In a radiation detector, scintillation material flouoresces and the produced light is converted to electrical energy in an adjacent converter, separators are provided in spaces between the adjacent scintillators and converters. The separators may have a greater length than the adjacent scintillators, so that they will extend beyond to reduce cross-talk. The separators can extend toward the source of radiation for a height substantially greater than, and particularly five times, the height of the spaces between the adjacent scintillators to prevent X-ray scattering and function as a collimator. Optically opaque adhesive may be provided on the opposite ends of separators and pairs of scintillators and collimators, to prevent cross-talk.

BACKGROUND OF THE INVENTION 
The present invention relates to a radiation detector, and more 
particularly to an X-ray detector suitable for a full-length X-ray 
computed tomograph apparatus, hereinafter referred to as "X-ray CT". 
The structure of a conventional X-ray solid detector is described in 
Japanese Patent Laid-Open No. 118977/1983. 
An ionization chamber X-ray detector using ionization of a rare gas is 
disclosed in Japanese Patent Application Publication No. 58429/1985. A 
solid state detector using fluorescence is compact and provides reduced 
cost of production, with solid detectors being disclosed in Japanese 
Patent Laid-Open Nos. 263456/1985, 81575/1984, 141087/1984, and U. S. Pat. 
No. 4,429,227. 
The Japanese Patent Laid-Open No. 263456/1985 shows a solid state detector 
that consists of a light emission portion using incident X-rays and a 
photo-electric conversion portion for receiving and detecting the light. 
SUMMARY 
It is an object of the present invention to provide an improved radiation 
detector of the solid state type. 
In a radiation detector, wherein scintillation material fluoresces and the 
produced light is converted to electrical energy in an adjacent converter, 
separators are provided in spaces between the adjacent scintillators and 
converters. The separators may have a greater length than the adjacent 
scintillators and converters, so that they will extend therebeyond to 
reduce cross-talk and assembly misalignment problems. The separators can 
also extend toward the source of radiation for a height substantially 
greater than, particularly five times, the height of the grooves between 
the adjacent scintillators to prevent X-ray scattering and function as a 
collimator. Optically opaque adhesive may be provided on the opposite ends 
of separators and pairs of scintillators and collimators, to prevent 
cross-talk. The converters can be constructed as diodes, particularly on a 
substrate with spaces therebetween aligned with the separators. The diodes 
extend beyond the ends of the scintillators to provide reference locations 
for the cutting of the scintillators from a solid block of scintillation 
material. Vacuum deposition forming may be used for a light reflective 
layer on the separators to provide for very accurate matching of separator 
width with groove width, within the range of 10 to 20 microns. A group of 
scintillators with separators between scintillators and converters may be 
integrally and rigidly joined together as a unitary detector element, with 
a plurality of like elements being connected together. Side separators are 
provided therebetween, for forming larger units, and the side separators 
between the adjacent element are formed on at least one of the sides of 
each element, and preferably both opposite sides of each elements, with 
the total width of the side separator between adjacent detector elements 
being substantially equal to the width of each of the separators within 
each element.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
As one portion of the present invention, there is the following analysis of 
a problem that may be encountered in conventional structure, with 
reference to FIG. 2. An incident X-ray radiation 101 falls upon a 
scintillator 102, which generates light or fluorescence 210 and a 
scattering X-ray 211. The resulting fluorescence 210 is guided to a 
photo-electric converter 206 by a separator 104. The separator 104 is 
located on both sides of the scintillator 102 and is impervious to X-ray 
radiation while being reflective to light. At opposite sides of the 
photo-electric element there are outer side separators 204, 205, which are 
adjacent to each other for adjacent detector elements A and B, when a 
plurality of like elements are placed side by side to construct a larger 
detector. 
The photo-electric converters 206 are supported by a casing or support 207 
on one side, and secured on the other side to the scintillator blocks. 
That is, the scintillation devices A and B are mounted and fixed on the 
photo-electric converters 206, which are in corresponding groupings C and 
D. A plurality of the thus constructed elements A, C and B, D are 
connected together to form a larger detector. 
In FIG. 2, the thickness to of the separator 104 inside the element block 
and the thickness t1, t2 of the outermost separators 204, 205 have 
conventionally held the relationship that thickness to equals t1 plus t2. 
