U.S. patent application number 15/344853 was filed with the patent office on 2017-09-28 for radiation detectors.
This patent application is currently assigned to Radiation Monitoring Devices, Inc.. The applicant listed for this patent is Radiation Monitoring Devices, Inc.. Invention is credited to Leonard Cirignano, Andrey Gueorguiev, Alireza Kargar, Hadong Kim, Kanai S. Shah.
Application Number | 20170279001 15/344853 |
Document ID | / |
Family ID | 57210878 |
Filed Date | 2017-09-28 |
United States Patent
Application |
20170279001 |
Kind Code |
A1 |
Shah; Kanai S. ; et
al. |
September 28, 2017 |
RADIATION DETECTORS
Abstract
A detector for detecting radiation is generally described. The
detector can comprise at least one ionic semiconductor material.
For example, the ionic semiconductor material comprises a thallium
halide and/or an indium halide. Electrical contacts are formed on
the semiconductor material to provide a voltage to the detector
during use. At least one of the electrical contacts may comprise a
liquid that contains ions. In some instances, at least one
electrical contact comprises a metal, such as Cr, Ti, W, Mo, or Pb.
In some embodiments, the detector comprises both an electrical
contact comprising liquid comprising ions and an electrical contact
comprising a metal selected from a group consisting of Cr, Ti, W,
Mo, and Pb. Detectors for detecting radiation, as described herein,
may have beneficial properties.
Inventors: |
Shah; Kanai S.; (Watertown,
MA) ; Gueorguiev; Andrey; (Burlington, MA) ;
Cirignano; Leonard; (Cambridge, MA) ; Kim;
Hadong; (Methuen, MA) ; Kargar; Alireza;
(Watertown, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Radiation Monitoring Devices, Inc. |
Watertown |
MA |
US |
|
|
Assignee: |
Radiation Monitoring Devices,
Inc.
Watertown
MA
|
Family ID: |
57210878 |
Appl. No.: |
15/344853 |
Filed: |
November 7, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13888277 |
May 6, 2013 |
9490374 |
|
|
15344853 |
|
|
|
|
61642876 |
May 4, 2012 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 31/085 20130101;
H01L 31/032 20130101; G01T 1/241 20130101 |
International
Class: |
H01L 31/08 20060101
H01L031/08; H01L 31/032 20060101 H01L031/032; G01T 1/24 20060101
G01T001/24 |
Claims
1. A radiation detector, comprising: an ionic semiconductor
material; and an electrical contact on the ionic semiconductor
material, wherein the electrical contact comprises a liquid
comprising ions.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 13/888,277, filed May 6, 2013, which claims
priority under 35 U.S.C. .sctn.119(e) to U.S. Provisional Patent
Application Serial No. 61/642,876, filed May 4, 2012, which are
incorporated herein by reference in their entirety for all
purposes.
TECHNICAL FIELD
[0002] Detectors and methods for detecting radiation are generally
described.
BACKGROUND
[0003] Radiation detection is of major interest in a host of
applications in nuclear medicine, fundamental physics, industrial
gauging, baggage scanners, and oil well logging, amongst
others.
[0004] Semiconductor detectors, such as silicon avalanche
photodiodes (Si-APDs), are widely used for the detection of X-rays,
gamma-rays, as well as particles like neutrons, alpha particles
etc. Ionic semiconductor detectors can have higher photoelectric
and total attenuation coefficients than other semiconductor
detectors for gamma-rays. Ionic semiconductor detectors can also
operate at room temperature with low dark current in the same
manner as other semiconductor detectors. However, ionic
semiconductor detectors, such as thallium bromide, generally have
not been widely used due performance problems, such as reduced
internal field and detector instability, which can result from
polarization under applied bias at room temperature. Accordingly,
improved detectors and methods are would be useful.
SUMMARY
[0005] A detector for detecting radiation is generally
described.
[0006] In one set of embodiments, a radiation detector comprises an
ionic semiconductor material and an electrical contact on the ionic
semiconductor material, wherein the electrical contact comprises a
liquid comprising ions.
[0007] In another set of embodiments, a radiation detector
comprises an ionic semiconductor material and an electrical contact
on the ionic semiconductor material, wherein the electrical contact
comprises at least one layer. In some embodiments, the layer
comprises an element selected from the group consisting of Cr, Ti,
W, Mo, and Pb and the layer forms substantially the entire
interface between the electrical contact and the semiconductor
material.
