U.S. patent application number 12/707177 was filed with the patent office on 2010-06-10 for radiation detecting apparatus, scintillator panel, radiation detecting system, and method for producing scintillator layer.
This patent application is currently assigned to CANON KABUSHIKI KAISHA. Invention is credited to Masato Inoue.
Application Number | 20100144082 12/707177 |
Document ID | / |
Family ID | 38470716 |
Filed Date | 2010-06-10 |
United States Patent
Application |
20100144082 |
Kind Code |
A1 |
Inoue; Masato |
June 10, 2010 |
RADIATION DETECTING APPARATUS, SCINTILLATOR PANEL, RADIATION
DETECTING SYSTEM, AND METHOD FOR PRODUCING SCINTILLATOR LAYER
Abstract
A radiation detecting apparatus includes: a sensor panel that
has a substrate, and has a plurality of pixels each of which has a
photoelectric conversion element for converting light into an
electric signal, arranged on the substrate; and a scintillator
layer arranged on a reverse side of the pixels with respect to the
substrate, wherein the scintillator layer contains an activator
added in a main ingredient, and has a higher concentration of the
activator in a peripheral area than in a center area, in a surface
direction of the scintillator layer.
Inventors: |
Inoue; Masato;
(Kumagaya-shi, JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
1290 Avenue of the Americas
NEW YORK
NY
10104-3800
US
|
Assignee: |
CANON KABUSHIKI KAISHA
Tokyo
JP
|
Family ID: |
38470716 |
Appl. No.: |
12/707177 |
Filed: |
February 17, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11680746 |
Mar 1, 2007 |
7692152 |
|
|
12707177 |
|
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Current U.S.
Class: |
438/59 ;
257/E31.092; 257/E31.103 |
Current CPC
Class: |
A61B 6/4258 20130101;
G01T 1/2018 20130101 |
Class at
Publication: |
438/59 ;
257/E31.103; 257/E31.092 |
International
Class: |
H01L 31/18 20060101
H01L031/18 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 2, 2006 |
JP |
2006-056473 |
Claims
1. A manufacturing method of a radiation detecting apparatus
including steps of: placing a substrate having a photoelectric
conversion element at a substrate holder; and forming a
scintillator layer, on the substrate, from a main ingredient
evaporated from a main ingredient evaporation boat placed at a
first side of the substrate, and from an activator evaporated from
an activator evaporation boat placed, at the first side of the
substrate, at a position apart from a center axis of the substrate,
such that the scintillator layer contains the activator in a higher
concentration in a peripheral area rather than the concentration in
a center area.
2. The manufacturing method of a radiation detecting apparatus
according to claim 1, further comprising a step of arranging a
metal layer covering the scintillator layer.
3. The manufacturing method of a radiation detecting apparatus
according to claim 1, wherein the concentration of the activator in
the peripheral area of the scintillator layer is 1.0 mol % or more
with respect to the concentration of main ingredient, and the
concentration of the activator in a central part of the
scintillator layer is 0.5 mol % or more but 1.5 mol % or less with
respect to the concentration of main ingredient.
4. The manufacturing method of a radiation detecting apparatus
according to claim 1, wherein the scintillator layer is made of a
columnar crystal structure.
5. The manufacturing method of a radiation detecting apparatus
according to claim 1, further comprising a step of annealing the
scintillator layer such that an annealing temperature of the center
area is higher than an annealing temperature of the peripheral
area.
6. The manufacturing method of a scintillator panel according to
claim 2, further comprising a step of arranging a light
transmitting resin layer covering the scintillator layer.
7. A manufacturing method of a scintillator panel including steps
of: placing a base plate at a holder; and forming a scintillator
layer, on the substrate, from a main ingredient evaporated from a
main ingredient evaporation boat placed at a first side of the base
plate, and from and an activator evaporated from an activator
evaporation boat placed, at the first side of the base plate, at a
position apart from a center axis of the base plate, such that the
scintillator layer contains the activator in a higher concentration
in a peripheral area rather than the concentration in a center
area.
8. The manufacturing method of a scintillator panel according to
claim 7, wherein the concentration of the activator in the
peripheral area of the scintillator layer is 1.0 mol % or more with
respect to the concentration of main ingredient, and the
concentration of the activator in a central part of the
scintillator layer is 0.5 mol % or more but 1.5 mol % or less with
respect to the concentration of main ingredient.
9. The manufacturing method of a scintillator panel according to
claim 7, wherein the scintillator layer is made of a columnar
crystal structure.
10. The manufacturing method of a scintillator panel according to
claim 7, further comprising a step of annealing the scintillator
layer such that an annealing temperature of the center area is
higher than an annealing temperature of the peripheral area.