However, in the conventional construction, there has been no particular 
analysis or consideration given to these relative thicknesses. 
Conventionally, either t1 or t2 has been set to zero, and the other of t2, 
t1 has been set equal to t0, as shown in FIG. 3. That is, one of the 
separators 204, 205 has been the same as one of the interior separators 
104, with the other of the separators 205, 204 is effectively nonexistent. 
As shown in FIG. 3, detector elements E and F are arranged on one side of a 
polygon to construct a larger element, and they are adjacent to each other 
with a small acute angle, so that all of the elements together may form an 
approximation of an arc having its center at the X-ray focus. Therefore, a 
gap d is defined at the lower portions of the blocks E and F. Since the 
outermost separator exists on only either the block E or the block F, 
converging efficiency of the resulting fluorescence will drop for the 
element 301, because the scattering X-rays and light will escape through 
the gap d; for this reason, sensitivity, energy characteristics and noise 
quantity of the scintillation 102 at the end portion, for one end, become 
different from that at the opposite end, and a ring-like artifact occurs 
as a false image. If a block E having a separator at its end portions 
exists, than a block F not having separators at its ends must also exist, 
requiring two different kinds of blocks to be manufactured, and 
complicating the assembly process of a larger device constructed of a 
number of elements. Accordingly, this imposes some limitations on the 
mounting and arrangement of the support, so that the production yield 
eventually drops. 
Accordingly, it is seen from an analysis of the conventional style of 
structure that a ring-like artifact or false image occurs and production 
yield drops when one of the outermost separators is constructed to be of 
equal thickness to the internal separators. 
Further, the conventional methods do not consider the variations in 
thickness of the separators and the resulting fluctuations in cross-talk 
quantity. Thus, the conventional techniques have employed variations for 
the thicknesses t0, t1 and t2, within a single detector element and with 
respect to a plurality of detector elements. The factors that determine 
the upper limit of the error are a geometric pitch error and a cross-talk 
quantity to adjacent channels due to scattering X-rays. In FIG. 2, 
cross-talk occurs if the scattering X-ray 211 is incident into adjacent 
elements through a separator 104, or separators 204 and 205. If the 
quantity of this cross-talk varies between elements, the ring-like 
artifact and a linear artifact occur on a CT reproduced image. 
The quantity of the scattering X-ray incident into the adjacent elements 
through the separators 104, 204 and 205, that is, the cross-talk quantity 
is determined by the wave length of the scattering X-rays, self-absorption 
inside the scintillation element, and the material and thickness of the 
separator. In the CT X-ray detector, the variations of t0 and t1 plus t2 
result in the variation in the cross-talk quantity due to the scattering 
X-rays. The allowable value of variation in the cross-talk quantity varies 
with the system or with an imaging portion. Therefore, the upper limit 
value of radiation and thickness of the separator generally cannot be be 
determined. When a 0.1 to 0.2 mm - thick material of tungsten, or 
molybdenum or tantalum is used, for example, it is on the order of several 
microns. 
The required value for the variation in the thickness of the separators is 
more severe than the requirement for the geometric pitch deviation. 
Therefore, if the difference between t0 and t1 plus t2 is above a value 
that generates a significant difference of the cross-talk quantity due to 
the scattering X-rays, there is a possibility that the ring-like artifact 
and the linear artifact will form. 
The various conventional techniques described above do not sufficiently 
take into consideration the share of the thickness of the separators 
inside the detector elements; the thickness of the separators at the 
outermost sides of the detector elements, and the error of the thickness 
of the separators. The problem occurs that the ring-like artifact or the 
linear artifact is present in the CT reproduced image. The present 
invention overcomes the problems described above and provides a 
multi-element radiation detector that can reduce the occurrence of the 
artifacts on the CT reproduced image by optimizing the thickness of the 
separators inside the element blocks and the thickness of the separators 
at the outermost side portions of the detector elements, and by taking the 
error of the separators into consideration. 
In the multi-element radiation detector in accordance with the present 
invention, the errors of the thickness of the separators inside the 
detector elements and the thickness of the separators at the outermost 
side portions are reduced to such an extent that the difference in the 
cross-talk quantity due to the scattering X-rays can be neglected. 
