JPS6049281A - Radiation measuring element - Google Patents

Abstract

PURPOSE:To enable reduction in size and weight and to obtain an element particularly suitable for tomography, etc. by sandwiching a scientillator layer between a semiconductor photodetecting element layer constituting a radiation incident plane and a semiconductor photodetecting element layer facing said layer thereby increasing radiation detection output. CONSTITUTION:A silicon photodiode layer 1A of about 0.3mm. thickness constituting an X-ray incident plane is constituted of a p type semiconductor layer 11A and an n type semiconductor layer 12A. On the other hand, a photodiode layer 1B facing the layer 1A is constituted of a p type semiconductor layer 11B and an n type semiconductor layer 12B. A scintillator layer 2 consisting of NaI(Tl), CdWO4, etc. held by the layers 12A and the layer 12B is sandwiched between the layers 1A and 1B and a protective film 3 of Al, etc. is provided on the side face of the layer 2 so as to shield visible light from the outside. A photodiode may be further provided after the scintillator layer is sandwiched between the layers 1A and 1B. The radiation detection output is thus increased and the formation of a sharper tomographic (CT) image or the like is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field The IJJ is used in radiation measurement elements. In more detail, V, Input 11 Radiation #It - relates to a radiation measuring element that can efficiently convert into electrical signals.

(b) 1 degree Celsius (surgery) In recent years, medical devices using radiation such as CT and various 1 anti Q =
j I! 3111 constant (t'2 With the advancement of the technology, the jli1 tail of the radiation intensity distribution becomes important WiI:!l
Tl and Natsu ℃ are here. As a measuring device for measuring the frequency distribution of X-rays based on such radiation qJ-ray ξ, there is a known device that combines an ionization chamber with a large number of sections t/4 and determines the radiation intensity of each section by /1 m. However, these were weak against vibration, and their groove structure was complex and heavy, which was disadvantageous in terms of JI'V, R'2, and construction.

There was a desire for an element that could measure vI-, a small-scale distribution, and a shifted M distribution.

Regarding this point, j! Various ray measurement elements have been proposed that combine a scintillator with IW04% and a semiconductor photodetector element (so-called photodimate). ', ), as shown in Fig. 1, there is a scintillator layer (2) forming an incident surface e(ff) and a photodiode layer (
1). In the figure, (3)) a protective film made of aluminum or the like that recoils or blocks visible light from the outside that causes i error; (11) is a p-type (also t-type) semiconductor region; (12) ) is the J1 state (or p-type) semiconductor region, (4)
indicates the measurement display section. Such radiation measurement elements are required to meet the requirements of miniaturization and light weight, but the scintillation efficiency of the scintillator layer, which converts the received ff1l+constant radiation such as X-rays, into visible light is essential. There were problems with insufficient efficiency and low radiation detection output.

(2) Purpose of IJJ The purpose of this IJJ is to address the above-mentioned conventional problems and to provide a scintillation type radiation measurement element with increased radiation detection output. It is.

(d) 47g of radiation j Therefore, according to the present invention, the radiation incident ili'r is (
A scintillator layer comprising a semiconductor photodetecting element layer formed into a semiconductor photodetecting element layer 7 and a semiconductor photodetecting element layer disposed opposite to the semiconductor photodetecting element layer, and further including a scintillator layer, an IJ, and a semiconductor photodetecting element layer between these two semiconductor photodetecting element layers. A radiometer 711 element is provided, which is made by holding a .

One of the most distinctive features of the FJ is that the radiation incident surface is composed of a photodiode, that is, a semiconductor photodetector element itself, which is in combination with a conventional scintillator. The other most distinctive feature is that the scintillator layer is sandwiched between the semiconductor photodetector element and another semiconductor photodetector element facing the scintillator layer.

Is the semiconductor photodetector in this invention a p-type? 1′
PN LI with a nm semiconductor region formed on the surface of a conductive substrate
Examples include a composite photodiode and an np junction type photodiode, and in addition to these, a surface Fl and wall type photodiode using metal-semiconductor contact may also be used.