11. A manufacturing method of a radiation detecting apparatus
including: a step of preparing a substrate having a photoelectric
conversion element; a step of preparing a scintillator panel
according to claim 7; and a step of bonding together the substrate
and the scintillator panel.
Description
RELATED APPLICATIONS
[0001] This application is a divisional of application Ser. No.
11/680,746, filed Mar. 1, 2007, claims benefit under 35 U.S.C.
.sctn.120 of the filing date of that application, and claims
benefit under 35 U.S.C. .sctn.119 of Japanese Patent Application
No. 2006-056473, filed Mar. 2, 2006; the entire contents of each of
the two mentioned prior applications are hereby incorporated by
reference herein in their entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a radiation detecting
apparatus, a scintillator panel, a radiation detecting system, and
a method for forming a scintillator layer by deposition; and
particularly relates to the scintillator panel, the radiation
detecting apparatus, the radioactive rays detection system, which
are used in radiographing used in medical diagnosis equipment and
non-destructive inspection equipment, and the method for forming a
scintillator layer by deposition. In the present specification,
"radiation" shall include corpuscular rays such as X-rays,
gamma-rays, and alpha-particles and beta-particles. In addition,
the "scintillator" shall be a device that converts incident
radiation such as X-rays and gamma-rays to light having a
wavelength range that can be sensed by a photoelectric conversion
element.
[0004] 2. Description of the Related Art
[0005] A radiation detecting apparatus conventionally used in
general radiographing uses a radio-sensitized paper having a
scintillator layer which converts X-rays into light, and a
radiation film having a photosensitive layer.
[0006] However, a digital radiation detecting apparatus has been
recently developed which has a scintillator layer and a
two-dimensional photodetector including photoelectric conversion
elements. The digital radiation detecting apparatus facilitates
image processing because the obtained data is digital and the data
can be shared among multiple persons, when the data is taken into a
networked computer system. In addition, if the image digital data
is saved in a magneto-optical disk or the like, the digital
radiation detecting apparatus can remarkably reduce the storage
space required, compared to the case of saving image data in a
film, and has an advantage of facilitating a search for past
images. In addition, the digital radiation detecting apparatus can
reduce the dosage of exposure to radiation for the patient, because
a digital radiation detecting apparatus having characteristics of
high sensitivity and high sharpness has been proposed along with
the progress of the apparatus.
[0007] For instance, International Publication Number WO 98/036290
discloses a digital radiation detecting apparatus that has a
scintillator layer which is produced with a vacuum deposition
technique and includes crystals of cesium iodide (hereafter
referred to as CsI) grown into a columnar shape, connected with a
photodetector directly or through a protection film. A thus
configured digital radiation detecting apparatus can be made with
improved sensitivity and sharpness in comparison with that provided
with a scintillator layer having conventional scintillators made of
granular crystals assembled together.
[0008] In addition, International Publication Number WO 99/066350
discloses a digital radiation detecting apparatus having a
configuration of adhesively bonding a CsI surface of a scintillator
prepared, for instance, by vapor-depositing CsI on a base plate, to
a photodetector (which is not shown in the drawings).
[0009] A columnar crystal of CsI or the like, which forms a
scintillator layer, has properties of absorbing external moisture
and deliquescing. A scintillator layer having absorbed moisture
deteriorates in its light emission properties and sharpness. For
this reason, the above-described conventional radiation detecting
apparatus or scintillator panel has a moisture proof protective
film for preventing the entry of external moisture.
[0010] In addition, a radiation detecting apparatus disclosed in
U.S. Pat. No. 4,820,926 has an outermost layer containing only the
activator of Tl formed on a light emission material layer.
[0011] However, it has been demanded to further improve a
moisture-proof effect. Particularly, radiation detecting apparatus
for use in a hostile environment like a high-temperature and
high-humidity environment has been required to have an improved
moisture-proof effect.
SUMMARY OF THE INVENTION
[0012] Accordingly, an object of the present invention is to
provide a radiation detecting apparatus and a scintillator panel
which have a higher moisture-proof effect than ever before, and a
method for producing a scintillator layer having a sufficient
moisture proof function.
[0013] A radiation detecting apparatus according to the present
invention has: a sensor panel that has a substrate, and has a
plurality of pixels each of which has a photoelectric conversion
element for converting light into an electric signal, arranged on
the substrate; and a scintillator layer arranged over the pixels,
wherein the scintillator layer contains an activator and a main
ingredient, and has a higher concentration of the activator in a
peripheral area than in a center area, in a surface direction of
the scintillator layer.
[0014] In addition, a scintillator panel according to the present
invention has: a substrate; and a scintillator layer arranged on
the substrate, wherein the scintillator layer contains an activator
added in a main ingredient and has a higher concentration of the
activator in a peripheral area than in a center area, in a surface
direction of the scintillator layer.