Accordingly, the ring-like artifact and the linear artifact due to the 
cross-talk difference can be prevented. In the present invention, it is 
preferable that the thickness of the separator at the outermost side 
portions of the detector element is one half of the thickness of the 
separator inside of the detector element, with separators are disposed at 
both outermost side portions of each detector element, so that the gap 
between the scintillator element at the outermost side portions and the 
separator is eliminated and the ring-like artifact due to the occurrence 
of this gap can therefore be prevented. 
FIG. 1 is an illustration, schematic, of the relationship of the separators 
to be employed throughout the embodiments of the present invention. 
In the cross-sectional view of FIG. 1, two detector elements are placed 
side-by-side in the construction of a detector composed of many such 
detector elements that are identical to each other. The scintillation 
blocks 102 an the separators 104 are arranged alternately, and outermost 
side separators 204' and 205' of adjacent scintillation elements are 
arranged adjacent to each other. These outermost separators 204' and 205' 
each have a thickness equal to one-half of the thickness of the interior 
separators 104, and the outermost separators 204', 205' are bonded or 
otherwise connected by adhesive to the outermost sides of the 
scintillation elements, at the opposite outermost sides of each 
scintillation element. The scintillation blocks 102 and separators 104, 
204', 205' are joined to the photo-electric converters 206, and in turn 
connected to the support 207. 
The sum of the thicknesses of the outermost separators 204', 205' that, t3 
plus t4, is made equal to the thickness t0 of the interior separators 104, 
within an accuracy of 5 micrometers, for example, so that no significant 
difference will occur in the cross-talk quantity due to the scattering of 
X-rays. Tungsten, tantalum or molybdenum is used as the material of the 
separators 104, 204' and 205' 
Accordingly, separators 204' and 205' exist at both outermost side portions 
of the detector element and no gaps occur between the separators and the 
scintillation blocks 102 when the blocks and separators are mounted on to 
the support 207. Therefore, there is no difference in the characteristics 
between the scintillation blocks at the outermost side of a detector 
element and scintillation blocks interior of the detector element. The 
thickness t0 of the internal separators 104 and the thickness t3, t4 of 
the separators 204' and 205' at the outermost side portions are adjusted 
so that no significant difference exists that would incur cross-talk 
quantities due to scattering X-rays. The benefits of the above described 
structure are the reduction of the occurrence of the ring-like or linear 
artifact on the CT reproduced image. Since the thicknesses t3 and t4 of 
the outermost side separators 204' and 205' are made equal to each other, 
only one type of outermost separator need be employed and the detector 
elements are identical and symmetrical to make their assembly easier to 
produce a larger detector. Therefore, a mounting of the detector elements 
on the support can be made easier and smoothly without a limitation to the 
mounting direction or the sequence of arrangement so that production yield 
can be improved. In the preferred embodiment, it is preferable that the 
thickness of each of the outermost separators 204' and 205' be equal to 
each other and equal to one-half of the thickness t0 of the interior 
separators 104, but in any event the sum of the thicknesses 204' and 205' 
is made equal to that of the internal separators, because of significant 
errors that will produce the difference in cross-talk quantities due to 
scattering of X-rays. The present invention is also effective when it is 
supplied to the X-ray CT. While the section of the separators is kept 
triangular (with both surfaces being non-parallel) as shown in FIG. 5 of 
the aforementioned Japanese Patent Laid-Open No. 24174/1987. 
The above-discussed thickness relationships of the separators is usable 
throughout the remainder of the described preferred embodiments, wherein 
the structure of the separators, scintillation blocks, photo-electric 
converters, and their method of construction will be set forth in more 
detail. 
An ionization chamber X-ray detector using ionization of a rare gas has 
been widely employed in the past as an X-ray detector for X-ray CT, as 
described, for example, in Japanese Patent Publication No. 58429/1985. 