Further, while silicon is suitable as a semiconductor material, germanium, various compound semiconductors, etc. can also be used.

Among these, it is preferable to reduce the base impurity concentration as much as possible (sieve purity) and to make the depletion layer formed in the pn junction 31L as thick as possible. Of course, p type (or n
It is also possible to use an array-type semiconductor photodetector element in which n-type (or 9-type) semiconductor regions are formed on the surface of a semiconductor substrate, and spatially resolved Fit based on radiation distribution may be used.
Is 9J' suitable for measuring with 8? There is 1'. At this time, it is preferable to apply the tlf structure described later in order to prevent crosstalk.

Radiation incidence surface t? The thickness of the F& region of the groove-forming semiconductor photodetection element is about oh~1 pta for an element with t% purity, and the thickness of the sensitive area of another semiconductor photodetection element placed opposite to this is that of a low purity element. Even if it is, it may be relatively thin, and 0.1 or less is sufficient.

Note that each of these can be produced in the form of a plate by a method known in the art.

By interposing a scintillator layer between the two semiconductor photodetecting element layers, the radiation measuring element of the present invention can be obtained. 1 as the material of the scintillator layer, DI 1
1.王(llj'), Ca1(工6su, C5I(
Na), Kl (T#), ZuS (Cu), C6, WO
Organic scintillators may be used depending on the station.

What does the scintillator layer look like? ~3 gates is enough. However, as a scintillator layer where A is present,
A composite scintillator layer having a semiconductor photodetecting element layer therein may be used. In this case, the detection output can be further increased by J~
It is preferable from the viewpoint that the exposed scintillator r is coated with a protective film (e.g., Ano I/Minicum Aζ film, adiazonium oxide CVD film, etc.) that reflects or blocks visible light from the outside. ) is preferably coated with a protective film (for example, Pb) to prevent human IH due to scattered radiation.

It is more preferable to form a coating with a heavy metal (F6m) such as W% Au.

In addition, it is appropriate to bond the thin 1'' rake layer between the two semiconductor photodetecting elements using an elongated optical adhesive.

The radiation measurement element obtained in this way can efficiently convert incident radiation into electrical signals, and has low energy (several keV).
)/)) Medium energy (several hundred KeV) X-rays and γ-rays? It is possible to obtain a high detection output.

That is, the rays of light first enter the semiconductor photodetection element that constitutes the incident surface, and detection is performed here because the semiconductor photodetection element itself is directly sensitive to radiation.Next, the semiconductor photodetection element Radiation that is not detected by the element, that is, transmitted radiation, enters the scintillator layer, but
Here, most of the light is converted into visible light by scintillation, and human light is efficiently detected by the semiconductor photodetector element on the upper surface or the semiconductor photodetector element layer on the TiF surface. That is, (1) the direct radiation detection action of the semiconductor photodetector element forming the incident surface tA;
This book is considered to be a book that, in combination with the detection effect of scintillation light collection efficiency according to No. 1, provides a high detection efficiency.

(e) FIG. 2 is a schematic cross-sectional view of an X-ray measuring element showing a specific example of the radiation measuring element of FIG. In the diagram
The radiation measuring element is made of a silicon photodimate N4 (IA; minimal layer thickness 0.01 pm) with a thickness of approximately 1. Between the opposing lulu and the silicon photodiode layer (1B: depletion layer thickness (, lJ silk) with a thickness of about 0.3 vn,
It consists of a scintillator layer (2) of CdWOi with a thickness of about one layer tightly sandwiched therebetween.

Each photodiode layer tJ: p! 51 semiconductor layer (I
IA), (IIB) with Il type semiconductor VI region (, L2A)
, (12B) are each formed by diffusion formation [2], and are spaced 4M apart so that the surfaces of these 11-type semiconductor regions face each other. Note that (3) is a reflective film coated on the side arm of the scintillator (2) to be exposed, and (4 is the output from each semiconductor photodetector element) r3'? , L* and place it on the constant display section.

