintillation crystal formed from a
melt that includes 0.5 wt % NaBr can have ER Ratio less than 1,
while a a scintillation crystal formed from a melt that includes 2
wt % NaBr can have ER Ratio greater than 1 at the same energies.
After reading this specification, skilled artisans will be able to
determine dopants and concentrations to provide an ER Ratio that
meets the needs or desires for a particular application.
[0056] Non-proportionality (nPR) refers to much a scintillation
crystal deviates perfect proportionality between gamma ray energy
captured and light output. A scintillation crystal having perfect
proportionality would always create the same number of photons per
unit energy absorbed, regardless of the energy of the gamma ray.
Thus, its departure from perfect proportionality is zero. For the
purposes of this specification, nPR for each scintillation crystal
is normalized at 662 keV. When nPR is 100%, the photoelectrons at a
particular energy, referred to as Z keV will be:
Ph.sub.Z keV, 100% nPR=Ph.sub.662 keV*(ZkeV/662 keV),
[0057] wherein Ph.sub.Z kev, 100% nPR is the number of
photoelectrons predicted to be sensed by a photosensor at an energy
of Z keV when nPR is 100%, and
[0058] Ph.sub.662 keV is the number of photoelectrons sensed by the
photosensor at 662 keV.
[0059] Thus, nPR is:
nPR=(Ph.sub.Z keV, measured/Ph.sub.Z keV, 100% nPR)*100%,
[0060] wherein Ph.sub.Z keV, measured is the number of
photoelectrons sensed by the photosensor at an energy of Z keV.
[0061] The value of nPR is the same or improved at energies in a
range of 10 keV to 2000 keV when a Group 1 element or a Group 2
element is added as a co-dopant or a dopant in the melt when
forming the crystal. The value of nPR for rare earth halides when
doped with a Group 2 element is more significant at lower energies
than it is for higher energies. If the scintillation crystal
generates less scintillating light for lower energy gamma rays, the
scintillation crystal has poor proportionality. Thus, the response
of the scintillation crystal to gamma rays at lower energies, such
no greater than 60 keV, can be more significant to proportionality
than the response at higher gamma ray energies, such as greater
than 60 keV. At energies lower than 30 keV, the improvement in nPR
can be even more significant as compared to 30 keV to 60 keV.
[0062] Proportionality can be determined with measuring the
scintillation response at many different X-ray or gamma ray
energies. A particular useful method uses a tunable monochromatic
synchrotron X-ray beam, such as provided by the X1 beam line of
Hamburger Synhrotronstrahlungslabor at Deutsches
Elektronen-Synchrotron, Hamburg, Germany. Details for an
experimental setup can be found in "Nonproportional Response of
LaBr:Ce and LaCl:Ce Scintillators to Synchrotron X-ray
Irradiation," by I. V. Khodyuk and P. Dorenbos, J. Phys. Condens.
Matter, vol. 22, p. 485402, 2010, which is incorporated herein for
its detail regarding the experimental setup. X-ray excited
luminescence spectra can be recorded using an X-ray tube with a Cu
anode operating at 60 kV and 25 mA. The emission of the sample can
be focused via a quartz window and a lens on the entrance slit of a
monochromator, such as an ARC Model VM-504 monochromator (available
from Acton Research Corporation of Acton, Mass., US) (blazed at 300
nm, 1200 grooves/mm), dispersed and recorded with a photomultiplier
tube, such as a Hamamatsu Model R943-02 PMT (available from
Hamamatsu Photonics Deutschland GmbH of Herrsching am Ammersee,
Del.). The spectra can be corrected for the monochromator
transmission and for the quantum efficiency of the PMT. X-ray
excited luminescence measurements may be performed between 80 and
600K using a cryostat. The PMT can be located outside the cryostat
and be at room temperature.
[0063] The deviation from perfect proportionality (nPR.sub.dev) is
nPR minus 100%. The parameter nPR.sub.dev provides an value to
quantify how much nPR is away from 100% and an indicator for
direction; minus (-) is below 100%, and plus (+) is above 100%. For
a set of nPR data points, an averaged value, a largest positive
value, a largest negative value, a maximum value, an absolute value
of any of the foregoing, a derivative of any of the foregoing, or
any combination thereof can be obtained. The averaged value can be
an average, a median, or a geometric mean, or may be determined
using an integration. In a particular embodiment, the average
deviation of nPR from 100% can be determined using an integral in
accordance with the equation below.
n PR dev average = .intg. E lower E upper ( ( nPR ( E i ) - 100 % )
E i E upper - E lower ##EQU00001##
[0064] where [0065] nPR(Ei) is nPR at energy E.sub.i;
[0066] E.sub.upper is the upper limit of the energy range; and
[0067] E.sub.lower is the lower limit of the energy range.
[0068] In the equation above, the absolute value of the deviation
is used, and thus, any deviation, whether - or +, is accounted for
within the equation. In particular, a positive deviation is not
offset by a negative deviation. Thus, the measure provides a good
indicator of the degree of deviation over a range of energies
[0069] For a radiation energy range from 11 keV to 30 keV, the rare
earth halide scintillator crystal can have an nPR.sub.dev average
of no greater than approximately 8.0%, or more particularly no
greater than approximately 5.0%, or even more particularly no
greater than approximately 3.0%. For the radiation energy range of
30 keV to 60 keV, the rare earth scintillation crystal can have an
nPR.sub.dev average of no greater than approximately 3.6%, or more
particularly no greater than approximately 3.3%, or even more
particularly no greater than approximately 2.9%.
[0070] For a radiation energy range from 60 keV to 356 keV, the
rare earth halide scintillator crystal can have an nPR.sub.dev
average of no greater than approximately 2.4%, or more particularly
no greater than approximately 1.7%, or even more particularly no
greater than approximately 0.7%. For the radiation energy range of
356 keV to 1332 keV, the rare earth scintillation crystal has an
nPR.sub.dev average of no greater than approximately 0.5%, or more
particularly no greater than approximately 0.20%, or even more
particularly no greater than approximately 0.07%.
[0071] CeBr.sub.3 scintillation crystals may have values that
depart more strongly from perfect proportionality, as compared to
LaBr.sub.3:Ce scintillation crystal. For a radiation energy range
from 13 keV to 30 keV, the CeBr.sub.3 scintillation crystal can
have an nPR.sub.dev average of no greater than approximately 14%,
or more particularly no greater than approximately 12%, or even
more particularly no greater than approximately 9%. For the
radiation energy range of 30 keV to 60 keV, the CeBr.sub.3
scintillation crystal can have an nPR.sub.dev average of no greater
than approximately 8.0%, or more particularly no greater than
approximately 6.0%, or even more particularly no greater than
approximately 4.0%.
[0072] For a radiation energy range from 60 keV to 356 keV, the
CeBr.sub.3 scintillation crystal can have an nPR.sub.dev average of
no greater than approximately 2.0%, or more particularly no greater
than approximately 1.3%, or even more particularly no greater than
approximately 0.7%. For the radiation energy range of 60 keV to 150
keV, the CeBr.sub.3 scintillation crystal can have nPR.sub.dev
average of no greater than approximately 0.20%, or more
particularly no greater than approximately 0.15%, or even more
particularly no greater than approximately 0.09%.
[0073] Many different aspects and embodiments are possible. Some of
those aspects and embodiments are described herein. After reading
this specification, skilled artisans will appreciate that those
aspects and embodiments are only illustrative and do not limit the
scope of the present invention. Embodiments may be in accordance
with any one or more of the items as listed below.
[0074] Item 1. A scintillation crystal comprising
Ln.sub.(1-y)RE.sub.yX.sub.3:Me, wherein:
[0075] Ln represents a rare earth element;
[0076] RE represents a different rare earth element;
[0077] y has a value in a range of 0 to 1;
[0078] X represents a halogen;
[0079] Me represents a Group 1 element, a Group 2 element, or any
mixture thereof; and
[0080] the scintillation crystal is formed from a melt having a Me
concentration of at least approximately 0.02 wt. %.