[0008] In one set of embodiments, a radiation detector comprises an
ionic semiconductor material and an electrical contact on the ionic
semiconductor material, wherein the electrical contact comprises at
least one layer. In some embodiments, the layer comprises an
element selected from the group consisting of Cr, Ti, W, Mo, and
Pb, and the thickness of the layer is greater than or equal to
about 40 nm.
[0009] In another set of embodiments, a radiation detector
comprises an ionic semiconductor material and an electrical contact
on the ionic semiconductor material, wherein the electrical contact
comprises a metal selected from the group consisting of Cr, Ti, W,
Mo, and Pb. In some embodiments, the detector has a stability of
greater than or equal to about 5 days at room temperature under
continuous bias of 100 V/mm.
[0010] Other advantages and novel features of the present invention
will become apparent from the following detailed description of
various non-limiting embodiments of the invention when considered
in conjunction with the accompanying figures. In cases where the
present specification and a document incorporated by reference
include conflicting and/or inconsistent disclosure, the present
specification shall control.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Non-limiting embodiments of the present invention will be
described by way of example with reference to the accompanying
figures, which are schematic and are not intended to be drawn to
scale. In the figures, each identical or nearly identical component
illustrated is typically represented by a single numeral. For
purposes of clarity, not every component is labeled in every
figure, nor is every component of each embodiment of the invention
shown where illustration is not necessary to allow those of
ordinary skill in the art to understand the invention. In the
figures:
[0012] FIG. 1 illustrates a detector, according to one set of
embodiments;
[0013] FIG. 2A-B illustrate detectors during use, according to
certain embodiments;
[0014] FIG. 3A-B illustrate detectors, according to certain
embodiments;
[0015] FIG. 4A-B illustrate a gold electrical contact (A) before
and (B) after use, according to one set of embodiments.
[0016] FIG. 5A-B illustrate (A) a pulse height spectra for a
Cr/TlBr/Cr detector and (B) a pulse height spectra for a Au/TlBr/Au
detector.
DETAILED DESCRIPTION
[0017] A detector for detecting radiation is generally described.
The detector can comprise at least one ionic semiconductor
material. For example, the ionic semiconductor material comprises a
thallium halide (e.g., TlBr) and/or an indium halide. Electrical
contacts are formed on the semiconductor material to provide a
voltage to the detector during use. At least one of the electrical
contacts may comprise a liquid that contains ions. For example, the
liquid comprises ions capable of associating with an ionic species
originating from the ionic semiconductor material. In some
instances, at least one electrical contact comprises a metal, such
as Cr, Ti, W, Mo, or Pb. In some embodiments, the detector
comprises both an electrical contact comprising liquid comprising
ions and an electrical contact comprising a metal selected from the
group consisting of Cr, Ti, W, Mo, and Pb. Detectors for detecting
radiation, as described herein, may have beneficial properties,
such as enhanced stability, sensitivity, and efficiency, amongst
others.
[0018] As shown in FIG. 1, a detector 10 for detecting radiation
may comprise an ionic semiconductor material 15. At least one
electrical contact may be positioned on, directly or indirectly,
the ionic semiconductor material, such that the ionic semiconductor
material is in electrical communication with the electrical
contact. In some instances, the detector comprises two or more
electrical contacts (e.g., 20 and 25) as shown in FIG. 1.
[0019] In some cases, an electrical contact on the ionic
semiconductor material is the same as another electrical contact on
the ionic semiconductor material. In certain cases, an electrical
contact on the ionic semiconductor material is different than
another electrical detector on the ionic semiconductor material. In
one example, an electrical contact comprising Cr and an electrical
contact comprising a liquid comprising halide ions are positioned
on the ionic semiconductor material.
[0020] As mentioned above, a detector for detecting radiation
includes an ionic semiconductor material. In general, any suitable
ionic semiconductor material may be used. In some embodiments, the
ionic semiconductor material comprises thallium. The ionic
semiconductor material may comprise one or more thallium compounds
(e.g., two, three, four). In some instances, one or more thallium
compounds in the ionic semiconductor material may be a thallium
halide. That is, a compound of thallium and one or more halide
element. For example, the ionic semiconductor material may comprise
thallium bromide, thallium iodide, thallium chloride, thallium
fluoride, thallium bromochloride, thallium bromoiodide, or
combinations thereof.