[0015] A method for producing a scintillator layer according to the
present invention includes: arranging a vapor deposition boat for a
main ingredient of the scintillator layer and a vapor deposition
boat for an activator in a vacuum chamber so as to face to a
substrate on which the scintillator layer is to be deposited;
arranging the vapor deposition boat for an activator at such a
position as to face to a peripheral area of the substrate; and
conducting a vapor-depositing operation.
[0016] The present invention can provide a radiation detecting
apparatus and a scintillator panel which inhibit the diffusion of
moisture in a peripheral area of a scintillator layer, and have a
sufficient moisture proof function; and a method for producing the
scintillator layer having the sufficient moisture proof
function.
[0017] Other features and advantages of the present invention will
be apparent from the following description taken in conjunction
with the accompanying drawings, in which like reference characters
designate the same or similar parts throughout the figures
thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate embodiments of
the invention and, together with the description, serve to explain
the principles of the invention.
[0019] FIG. 1 shows a sectional view of a radiation detecting
apparatus according to the first embodiment of the present
invention.
[0020] FIG. 2A is a plan view showing the Tl concentration in a
scintillator layer of a radiation detecting apparatus according to
the first embodiment of the present invention.
[0021] FIG. 2B is a plan view showing the Tl concentration in a
scintillator layer of a radiation detecting apparatus according to
the first embodiment of the present invention.
[0022] FIG. 3 is a characteristic view showing a relationship
between Tl concentration and a light emission coefficient.
[0023] FIG. 4 is a characteristic view showing a relationship
between Tl concentration and an MTF variation rate.
[0024] FIG. 5 is a schematic block diagram showing a
vapor-deposition apparatus for forming a scintillator layer by
vapor deposition.
[0025] FIG. 6 is a characteristic view showing the dependency of
characteristics of Tl concentration and a light emission
coefficient on temperature.
[0026] FIG. 7 is a sectional view showing another configuration
example of a radiation detecting apparatus according to the first
embodiment of the present invention.
[0027] FIG. 8 shows a sectional view of a radiation detecting
apparatus according to the second embodiment of the present
invention.
[0028] FIG. 9 is a sectional view showing another configuration
example according to the second embodiment of the present
invention.
[0029] FIG. 10 is an equivalent circuit diagram showing a
photoelectric conversion element array according to the first
embodiment of the present invention.
[0030] FIG. 11 is a view showing an example in which a radiation
detecting apparatus according to the present invention is applied
as a radiation detecting system.
[0031] FIG. 12 is a view showing a case of having heated a
scintillator layer with the use of a lamp heater.
DESCRIPTION OF THE EMBODIMENTS
[0032] In the next place, the best modes for carrying out the
present invention will be described in detail with reference to the
drawings.
First Embodiment
[0033] FIG. 1 shows a sectional view of a radiation detecting
apparatus according to the first embodiment of the present
invention. In FIG. 1, reference numeral 11 denotes a polyethylene
terephthalate resin layer which is a support for an electromagnetic
shield layer 12, and reference numeral 12 denotes an aluminum layer
which functions as an electromagnetic shield body, and has a light
reflection function and a moisture-proof function.
[0034] In FIG. 1, reference numeral 13 denotes a polyolefin-based
hot-melt adhesive resin layer which is a thermoplastic resin layer
having an adhesively bonding function and a moisture-proof
function, reference numeral 14 denotes a scintillator layer
including columnar crystals, reference numeral 15 denotes an
insulation layer, and reference numeral 16 denotes a glass
substrate. In addition, reference numeral 17 denotes a
photoelectric conversion element array in which pixels including a
photosensor and a TFT using amorphous silicon are arrayed into a
two-dimensional form.
[0035] In FIG. 1, a scintillator layer 14 including columnar
crystals is made from CsI as a main ingredient and Tl which is
added as an activator. In FIG. 1, as shown in the scintillator
layer 14, the variation of the concentration of added Tl among the
pixels is shown by a gray level using black and white. A black part
in a peripheral area shows where Tl exists in high concentration,
and as is clear from the figure, the concentration of Tl gradually
increases from a central part to the peripheral area. FIGS. 2A and
2B are two-dimensional views showing the distribution of the Tl
concentration when viewed from above. It is understood from the
figures that the concentration of Tl generally concentrically and
isotropically changes from the center of the scintillator layer 14
to the peripheral area on a glass substrate 16. The dashed line
means that the Tl concentration is particularly high in the
peripheral area outside the line. FIG. 2A shows an example in which
the Tl concentration is particularly high in four corners of the
square glass substrate, and FIG. 2B shows an example in which the
Tl concentration is high even in more inward parts. The Tl
concentration in the peripheral area does not need to be all
uniform, but may be higher in a part of the peripheral area than in
other parts, as needed. For instance, when a wire is drawn out from
a photoelectric conversion element array in a region 14a, in a
configuration in FIG. 2B, irregularities may be formed in an
insulation layer 15 by the wire, and facilitate moisture to enter
the inner part through an interface between the insulation layer 15
and the protection film 13. In such a case, the moisture durability
of the scintillator layer 14 can be improved by making the Tl
concentration in the region 14a higher than that in the other
peripheral areas. When it is a problem that moisture enters from
only one part of the peripheral area, it is also acceptable to make
the Tl concentration higher only in that part, while making the Tl
concentration in all other parts equal to that in the central
part.