[0081] Item 2. A radiation detection apparatus comprising:
[0082] a scintillation crystal including
Ln.sub.(1-y)RE.sub.yX.sub.3:Me, wherein Ln represents a rare earth
element; RE represents a different rare earth element; y has a
value in a range of 0 to 1; X represents a halogen; Me represents a
Group 1 element, a Group 2 element, or any mixture thereof; and the
scintillation crystal is formed from a melt having a Me
concentration of at least approximately 0.02 wt. %; and
[0083] a photosensor optically coupled to the scintillation
crystal.
[0084] Item 3. A scintillation crystal comprising:
[0085] a rare earth halide, wherein:
[0086] for a radiation energy range of 11 keV to 30 keV, the
scintillation crystal has an nPR.sub.dev average of no greater than
approximately 8.0%; or
[0087] for a radiation energy range of 30 keV to 60 keV, the
scintillation crystal has the nPR.sub.dev average of no greater
than approximately 3.6%.
[0088] Item 4. A scintillation crystal comprising:
[0089] a rare earth halide, wherein:
[0090] an energy resolution ratio is an energy resolution of the
scintillation crystal divided by a different energy resolution of a
different scintillation crystal having a different composition,
wherein the energy resolution ratio is no greater than
approximately 0.95 for an energy of 8 keV; no greater than
approximately 0.95 for an energy of 13 keV; no greater than
approximately 0.95 for an energy of 17 keV; no greater than
approximately 0.95 for an energy of 22 keV; no greater than
approximately 0.95 for an energy of 26 keV; no greater than
approximately 0.95 for an energy of 32 keV; or no greater than
approximately 0.97 for an energy of 44 keV.
[0091] Item 5. The scintillation crystal of claim 3 or 4, wherein
the scintillation crystal has a general formula of
Ln.sub.(1-y)RE.sub.yX.sub.3, wherein:
[0092] Ln represents a rare earth element;
[0093] RE represents a different rare earth element;
[0094] y has a value in a range of 0 to 1; and
[0095] X represents a halogen.
[0096] Item 6. The scintillation crystal or radiation detection
apparatus of Item 5, wherein the scintillation crystal further
comprises Me, wherein Me represents Li, Na, a Group 2 element, or
any mixture thereof; and the scintillation crystal is formed from a
melt having a Me concentration of at least approximately 0.02 wt.
%.
[0097] Item 7. The scintillation crystal or radiation detection
apparatus of any one of Items 1, 2, and 6, wherein the melt has the
Me concentration of at least approximately 0.08 wt %, at least
approximately 0.2 wt. %, or more particularly at least
approximately 0.3 wt. %, or even more particularly at least
approximately 0.4 wt. %; or no greater than approximately 1.0 wt.
%, or more particularly no greater than approximately 0.9 wt. %, or
even more particularly no greater than 0.7 wt. %.
[0098] Item 8. The scintillation crystal or radiation detection
apparatus of any one of Items 1, 2, 6, and 7, wherein the melt has
the Me concentration in range of approximately 0.2 wt. % to
approximately 0.9 wt. %, or more particularly in a range of
approximately 0.3 wt. % to approximately 0.7 wt. %.
[0099] Item 9. The scintillation crystal or the radiation detection
apparatus of any one of Items 1, 2, and 6 to 8, wherein Me is the
Group 2 element.
[0100] Item 10. The scintillation crystal or the radiation
detection apparatus of Item 9, wherein Me is Ca, Sr, Mg, Ba, or any
mixture thereof.
[0101] Item 11. The scintillation crystal or the radiation
detection apparatus of Item 9, wherein Me is Ca.
[0102] Item 12. The scintillation crystal or the radiation
detection apparatus of any one of Items 1, 2, and 6 to 8, wherein
Me is the Group 1 element.
[0103] Item 13. The scintillation crystal or the radiation
detection apparatus of Item 11, wherein Me is Li, Na, Rb, Cs, or
any mixture thereof.
[0104] Item 14. The scintillation crystal or the radiation
detection apparatus of Item 11, wherein Me is Li.
[0105] Item 15. The scintillation crystal or the radiation
detection apparatus of any one of Items 1, 2, and 6 to 8, wherein
Me includes at least two different Group 1 elements; at least two
different Group 2 elements; or at least one Group 1 element and at
least one Group 2 element.
[0106] Item 16. The scintillation crystal or radiation detection
apparatus of any one of the preceding Items, wherein Ln includes
La, Gd, Lu, or any mixture thereof.
[0107] Item 17. The scintillation crystal or radiation detection
apparatus of any one of the preceding Items, wherein RE includes
Ce, Eu, Pr, Tb, Nd, or any mixture thereof.
[0108] Item 18. The scintillation crystal or radiation detection
apparatus of any one of the preceding Items, wherein y is no
greater than approximately 0.5, or more particularly no greater
than approximately 0.2, or even more particularly no greater than
approximately 0.09; or at least approximately 0.005, or more
particularly at least approximately 0.01, or even more particularly
at least approximately 0.02.
[0109] Item 19. The scintillation crystal or radiation detection
apparatus of any one of the preceding Items, wherein y is in a
range of approximately 0.01 to approximately 0.09, or more
particularly in a range of at least approximately 0.03 to
approximately 0.07.
[0110] Item 20. The scintillation crystal or radiation detection
apparatus of any one of the preceding Items, wherein Ln is La, RE
is Ce, and X is Br.
[0111] Item 21. The scintillation crystal or radiation detection
apparatus of any one of Items 1 to 17 and 20, wherein y is
approximately 1.0 f.u.
[0112] Item 22. The scintillation crystal or the radiation
detection apparatus of Item 21, wherein for a radiation energy
range of 13 keV to 30 keV, the scintillation crystal has a
PR.sub.dev average of no greater than approximately 14%, or more
particularly no greater than approximately 12%, or even more
particularly 9%.
[0113] Item 23. The scintillation crystal or the radiation
detection apparatus of Item 21 or 22, wherein for a radiation
energy range of 30 keV to 60 keV, the scintillation crystal has a
PR.sub.dev average of no greater than approximately 8.0% or more
particularly no greater than approximately 6.0%, or even more
particularly no greater than 4.0%.
[0114] Item 24. The scintillation crystal or the radiation
detection apparatus of any one of Items 21 or 23, wherein for a
radiation energy range of 60 keV to 356 keV, scintillation crystal
has a PR.sub.dev average of no greater than approximately 2.0% or
more particularly no greater than approximately 1.3%, or even more
particularly no greater than 0.7%.
[0115] Item 25. The scintillation crystal or the radiation
detection apparatus of any one of Items 21 to 24, wherein for a
radiation energy range of 356 keV to 1372 keV, scintillation
crystal has a PR.sub.dev average of no greater than approximately
0.20% or more particularly no greater than approximately 0.15%, or
even more particularly no greater than 0.09%.
[0116] Item 26. The scintillation crystal or the radiation
detection apparatus of any one of Items 1, 2, and 6 to 20, wherein
for a radiation energy range of 11 keV to 30 keV, the scintillation
crystal has a PR.sub.dev average of no greater than approximately
8.0%; or for a radiation energy range of 30 keV to 60 keV, the
scintillation crystal has the PR.sub.dev average of no greater than
approximately 3.6%.
[0117] Item 27. The scintillation crystal or the radiation
detection apparatus of any one of Items 1 to 20, and 26, wherein
for a radiation energy range of 11 keV to 32 keV, scintillation
crystal has a PR.sub.dev average of no greater than approximately
8.0% or more particularly no greater than approximately 5.0% or
even more particularly no greater than approximately 3.0%.
[0118] Item 28. The scintillation crystal or the radiation
detection apparatus of any one of Items 1 to 20, 26, and 27,
wherein for a radiation energy range of 30 keV to 60 keV,
scintillation crystal has a PR.sub.dev average of no greater than
approximately 3.6% or more particularly no greater than
approximately 3.3% or even more particularly no greater than
approximately 2.9%.