[0021] In some embodiments, the ionic semiconductor material
comprises indium. The ionic semiconductor material may comprise one
or more indium compounds (e.g., two, three, four). In some
instances, one or more indium compounds in the ionic semiconductor
material may be an indium halide. That is, a compound of indium and
one or more halide element. For example, the ionic semiconductor
material may comprise indium bromide, indium iodide, indium
chloride, indium fluoride, indium bromochloride, indium
bromoiodide, or combinations thereof.
[0022] In some embodiments, the ionic semiconductor material
comprises thallium and indium. For example, the ionic semiconductor
material may comprise at least one thallium compound and at least
one indium compound. Those of ordinary skill in the art would be
knowledgeable of suitable ionic semiconductor materials for use in
a radiation detector, including those comprising thallium and/or
indium.
[0023] In some embodiments, the ionic semiconductor material may be
relatively thick. For instance, in some embodiments, the ionic
semiconductor material has a thickness of greater than or equal to
about 0.5 mm, greater than or equal to about 1 mm, greater than or
equal to about 5 mm, greater than or equal to about 10 mm, or
greater than or equal to 15 mm. In some instance, the ionic
semiconductor material has a thickness of less than or equal to
about 20 mm, less than or equal to about 15 mm, less than or equal
to about 10 mm, or less than or equal to about 5 mm. It should be
understood that all combinations of the above-referenced ranges are
also possible (e.g., greater than or equal to about 5 mm and less
than or equal to about 20 mm).
[0024] As described herein, electrical contacts are formed on the
semiconductor material to provide a voltage on the detector during
use. In some embodiments, certain ionic semiconductor materials may
comprise ionic species that move in response to an applied voltage.
In some such cases, certain ionic species may move toward an
electrical contact. In certain instances, the ionic species move
until they are associated (e.g., via a chemical bond, via physical
proximity) with the at least a portion of the electrical contact.
In some cases, the ionic species may accumulate at or near at least
a portion of the electrical contact.
[0025] In some embodiments, an electrical contact on the ionic
semiconductor comprises a liquid. The liquid may comprise ions that
are capable of associating with ionic species originating from the
ionic semiconductor material. The ions in the liquid and the ionic
species originating from the ionic semiconductor material may
associate via a chemical interaction, such as a chemical bond
(e.g., covalent bond, non-covalent bond). In some instances, the
ions in the liquid (e.g., halide ions) and the ionic species
originating (e.g., thallium ions, indium ions) from the ionic
semiconductor material may associate to form new ionic
semiconductor material (e.g., a thallium, halide, indium halide)
and/or ionic compounds. In some embodiments, the association
between the ions in the liquid and the ionic species originating
from the ionic semiconductor material can overcome one or more
problems (e.g., reduced equivalent internal field, reduced charge
collection efficiency, damaged electrical contact, limited
operating conditions, limited lifetime) which may otherwise be
associated with the movement of certain ionic species in the ionic
semiconductor material. Without wishing to be bound by theory, it
is believed that the association between ions in the liquid and the
ionic species prevent or mitigate the association of certain ionic
species with the electrical contact and/or accumulation of certain
ionic species at or near the interface between the ionic
semiconductor material and the electrical contact.
[0026] For example, as illustrated in FIG. 2A-B, a detector 30
comprises a first electrical contact 35, a second electrical
contact 40, and an ionic semiconductor material 45 that comprises
thallium bromide. The ionic semiconductor material may contain
thallium ions 46 and bromide ions 47. The first and second
electrical contacts comprise a liquid 55 that contains cations
(e.g., sodium, potassium, ammonium) 56 and bromide ions as
illustrated in FIG. 2A. Under voltage, the thallium and bromide
ions in the ionic semiconductor material move based on polarity,
such that the thallium and bromide ions travel toward the first and
second electrical contacts, respectively. The cations and bromide
ions in the electrical contact also move based on polarity as
illustrated in FIG. 2A. In the first electrical contact, the
cations move toward the negative potential and the bromide ions
move toward the ionic semiconductor material. In the second
electrical contact, the cations move toward the ionic semiconductor
material and the bromide ions move toward the positive potential.
As illustrated in FIG. 2B, the ionic species that are present at or
near the interfaces 50 between the electrical contacts and the
ionic semiconductor material may associate with ions in the liquid
that are present at or near the interfaces. Thallium ions at or
near the first electrical contact may associate with bromide ions
from the liquid to form new thallium bromide 60 (e.g., in the solid
state). Bromide ions originating from the ionic semiconductor
material and cations in the second electrical contact may associate
to from new compounds 65. The association of ions from the liquid
and ionic species from the ionic semiconductor material may prevent
the accumulation of ionic species at the interfaces, which can
reduce the internal electrical field of the ionic semiconductor
material.