[0036] It is considered that the moisture enters into the
scintillator layer 14 from the perimeter of the scintillator layer
14. In other words, it is considered that the moisture enters from
an interface between the hot melt adhesive resin layer 13 that
serves as the moisture proof protective film and a member
(insulation layer) which directly contacts with the hot melt
adhesive resin layer 13, gradually invades the inner part, and
diffuses toward the central part from a circumferential part
(peripheral area) of the scintillator layer 14. In the present
embodiment, the scintillator layer 14 can prevent its peripheral
area from deliquescing even when the moisture has invaded into the
scintillator layer 14, and further inhibit moisture from diffusing
into the center area, by making the Tl concentration in the
peripheral area higher than that in the center area.
[0037] In the next place, a method for adding Tl will be described.
It has been elucidated from an experiment that a Tl concentration
for making the scintillator layer 14 emit more light can be in a
range shown by the following expression, due to properties of CsI,
when the concentration of CsI containing Tl is determined as 100
[mol %]:
CsI(Tl):Tl=100:0.5 to 2.0[mol %]
[0038] FIG. 3 is a graph showing a relationship between Tl
concentration and a quantity of light emission (light emission
coefficient). The light emission coefficient in FIG. 3 shows a
ratio of a quantity of light emission to the maximum quantity of
light emission when the maximum quantity is determined as 1. As is
shown in FIG. 3, the quantity of light emission becomes maxim when
the Tl concentration is about 1 to 1.5 [mol %]. However, the Tl
concentration can not be determined only from the quantity of light
emission, because it is known that the sharpness of the obtained
image decreases with the increase of the Tl concentration.
[0039] It is also elucidated from an experiment that the Tl
concentration for giving the scintillator layer 14 sufficient
moisture-proof effects, namely, for effectively inhibiting moisture
from diffusing can be in such a range as to satisfy the following
expression:
CsI(Tl):Tl=100:1.0[mol %] or more
[0040] FIG. 4 shows a relationship between Tl concentration and a
variation rate of MTF (Modulation Transfer Function). In the
experiment, the variation rate of the MTF was determined by
measuring the MTFs of a sample before and after having been left in
an environment with humidity of 50% at 25.degree. C. for 24 hours.
As is shown in FIG. 4, the variation rate of the MTF decreases
along with the increase of the Tl concentration. When the Tl
concentration is 0.7 [mol %] or higher, the variation rate is
little affected by deliquescence, when the Tl concentration is 1.0
[mol %] or higher, the deliquescence does not substantially cause
any problem, and furthermore, when the Tl concentration exceeds 1.5
[mol %], the Tl concentration should show a sufficient protective
effect even in a more severe environment. The reason why the MTF
was adopted as an index of the moisture-proof effect will now be
described. When a columnar crystal of CsI (Tl) absorbs moisture and
deliquesces, an area of the surface from which the columnar crystal
emits light increases, or adjacent crystals adhere to each other,
and consequently the crystals emit light from almost one surface;
in other words, lights emitted from the adjacent crystals are
superposed. For this reason, as the columnar crystals deliquescence
over a wider range, the columnar crystals in the wider range cohere
with each other, and their output light beams are superimposed on
each other.
[0041] Then, an image including signals detected by a sensor
becomes blurred, because the sensor detects many superposed light
beams (information). In other words, the MTF, which is the
sharpness of the image, is decreased. The MTF is an index of the
sharpness.
[0042] The MTF is measured by: firstly arranging a lead plate (or a
lead plate having an aperture of slit shape) for intercepting
X-rays on an incident side of the X-rays; irradiating a sensor with
X-rays; determining an output of a sensor in a part intercepted by
the lead plate as zero and an output of the sensor in a part not
intercepted by the lead plate as 1; measuring the output of the
sensor in the end of the lead plate; Fourier-transforming the
output in order to know how the output varies in the vicinity of
the end; and numerically expressing a degree of blurring in every
spatial frequency. When the MTF is 0.5 at 21 p/mm for instance, the
value means that when two pairs of information of 1 and 0 exist in
one millimeter, the information changes from 1 to 0.5. In other
words, it means that the information is blurred. The smaller the
value of the MTF, the more difficult the judgment for the
difference between 1 and 0 becomes.
