JPH03195992A - Radiation detector - Google Patents

Abstract

PURPOSE:To correct energy characteristics through an electrical method by applying cyclic voltage, for changing the voltage according to predetermined variation characteristics to a semiconductor radiation detection element, as a bias voltage. CONSTITUTION:A semiconductor radiation detection element 1 is formed into a three-layer structure but a cycle voltage generator 7 cyclically showing voltage change of a predetermined function is connected between an intermediate layer 1b and a cathode layer 1c and this cyclical voltage is applied as bias voltage. Usually, when the bias voltage applied across the intermediate layer 1b and the cathode layer 1c is increased and the peak value of detection output is reduced, a pulse having low peak generated by the mutual action with radiation of low energy can be set at the discrimination voltage of a peak discriminating and setting device 6 or lower and a signal is cut by a peak discriminator 5. By controlling the output of the detection element 1 through this constitution, a radiation detection characteristic can be made flat. Therefore, the bias voltage applied across the intermediate layer 1b and the cathode layer 1C is cyclically changed using the generator 7.

Description

DETAILED DESCRIPTION OF THE INVENTION [Purpose of the Invention (Field of Industrial Application) The present invention relates to a semiconductor radiation detection device used in a radiation monitoring device or the like for monitoring and measuring the intensity of radiation in a nuclear facility.

(Prior Art) Some radiation monitor devices for monitoring and measuring the intensity of radiation in nuclear facilities use small semiconductor radiation detectors that do not require high voltages like ionization chambers.

The semiconductor radiation detector has an anode layer 1a made of semiconductor.

This semiconductor radiation detection element uses a three-layer structure consisting of an intermediate layer 1b and a cathode layer 1c.By applying a DC voltage of several volts to several tens of volts to this semiconductor radiation detection element, this semiconductor radiation detection can be performed. When radiation is incident on a device, the radiation energy generates electron-hole pairs in the semiconductor. Of the generated electron-hole pairs, the electrons are on the anode side,
As a result of the holes being collected on the cathode side, a pulsed current flows between the anode and the cathode of the semiconductor radiation detector, and this becomes a radiation detection signal.

A semiconductor radiation detector has a structure in which the output of such a semiconductor radiation detection element is amplified by an amplifier, the output with a level higher than a set value is discriminated and extracted by a pulse height discriminator, and this extracted output is obtained as a detection output. .

By the way, due to the response characteristics of the semiconductor radiation detection element used in the semiconductor radiation detector, the relationship between the output count rate and the radiation energy of the semiconductor radiation detector is 0, as indicated by the symbol a in FIG. There is a tendency for a peak to occur in a low energy region of about .1 [MeV]. This is due to the fact that there is a large amount of noise component radiation in this energy range due to radiation scattering, etc., and that it reacts sensitively to this energy range (good response).

On the other hand, the energy of the radiation to be measured is unspecified, and therefore, in order to perform highly accurate radiation detection, flat radiation detection characteristics are required for the entire energy range to be measured.

That is, as generally indicated by the reference numeral in FIG. 6,
It is required to have characteristics with low energy dependence.

Therefore, in order to improve the detection energy characteristics, a method of covering the detection element with a metal cap has conventionally been used.

This is because scattered radiation has a low energy level, so by covering the detection element with a metal cap, the low-energy radiation is absorbed and not detected by the semiconductor radiation detector.

(Problem to be Solved by the Invention) Since the energy of the radiation to be measured by the radiation monitor device is unspecified, the radiation detector is generally required to have flat detection characteristics for the entire energy range of the radiation to be measured. , Therefore, the semiconductor radiation detector used is required to have characteristics with low energy dependence.

However, semiconductor radiation detectors used in radiation monitoring devices generally tend to have high detection sensitivity in low energy regions. Therefore, in order to obtain a detector with low energy dependence, a method of attaching a metal cap around the radiation detection element has conventionally been adopted.

This method utilizes the absorption characteristics of metals (easily absorbing low-energy radiation), selects parameters such as material, thickness, and slits, and is characterized by obtaining characteristics with low energy dependence in the detector output. There is.