[0027] In general, the ions in the liquid may be selected as
desired. In some embodiments, the ions in the liquid are capable of
associating with certain ionic species originating from the ionic
semiconductor material, as described herein. In certain
embodiments, the ions in the liquid and the ionic species from the
ionic semiconductor material may associate to from a solid or
dissolved compound. In one example, halide ions in the liquid may
form a chemical bond with a thallium and/or indium ions from the
ionic semiconductor material. The newly formed thallium halide
and/or indium halide compounds may be present in solid form or
dissolved in solution. In another example, inorganic cations (e.g.,
Na.sup.+, K.sup.+, Cs.sup.+, NH.sub.4.sup.+) in the liquid may
associate with anions (e.g., halide ions) from the ionic
semiconductor material.
[0028] In some embodiments, one or more ions (e.g., an anion) in
the liquid is selected to be the same or to have similar chemical
properties as a certain ionic species (e.g., an anion) in the ionic
semiconductor material. For example, in embodiments in which the
ionic semiconductor material is thallium bromide, the liquid
includes bromide ions and/or other halide ions. In certain
embodiments, one or more ions in the liquid is selected based on
the ability to produce compounds (e.g., via association with ionic
species from the semiconductor material) that are the same or have
similar chemical properties as a compound in the ionic
semiconductor material. In some such cases, the newly formed
compound may be in close proximity to or in direct contact with at
least a portion of the ionic semiconductor material. In one example
in which the ionic semiconductor material is thallium
bromochloride, the liquid contains bromide and chloride ions that
associate with thallium ions from the ionic semiconductor material
to produce newly formed thallium bromochloride on at least a
portion of the surface of the ionic semiconductor material.
[0029] In some embodiments, one or more ions in the liquid is
selected to prevent accumulation of charge at or near the interface
between the electrical contact and the ionic semiconductor
material. The liquid may contain one or more ions capable of
associating with an ionic species that accumulate at the interface.
For example, the liquid may include organic and/or inorganic
cations that form ionic compounds with anions from the ionic
semiconductor material.
[0030] Non-limiting examples of ions that a liquid may comprise
include inorganic ions (e.g., sodium, ammonium, potassium, cesium,
halides), organic ions (e.g., molecules with a molecular weight
greater than about 100 g/mol, C.sub.10H.sub.19N.sub.2--Br,
C.sub.10H.sub.19N.sub.2--Cl, C.sub.12H.sub.23N.sub.2--Br,
C.sub.12H.sub.23N.sub.2--Cl), and combinations thereof. In one
example, a liquid comprises one or more organic cations and one or
more inorganic anions (e.g., halide ion). In another example, a
liquid comprises one or more inorganic cations and one or more
inorganic anions (e.g., halide ion). In general, an electrical
contact comprising a liquid may comprise any suitable number of
inorganic and/or organic ions.
[0031] Those of ordinary skill in the art would be able to select
suitable ions for an electrical contact comprising a liquid based
on knowledge in the art and the description herein.
[0032] Any suitable liquid may be used in the electrical contact.
In some embodiments, the liquid comprises water, a non-aqueous
solvent, an organic solvent, or combinations thereof. Non-limiting
examples of organic solvents include methanol, aliphatic alcohols,
aromatic alcohols, and combinations thereof. In some embodiments,
an electrical contact may comprise an alcohol, such as
methanol.
[0033] In general, the liquid comprising ions may be sufficiently
conductive. The conductivity of the liquid may be measured using
resistivity and may be on the order of, e.g., about 1 k.OMEGA./cm.
It should be understood that the liquid can have any suitable
conductivity.
[0034] In some embodiments, the pH of a liquid in an electrical
contact is selected to not adversely affect the ionic semiconductor
material. For example, the pH of the liquid is between 6 and 8
(e.g., 7).
[0035] In some embodiments, an electrical contact comprises a metal
that can prevent and/or mitigate one or more problems (e.g.,
damaged electrical contact, limited operating conditions, limited
lifetime) associated with the movement of certain ionic species in
the ionic semiconductor material. In certain embodiments, the
electrical contact comprises at least one layer. The layer may
comprise an element selected from the group consisting of Cr, Ti,
W, Mo, and Pb. It should be understood that the electrical contact
may include additional layers, formed of Au or other precious
metals.