[0043] As was described above, the Tl concentration in a peripheral
area of a scintillator layer can be set at 1.0 [mol %] or higher,
and further can be set at a concentration higher than 1.5 [mol %].
On the other hand, the Tl concentration in the inner part than the
peripheral area of the scintillator layer is 0.5 [mol %] or more
but 1.5 [mol %] or less, in consideration of a balance between the
quantity of light emission and sharpness.
[0044] A practical method for forming a scintillator layer with a
vapor deposition technique will be now described with reference to
FIG. 5.
[0045] FIG. 5 shows a vapor deposition apparatus for
vapor-depositing CsI (Tl) for forming a scintillator layer. In FIG.
5, reference numeral 16 denotes a glass substrate on which a
photoelectric conversion element array 17 is formed and the
scintillator layer will be formed with a vapor deposition
technique, reference numeral 50 denotes a vacuum tank (vacuum
chamber) in the vapor deposition apparatus, reference numeral 51
denotes an evaporation boat on which TlI is placed, and reference
numeral 52 denotes an evaporation boat on which CsI is placed.
[0046] An evaporation boat 51 is arranged so as to face toward a
peripheral area of a glass substrate 16.
[0047] A scintillator layer having activators distributed in its
plane direction by a vapor deposition method is formed, for
instance, by: arranging a glass substrate 16 to be a base on a
substrate holder as shown in FIG. 5 so that a surface to be
vapor-deposited faces downward; arranging, for instance, many boats
52 for evaporating CsI and a boat 51 for evaporating TlI on a heat
source for vapor deposition at positions shown in FIG. 5;
evacuating a vacuum tank (vacuum chamber) 50 of a vapor deposition
apparatus; and heating each boat by using the vapor deposition
source while rotating the substrate holder around its center. Then,
the vapor of CsI flies out from many boats of CsI, and deposits on
the surface to be vapor-deposited (shown by an arrow of a
continuous line). On the other hand, Tl which is an activator
deposits in high amounts in the peripheral area of the substrate
holder, and deposits in low amounts in the central part to form
distribution, because Tl is supplied from one vapor deposition
source and the vapor deposition source is placed at a position
apart from the rotation axis of the substrate holder.
[0048] The thus obtained scintillator is subjected to activating an
activator by heating the scintillator at an annealing temperature
of 200.degree. C. to 400.degree. C. for 0.5 to 5 hours, and then is
used for producing a radiation detecting apparatus. The annealing
temperature must be set at such a temperature as not to affect
photoelectric transfer characteristics of a photoelectric
conversion element formed on a glass substrate.
[0049] In the present embodiment, as described above, the Tl
concentration can be set at 1.5 [mol %] or higher in a peripheral
area of a scintillator layer, and at 0.5 to 1.5 [mol %] in an inner
portion than the peripheral area, in consideration of a balance
between the quantity of light emission and sharpness. Then, there
may be cases where the quantity of light emission in the center
area is larger than that in the peripheral area, or the quantity of
light emission in the peripheral area is larger than that in the
center area.
[0050] In other words, when the concentration of an activator is
distributed in a scintillator layer, a quantity of light emission
is distributed on the surface of the scintillator layer. When it
becomes a problem that the quantity of light emission varies from
one portion to another, this variability of the quantity of light
emission can be reduced, by annealing the scintillator layer in
response to light emission quantity distribution while making use
of a phenomenon that the quantity of light emission varies
depending on an annealing temperature.
[0051] FIG. 6 is a view showing a dependency of the quantity of
light emission on an annealing temperature. In FIG. 6, the
annealing temperature B is set at about 20% higher than the
annealing temperature A. Then, it is clear that a scintillator
layer annealed at a higher temperature is more activated by an
activator and emits more light. However, after the scintillator
layer is sufficiently activated, the quantity of light emission
does not increase any more, so that there is naturally an upper
limit in the annealing temperature. For instance, when the quantity
of light emission in a center area is lower than that in a
peripheral area, the quantity of light emission in the central part
can be increased by setting the annealing temperature in the
vicinity of the central part at a higher temperature, and the
quantity of light emission in a plane of a scintillator layer can
be made uniform by setting the annealing temperature so as to be
distributed in an annealing environment. In order to set the
annealing temperature in the center area at a higher temperature,
it is recommended to arrange a heat source such as a ceramic
heater, a lamp heater, and a combination of a metal plate and a
sheath heater at a position facing the center area of a substrate
(while not arranging such a heat source facing the peripheral
area), and to heat the scintillator layer. FIG. 12 is a view
showing a case of having heated a scintillator layer with the use
of a lamp heater 18. Usable lamp heaters include a tungsten halogen
lamp, a xenon arc lamp and a graphite heater.
[0052] Materials for a scintillator having a columnar structure
include cesium iodide and cesium bromide.
