JPH0619460B2 - Radiation detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a technique for improving detection efficiency in a semiconductor radiation detector.

(Prior Art) A conventional semiconductor detector technology will be described with reference to FIGS. 7 and 8. FIG.

There are several types of semiconductor radiation detectors, and in this example, a Pn junction type detector will be described as a general detector.

The Pn junction type detector is made by diffusing impurities such as phosphorus to a thickness of 0.1 to 2 μm as an n layer (2) on the surface of a P layer (1) made of a P type material having a surface corresponding to the detection surface. It has been done.

Electrodes are joined to the n layer (2) and the P layer (1) to apply a reverse bias voltage. That is, the n layer (2) is positive, P
A negative voltage is applied to the layer (1).

In this state, the positive charge in the detector is drawn to the electrode of P layer (1) and the negative electrode is drawn to the electrode of n layer (2).

Therefore, a layer called a depletion layer is formed in the detector, and no current flows between the two electrodes described above.

When radiation enters this depletion layer, electrons are excited from the valence band (see FIG. 8) to the conduction band (see FIG. 8) in the vicinity of the track of the radiation, and holes are generated in the valence band. P
If no voltage is applied to the layers (1) and n layers (2), the electrons fall back to the valence band and become stable, but if a reverse bias voltage is applied, electrons and holes are applied to the electrodes respectively. It is pulled and moves, and at the electrodes, it is combined with charges opposite to each other and disappears. This charge flow is detected as a current flow.

Therefore, the intensity of radiation can be measured by detecting this current.

By the way, the energy of gamma rays of radiation is 80 KeV.
In the range of ~ 3MeV, the higher the energy, the easier it is for the object to pass through. Therefore, the detection sensitivity of high-energy γ-rays is lower than the detection sensitivity of other energy bands. The degree depends on the type of object.

Therefore, when γ-rays with a uniform energy distribution from low energy to high energy are incident on the semiconductor detector, the transmitted γ-rays have a small energy distribution in the low energy band and a large energy distribution in the high energy band. .

This does not mean that the measurements were made evenly over the entire energy band. Therefore, generally, as shown in FIG. 7, correction is performed through the filter (3) immediately before entering the semiconductor radiation detector.

The distribution of γ-rays transmitted through this filter (3) is low for low energy ones, and high for high energy ones because it is hard to cut by the filter (3). By making γ-rays having this energy distribution incident on the semiconductor radiation detector, many γ-rays in the energy band that are easily transmitted are made incident, and γ-rays in each part of the energy band excite electrons at the same ratio, As a result, the difference in detection sensitivity in each energy band is corrected.

As described above, conventionally, the detection sensitivity has been corrected using the filter (3).

(Problems to be Solved by the Invention) In the prior art, since the filter is made of metal, the γ-rays incident on the semiconductor radiation detector are reduced in the entire band when viewed as a whole. This decrease was linked to a decrease in detection sensitivity.

In the present invention, the detection efficiency is the same in any energy band of the measurement target without lowering the detection sensitivity. That is, the purpose is to reduce the energy dependence of the detection efficiency.

〔The invention's effect〕

(Means for Solving Problems) In the semiconductor radiation detector described in the related art, n
The layers are so thin that they allow light to pass through. Since the electrons in the depletion layer are also excited by this light, they can also be used for detecting light.

In the present invention, by utilizing this property, in a radiation detector for detecting radiation and light, one or a plurality of scintillators whose emission amount is sequentially decreased by the incidence of a certain amount of radiation, the light of which is the radiation detector. To be incident on
As the detection efficiency of the radiation detector decreases, the detection signal of the scintillator having a large emission amount is sequentially added to the detection signal of the radiation detector.

(Operation) Generally, the detection signal of the semiconductor radiation detector is in the form of pulse. The peak value is different between the detection signal of the semiconductor radiation detector and the detection signal by the light emission of the scintillator,
The peak value of the detection signal of the semiconductor radiation detector is larger.
In addition, the peak value of the detection signal by the scintillator differs depending on the type of scintillator. This peak value is also affected by the energy of γ rays.

The measurement of γ-rays is carried out with a detection signal having a certain peak value or more counted within a certain period of time. This peak value can be set arbitrarily.