[0119] Item 29. The scintillation crystal or the radiation
detection apparatus of any one of Items 1 to 20, and 26 to 28,
wherein for a radiation energy range of 60 keV to 356 keV,
scintillation crystal has a PR.sub.dev average of no greater than
approximately 2.4% or more particularly no greater than
approximately 1.7% or even more particularly no greater than
approximately 0.7%.
[0120] Item 30. The scintillation crystal or the radiation
detection apparatus of any one of Items 1 to 20, and 26 to 29,
wherein for a radiation energy range of 356 keV to 1332 keV,
scintillation crystal has a PR.sub.dev average of no greater than
approximately 0.50% or more particularly no greater than
approximately 0.20% or even more particularly no greater than
approximately 0.07%.
[0121] Item 31. The scintillation crystal or radiation detection
apparatus of any one of Items 3 and 22 to 30, wherein the averaged
value for deviation of nPR from 100% (nPR.sub.dev average) is
determined by:
n PR dev average = .intg. E lower E upper ( ( nPR ( E i ) - 100 % )
E i E upper - E lower , ##EQU00002##
where
[0122] nPR(Ei) is nPR at energy E.sub.i;
[0123] E.sub.upper is the upper limit of the energy range; and
[0124] E.sub.lower is the lower limit of the energy range.
[0125] Item 32. The scintillation crystal or the radiation
detection apparatus of any one of the preceding Items, wherein an
energy resolution ratio is an energy resolution of the
scintillation crystal divided by a different energy resolution of a
different scintillation crystal of a different composition, wherein
the energy resolution ratio is no greater than approximately 0.95
for an energy of 8 keV; no greater than approximately 0.95 for an
energy of 13 keV; no greater than approximately 0.95 for an energy
of 17 keV; no greater than approximately 0.95 for an energy of 22
keV; no greater than approximately 0.95 for an energy of 26 keV; no
greater than approximately 0.95 for an energy of 32 keV; no greater
than approximately 0.97 for an energy of 44 keV; no greater than
approximately 0.95 for an energy of 60 keV; no greater than
approximately 0.95 for an energy of 81 keV; no greater than
approximately 0.95 for an energy of 276 keV; no greater than
approximately 0.95 for an energy of 303 keV; no greater than
approximately 0.95 for an energy of 356 keV; no greater than
approximately 0.95 for an energy of 384 keV; no greater than
approximately 0.95 for an energy of 511 keV; no greater than
approximately 0.95 for an energy of 662 keV; no greater than
approximately 0.95 for an energy of 1173 keV; no greater than
approximately 0.95 for an energy of 1274 keV; no greater than
approximately 0.95 for an energy of 1332 keV; or any combination
thereof.
[0126] Item 33. The scintillation crystal or the radiation
detection apparatus of any one of Items 4 and 32, wherein the
energy resolution ratio is no greater than approximately 0.95 for
the energy of 8 keV, or more particularly no greater than
approximately 0.88 for the energy of 8 keV, or still more
particularly no greater than approximately 0.80 for the energy of 8
keV.
[0127] Item 34. The scintillation crystal or the radiation
detection apparatus of any one of Items 4, 32, and 33, wherein the
energy resolution ratio is in a range approximately 0.79 to
approximately 0.95 or more particularly in a range of approximately
0.79 to approximately 0.86 for the energy of 8 keV.
[0128] Item 35. The scintillation crystal or the radiation
detection apparatus of any one of Items 4 and 32 to 34, wherein the
energy resolution ratio is no greater than approximately 0.95 for
the energy of 13 keV, or more particularly no greater than
approximately 0.88 for the energy of 13 keV, or still more
particularly no greater than approximately 0.80 for the energy of
13 keV.
[0129] Item 36. The scintillation crystal or the radiation
detection apparatus of any one of Items 4 and 32 to 35, wherein the
energy resolution ratio is in a range approximately 0.78 to
approximately 0.95 or more particularly in a range of approximately
0.79 to approximately 0.88 for the energy of 13 keV.
[0130] Item 37. The scintillation crystal or the radiation
detection apparatus of any one of Items 4 and 32 to 36, wherein the
energy resolution ratio is no greater than approximately 0.95 for
the energy of 17 keV, or more particularly no greater than
approximately 0.90 for the energy of 17 keV, or still more
particularly no greater than approximately 0.80 for the energy of
17 keV.
[0131] Item 38. The scintillation crystal or the radiation
detection apparatus of any one of Items 4 and 32 to 37, wherein the
energy resolution ratio is in a range approximately 0.76 to
approximately 0.95 or more particularly in a range of approximately
0.78 to approximately 0.90 for the energy of 17 keV.
[0132] Item 39. The scintillation crystal or the radiation
detection apparatus of any one of Items 4 and 32 to 38, wherein the
energy resolution ratio is no greater than approximately 0.95 for
the energy of 22 keV, or more particularly no greater than
approximately 0.90 for the energy of 22 keV, or still more
particularly no greater than approximately 0.87 for the energy of
22 keV.
[0133] Item 40. The scintillation crystal or the radiation
detection apparatus of any one of Items 4 and 32 to 39, wherein the
energy resolution ratio is in a range approximately 0.84 to
approximately 0.95 or more particularly in a range of approximately
0.85 to approximately 0.90 for the energy of 22 keV.
[0134] Item 41. The scintillation crystal or the radiation
detection apparatus of any one of Items 4 and 32 to 40, wherein the
energy resolution ratio is no greater than approximately 0.95 for
the energy of 26 keV, or more particularly no greater than
approximately 0.86 for the energy of 26 keV, or still more
particularly no greater than approximately 0.80 for the energy of
26 keV.
[0135] Item 42. The scintillation crystal or the radiation
detection apparatus of any one of Items 4 and 32 to 41, wherein the
energy resolution ratio is in a range approximately 0.75 to
approximately 0.95 or more particularly in a range of approximately
0.77 to approximately 0.90 for the energy of 26 keV.
[0136] Item 43. The scintillation crystal or the radiation
detection apparatus of any one of Items 4 and 32 to 42, wherein an
energy resolution ratio is no greater than approximately 0.95 for
the energy of 32 keV, or more particularly no greater than
approximately 0.90 for the energy of 32 keV, or still more
particularly no greater than approximately 0.80 for the energy of
32 keV.
[0137] Item 44. The scintillation crystal or the radiation
detection apparatus of anyone of Items 4 and 32 to 43, wherein the
energy resolution ratio is in a range of approximately 0.75 to
approximately 0.95 or more particularly in a range of approximately
0.76 to approximately 0.90 for the energy of 32 keV.
[0138] Item 45. The scintillation crystal or the radiation
detection apparatus of any one of Items 4 and 32 to 44, wherein the
energy resolution ratio is no greater than approximately 0.97 for
the energy of 44 keV, or more particularly no greater than
approximately 0.88 for the energy of 44 keV, or still more
particularly no greater than approximately 0.80 for the energy of
44 keV.
[0139] Item 46. The scintillation crystal or the radiation
detection apparatus of any one of Items 4 and 32 to 45, wherein the
energy resolution ratio is in a range approximately 0.70 to
approximately 0.97 or more particularly in a range of approximately
0.73 to approximately 0.85 for the energy of 44 keV.
[0140] Item 47. The scintillation crystal or the radiation
detection apparatus of any one of Items 4 and 32 to 46, wherein the
energy resolution ratio is no greater than approximately 0.95 for
the energy of 60 keV, or more particularly no greater than
approximately 0.90 for the energy of 60 keV, or still more
particularly no greater than approximately 0.80 for the energy of
60 keV.
[0141] Item 48. The scintillation crystal or the radiation
detection apparatus of any one of Items 4 and 32 to 47, wherein the
energy resolution ratio is in a range approximately 0.70 to
approximately 0.95 or more particularly in a range of approximately
0.76 to approximately 0.91 for the energy of 60 keV.