[0053] In addition, activators for these scintillators include
sodium and thallium.
[0054] A support 11 in FIG. 1 can employ not only a
polyethylene-based resin but also a resin such as an acrylic resin,
a phenol resin, a vinyl chloride resin, a polypropylene resin, a
polycarbonate resin and a cellulosic resin, as its material.
[0055] In addition, an electromagnetic shield 12 can employ not
only aluminum but also a metal such as silver, a silver alloy,
copper and gold, as its material.
[0056] Furthermore, a protection film 13 has only to be made from a
thermoplastic resin, but can be made from a hot melt resin of not
only a polyolefin resin but also a polyester-based resin, a
polyurethane-based resin and an epoxy-based resin. The hot melt
resin is defined as an adhesive resin made from a thermoplastic
material which does not contain any of water and a solvent, is
solid at a room temperature, and is completely nonvolatile. (Thomas
P. Flanagan, Adhesive Age, 9, No. 3, 28 (1966)).
[0057] Thus, a hot melt resin contains no solvent and no water, and
accordingly hardly dissolves a scintillator made from an alkali
halide. A scintillator-protecting film using the hot melt resin
hardly dissolves the scintillator even in a production process,
because of being stacked on a scintillator layer without using a
solvent.
[0058] A hot melt resin melts when the temperature rises and
adheres to a body to be bonded, and when the resin temperature
falls, the resin becomes a solid. The adhesive resin layer made of
the hot melt resin is different from a solvent-volatilizing and
curing type of an adhesive resin layer which is formed by a method
of dissolving a thermoplastic resin in a solvent and applying the
liquid on the body. The hot melt resin is different also from a
chemical reaction type of an adhesive resin which is represented by
an epoxy resin and is formed by a chemical reaction.
[0059] Hot melt resin materials can be classified mainly into a
polyolefin-based resin, a polyester-based resin and a
polyamide-based resin. It is important for the protection film 13
to have a high function as a moisture-proof film and transmit
visible rays (350 nm to 700 nm) emitted from a scintillator. Hot
melt resins having a sufficient moisture-proof function can include
polyolefin resins and polyester resins. Particularly, polyolefin
resins can be employed because of having a low coefficient of
moisture absorption. Polyolefin resins are also suitable because of
having high optical transparency.
[0060] Accordingly, a polyolefin-based hot melt resin for a
protective layer of the scintillator can be used.
[0061] The hot melt resin can contain at least one compound
selected from the group consisting of an ethylene-acrylic acid
copolymer (EAA), an ethylene-acrylate copolymer (EMA), an
ethylene-methacrylic acid copolymer (EMAA), an
ethylene-methacrylate copolymer (EMMA) and an ionomer resin, as a
main component.
[0062] Additives to be added to an adhesive include, for instance,
a tackifier and a softener.
[0063] Tackifiers include: a natural resin such as rosin,
polymerized rosin, hydrogenated rosin and a rosin ester; a modified
product thereof; an aliphatic compound; an alicyclic compound; an
aromatic compound; a petroleum resin; a terpene resin; a
terpene-phenolic resin; a hydrogenated terpene resin and a chroman
resin. Softeners, for instance, include: process oil, paraffin oil,
castor oil, polybutene and low-molecular-weight polyisoprene.
[0064] A copolymer contained in an adhesive layer has a weight
average molecular weight of about 5,000 to 1,000,000. An
ethylene-acrylic copolymer (EAA) has a structure in which a
carboxyl group is contained in a polyethylene structure at random
as shown in the following structural formula (I):
--(CH.sub.2--CH.sub.2)n-(CH.sub.2--CHCOOH)m-
(wherein m and n are positive integers).
[0065] In addition, an ethylene-acrylate copolymer is a copolymer
of ethylene and acrylate, as is shown in the following structural
formula (II):
--(CH.sub.2--CH.sub.2)n-(CH.sub.2--CHCOOR)m-
(wherein m and n are positive integers, and R represents CH.sub.3,
C.sub.2H.sub.5 or C.sub.3H.sub.7).
[0066] In addition, an ethylene-methacrylic copolymer has a
structure in which a carboxyl group is contained in a polyethylene
structure at random as shown in the following structural formula
(III):
--(CH.sub.2--CH.sub.2)n-(CH.sub.2--CCH.sub.3COOH)m-
(wherein m and n are positive integers).
[0067] Furthermore, an ethylene-methacrylate copolymer has such a
structure as is shown in the following structural formula (IV):
--(CH.sub.2--CH.sub.2)n-(CH.sub.2--CCH.sub.3COOR)m-
(wherein m and n are positive integers, and R represents CH.sub.3,
C.sub.2H.sub.5 or C.sub.3H.sub.7).