[0036] Without wishing to be bound by theory, it is believed that
an electrical contact comprising a certain thickness and/or
placement of a certain metal is resistant to the association with
and/or accumulation of certain ionic species that adversely affect
the detector. For example, in some instances, Cr, Ti, W, Mo, Pb, or
combinations thereof are resistant to association with certain
ionic species originating from the ionic semiconductor material. In
another example, an electrical contact comprises at least one layer
of a metal selected from the group consisting of Cr, Ti, W, Mo, and
Pb and at least one additional layer of another metal (e.g., Au,
other precious metals). The electrical contact may be resistant to
association with ionic species when the layer of metal selected
from a group consisting of Cr, Ti, W, Mo, and Pb forms
substantially the entire interface between the electrical contact
and the ionic semiconductor material. Detectors comprising one or
more electrical contacts with an approximate thickness and/or
placement of Cr, Ti, W, Mo, Pb, or combinations thereof may have
enhanced stability and/or reduced damage to an electrical contact
due to the movement of certain ionic species in the ionic
semiconductor material.
[0037] As described herein, a detector for detecting radiation may
comprise an electrical contact that comprises a metal selected from
the group consisting of Cr, Ti, W, Mo, and Pb. In certain
embodiments, an electrical contact comprises a layer of a metal
selected from the group consisting of Cr, Ti, W, Mo, and Pb. In
some embodiments, an electrical contact on the ionic semiconductor
material comprises Cr. It may be preferable for the layer of the
electrical contact to comprise Cr (e.g., greater than 50 wt.% Cr,
greater than 75 wt.% Cr, greater than 95 wt.% Cr).
[0038] In some embodiments, the thickness of Cr, Ti, W, Mo, Pb, or
combinations thereof layer in the electrical contact is greater
than or equal to about 40 nm, greater than or equal to about 60 nm,
greater than or equal to about 80 nm, greater than or equal to
about 100 nm, greater than or equal to about 200 nm, greater than
or equal to about 500 nm, or greater than or equal to about 750 nm.
In some instance, the thickness of Cr, Ti, W, Mo, Pb, or
combinations thereof layer in the electrical contact is less than
or equal to about 1,000 nm, less than or equal to about 750 nm,
less than or equal to about 500 nm, less than or equal to about 250
nm, or less than or equal to about 100 nm. It should be understood
that all combinations of the above-referenced ranges are also
possible (e.g., greater than or equal to about 40 nm and less than
or equal to about 100 nm).
[0039] As described herein, detectors for detecting radiation may
have beneficial properties, such as enhanced stability, charge
collection efficiency, and/or advantageous operating conditions. In
some embodiments, a detector comprising an ionic semiconductor
material and at least one electrical contact, described herein, has
a greater stability than a detector comprising an equivalent ionic
semiconductor material but different electrical contacts. As used
herein, stability refers to the number of days that the coefficient
of variation of the peak position (i.e., peak centroid location) on
a pulse height spectra acquired using the detector at room
temperature under continuous bias at 100 V/mm (e.g., with a 60 keV
gamma source) is less than or equal to about 10% (e.g., less than
or equal to about 8%, less than or equal to about 5%, less than or
equal to about 3%, or less than or equal to about 1%). A detector
comprising an ionic semiconductor material and at least one
electrical contact, described herein, may have enhanced stability
(i.e., no polarization, little polarization) over a relatively long
period of time.
[0040] In some embodiments, the stability of a detector, described
herein, is greater than or equal to about 5 days, greater than or
equal to about 15 days, greater than or equal to about 25 days,
greater than or equal to about 50 days, greater than or equal to
about 75 days, greater than or equal to about 100 days, greater
than or equal to about 125 days, greater than or equal to about 150
days, or greater than or equal to about 175 days. In some
instances, the stability of a detector, described herein, is
between about 25 days and about 200 days or between about 50 days
and about 200 days.
[0041] In some embodiments, a detector comprising an ionic
semiconductor material and at least one electrical contact,
described herein, has an enhanced charge collection and accordingly
detector efficiency. The detector may exhibit improved detector
efficiency over a relatively long period of time. In some
instances, the improved detector efficiency has the same time scale
as the stability. In some embodiment, detector, described herein,
may be relatively stable at higher temperatures (e.g., room
temperature) than conventional ionic semiconductor materials.