[0142] Item 49. The scintillation crystal or the radiation
detection apparatus of any one of Items 4 and 32 to 48, wherein the
energy resolution ratio is no greater than approximately 0.95 for
the energy of 81 keV, or more particularly no greater than
approximately 0.90 for the energy of 81 keV, or still more
particularly no greater than approximately 0.81 for the energy of
81 keV.
[0143] Item 50. The scintillation crystal or the radiation
detection apparatus of any one of Items 4 and 32 to 49, wherein the
energy resolution ratio is in a range approximately 0.75 to
approximately 0.95 or more particularly in a range of approximately
0.79 to approximately 0.90 for the energy of 81 keV.
[0144] Item 51. The scintillation crystal or the radiation
detection apparatus of any one of Items 4 and 32 to 50, wherein the
energy resolution ratio is no greater than approximately 0.95 for
the energy of 276 keV, or more particularly no greater than
approximately 0.85 for the energy of 276 keV, or still more
particularly no greater than approximately 0.75 for the energy of
276 keV.
[0145] Item 52. The scintillation crystal or the radiation
detection apparatus of any one of Items 4 and 32 to 51, wherein the
energy resolution ratio is in a range approximately 0.70 to
approximately 0.95 or more particularly in a range of approximately
0.73 to approximately 0.85 for the energy of 276 keV.
[0146] Item 53. The scintillation crystal or the radiation
detection apparatus of any one of Items 4 and 32 to 52, wherein the
energy resolution ratio is no greater than approximately 0.95 for
the energy of 303 keV, or more particularly no greater than
approximately 0.88 for the energy of 303 keV, or still more
particularly no greater than approximately 0.83 for the energy of
303 keV.
[0147] Item 54. The scintillation crystal or the radiation
detection apparatus of any one of Items 4 and 32 to 53, wherein the
energy resolution ratio is in a range approximately 0.80 to
approximately 0.95 or more particularly in a range of approximately
0.81 to approximately 0.90 for the energy of 303 keV.
[0148] Item 55. The scintillation crystal or the radiation
detection apparatus of any one of Items 4 and 32 to 54, wherein the
energy resolution ratio is no greater than approximately 0.95 for
the energy of 356 keV, or more particularly no greater than
approximately 0.90 for the energy of 356 keV, or still more
particularly no greater than approximately 0.85 for the energy of
356 keV.
[0149] Item 56. The scintillation crystal or the radiation
detection apparatus of any one of Items 4 and 32 to 55, wherein the
energy resolution ratio is in a range approximately 0.80 to
approximately 0.95 or more particularly in a range of approximately
0.81 to approximately 0.86 for the energy of 356 keV.
[0150] Item 57. The scintillation crystal or the radiation
detection apparatus of any one of Items 4 and 32 to 56, wherein the
energy resolution ratio is no greater than approximately 0.95 for
the energy of 384 keV, or more particularly no greater than
approximately 0.90 for the energy of 384 keV, or still more
particularly no greater than approximately 0.85 for the energy of
384 keV.
[0151] Item 58. The scintillation crystal or the radiation
detection apparatus of any one of Items 4 and 32 to 57, wherein the
energy resolution ratio is in a range approximately 0.80 to
approximately 0.95 or more particularly in a range of approximately
0.81 to approximately 0.88 for the energy of 384 keV.
[0152] Item 59. The scintillation crystal or the radiation
detection apparatus of any one of Items 4 and 32 to 58, wherein the
energy resolution ratio is no greater than approximately 0.95 for
the energy of 511 keV, or more particularly no greater than
approximately 0.88 for the energy of 511 keV, or still more
particularly no greater than approximately 0.83 for the energy of
511 keV.
[0153] Item 60. The scintillation crystal or the radiation
detection apparatus of any one of Items 4 and 32 to 59, wherein the
energy resolution ratio is in a range approximately 0.78 to
approximately 0.95 or more particularly in a range of approximately
0.80 to approximately 0.88 for the energy of 511 keV.
[0154] Item 61. The scintillation crystal or the radiation
detection apparatus of any one of Items 4 and 32 to 60, wherein the
energy resolution ratio is no greater than approximately 0.95 for
the energy of 662 keV, or more particularly no greater than
approximately 0.88 for the energy of 662 keV, or still more
particularly no greater than approximately 0.80 for the energy of
662 keV.
[0155] Item 62. The scintillation crystal or the radiation
detection apparatus of any one of Items 4 and 32 to 61, wherein the
energy resolution ratio is in a range approximately 0.74 to
approximately 0.95 or more particularly in a range of approximately
0.76 to approximately 0.85 for the energy of 662 keV.
[0156] Item 63. The scintillation crystal or the radiation
detection apparatus of any one of Items 4 and 32 to 62, wherein the
energy resolution ratio is no greater than approximately 0.95 for
the energy of 1173 keV, or more particularly no greater than
approximately 0.90 for the energy of 1173 keV, or still more
particularly no greater than approximately 0.80 for the energy of
1173 keV.
[0157] Item 64. The scintillation crystal or the radiation
detection apparatus of any one of Items 4 and 32 to 63, wherein the
energy resolution ratio is in a range approximately 0.70 to
approximately 0.90 or more particularly in a range of approximately
0.74 to approximately 0.90 for the energy of 1173 keV.
[0158] Item 65. The scintillation crystal or the radiation
detection apparatus of any one of Items 4 and 32 to 64, wherein the
energy resolution ratio is no greater than approximately 0.95 for
the energy of 1274 keV, or more particularly no greater than
approximately 0.83 for the energy of 1274 keV, or still more
particularly no greater than approximately 0.80 for the energy of
1274 keV.
[0159] Item 66. The scintillation crystal or the radiation
detection apparatus of any one of Items 4 and 32 to 65, wherein the
energy resolution ratio is in a range approximately 0.60 to
approximately 0.95 or more particularly in a range of approximately
0.64 to approximately 0.85 for the energy of 1274 keV.
[0160] Item 67. The scintillation crystal or the radiation
detection apparatus of any one of Items 4 and 32 to 66, wherein the
energy resolution ratio is no greater than approximately 0.95 for
the energy of 1332 keV, or more particularly no greater than
approximately 0.90 for the energy of 1332 keV, or still more
particularly no greater than approximately 0.86 for the energy of
1332 keV.
[0161] Item 68. The scintillation crystal or the radiation
detection apparatus of any one of Items 4 and 32 to 67, wherein the
energy resolution ratio is in a range approximately 0.60 to
approximately 0.95 or more particularly in a range of approximately
0.67 to approximately 0.90 for the energy of 1332 keV.
[0162] Item 69. The radiation detection apparatus of any one of
Items 2 and 6 to 68, wherein the radiation detection apparatus is a
medical imaging system or a well logging apparatus.
EXAMPLES
[0163] The concepts described herein will be further described in
the Examples, which do not limit the scope of the invention
described in the claims. The Examples demonstrate performance of
scintillation crystals of different compositions. Numerical values
as disclosed in this Examples section may be averaged from a
plurality of readings, approximated, or rounded off for
convenience.
[0164] Scintillator crystals were formed from an open crucible
using different combinations of LaBr.sub.3, CeBr.sub.3, NaBr,
SrBr.sub.2, and BaBr.sub.2. For the co-dopants and dopants, the
values in Table 1 reflect the amounts of the co-dopants and dopants
added to the melt.