However, the development of a solid-state detector using fluorescence has 
been made in order to obtain high resolution, to make the apparatus 
compact and to reduce the cost of production. Examples of such solid state 
detectors are disclosed in Japanese Patent Laid-Open Numbers 263456/1985, 
81575/1984, 141087/1984 and U.S. Pat. No. 4,429,227. The typical 
construction of the solid state detector will be described with reference 
to the contents of Japanese Patent Laid-Open Number 263456/1985. This 
solid state detector has a light-emission portion using incident X-rays as 
the incident radiation to be detected and a photo-electric converter for 
receiving and detecting the emitted light. As shown in FIG. 6, a 
multi-channel scintillation element 145 is produced by sequentially 
bonding scintillation elements 141 through separators 140, which are 
coated with a light-reflecting agent and consist of a thin sheet of heavy 
metal having high X-ray absorbance. Various types of photo-electric 
converters are used for the light reception portion immediately below the 
scintillation blocks, but multi-channel photo-electric converters are used 
to implement the multi-channel scintillation device as shown in FIG. 6. 
PIN or PN type silicon photo diodes are mostly used as the photo-electric 
converters. FIG. 7 shows the structure of a multi-channel photo-electric 
converter element. A plurality of photo-electric converters 116, which 
detect the light, are formed on one semi-conductor substrate 110 and this 
semi-conductor substrate is integrated with an insulating substrate 109. 
The solid state detector is produced by bonding the multi-channel 
scintillation element 145 shown in FIG. 6 to the multi-channel 
photo-electric converter shown in FIG. 7 with an optically transparent 
adhesive in such a manner that each channel is in alignment with the 
other. 
In order to bring each channel into alignment, dimensional accuracy of the 
multi-channel scintillation blocks in FIG. 3, particularly the pitch 
accuracy of the scintillator blocks and accuracy of width of the 
scintillator blocks are very important. Channel misalignment results in 
variations in detection sensitivity for each channel and produces the 
X-ray CT image with an artifact. The bond surface between the 
multi-channel scintillation blocks 145 and the multi-channel 
photo-electric converter elements must be flat. Any corrulation on the 
fluorescent output surface of the scintillation elements, any corrugation 
of the partitions in the direction of height of the scintillation blocks 
and any corrugation of the light receptive surface of the photo-electric 
converters will result in optical leakage between the channels and also 
provide the X-ray CT image with the artifact. The production of the 
multi-channel scintillation blocks 145 shown in FIG. 6 needs complicated 
production steps for which high accuracy is required. FIG. 8 shows the 
outline of an improved production method of the multi-channel 
scintillation blocks 145 disclosed in Japanese Patent Laid-Open No. 
81575/1984. A predetermined number of scintillation thin sheets 141 and 
thin sheets of separators 140 of specific sizes are alternately bonded and 
integrated with an adhesive, and after the adhesive has solidified, the 
multi-channel scintillation element 145 is produced effectively by using a 
diamond cutter or a multi-wire saw to provide the cuts schematically shown 
in FIG. 8. Since a high level of accuracy is necessary for the 
scintillation element 145 as described already, bonding of the 
scintillation thin sheets 141 and separators 140 must be made uniform and 
accurate for each of the bonding surfaces, so that the thickness of the 
bonding layer becomes uniform, which is quite difficult. In such a 
construction as shown in FIGS. 6-8, both the scintillation sheets 141 and 
the separator sheets 140 have the same height so that the detector 
produced therefrom has low directivity to the incident X-rays and produces 
a large quantity of scattering beams of radiation. To solve this problem, 
it has been known to provide a detector wherein the quantity of scattering 
is reduced. FIG. 9, with reference to U.S. Pat. No. 4,429,227, discloses 
thin sheet separators 150, which function as a collimator for reducing the 
quantity of incident radiation scattering beams and also as separators for 
preventing optical linkage between the adjacent channels. These separators 
are made of tungsten or a high-density material and are mounted in such a 
manner as to keep a predetermined positional relationship with the 
scintillation blocks 151. The scintillation blocks 151 face the light 
receptive surface 155 of photo diodes 153 that are on a substrate 154 
through the employment of optical grease 152. In this conventional 
example, the thin sheet 150 must have a complicated shape and optical 
leakage exists between the adjacent channels through the gaps between the 
thin sheets 150 and the light reception surfaces 155. 