If the wave height is set to be between the wave heights of the detection signal of the semiconductor radiation detector and the detection signal of the scintillator, only the detection signal of the semiconductor radiation detector can be detected.

On the other hand, when the set value is equal to or lower than the wave height of the detection signal by the scintillator, the γ-ray detection also includes the result detected by the scintillator. That is, even high-energy γ-rays that cannot be detected by the semiconductor radiation detector and can be detected by the emission of the scintillator.

(Embodiment) A first embodiment of the present invention will be described with reference to FIG.

In this embodiment, two scintillators are attached to the detection surface of the semiconductor radiation detector, and if the semiconductor radiation detector is in an energy band in which the efficiency is lowered, the output signal by the light of one or two scintillators is semiconductor if necessary. By adding to the output signal of the radiation detector, the decrease in efficiency is corrected.

A block diagram is shown in FIG. First, the base of this semiconductor radiation detector is a thin n layer on the P layer (1) of the P type semiconductor.
The n-layer (2) of the type semiconductor is formed. This n layer (2)
Two scintillators a (4) and scintillator b (5) are attached to the.

The scintillator a (4) and the scintillator b (5) are covered with a reflective film (6) so that the light generated by the radiation enters only the n layer (2).

Further, the n-layer (2) also detects the light when there is a light source other than the scintillator (4,5), so the entire n-layer (2) including the scintillator (4,5) is a light-shielding film (7). Is covered by.

In the semiconductor radiation detector configured as described above,
The scintillators (4,5) emit light when γ-rays are incident, but the semiconductor radiation detector may or may not be detected by the energy of γ-rays. This emission and detection signal is P-
n Detected as a current flowing in the circuit applying voltage to both electrodes.

This detection signal is amplified by the amplifier (8), then by the wave height discriminator (9) only the detection signal having a preset wave height or higher is selected, and only the selected signal is counted (10). Count with. This counting is performed for a certain period of time, and the count value becomes the measured value.

The detection signal is pulsed, and the output waveform of the amplifier (8) is shown in FIG. The width of this pulse is about 5 × 10 ^-6 sec, the signal obtained by detecting the γ-rays by the semiconductor radiation detector is a, and its peak value is V.

When the same γ-ray is made incident, the peak value of the detection signal by the semiconductor radiation detector is larger than the peak value of the detection signal by the light emission of the scintillator. In this embodiment, two types of scintillators having different peak values of detection signals are prepared. Among these scintillators, the pulse generated by the scintillator a (4) has a signal b and a wave height V / x, and the pulse generated by the scintillator b (5) has a signal c and a wave height V / xy. That is, the signal b
Has a height y times that of the signal c, and the signal a has a height x times that of the signal b.

In the wave height discriminator (9), if the wave height to be set is provided between the signal a and the signal b, the measurement value counted by the counter (10) is a signal obtained by directly detecting γ rays by the semiconductor radiation detector, That is, only the signal a is measured.

If the wave height to be set is between the signal b and the signal c, the measured value is the sum of the signal a and the signal b, that is, the detection signal by the scintillator a (4).

If the wave height to be set is less than or equal to the signal c, the measured value is the sum of the signal a, the signal b, and the signal c, that is, the detection signal from the scintillator b (5).

Figure 3 shows a silicon detector with an effective area of 100 mm ² and a depletion layer thickness of 16 μm. The scintillator a has a size of 1 mm × 10 mm ² and the material is C _S I (Tl) and the scintillator b has a size of 1 mm ×. 10 mm ² and material is C _S I
6 is a graph showing the relationship between incident γ-ray energy and γ-ray detection efficiency when (Na) is used.

In this embodiment, as indicated by the line segment l-1 'in FIG. 3, the semiconductor radiation detector has a lower detection efficiency when the .gamma.-ray energy becomes higher. That is, although some light is transmitted without being detected, the scintillators (4,5) emit light even with this γ-ray. As a result, it is detected, and the detection efficiency is improved.