[0042] As mentioned above, a detector for detecting radiation may
include an ionic semiconductor material and at least one electrical
contact. In some embodiments, the detector may also include other
components. Non-limiting example of detectors according to certain
embodiments can be seen in FIG. 3A-B. As shown in FIG. 3A, in some
instances, a detector includes two electrical contacts 100 and 110
comprises a metal selected from the group consisting of Cr, Ti, W,
Mo, and Pb on the ionic semiconductor material. The two electrical
contacts may serve as a cathode and anode for the detector. In some
instances, at least a portion of electrical contacts are in direct
physical contact with the ionic semiconductor material. The
detector may also comprise a substrate 120 that supports the ionic
semiconductor material 130. At least one electrical contact may be
connected to a voltage source via a wire 140, as illustrated in
FIG. 3A.
[0043] In some embodiments, as illustrated in FIG. 3B, a detector
includes two electrical contacts105 and 115 comprising liquids that
comprise ions, on the ionic semiconductor material. In some
instances, at least a portion of electrical contacts are in direct
physical contact with the ionic semiconductor material. The
detector may also comprise a substrate 120 that supports the ionic
semiconductor material 130. At least one electrical contact may be
connected to the substrate via a wire and 145, as illustrated in
FIG. 3A.
[0044] In some embodiments, as illustrated in FIG. 3B, the ionic
semiconductor material and electrical contacts may be attached to a
substrate 120 via a holder 150. The holder may prevent a liquid
from contacting the substrate, e.g., to ensure confinement to a
fixed location and or prevent adverse interactions between the
liquid and the substrate. In some instances, the liquid may be in
electrical communication with a voltage source via wires 140 and
145.
[0045] In some embodiments, the detector comprises structures to
confine the electrical contacts comprising liquids to a specific
location on the ionic semiconductor material. For example, the
detector may comprise a mechanical barrier. Those of ordinary skill
in the art would be knowledgeable of suitable mechanical barriers
to confine a liquid to a certain area on a material.
[0046] In certain embodiments, the electrical contact may be
constructed, such that the liquid remains at a specific location on
the ionic semiconductor material. In some instances, the liquid may
be combined with a substance that alters (e.g., lowers) the
interfacial tension between the liquid and the semiconductor
material. In some cases, the liquid may be combined with a
substance that alters the viscosity of the liquid. In some
examples, the liquid may be combined with a substance (e.g.,
glycerol, glycerin) to form a gel. The viscosity of the gel may
allow the electrical contact comprising a liquid to remain in a
specific location. Those of ordinary skill in the art would be
knowledgeable of substances that can be added to a liquid to alter
the interfacial tension and viscosity, amongst other
properties.
[0047] It should be understood that the electrical contact
comprising liquid is constructed to not adversely affect the
function of the ionic semiconductor material (e.g., dissolve at
least a portion of the ionic semiconductor material, diffuse into
the ionic semiconductor material) and the detector. Those of
ordinary skill in the art would be knowledgeable of substances that
can be included in the electrical contact without adversely
affecting the function of the electrical contact and the
detector.
[0048] In some embodiments, a detector (not shown) may include an
ionic semiconductor material, an electrical contact comprising a
metal selected from a group consisting of Cr, Ti, W, Mo, and Pb
(e.g., Cr) and an electrical contact comprising a liquid comprising
ions. In some such cases, the electrical contact comprising a metal
selected from the group consisting of Cr, Ti, W, Mo, and Pb (e.g.,
Cr) may serve as a cathode and the electrical contact comprising a
liquid may serve as an anode. In some instances, the electrical
contact comprising a metal selected from the group consisting of
Cr, Ti, W, Mo, and Pb (e.g., Cr) may serve as an anode and the
electrical contact comprising liquid may serve as a cathode. In
general, in embodiments in which an electrical contact comprises a
metal selected from the group consisting of Cr, Ti, W, Mo, and Pb
(e.g., Cr) is an anode, specialized anode structures (e.g.,
pixelated array detector, coplanar greater detector) can be
formed.