[0068] A protection film 13 contains at least one copolymer among
the above described five copolymers or may contain a mixture of two
or more of the copolymers. An adhesive layer in the present
invention may contain the mixture of the two or more different but
similar copolymers, for instance, the mixture of an ethylene-methyl
methacrylate copolymer and an ethylene-ethyl methacrylate
copolymer.
[0069] A melting-starting temperature, melt viscosity and adhesion
strength of a hot melt resin for a scintillator-protecting film can
be controlled, by mainly appropriately changing the following three
elements alone or in combination of two or more: (1) contents of
vinyl acetate, acrylic acid, acrylate, methacrylic acid and
methacrylic ester in the above described respective copolymers
contained in a hot melt resin; (2) a content of the above described
copolymer in a hot melt resin; and (3) an additive in a hot melt
resin.
[0070] A hot melt resin can be used as a scintillator-protecting
film in a radiation imaging element for a human body not to
aggravate its function as a scintillator-protecting layer, even
when sterilizing alcohol has been scattered thereon.
[0071] A hot melt resin which is insoluble or slightly soluble in
ethyl alcohol can contain an additive such as an adhesion-imparting
material in the hot melt resin in an amount of 20% or less, and
particularly in an amount of 10% or less.
[0072] In the next place, a photoelectric conversion element array
having pixels including a photo sensor and a TFT two-dimensionally
formed thereon will be described with reference to an equivalent
circuit diagram in FIG. 10. In FIG. 10, a photoelectric conversion
element 301, a transfer-switching element 302 and a resetting
switch element 303 are two-dimensionally arranged. At first, a bias
is given on one electrode of a photoelectric conversion element 101
through a bias wiring 304. In this state, X-rays projected toward
an object pass through the object while being damped, and irradiate
a scintillator arranged on a photoelectric conversion element 301.
Then, the scintillator converts the X-rays to light such as visible
light. The light is incident on the photoelectric conversion
element 301 and is converted to electrical charge. The electrical
charge is transferred to a signal wire 306 by making a drive
apparatus 310 apply a gate-driving pulse to a gate wire 305 to
control a transfer-switching element 302 into a conductive state,
and is read to the outside by a read apparatus 309. Subsequently, a
resetting switch element 303 is converted into the conductive state
by making the drive apparatus 310 apply the gate-driving pulse to a
gate wire 307. Meanwhile, a bias for resetting the photoelectric
conversion element is applied to a resetting wire 308, and a
residual charge which has been generated in the photoelectric
conversion element 301 but has not been all transferred is
removed.
[0073] Picture signals for one image are obtained by repeating the
above-described operation, and an image is obtained by further
repeatedly acquiring the picture signals for another image. FIG. 10
shows 3.times.3 pixels, but practically more pixels such as
2,000.times.2,000 pixels are arranged on an insulation substrate to
compose a radiation detecting apparatus. In addition, a resetting
switch element is not necessarily provided.
[0074] A photoelectric conversion element array used in the present
embodiment has a TFT and a photoelectric conversion element formed
on a glass substrate so as to be aligned on the same plane.
However, a photoelectric conversion element array can also be used
which has a configuration having a switching element such as a TFT
formed on the glass substrate, a medium of an insulation layer, and
a photoelectric conversion element formed thereon. Even the
photoelectric conversion element array with such a configuration
has two types. One is a configuration in which a photoelectric
conversion layer (semiconductor layer) of the photoelectric
conversion element is not stacked on a TFT so that a defective
region produced in the TFT can be repaired by using a laser beam.
The other is a configuration in which the photoelectric conversion
layer (semiconductor layer) of the photoelectric conversion element
is stacked even on the TFT to increase an aperture ratio.
[0075] The present embodiment can impart a scintillator layer in
itself a moisture-proof function by increasing Tl concentration in
the perimeter of the scintillator layer for the purpose of further
enhancing the reliability for a moisture-proof effect, though the
moisture-proof effect can be obtained only by a single
moisture-proof protective layer of a hot melt resin.
[0076] Thereby, a radiation detecting apparatus having higher
reliability at a low cost can be accomplished, because there is no
need to add a mechanism for protecting a scintillator layer, so
that steps and materials can be reduced.
[0077] In the present embodiment, a thermoplastic resin layer is
used as a moisture-proof protective layer for a scintillator layer,
but this layer is not limited to the use of a thermoplastic resin.
Any material can be used as long as it has a moisture-proof effect
and an adhesive function. For instance, a sticky material is also
acceptable.