As described above, in the case of only the semiconductor radiation detector, by compensating for the decrease in the detection efficiency of high-energy γ-rays by the emission of the scintillator, the detection efficiency close to uniform in the γ-ray energy band to be measured. I was able to

In addition, although two types of scintillators are used in the present embodiment, the number of scintillators is not limited to two, and the use of multiple types of scintillators can uniformly increase the detection efficiency.

Second Embodiment The configuration of this embodiment will be described with reference to FIG. In this embodiment, the n layer (2) and the scintillator (4,5) are added to the structure of the first embodiment.
A film (11) is provided between the two scintillators (4,5)
Use the same kind.

The film (11) has a scintillator a (4) and a scintillator b (5).
The transparency is different at the position.

Thereby, even if the amount of light emitted by the γ-ray is the same, the amount of light is different when passing through the film (11), which is the same as the difference in the amount of light emitted when the type of scintillator is different. This light will enter the semiconductor radiation detector.

As a result, the same effect as in the first embodiment can be obtained, but the detection efficiency can be made more uniform than in the first embodiment by the combination of the number of scintillators and the film transmittance. .

Third Embodiment In the second embodiment, the number of scintillators is increased to make the detection efficiency uniform, but in the present embodiment, the film (11) is used.
By covering the film (11) with the scintillator (4) having the same area as the above, the effect similar to that of the scintillator in which the finely subdivided scintillator is provided in the second embodiment is aimed.

The film (11) used in this embodiment has a different transmittance for each part.

A scintillator having a high refractive index is used. The light emitted inside the scintillator is emitted in all directions and reaches the surface of the scintillator, but the light having a small incident angle with respect to the surface is reflected, and only the light that strikes the surface at an angle vertical or close to it can pass. Ideally, the emitted light should pass on a line drawn vertically from the light emitting point to the n layer. This is because the light passes through the film (11) in the process of reaching the n-layer, and if it passes through a line other than this line, a part of the transmittance different from the transmittance of the film (11) on the vertical line is detected. Because it will pass.

Since a scintillator having a different transmittance is used for each part, even if a continuous scintillator is used, the light is perpendicular to the n layer and the scintillator (4) and the film (1
Since the light passes through 1), the same effect can be obtained as if the scintillators whose transmittance is slightly changed are subdivided infinitely and arranged.

Fourth Embodiment A fourth embodiment is shown in FIG. 6 and will be described. This embodiment uses a high-refractive index scintillator (4) as in the third embodiment,
A diaphragm with many holes with different hole diameters instead of the film
(12) is provided.

In the third embodiment, a film having different transmissivity is used for adjusting the amount of light passing through the n-layer (2) for each part, but in this embodiment, the adjustment of the amount of light is limited (12). The size and number of the holes made in the holes are used to achieve the same effect.

〔The invention's effect〕

According to the present invention, when detecting γ-rays with a semiconductor radiation detector, by compensating for the decrease in the detection efficiency of high-energy γ-rays by combining with a scintillation detector, It is possible to perform detection with uniform detection efficiency in the energy band where

[Brief description of drawings]

FIG. 1 is a configuration diagram for explaining the first embodiment of the present invention, FIG. 2 is a graph comparing the wave heights of detection signals by a semiconductor radiation detector and two types of scintillators, and FIG. 3 is incident γ-ray energy. And FIG. 4 is a configuration diagram illustrating a second embodiment, FIG. 5 is a configuration diagram illustrating a third embodiment, and FIG. 6 is a fourth embodiment. FIG. 7 is a configuration diagram for explaining a conventional technique, and FIG. 8 is an energy state diagram for explaining excitation of electrons in a semiconductor radiation detector. 1 ... P layer, 2 ... n layer 3 ... Filter, 4 ... Scintillator a 5 ... Scintillator b, 6 ... Reflecting film 7 ... Shading film, 8 ... Amplifier 9 ... Wave height discriminator, 10 …… Counter 11 …… Film, 12 …… Aperture

Claims (1)

[Claims] 1. A semiconductor radiation detector for detecting radiation and light, wherein a plurality of scintillators having different emission amounts upon incidence of radiation are attached to an incident surface of the semiconductor radiation detector.
A radiation detector, wherein the semiconductor radiation detector outputs both a radiation and a signal in which light is detected.