TABLE-US-00001 TABLE 1 Crystal Compositions and Sample Sizes Sample
CaBr.sub.2 SrBr.sub.2 BaBr.sub.2 NaBr Sample Size # Description
(wt. %) (wt. %) (wt. %) (wt. %) (approx., cm.sub.3) 1 Undoped -- --
-- -- 0.05 La.sub.0.95Ce.sub.0.05Br.sub.3 2 Ca-doped 0.5 -- -- --
0.02 La.sub.0.95Ce.sub.0.05Br.sub.3 3 Sr-doped -- 0.5 -- -- 0.1
La.sub.0.95Ce.sub.0.05Br.sub.3 4 Ba-doped -- -- 0.5 -- 0.03
La.sub.0.95Ce.sub.0.05Br.sub.3 5 0.5% Na-doped -- -- -- 0.5 0.1
La.sub.0.95Ce.sub.0.05Br.sub.3 6 2% Na-doped -- -- -- 2 0.01
La.sub.0.965Ce.sub.0.035Br.sub.3 7 Undoped CeBr.sub.3 -- -- -- --
0.05 8 Ca-doped CeBr.sub.3 .5 -- -- -- 0.05 9 Sr-doped CeBr.sub.3
-- .5 -- -- 0.05 10 Na-doped CeBr.sub.3 -- -- -- 0.5 0.05
[0165] Additional scintillation crystals were formed based on the
La.sub.0.95Ce.sub.0.05Br.sub.3 formula and used 20 wt. % Na and 20
wt. % Na/20 wt. % Sr in the melt. For these crystals and the
crystals in Table 1, the crystal having the
La.sub.0.95Ce.sub.0.05Br.sub.3 formula with 20 wt. % Na/20 wt. % Sr
in the melt had cracks. The other crystals were transparent and did
not have cracks. Samples were obtained from the crystals and had
approximate sizes as listed in Table 1.
[0166] The scintillation crystals were analyzed for energy
resolution. Gamma ray excited pulse-height spectra at room
temperature were recorded with a Hamamatsu Model R1791 PMT
connected to a Cremat Model CR-112 pre-amplifier and an ORTEC Model
672 spectroscopic amplifier with 10 .mu.s shaping time. The voltage
of the PMT was set to 400 V to avoid saturation due to intensive
signals in short time interval. The bare crystals were mounted on
the window of the PMT and covered with several Teflon layers; all
pulse-height measurements were performed inside an M-Braun UNILAB
dry box with a moisture content less than 1 part per million. The
yield expressed in photoelectrons per MeV of absorbed gamma ray
energy (phe/MeV) was determined without an optical coupling between
the scintillator and the PMT-window. The yield was obtained from
the ratio between the peak position of the 662-keV photopeak and
the position of the mean value of the so-called single
photoelectron peak in pulse-height spectra. Single photoelectron
spectra were recorded with a Hamamatsu Model R1791 PMT connected to
a Cremat Model CR-110 pre-amplifier. The absolute light yield
expressed in photons per MeV (ph/MeV) was determined by correcting
for the quantum efficiency and reflectivity of the PMT.
[0167] The energy resolution ("ER") is obtained from the data
collected using the samples and equipment as previously described.
Tables 2 and 3 include the energy resolution data for Samples 1 to
10.
TABLE-US-00002 TABLE 2 Energy Resolution Data Sample 8 13 17 22 26
32 44 60 81 # Description keV keV keV keV keV keV keV keV keV 1
Undoped 40.8 30.9 23.9 20.1 16.7 15.9 14.3 11.3 9.35
La.sub.0.95Ce.sub.0.05Br.sub.3 2 Ca-doped 32.3 24.4 18.7 17.2 --
12.1 10.5 8.52 7.38 La.sub.0.95Ce.sub.0.05Br.sub.3 3 Sr-doped 34.9
26.5 21.3 18.0 14.9 14.4 12.2 9.08 7.62
La.sub.0.95Ce.sub.0.05Br.sub.3 4 Ba-doped 33.4 31.6 19.7 16.9 --
15.3 13.9 10.3 8.70 La.sub.0.95Ce.sub.0.05Br.sub.3 5 0.5% Na-doped
41.7 29.6 23.8 19.8 14.9 15.1 13.9 10.1 8.38
La.sub.0.95Ce.sub.0.05Br.sub.3 6 2% Na-doped -- -- -- -- -- 16.7 --
11.7 -- La.sub.0.95Ce.sub.0.05Br.sub.3 7 Undoped CeBr.sub.3 72.7
44.6 36.1 30.5 -- 24.9 23.4 18.0 14.7 8 Ca-doped CeBr.sub.3 53.4
36.0 29.7 24.8 -- 19.2 17.8 13.6 11.3 9 Sr-doped CeBr.sub.3 55.5
34.1 28.6 23.7 -- 18.3 16.9 12.8 10.7 10 Na-doped CeBr.sub.3 64.7
40.4 34.0 28.0 -- 22.5 22.0 16.8 13.5
TABLE-US-00003 TABLE 3 Energy Resolution Data Sample 276 303 356
384 511 662 1173 1274 1332 # Description keV keV keV keV keV keV
keV keV keV 1 Undoped 5.45 4.83 4.68 4.51 3.96 3.57 2.96 3.33 2.81
La.sub.0.95Ce.sub.0.05Br.sub.3 2 Ca-doped 4.55 4.11 3.93 3.74 3.43
2.94 2.66 2.64 2.27 La.sub.0.95Ce.sub.0.05Br.sub.3 3 Sr-doped 4.02
3.90 3.88 3.82 3.39 2.95 2.32 2.71 2.40
La.sub.0.95Ce.sub.0.05Br.sub.3 4 Ba-doped 5.37 4.88 4.97 4.62 4.37
3.8 3.24 4.13 2.52 La.sub.0.95Ce.sub.0.05Br.sub.3 5 0.5% Na-doped
4.57 3.99 3.83 3.69 3.20 2.73 2.20 2.12 1.97
La.sub.0.95Ce.sub.0.05Br.sub.3 6 2% Na-doped -- -- -- -- -- -- --
-- -- La.sub.0.95Ce.sub.0.05Br.sub.3 7 Undoped CeBr.sub.3 7.50 6.80
6.98 5.60 5.71 4.93 4.51 4.67 3.09 8 Ca-doped CeBr.sub.3 5.96 5.63
5.28 4.93 4.39 3.64 3.41 3.44 3.16 9 Sr-doped CeBr.sub.3 6.00 5.05
4.81 4.40 4.03 3.45 3.00 2.73 2.60 10 Na-doped CeBr.sub.3 5.99 6.03
5.83 5.76 4.78 4.11 3.41 3.16 3.01
[0168] FIGS. 2 and 3 include plots for the data for Samples 1 to 5.
FIG. 2 includes energy resolution the data for energies in a range
of 8 keV to 81 keV, and FIG. 3 includes the energy resolution data
for energies in a range of 276 keV to 662 keV. FIGS. 4 and 5
include plots for the data for Samples 7 to 10. FIG. 4 includes
energy resolution the data for energies in a range of 8 keV to 81
keV, and FIG. 5 includes the energy resolution data for energies in
a range of 276 keV to 662 keV.
[0169] The energy resolution ratio ("ER Ratio) is the ratio of the
energy resolution of a particular sample divided by the energy
resolution of another sample. By using the ER Ratio, the comparison
between two different scintillation crystals should have less
dependence on the energy, as opposed to using only the energy
resolution. Tables 4 and 5 include the ER Ratio data. Samples 2 to
6 are compared to Sample 1, and Samples 8 to 10 are compared to
Sample 7. For example, the ER Ratio for Sample 2 (in Tables 4 and
5) is the ER for Sample 2 (in Tables 2 and 3) divided by the ER for
Sample 1 (in Tables 2 and 3). "N/A" indicates that the ER Ratio is
not applicable for the particular sample.