FIG. 10 relates to an analysis of the structure shown in Japanese Patent 
Laid-Open No. 141087/1984, which uses a cadmium tung-state crystal 162 as 
the scintillation block material. This example utilizes high X-ray 
absorbance and eliminates the separators between the scintillation 
elements. A light reflection layer 161 is formed on the surface of the 
scintillation blocks 162 to prevent optical leakage to the adjacent 
channels. The collimators 160 are positioned by the use of a jig to be 
located correctly with respect to a bonding portion of the scintillation 
blocks. The scintillation blocks face the light reception devices or 
photo-electric converters 163 that are on a substrate 164 through an 
optical coupler. This example provides the advantage that the collimator 
portion can be produced independently of the X-ray detection element 
portion. However, the scintillation blocks must be produced accurately one 
by one in the same way as in the example shown in FIG. 9, and optical 
treatment must be made to the scintillation surface, whenever necessary. 
Thus, a large number of production steps are necessary. 
The conventional techniques as analyzed above, did not take into 
consideration the production requirement for the X-ray detector in regard 
to the corrugation of the fluorescence output surface of the multi-channel 
scintillation blocks and the corrugation of the light reflection surface 
of the multi-channel photo-electric converters that cause optical leakage 
between adjacent channels. Therefore, the conventional techniques involve 
the limit in reducing optical leakage. Further, since complicated 
production steps are needed, the production is not free from the problems 
of production cost and yield of the multi-channel scintillation blocks. 
According to preferred structure and manufacturing techniques in the 
present invention, detectors may be economically made with high 
performance for the X-ray CT through simple production steps while 
minimize leakage between adjacent channels. The above described problems 
can be solved by bonding and fixing scintillation block thin sheets, each 
having a fixed thickness, to the light reception surface of a 
multi-channel photo-electric element with an optically transparent 
adhesive; thereafter forming grooves for inserting separators at the 
center of the dead zone between adjacent photo-electric converters in such 
a manner as to reach the inside of the semi-conductor substrate, 
preferably. The grooves start at the scintillation block incident 
radiation surface. The electrically insulating substrate can support, or 
carry, thin film-type photo-electric converters, manufactured according to 
thin film technology. Thereafter the separators are inserted and fixed 
within the grooves. 
Each separator is inserted to the bottom of its groove, preferably down to 
the inside of the semi-conductor substrate that forms the photo-electric 
converter elements or the inside of an electrically insulating substrate 
that forms the support or carrier of the semi-conductor substrate or the 
thin film technology-type photo-electric converters. Accordingly, optical 
leakage between the adjacent channels can be minimized without being 
affected by the corrugation on the fluorescence output surface of 
multi-channel scintillation blocks or the corrugation of the light 
reception surface of multi-channel photo-electric converter elements as in 
conventional technology. 
With reference to FIG. 4, each scintillation block 102 faces the light 
reception surface at the top of layer 106 of a multi-channel 
photo-electric converter grouping, through an optically transparent 
adhesive layer 105. The photo-electric converters shown in FIG. 4 are of 
the PIN type silicon photo diodes. These diodes consist of a P plus layer 
106 and I layer 107 and N plus layer 108, all on an electrically 
insulating substrate 109, according to known technology. The light 
reception surface of the layer 106 corresponds to the portion Where the P 
plus layer 106 is formed in the shape of a thinly elongated island. Light 
reflection layers 103 are formed on the surfaces of the scintillation 
blocks 102 on the X-ray incident side 101 and on the two side surfaces 
(not shown in FIG. 4) of the detector element in the longitudinal 
direction LD, that is both side surfaces having smaller surface areas 
among the surfaces crossing at right angles the X-ray incident surface 
103. Each separator 104 has surfaces of, for example aluminum, to help 
with reflectivity, and on top of this, to prevent conduction, is an 
optically transparent and electrically insulating layer made of 
molybdenum, tantalum, tungsten, lead or an alloy consisting principally of 
these elements, and such layer is 0.1 to 0.2 mm thick in order to prevent 
optical leakage between the adjacent channels and to improve converging 
efficiency of the fluorescence generated inside the scintillation blocks 
to the photo-electric converters. Each groove into which each separator 
104 described above is to be inserted is positioned at the center of the 
dead zone existing between adjacent light receptive surfaces 106, that is 
between adjacent P plus layers of the diode. These grooves are preferably 
formed by means of a diamond cutter with extreme accuracy, and the 
grooves, in FIG. 4, extend inwardly to the intermediate portion of the 1 
layer 107 through the scintillation blocks 102 and the adhesive layer 105. 