For the X-ray measurement element with the above configuration, 120 KV.

X-rays emitted from an X-ray tube with a tube voltage pass through an aluminum plate IV filter of lrm and a water layer of O~30σ (
A simulation model was set up to detect the object passing through a human body (assumed to be a human body in CT), and the detection output was calculated. The results are shown in FIG. 6 and Table 1 together with 11] soft examples. In addition, Comparative Example 1 adopts the conventional configuration shown in FIG. 1, and the detection output obtained during fc is
The opposite photodiode layers (except for 1υ)
The detection outputs obtained with the same X-ray n1 detector as shown in FIG. '! It can be seen that the 11 elements provide excellent detection output.

A specific example ir in which a photodiode layer is further provided inside the scintillator R(2) is shown in FIG. 153.

In the figure, the scintillator layers (two are composed of a three-layer scintillator R (21) and a two-layer 7:A diode layer (22) interlayered between each scintillator layer, and the others are the same as in Figure 2). It consists of a multilayer radiation I (ray measurement element t).
It is a measure of especially highly penetrating radiation! It is useful for II.

Further, a specific example using an array type photodiode layer as the photodiode layer is shown in Fig. t4'54 and Fig. 51. In the figure, (12A, (12B') are n-extended semiconductor regions t formed by multiple fractional diffusion on the surface of a p-type semiconductor substrate (11B'), and each photodiode layer (12A, (11B') The 113 n-shaped conductor regions (1280 and 128) are also configured to face each other.

Then, the scintillator layer (on the 2' side, 1 layer parallel to the incident direction)
) A large number of J-cut grooves 714 (ri) are provided correspondingly, and the inner surface of the 117 J-cut grooves is coated with aluminum (e.g., vapor-deposited or sputtered film; 51). This groove is shown in FIG. As shown, a scintillator layer (2') is formed on the same side of the lower n-type semiconductor region (12y) that reflects the scintillation light due to the radiation rj'jM (ZjL+'' at 12A). It acts to efficiently guide iL to the depletion layer. Therefore, the so-called Stokes phenomenon is p summed, and in combination with an array type photodiode, it is possible to measure the radiation distribution n1 before convex spatial resolution. Of course, at this time However, it is still t larger than before.4
Eating output will be exerted.

Note that P11 is used instead of the scintillator layer having the notches M.
A similar effect can be obtained by using a scintillator layer having a large number of vertically extending 11181-shaped compartment structures.

(To) The effect of emitted j As mentioned above, this emitted IJJ radiation meter IT! 11
Element V, it is possible to convert incident radiation into an electrical signal without waste,
The detection efficiency is superior to that of the conventional method. In addition, compared to the conventional ionization chamber, it is smaller and lighter in weight, and has advantages in terms of ease of handling and installation. Therefore, it is useful for various radiation measurements, and is especially useful when used in an array sensor for both CT and CT images, as it allows for extremely sharp IJI images.

In addition, 11 (Is it necessary to form a protective film on the incident surface of the side line? 1)
It also has the advantage of not having any.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view illustrating a conventional radiation measuring element, FIG. 2 is a schematic sectional view illustrating a radiation measuring element of this invention, and FIGS. 3 and 4 are 5 is an enlarged view of the main part of FIG. 4, and FIG. 6 is a comparative example of the detection output of the radiation measuring element of this IJJ. This is a graph illustrating the same. (1) ,(LA,),(IB),(,LAli,
(IB'J, (22)...Photodiode layer, (2), (2S, (2//)...Scintillator layer (3)
)...Protective film, (4...Measurement display section. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] (A semiconductor photodetector layer constituting the υ radiation incident surface and a semiconductor photodetector layer 7 disposed therein, and between these two semiconductor photodetector layers, a scintillator layer, and a semiconductor photodetector layer 7) A scintillator at which further layers the detection water molecules R
- A radiation measuring element which is held by 'C'.