[0078] In the above described example, the Tl concentration
approximately concentrically and isotropically changes from the
center to a peripheral area, as is shown in FIG. 1. The present
embodiment can employ not only such concentration distribution as
is shown in FIG. 7, but also a concentration distribution in which
a region 21a with a high TlI concentration is arranged only in a
peripheral end within a scintillator layer. FIG. 7 is a sectional
view of a radiation detecting apparatus. In FIG. 7, only the black
region 21a in the peripheral end of the scintillator layer 21 has a
high Tl concentration. In this case, it is acceptable that the Tl
concentration is uniform within a concentric circle and the Tl
concentration is higher outside the concentric circle. In addition,
the concentration distribution is not limited to a concentric
circle shape, but may be a frame shape in which the peripheral area
has a frame shape and high Tl concentration, and the inner part
inside the frame part has a uniform Tl concentration.
[0079] The scintillator layer having a uniform Tl concentration in
a part other than the peripheral area can also show uniform
characteristics such as a quantity of light emission and sharpness.
In other words, an example as shown in FIG. 7 can have uniform
characteristics in a part other than the peripheral end, while
reliably imparting a moisture-proof effect to a scintillator in
itself.
Second Embodiment
[0080] FIG. 8 shows a sectional view of a radiation detecting
apparatus according to the second embodiment of the present
invention. In the present embodiment, the radiation detecting
apparatus is composed by laminating a scintillator panel with a
sensor panel through an adhesive.
[0081] The scintillator panel is produced by forming a scintillator
layer on a base plate which allows X-rays to pass through itself as
amorphous carbon does, with a vapor-deposition technique. The used
sensor panel has an insulation layer 15 formed on a glass substrate
16 having a photoelectric conversion element array 17 formed
thereon, as is shown in FIG. 1. The radiation detecting apparatus
is produced by bonding the surface of the scintillator panel in a
reverse side to the base plate, with the sensor panel having a
photoelectric conversion element formed thereon, by using an
adhesive.
[0082] In FIG. 8, reference numeral 31 denotes a base plate made
from amorphous carbon, reference numeral 32 denotes an insulation
layer, reference numeral 33 denotes an Al layer for reflecting
light, reference numeral 34 denotes an insulation layer, and
reference numeral 35 denotes a scintillator layer made from CsI and
TlI. In addition, reference numeral 36 denotes a thermoplastic
resin which is a moisture-proof protective layer, and reference
numeral 37 denotes a polyethylene terephthalate resin layer which
allows light to pass through it.
[0083] A concentration distribution of Tl and a method of adding Tl
are omitted because of being similar to the case which was
described in the first embodiment with reference to FIGS. 1, 2A,
2B, 3, 4, 5 and 6.
[0084] It goes without saying that an effect equal to that in the
first embodiment is obtained in the present embodiment as well. In
addition, the present embodiment can confirm the characteristics by
using a single scintillator panel alone. The radiation detecting
apparatus according to the present embodiment can be manufactured
with an enhanced yield, because when the scintillator panel or the
sensor panel has a defect, it can be eliminated before being
laminated.
[0085] FIG. 9 shows another example of a configuration according to
the present embodiment. The configuration example in FIG. 9 employs
the configuration shown in FIG. 7 as a scintillator panel.
Specifically, a scintillator layer 41 has a higher Tl concentration
only in a peripheral end 41a. It goes without saying that the
configuration example also shows the same effect as in the case of
the first embodiment described with reference to FIG. 7.
Third Embodiment
[0086] FIG. 11 is a view showing an example in which a radiation
detecting apparatus according to the present invention is applied
as a radiation detecting system. The radiation detecting apparatus
is the radiation detecting apparatus in the above described
respective embodiments.
[0087] As shown in FIG. 11, X-rays 6060 generated in an X-ray tube
6050 of a radiation source pass through the thorax 6062 of a
patient or subject 6061, and is incident on a radiation detecting
apparatus 6040 for taking a radiation image. The incident X-rays
include information about the interior of the body of the patient
6061. A scintillator in the radiation detecting apparatus 6040
emits light in response to incident X-rays, and the light is
photoelectrically converted to electric information. The
information is converted into digital signals. The digital signals
are image-processed into an image by an image processor 6070 of a
signal processing unit. Then, the image can be observed through a
display 6080 of a display unit in a control room.
[0088] The information can be also transferred to a remote place
through a transfer unit such as a telephone line 6090, and can be
displayed on a display 6081 of the display unit arranged in a
doctor's office located elsewhere, or can be saved in a recording
unit such as an optical disk. Thereby, a doctor at a remote place
can examine the patient. The information can be recorded in a film
6110 of a recording medium by using a film processor 6100 of a
recording unit.
[0089] As many apparently widely different embodiments of the
present invention can be made without departing from the spirit and
scope thereof, it is to be understood that the invention is not
limited to the specific embodiments thereof except as defined in
the claims.
[0090] While the present invention has been described with
reference to exemplary embodiments, it is to be understood that the
invention is not limited to the disclosed exemplary embodiments.
The scope of the following claims is to be accorded the broadest
interpretation so as to encompass all such modifications and
equivalent structures and functions.
* * * * *