That is, the scintillation material may be a thin sheet having a very flat 
lower surface bonded by adhesive 105 to the very flat upper surface of the 
optical-electrical conversion construction, to effectively form a solid 
integrated block, which is thereafter grooved With the diamond saw as 
mentioned. 
Such a structure can be produced by the following method. 
As shown in FIG. 11, a solid block of scintillation material 200 having the 
dimensions L, W and H is cut from a scintillation mass formed by a hot 
isostatic press of powdery fluorescent material such as ZnS:Ag, Ba.sub.2 
GdSbO.sub.4, Ba.sub.2 BiInO.sub.6, Ba.sub.2 BiYO.sub.6, GdPb.sub.2 
WO.sub.6, La.sub.2 O.sub.2 SiTb, ZnCdSiAg, LaOBr:DyCdS, etc., or a single 
crystal such as Zn.sub.2 SiO.sub.4, CaWO.sub.4, CdWO.sub.4, ZnWO.sub.4 
CsI:Na, CsIiTl, NaI:Tl, Gd.sub.2 SiO.sub.4 :Ce, Bi.sub.4 Ge.sub.3 
O.sub.12, CaF.sub.2 :Eu, etc. The two surfaces 203 defined by the 
dimensions W and H become the surfaces that eventually correspond to the 
longitudinal direction LD of the scintillation blocks. A light reflecting 
layer or coating containing barium sulfate or titanium dioxide is applied 
to the two surfaces 203 or an aluminum vacuum deposition layer is used to 
form a light reflecting layer on the two surfaces 203. The dimension L is 
equal to the length of the scintillation element, while the dimension W 
should be a little greater than the width of the multi-channel 
photo-electric conversion element in the channel direction. This dimension 
H may be such that a suitable number of scintillation thin sheets 102 
having a fixed thickness t, as shown in FIG. 12, can be cut therefrom. 
As shown in FIG. 12, the scintillation thin sheet 102 has an accurate 
thickness t, having been accurately cut from the scintillation block 200 
shown in FIG. 11. The light reflection layer 103 is formed on one of the 
surfaces having the maximum area in the same way as the surfaces 203. The 
surface of the scintillation thin sheet 102 having the maximum length, but 
not having the light reflection layer, is bonded and fixed to the surface 
of the multi-channel photo-electric conversion sheet 110, with a light 
transmissive adhesive. Since the multi-channel photo-electric converters 
are in sheet form and the scintillation material is in sheet form, 
surfaces to be bonded can be made very flat and accurate, to prevent light 
leakage or cross-talk. 
FIG. 13 shows the state when the bonding, described above, is completed, 
and FIG. 14 shows a cross-sectional section of the lamination, as taken 
along line IV--IV. The existence of the adhesive layer 105 provides the 
advantage that the output can be improved by 30 to 40% in comparison with 
the case where the light detection portion and the light emission portion 
are such as those described above with respect to the conventional 
structure. This highly advantageous result is obtained by the above 
method, for the above reasons, particularly involving the handling of 
sheets that may be provided with very flat mating surfaces, to thereafter 
reduce cross-talk when they are assembled, all prior to forming any 
grooves. The 30 to 40% output advantage with the present structure is 
compared with a structure such as that produced by Japanese Utility Model 
patent Laid-Open No. 154880/1985, which is otherwise identical in 
structure to a detector constructed according to the present teachings. 
As shown in FIG. 13, the length of the multi-channel photo-electric 
detector 110 is greater than the length of the scintillation element 102 
and the positions of the dead zones (not seen in FIG. 10) that exists 
between the adjacent light reception surfaces of P plus layer 106 of the 
photo-electric converter 110 can be visually observed, because they are 
visually exposed on the top surface of the sheet 110, without being 
covered by the scintillation thin sheet 102. This exposure is at both ends 
of the detector element, in the direction of the grooves (not yet made). 