TABLE-US-00004 TABLE 4 ER Ratios Sample 8 13 17 22 26 32 44 60 81 #
Description keV keV keV keV keV keV keV keV keV 1 Undoped N/A N/A
N/A N/A N/A N/A N/A N/A N/A La.sub.0.95Ce.sub.0.05Br.sub.3 2
Ca-doped 0.791 0.791 0.781 0.848 -- 0.762 0.730 0.757 0.789
La.sub.0.95Ce.sub.0.05Br.sub.3 3 Sr-doped 0.857 0.860 0.891 0.897
0.889 0.889 0.850 0.806 0.806 La.sub.0.95Ce.sub.0.05Br.sub.3 4
Ba-doped 0.820 1.02 0.823 0.843 -- 0.962 0.971 0.910 0.930
La.sub.0.95Ce.sub.0.05Br.sub.3 5 0.5% Na-doped 1.02 0.960 0.996
0.989 0.889 0.949 0.966 0.898 0.896 La.sub.0.95Ce.sub.0.05Br.sub.3
6 2% Na-doped -- -- -- -- -- 1.05 -- 1.04 --
La.sub.0.95Ce.sub.0.05Br.sub.3 7 Undoped CeBr.sub.3 N/A N/A N/A N/A
N/A N/A N/A N/A N/A 8 Ca-doped CeBr.sub.3 0.732 0.807 0.822 0.812
0.771 0.771 0.769 0.754 0.765 9 Sr-doped CeBr.sub.3 0.762 0.763
0.791 0.778 0.733 0.733 0.722 0.708 0.725 10 Na-doped CeBr.sub.3
0.892 0.906 0.941 0.920 0.904 0.905 0.942 0.935 0.917
TABLE-US-00005 TABLE 5 ER Ratios Sample 276 303 356 384 511 662
1173 1274 1332 # Description keV keV keV keV keV keV keV keV keV 1
Undoped N/A N/A N/A N/A N/A N/A N/A N/A N/A
La.sub.0.95Ce.sub.0.05Br.sub.3 2 Ca-doped 0.834 0.851 0.840 0.829
0.866 0.824 0.899 0.793 0.808 La.sub.0.95Ce.sub.0.05Br.sub.3 3
Sr-doped 0.738 0.807 0.829 0.847 0.856 0.826 0.784 0.814 0.854
La.sub.0.95Ce.sub.0.05Br.sub.3 4 Ba-doped 0.985 1.01 1.06 1.02 1.10
1.06 1.09 1.24 0.897 La.sub.0.95Ce.sub.0.05Br.sub.3 5 0.5% Na-doped
0.839 0.826 0.818 0.818 0.808 0.765 0.743 0.647 0.676
La.sub.0.95Ce.sub.0.05Br.sub.3 6 2% Na-doped -- -- -- -- -- -- --
-- -- La.sub.0.95Ce.sub.0.05Br.sub.3 7 Undoped CeBr.sub.3 N/A N/A
N/A N/A N/A N/A N/A N/A N/A 8 Ca-doped CeBr.sub.3 0.795 0.828 0.756
0.880 0.769 0.738 0.756 0.737 1.02 9 Sr-doped CeBr.sub.3 0.800
0.743 0.689 0.786 0.706 0.700 0.665 0.858 0.840 10 Na-doped
CeBr.sub.3 0.799 0.887 0.835 1.03 0.837 0.829 0.756 0.677 0.974
[0170] The data show some variation in ER Ratios for each of the
dopants. The variation for Samples 2 and 3 (Ca-doped and Sr-doped)
have ER Ratios with relatively low standard deviation. Sample 2 has
an average ER Ratio of 0.81 and a standard deviation of 0.04, and
Sample 3 has an average ER Ratio of 0.84 and a standard deviation
of 0.04. Sample 4 (Ba-doped) has a significantly higher ER Ratio
average of 0.99 and a standard deviation of 0.11. Sample 5
(Na-doped) has an intermediate ER Ratio of 0.86 and a standard
deviation 0.11. The data suggest that, starting at 60 keV, the ER
Ratio for Sample 5 decreases with increasing energy. At 511 keV,
Sample 5 has an ER Ratio less than 0.8, and at 1274 keV, Sample 5
has an ER Ratio less than 0.7. Unlike Sample 5, Samples 2 to 4 do
not appear to have any discernible trends regarding ER Ratio as
energy increases or decreases.
[0171] Data for proportionality was also gathered. Proportionality
was studied with a set of set of radioactive sources .sup.60Co,
.sup.22Na, .sup.137Cs, .sup.133Ba, .sup.241 Am, plus Amersham
variable energy X-ray source, and at the X-1 beamline at the
Hamburger Synchrotronstrahlungslabor (HASYLAB) synchrotron
radiation facility in Hamburg, Germany using the experimental setup
previously references. X-ray excited luminescence spectra were
recorded using an X-ray tube with Cu anode operating at 60 kV and
25 mA. The emission of the sample was focused via a quartz window
and a lens on the entrance slit of an ARC Model VM-504
monochromator (blazed at 300 nm, 1200 grooves/mm), dispersed and
recorded with a Hamamatsu Model R943-02 PMT. The spectra were
corrected for the monochromator transmission and for the quantum
efficiency of the PMT. X-ray excited luminescence measurements were
performed between 80K and 600K using a Janis Model VPF-800 Cryostat
operated with a LakeShore Model 331 Temperature Controller. The PMT
was outside the cryostat and remained at room temperature.
[0172] As previously discussed, the departure from perfect
proportionality is more significant at lower gamma ray energies
because higher energy gamma rays can collide with the scintillator
crystal and result in lower energy gamma rays. Tables 6 and 7
include nPR data collected for the scintillation crystals when
exposed to gamma ray energies in a range of approximately 8 keV to
approximately 1332 keV. Table 8 includes nPR data collected for the
LaBr.sub.3:Ce scintillation crystals when exposed to gamma ray
energies in a range of approximately 11 keV to approximately 100
keV. Table 9 includes nPR data collected for the CeBr.sub.3
scintillation crystals when exposed to gamma ray energies in a
range of approximately 13 keV to approximately 100 keV. Data
collected at 662 keV was used for determining the nPR data in Table
6 to 9.
TABLE-US-00006 TABLE 6 nPR Data Sample 8 13 17 22 26 32 44 60 81 #
Description keV keV keV keV keV keV keV keV keV 1 Undoped 90.4 96.8
94.1 95.7 96.9 98.4 97.7 98.6 99.6 La.sub.0.95Ce.sub.0.05Br.sub.3 2
Ca-doped 100 105 103 103 -- 104 103 104 102
La.sub.0.95Ce.sub.0.05Br.sub.3 3 Sr-doped 98.0 102 100 101 100 102
101 102 102 La.sub.0.95Ce.sub.0.05Br.sub.3 4 Ba-doped 96.5 -- 99.3
101 101 101 101 102 101 La.sub.0.95Ce.sub.0.05Br.sub.3 5 0.5%
Na-doped 88.8 96.4 94.2 96.1 97.0 98.3 97.0 99.4 99.8
La.sub.0.95Ce.sub.0.05Br.sub.3 7 Undoped CeBr.sub.3 71.1 81.7 82.2
85.7 -- 90.4 90.0 91.6 95.0 8 Ca-doped CeBr.sub.3 84.5 93.2 92.1
94.9 -- 96.8 96.0 98.4 98.8 9 Sr-doped CeBr.sub.3 84.7 93.5 92.9
95.4 -- 97.5 96.1 97.7 99.2 10 Na-doped CeBr.sub.3 74.0 83.3 83.8
87.3 -- 91.8 91.4 92.8 96.4
TABLE-US-00007 TABLE 7 nPR Data Sample 276 303 356 384 511 662 1173
1274 1332 # Description keV keV keV keV keV keV keV keV keV 1
Undoped 100 100 100 100 101 100 100 100 100
La.sub.0.95Ce.sub.0.05Br.sub.3 2 Ca-doped 101 101 101 101 101 100
100 100 100 La.sub.0.95Ce.sub.0.05Br.sub.3 3 Sr-doped 101 101 100
100 101 100 100 100 100 La.sub.0.95Ce.sub.0.05Br.sub.3 4 Ba-doped
101 101 100 101 101 100 100 100 100 La.sub.0.95Ce.sub.0.05Br.sub.3
5 0.5% Na-doped 100 101 101 100 101 100 100 100 100
La.sub.0.95Ce.sub.0.05Br.sub.3 7 Undoped CeBr.sub.3 99.3 100 100