[0049] In general, the electrical contact may be formed by any
suitable method known to those of skill in the art. In some
embodiments, an electrical contact comprising one or more metal may
be deposited on at least a portion (e.g., surface) of the ionic
semiconductor material. For example, the electrical contact may be
sputtered, evaporated, or deposited on the ionic semiconductor
material by any other known deposition technique. In certain
embodiments, an electrical contact comprising a liquid may be
deposited and confined to a fixed location on the ionic
semiconductor material using any suitable technique known to those
of skill in the art. For instance, the liquid may be dispensed on
at least a portion of the ionic semiconductor material and confined
by structural barrier (e.g. holder, coverslip) and/or via the
interfacial tension.
[0050] It should be understood that the detectors, as described
herein, can be used to detect gamma radiation. A method for
detecting radiation may comprise providing a detector, as described
herein, exposing the detector to gamma radiation, and generating an
electrical signal. In some instances, the presence or absence of
gamma radiation may be determined by the presence or absence,
respectively, of an electrical signal.
[0051] The following examples are intended to illustrate certain
embodiments of the present invention, but do not exemplify the full
scope of the invention.
EXAMPLES
Example 1
[0052] This example describes the stability of electrical contacts
comprising liquids. The electrical contacts had no visible damage
after 100 days under a continuous bias of 100 V/mm. Moreover, the
detector did not exhibit a shift in peak position for more than 14
days under a continuous bias of 100 V/mm.
[0053] A radiation detector containing thallium bromide ingot and
two electrical contacts containing NH.sub.4Br in methanol were
formed. The resulting solution was mixed with glycerol to form a
gel. The gel was then pipetted onto the thallium bromide ingot. Pd
wires were contacted to the electrical contacts and a substrate to
for a detector.
[0054] A pulse height spectra was acquired using the detector at
room temperature under continuous bias at 100 V/mm with .sup.41Am
as the gamma radiation source. The detector had a constant peak
position (i.e., no polarization) for more than 14 days of use. In
addition, the electrical contacts showed no visible signs of damage
after 100 days.
Comparative Example 1
[0055] A detector was formed and tested using the same procedures
as Example 1, except the electrical contacts were gold and were
sputtered onto the thallium bromide. As shown in FIG. 4, the gold
electrical contact was damaged after 4 days of use at room
temperature under continuous bias at 100 V/mm with .sup.41Am as the
gamma radiation source. FIG. 4A shows the gold electrical contact
after deposition and FIG. 4B shows the gold electrical contact
after 4 days of use.
Example 2
[0056] This example describes the detectors with Cr electrical
contacts. The detector contained thallium bromide and chrome
electrical contacts and exhibited good charge collection
properties.
[0057] TlBr ingot with a thickness of about 0.8 mm was used as the
ionic semiconductor material. The TlBr was lapped with 24 .mu.m
grains, then polished with 3 .mu.m grains, and etched with fresh 5%
Br in MeOH. Cr electrical contacts with a 3 mm diameter were
deposited on the ionic semiconductor material. The Cr electrical
contacts were annealed at 150.degree. C. for 24 hours in Argon
atmosphere after deposition. The TlBr with deposited Cr (i.e.,
Cr/TlBr/Cr) was mounted to a ceramic substrate and .sup.241Am (60
keV) pulse height spectra were acquired. FIG. 5A shows the pulse
height spectra of the Cr/TlBr/Cr detector at different biases. As
illustrated by the spectra, the Cr/TlBr/Cr detector had good charge
collection.
Comparative Example 2
[0058] A detector was formed and tested using the same procedures
as Example 2, except the electrical contacts were gold. The
Au/TlBr/Au detector exhibited a lower charge collection efficiency
than the detector in Example 2, as illustrated by FIG. 5B. FIG. 5B
shows the pulse height spectra of the Au/TlBr/Au detector at
different biases.
[0059] While several embodiments of the present invention have been
described and illustrated herein, those of ordinary skill in the
art will readily envision a variety of other means and/or
structures for performing the functions and/or obtaining the
results and/or one or more of the advantages described herein, and
each of such variations and/or modifications is deemed to be within
the scope of the present invention. More generally, those skilled
in the art will readily appreciate that all parameters, dimensions,
materials, and configurations described herein are meant to be
exemplary and that the actual parameters, dimensions, materials,
and/or configurations will depend upon the specific application or
applications for which the teachings of the present invention
is/are used. Those skilled in the art will recognize, or be able to
ascertain using no more than routine experimentation, many
equivalents to the specific embodiments of the invention described
herein. It is, therefore, to be understood that the foregoing
embodiments are presented by way of example only and that, within
the scope of the appended claims and equivalents thereto, the
invention may be practiced otherwise than as specifically described
and claimed.
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