As shown in FIG. 15, grooves 190 are each formed at the center of the dead 
zones, as previously described. To prevent entering of electrical noise 
and to keep the mechanical strength of the semi-conductor substrate 
forming the photo-electric converters, the depth of each groove is such 
that the groove reaches into the intermediate portion of the I layer 107, 
but does not reach the N plus layer 108. The width of the groove 190 is 
smaller than that of the dead zone, but is a little bit greater, for 
example by 10 to 20 microns, than the thickness of the separator 104 (not 
seen in FIG. 15). In order to increase the effective area of the 
scintillation blocks 102, the light reflective property is given to the 
surface of each of the separators, preferably by a thin aluminum layer 
vacuum deposited or the like on to the accurately formed separator 104, 
rather than applying a inaccurate coating. Such a separator 104 is thus 
accurately formed in width and inserted down to the bottom of the groove 
190. The height of the separator 104 is such that it is at the same level 
as the light reflection layer 103, or projects slightly from the latter. 
The separator 104 is longer than the scintillation block 102 as shown in 
FIG. 17 in order to prevent optical leakage between the adjacent channels 
at both ends of the element in the longitudinal direction. The separator 
104 is thus inserted and stiffly bonded and fixed to the surface of the 
substrate 109 for mounting the multi-channel photo-electric converters 110 
at both ends of the scintillation blocks in the longitudinal direction 
with an adhesive 120. 
The advantage of having the separator longer than the scintillation blocks 
will now be described in detail. If a separator having the same length as 
that of the scintillation block is used, the separator 104 will be pulled 
between the scintillator elements 102 due to a very small manufacturing 
error in the arrangement shown in FIG. 19. In other words, there develops 
the gap portion having a width d near one end portion where the separator 
104 does not exist and therefore the light 302 leaks through this gap d 
between the adjacent scintillation blocks 102, resulting in cross-talk. In 
FIG. 19, incident X-rays 101 are guided by the collimator 301. The 
quantity of cross-talk is determined by the gap width d, the X-ray 
absorption coefficient and light absorption coefficient of the 
scintillation blocks 102, the X-ray energy spectrum, the collimator 
opening t and the shape and size of the scintillation element 102. 
FIG. 20 shows an example of a relationship between the distance d of the 
gap mentioned above and the quantity of the cross-talk produced by the 
gap. 
If optical cross-talk occurs between the scintillation blocks and the 
quantity of cross-talk differs from the scintillation block to 
scintillation block, there is produced a ring-like artifact and the radial 
artifact. The threshold cross-talk quantity at which these artifacts do 
not occur is therefore different depending on the imaging conditions, but 
must be limited to below 0.05% in the case of a severe condition. In the 
case of the example shown in FIG. 20, the deviation quantity of the gap d 
must be below 20 micrometers in order to keep the quantity of cross-talk 
below 0.05%. The limit on the deviation quantity d becomes severe 
depending on the characteristics and shape of the scintillation blocks. In 
accordance with the conventional system shown in FIG. 2, it is not easy to 
secure such accuracy with a high yield. 
Therefore, as in the embodiment shown in FIG. 17, the length of the 
separator, that is the length in the direction of the slice thickness of 
the tomogram, is made greater than the length of the scintillation block 
so as to absorb any dimension error during production and any assembly 
error in placing the separators. In this manner, it is possible to prevent 
the end of the separator from being placed inside of the scintillation 
block end. This will prevent the occurrence of any gap d and therefore 
prevent the occurrence of the cross-talk that results in the artifact. 
According to FIG. 17, the accuracy of the corresponding positioning 
between the scintillation blocks 102 and the light reflective surface is 
determined solely by the mechanical accuracy of a machine tool forming the 
groove 190. Therefore, the multiple channel detection element having high 
performance can be produced without producing independently the 
multi-channel scintillation blocks as shown in FIG. 6. 
If an arrangement jig 121 for the scintillation blocks and the separators 
is used as shown in FIG. 21, it then becomes possible to limit the 
accurate positioning of the separators in the direction of slice 
thickness. 
As a further portion of the present invention, reference is made to FIG. 5. 