100 100 100 100 100 101 8 Ca-doped CeBr.sub.3 100 100 100 100 100
100 100 100 100 9 Sr-doped CeBr.sub.3 100 100 100 100 100 100 100
100 100 10 Na-doped CeBr.sub.3 100 101 101 100 101 100 100 100
100
TABLE-US-00008 TABLE 8 nPRs Data Energy Undoped Sr-doped Ca-doped
(keV) La.sub.0.95Ce.sub.0.05Br.sub.3 La.sub.0.95Ce.sub.0.05Br.sub.3
La.sub.0.95Ce.sub.0.05Br.sub.3 11 86.7 100 97.3 12 87.9 101 99.7 15
88.2 100 100 20 90.9 102 103 25 93.4 103 105 30 95.1 103 105 35
96.3 103 104 38 96.7 103 104 48 95.8 102 103 50 96.2 102 103 55
96.8 102 103 60 97.2 102 103 65 97.4 102 103 70 97.9 102 103 75
98.0 102 103 80 98.3 102 103 85 98.5 102 102 90 98.5 102 102 95
98.6 102 102 100 98.8 102 102
TABLE-US-00009 TABLE 9 nPRs Energy Undoped Sr-doped (keV)
CeBr.sub.3 CeBr.sub.3 13 80.6 90.1 15 78.7 88.1 20 84.3 92.0 25
88.0 94.4 30 90.6 95.9 35 92.4 96.6 40 93.5 97.3 45 91.0 95.6 50
92.1 96.3 55 93.0 96.9 60 93.6 97.3 65 95.4 97.4 70 94.9 97.6 75
95.3 97.6 80 95.9 97.8 85 96.2 97.9 90 96.4 97.9 95 96.6 98.0 100
96.9 98.1
[0173] FIGS. 6 and 7 include plots that include the data for
Samples 1 to 5, which are the La.sub.0.95Ce.sub.0.5Br.sub.3
samples. FIG. 6 includes energy resolution the data for energies in
a range of 8 keV to 1332 keV. The plot shows that the Samples 2 to
4 (Ca-doped, Sr-doped, and Ba-doped) have nPRs values that are much
closer to 100% for lower energies, as compared to Sample 1
(undoped). Sample 5 (Na-doped) does not appear to have any
significant improvement for nPR as compared to Sample 1. FIG. 7
includes the nPR data for Samples 1 to 3 for energies in a range of
9 keV to 100 keV. The difference between Sample 1 and each of
Samples 2 and 3 is apparent in FIG. 7. The difference between
Sample 1 and each of Samples 2 and 3 is more evident at energies of
32 keV and lower. From the data, Sample 3 appears to have
proportionality that is the closest to perfect proportionality over
the energy ranges tested, as compared to the other Samples. Sample
2 has slightly less uniform proportionality than Sample 3 and has
significantly better proportionality as compared to Samples 1 and
5.
[0174] FIGS. 8 and 9 include plots that include the data for
Samples 7 to 10, which are the CeBr.sub.3 samples. FIG. 8 includes
energy resolution the data for energies in a range of 8 keV to 1332
keV. The plot shows that the Samples 8 and 9 (Ca-doped and
Sr-doped) have nPRs values that are much closer to 100% for lower
energies, as compared to Sample 7 (undoped). Samples 8 and 9 have
proportionalities that are close to each other over the range of
energies tested. Sample 10 (Na-doped) does not appear to have any
significant improvement for nPR as compared to Sample 7. FIG. 9
includes the nPR data for Samples 7 and 9 for energies in a range
of 10 keV to 100 keV. The difference between Sample 7 and Sample 9
is apparent in FIG. 9. The difference between Sample 7 and Sample 9
is more evident at energies of 32 keV and lower.
[0175] The amount of deviation from 100% and the direction of the
deviation can be obtained by subtracting 100% from the nPR values,
which is nPR.sub.dev that is also in units of %. The equation is
provided below.
nPR.sub.dev=nPR-100%.
[0176] Tables 10 to 13 include the nPR.sub.dev data that is derived
from the nPR data in Tables 6 to 9.
TABLE-US-00010 TABLE 10 nPR.sub.dev Data Sample 8 13 17 22 26 32 44
60 81 # Description keV keV keV keV keV keV keV keV keV 1 Undoped
-9.6 -3.2 -5.9 -4.3 -3.1 -1.6 -2.3 -1.4 -0.4
La.sub.0.95Ce.sub.0.05Br.sub.3 2 Ca-doped 0.3 4.6 2.5 3.1 -- 3.7
3.0 3.5 2.2 La.sub.0.95Ce.sub.0.05Br.sub.3 3 Sr-doped -2.0 1.5 -0.1
0.5 0.3 1.8 1.2 2.3 1.9 La.sub.0.95Ce.sub.0.05Br.sub.3 4 Ba-doped
-3.5 -- -0.3 0.7 1.1 1.3 0.7 1.5 1.2 La.sub.0.95Ce.sub.0.05Br.sub.3
5 0.5% Na-doped -11.2 -3.6 -5.8 -3.9 -3.0 -1.7 -2.3 -0.6 -0.2
La.sub.0.95Ce.sub.0.05Br.sub.3 7 Undoped CeBr.sub.3 -28.9 -18.3
-17.8 -14.3 -- -9.6 -10.0 -8.4 -5.0 8 Ca-doped CeBr.sub.3 -26.0
-6.8 -7.9 -5.2 -- -3.2 -4.0 -1.6 -1.3 9 Sr-doped CeBr.sub.3 -15.3
-6.5 -7.1 -4.6 -- -2.5 -3.9 -2.3 -0.8 10 Na-doped CeBr.sub.3 -15.5
-16.7 -16.2 -12.7 -- -8.2 -8.6 -7.2 -3.6
TABLE-US-00011 TABLE 11 nPR.sub.dev Data Sample 276 303 356 384 511
662 1173 1274 1332 # Description keV keV keV keV keV keV keV keV
keV 1 Undoped 0.1 0.4 0.3 0.3 0.8 0.0 0.0 0.0 0.1
La.sub.0.95Ce.sub.0.05Br.sub.3 2 Ca-doped 0.7 0.7 0.6 0.5 0.9 0.0
0.1 0.2 0.1 La.sub.0.95Ce.sub.0.05Br.sub.3 3 Sr-doped 0.6 0.6 0.4
0.2 0.5 0.0 0.1 -0.1 0.0 La.sub.0.95Ce.sub.0.05Br.sub.3 4 Ba-doped
0.7 0.6 0.4 0.5 0.5 0.0 0.1 0.2 0.3 La.sub.0.95Ce.sub.0.05Br.sub.3
5 0.5% Na-doped 0.3 0.5 0.5 0.2 0.6 0.0 -0.2 -0.4 -0.5
La.sub.0.95Ce.sub.0.05Br.sub.3 7 Undoped CeBr.sub.3 -0.7 -0.4 -0.3
0.1 0.1 0.0 0.0 0.4 0.6 8 Ca-doped CeBr.sub.3 -0.2 0.2 0.1 0.2 0.5
0.0 0.1 0.2 0.3 9 Sr-doped CeBr.sub.3 -0.1 0.1 0.1 0.0 0.4 0.0 0.0
0.0 0.0 10 Na-doped CeBr.sub.3 0.0 0.5 0.6 0.4 0.5 0.0 0.2 0.3
0.2
TABLE-US-00012 TABLE 12 nPR .sub.dev Data Energy Undoped Sr-doped
Ca-doped (keV) La.sub.0.95Ce.sub.0.05Br.sub.3
La.sub.0.95Ce.sub.0.05Br.sub.3 La.sub.0.95Ce.sub.0.05Br.sub.3 11
-13.3 0.38 -2.62 12 -12.1 0.02 0.32 15 -11.8 0.12 0.16 20 -9.03
1.62 3.45 25 -6.60 1.88 4.55 30 -4.85 2.58 4.63 35 -3.68 2.79 4.11
38 -3.27 2.62 3.74 48 -4.20 2.24 3.19 50 -3.80 2.26 3.22 55 -3.24
2.36 3.16 60 -2.82 2.30 3.00 65 -2.55 2.23 2.89 70 -2.08 2.12 2.87
75 -2.00 1.99 2.58 80 -1.67 1.96 2.59 85 -1.52 1.94 2.49 90 -1.45
1.78 2.30 95 -1.35 1.69 2.18 100 -1.21 1.70 2.10
TABLE-US-00013 TABLE 13 nPR .sub.dev Data Energy Undoped Sr-doped
(keV) CeBr.sub.3 CeBr.sub.3 13 -19.4 -9.88 15 -21.3 -11.9 20 -15.7
-9.02 25 -12.0 -5.59 30 -9.42 -4.12 35 -7.60 -3.38 40 -6.46 -2.66
45 -9.00 -4.41 50 -7.85 -3.72 55 -6.95 -3.09 60 -6.37 -2.70 65
-5.47 -2.58 70 -5.06 -2.42 75 -4.65 -2.37 80 -4.13 -2.25 85 -3.80
-2.10 90 -3.54 -2.05 95 -3.36 -2.00 100 -3.06 -1.89
[0177] FIGS. 8 and 9 include plots for the data for Samples 7 to
10, which are the CeBr.sub.3 samples. FIG. 8 includes energy
resolution the data for energies in a range of 8 keV to 1332 keV.
The plot shows that the Samples 8 and 9 (Ca-doped and Sr-doped)
have nPRs values that are much closer to 100% for lower energies,
as compared to Sample 7 (undoped). Samples 8 and 9 have
proportionalities that are close to each other over the range of
energies tested. Sample 10 (Na-doped) does not appear to have any
significant improvement for nPR, as compared to Sample 7. FIG. 9
includes the nPR data for Samples 7 and 9 for energies in a range
of 10 keV to 100 keV. The difference between Sample 7 and Sample 9
is apparent in FIG. 9. The difference between Sample 7 and Sample 9
is more evident at energies of 32 keV and lower.
[0178] Data for nPR.sub.dev can be used to determine an nPR.sub.dev
average for a particular range of energies. Table 14 includes
nPR.sub.dev average values determined as previously described.
TABLE-US-00014 TABLE 14 nPR dev average Data 11 or 13 Sam keV to 30
30 keV to 60 keV to 356 keV to ple # Description keV 60 keV 356 keV
1332 keV 1 Undoped 8.9 3.7 0.26 0.15 La.sub.0.95Ce.sub.0.05Br.sub.3
2 Ca-doped 2.6 3.6 1.3 0.23 La.sub.0.95Ce.sub.0.05Br.sub.3 3
Sr-doped 1.3 2.5 1.2 0.13 La.sub.0.95Ce.sub.0.05Br.sub.3 4 Ba-doped
-- -- 0.90 0.17 La.sub.0.95Ce.sub.0.05Br.sub.3 5 0.5% Na-doped --
-- 0.63 0.22 La.sub.0.95Ce.sub.0.05Br.sub.3 7 Undoped 15.8 7.7 2.5
0.08 CeBr.sub.3 8 Ca-doped -- -- 0.63 015 CeBr.sub.3 9 Sr-doped 8.0
3.4 0.43 0.06 CeBr.sub.3 10 Na-doped -- -- 1.7 0.20 CeBr.sub.3
[0179] Data for nPR.sub.dev average is good for distinguishing
which samples are more proportional over one or more ranges of
energies. For the La.sub.0.95Ce.sub.0.05Br.sub.3 samples, Sample 3
(Sr-doped) has the best performance over all the energies,
particularly at energies from 11 keV to 60 keV. Sample 2 has good
proportionality at 11 to 30 keV. At energies in a range of 30 to 60
keV, Sample 2 has nearly the same magnitude of deviation from
proportionality as compared to Sample 1. The deviation for Samples
1 and 2 are in opposite directions (- for Sample 1 and + for Sample
2). For energies in a range of 60 keV to 356 keV, Samples 2 to 4
have positive deviation from 100%, and Sample 1 has deviation from
100% that is closer to zero. For energies in a range of 356 keV to
1332 keV, the Samples 1 to 5 have nPR.sub.dev average values that
are less than 0.1% different from one another.
[0180] For the CeBr.sub.3 samples, Sample 9 (Sr-doped) has the best
performance over all the energies, particularly at energies from 11
keV to 60 keV. Although Sample 8 (Ca-doped) does not have as much
data, the relationship between Samples 8 and 9 for nPR.sub.dev
average is expected to be about the same as the relationship
between Samples 2 and 3 for nPR.sub.dev average. For energies in a
range of 60 keV to 356 keV, Samples 8 and 9 have better
proportionality compared to Sample 7 (undoped). For energies in a
range of 356 keV to 1332 keV, the Samples 7 to 9 have nPR.sub.dev
average values that are less than 0.1% different from one
another.
[0181] Data have been taken on the relative response of standard
and co-doped lanthanum bromide versus temperature. The samples
include LaBr.sub.3(Ce), LaBr.sub.3(Ce,Sr) and LaBr.sub.3(Ce,Ba).
The cerium concentration in each sample was 4.5 to 5%, meaning that
4.5 to 5% of the La atoms were replaced by Ce. The Sr concentration
was 180 parts per million by weight, and the Ba concentration was
160 parts per million by weight. Each crystal was formed as a right
circular cylinder with dimensions where the diameter was
approximately 2.5 cm and length was approximately 2.5 cm. The light
output was measured by locating the centroid of the 662 keV
photopeak from a 10 micro-Ci .sup.137Cs gamma ray source. The
source was placed at a distance of 10 mm from one end of the
crystal. The other end was coupled to a photomultiplier tube
(model: Photonis 20Y0) that was kept at a constant 30.degree.
C.
[0182] FIG. 10 includes a plot showing the temperature response of
standard, LaBr.sub.3(Ce), LaBr.sub.3(Ce,Sr) and LaBr.sub.3(Ce,Ba).
Specifically, the graph shows how the scintillation light output
changes with temperature from -40.degree. C. to 175.degree. C. Each
curve is normalized to 1.0 at 25.degree. C. When co-doped with Sr,
the light output is more constant than standard over the range of
-40.degree. C. to 175.degree. C., and is measurably brighter than
standard at the highest temperatures. This makes Sr co-doped
lanthanum bromide desirable for applications that involve extreme
temperature excursions, such as oil well logging and space
applications. When co-doped with Ba, the light output increases
over the range of room temperature (approximately 22.degree. C.) to
about 70.degree. C. This makes Ba co-doped lanthanum bromide
desirable for outdoor applications, for example for port-of-entry
detectors that can be used for vehicles and cargo.
[0183] Note that not all of the activities described above in the
general description or the examples are required, that a portion of
a specific activity may not be required, and that one or more
further activities may be performed in addition to those described.
Still further, the order in which activities are listed is not
necessarily the order in which they are performed.
[0184] Certain features that are, for clarity, described herein in
the context of separate embodiments, may also be provided in
combination in a single embodiment. Conversely, various features
that are, for brevity, described in the context of a single
embodiment, may also be provided separately or in any
subcombination. Further, reference to values stated in ranges
includes each and every value within that range.
[0185] Benefits, other advantages, and solutions to problems have
been described above with regard to specific embodiments. However,
the benefits, advantages, solutions to problems, and any feature(s)
that may cause any benefit, advantage, or solution to occur or
become more pronounced are not to be construed as a critical,
required, or essential feature of any or all the claims.
[0186] The specification and illustrations of the embodiments
described herein are intended to provide a general understanding of
the structure of the various embodiments. The specification and
illustrations are not intended to serve as an exhaustive and
comprehensive description of all of the elements and features of
apparatus and systems that use the structures or methods described
herein. Separate embodiments may also be provided in combination in
a single embodiment, and conversely, various features that are, for
brevity, described in the context of a single embodiment, may also
be provided separately or in any subcombination. Further, reference
to values stated in ranges includes each and every value within
that range. Many other embodiments may be apparent to skilled
artisans only after reading this specification. Other embodiments
may be used and derived from the disclosure, such that a structural
substitution, logical substitution, or another change may be made
without departing from the scope of the disclosure. Accordingly,
the disclosure is to be regarded as illustrative rather than
restrictive.
* * * * *