The separator is made of molybdenum, Tantalum, Tungsten, lead or the alloy 
consisting of these elements as its principal component. The separator is 
preferably 0.1 to 0.2 mm thick, as measured between adjacent scintillation 
blocks, and has the light reflecting property in the same manner as 
described above. The separators are inserted down to the bottom of the 
groove 190. Each separator 104A projects in the direction of the X-ray 
incident radiation 101 by at least five times the height of the 
scintillation element 102 from its surface as measured in the same 
direction. The difference between this construction and that previously 
described with respect to FIG. 4 resides in that the separator 104A is 
provided with the function of the collimator and reduces the quantity of 
scattering X-rays. It is thus possible to reduce the quantity of the 
occurrence of scattering X-rays and at the same time minimize optical 
leakage between the adjacent channels. In this case, since the height of 
the separator in the direction of incidents of X-rays becomes great, the 
separator 104A must be held sufficiently stiffly. An example of the 
support method is shown in FIG. 18. Supports 130, each having grooves 131, 
are located so that the pitch between the grooves 190 of the substrate 109 
and the grooves 131 is set accurately by the jig, and members 102 and 109 
are then fixed integrally. Each separator is inserted into the bottom of 
the groove 190 formed to the interior of the photo-electric converters 110 
through the groove 131 and stiffly bonded and fixed into the grooves 131. 
Each group 131 is formed precisely by the same machine means as the means 
for performing the grooves 190 shown in FIG. 15 or FIG. 16. 
A suitable example of the scintillation material for the scintillation 
blocks in the constructions of FIGS. 1 and 4, is (Gd.sub.1-x-y Pr.sub.x 
Ce.sub.y).sub.2 O.sub.2 S:F, which is described in Japanese Patent 
Publication No. 4856/1985 and has a high conversion deficiency and a short 
persistence time. The fluorescence material is powdery and can be 
synthesized easily by hot isostatic pressing as described in Japanese 
Patent Laid-Open No. 52481/1987, and is from 1 to 1.5 mm thick, for 
example, with sufficient X-ray absorbance and light transmissivity. 
Therefore, X-ray detectors have been produced with high sensitivity and 
high performance by the structures according to FIGS. 1 and 4 described 
above. 
If the X-ray absorbency of the scintillation material is not sufficiently 
great, the structures according to FIGS. 1 and 5 can be modified by 
bonding the material having a high light transmissivity and X-ray 
absorbance to the surface of the scintillation thin sheet that has the 
largest area but does not have the light reflecting property. An example 
of this modification is shown in FIG. 12, wherein the object of the 
present invention can be accomplished without forming the light reflection 
layer on the surfaces 203, 103. This is because, in FIG. 17, the black 
light intercepting adhesive or an optically opaque adhesive is used as the 
adhesive 120 and the optical leakage at both end portions of the 
scintillation blocks in the longitudinal direction can be minimized. 
Furthermore, if the structure shown in Japanese Patent Laid-open No. 
59(1984)-46877 is employed for the X-ray incidence surface, optical 
leakage on the the X-ray incidence surface can be minimized. 
Although the above description is given with respect to a case where the 
depth of the groove for the insertion of the separator 104 is greater than 
that of the P plus layer of the photo-electric conversion element but is 
not below one-half of the thickness of the semiconductor substrate forming 
the photo-electric converters, FIG. 16 shows a further structure of the 
present invention where the groove reaches the inside of the substrate 
109. In this case, each multi-channel photo-electric converter is 
separated by the grooves in the position of the dead zone so that the 
semiconductor material 106, 107, 108 forming the photo-electric converters 
and the substrate 109 must be bonded and connected stiffly to each other. 
In contrast, if the multi-channel photo-electric converters are formed 
directly on the electrically insulating substrate 109 using thin film 
technology, the above requirement with respect to stiff bonding becomes 
almost unnecessary. The method of forming the photo-electric converters by 
the thin film technology with amorphous silicon is well known in the art 
and is intended to be a part of the present invention. The structure shown 
in the various figures described above, can be used in combination with 
each other. Accordingly, optical leakage between adjacent channels can be 
minimized with the various described techniques and production is 
simplified. In the description of these embodiments, the explanation of 
the signal pickup route has been omitted because a large number of 
conventional techniques are well known, and such does not really form a 
part of the present invention. Although, PIN type silicon photo-diodes 
have been described in detail, various types of photo-electric converters 
may be used with the present invention. 
While preferred embodiments along with variations and modifications have 
been set forth for disclosing the best mode and important details, further 
embodiments, variations and modifications are contemplated according to 
the broader aspects of the present invention, all as set forth in the 
spirit and scope of the following claims