However, this method may require a thick metal layer depending on the characteristics of the detection element, resulting in a problem of increased weight. Furthermore, since there is no adjustment means after manufacturing, there is a drawback that the metal cap must be remade in order to correct variations in characteristics of each radiation detection element and changes over time.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a semiconductor radiation detection device that can correct energy characteristics using an electrical method.

[Configuration of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention is configured as follows. That is, in a radiation detection device using a semiconductor radiation detection element as a detection element, a periodic voltage generating means for generating a periodic voltage that changes the voltage with a predetermined change characteristic in accordance with the detection characteristics of the semiconductor radiation detection element is used. The generated periodic voltage is configured to be applied to the semiconductor radiation detection element as a bias voltage.

(Function) In such a configuration, a periodic voltage generating means that generates a periodic voltage that changes the voltage with predetermined change characteristics in accordance with the detection characteristics of the semiconductor radiation detection element is used, and the generated periodic voltage is applied to the semiconductor radiation detection device. Apply as a bias voltage to the detection element.

The semiconductor radiation detection element can change the energy characteristics it detects by changing the applied bias voltage, so this is utilized to improve the detection characteristics of the semiconductor radiation detection element to desired characteristics. In order to reduce the detection sensitivity so that the detection sensitivity in the energy region where the peak occurs is almost equal to that in other energy regions, the voltage change and its change period are optimized to match the detection characteristics of the semiconductor radiation detection element. By setting the periodic voltage generating means to apply it to the semiconductor radiation detection element as a bias voltage, the detection characteristics can be made flat without being affected by the energy of the radiation.

In the present invention, when a constant voltage is applied to a semiconductor radiation detection element having a three-layer structure, electron-hole pairs are generated inside the semiconductor radiation detection element by interaction with the radiation at the time of incidence of radiation, but the semiconductor radiation This method utilizes the characteristic that the collection efficiency of electron-hole pairs changes when the voltage level of the intermediate layer of the detection element is changed. The output pulse height can be changed by changing the collection efficiency, so if the pulse height that has been outputted unnecessarily is controlled to a pulse height smaller than the discrimination level at a constant cycle, then the pulse height discriminator As a result, the detection characteristics of the semiconductor radiation detection element become flat regardless of the energy of the incident radiation.

Therefore, by adjusting the voltage control speed of the intermediate layer in the direction of cutting off many of the parts of the semiconductor radiation detection element with high radiation response, it is possible to obtain a semiconductor radiation detection device with characteristics that do not depend on the radiation energy. That's how it is.

As described above, the present invention utilizes the fact that by changing the bias voltage applied to a semiconductor radiation detection element, the detected energy characteristics can be changed, and improves the detection characteristics of the semiconductor radiation detection element to desired characteristics. This device uses a periodic voltage generation means that generates a periodic voltage that matches the detection characteristics of the semiconductor radiation detection element, and changes the bias voltage applied to the semiconductor radiation detector by adjusting the speed of voltage change. This eliminates the need to use a metal cap to improve the detection characteristics of semiconductor radiation detection elements, which is required in the past. On the other hand, it becomes possible to cope with this problem by simply adjusting the output characteristics of the periodic voltage generating means without any special modification.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of the present invention. In FIG. 1, 1 is a semiconductor radiation detection element, and an anode layer 1
It consists of three layers: a, an intermediate layer 1b, and a cathode layer 1c.

In this device, one pole side (anode layer 1a) of the semiconductor radiation detection element 1 having three layers is connected to a positive pole voltage +V (for example, about several V to several +V) via a resistor 2, and the other pole side (anode layer 1a) is By grounding the pole, a constant voltage is applied.

Further, a capacitor 3 is connected between the semiconductor radiation detection element 1 and the resistor 2, and the capacitor 3 is further connected to a pulse height discriminator 5 via a preamplifier 4. A wave height discrimination setter 6 is connected to the wave height discriminator 5, and the wave height discriminator 5 outputs an output when there is an input exceeding the reference value based on the reference value set by the wave height discrimination setter 6. It is configured to be released.

Note that the semiconductor radiation detection element 1 has a three-layer structure, and a periodic voltage generator 7 that periodically shows a voltage change of a predetermined function is connected between the intermediate layer tb and the cathode layer 1c. This configuration applies a voltage as a bias.

In such a configuration, when radiation is incident on the semiconductor radiation detection element 1, electron-hole pairs are generated inside the element. Then, electrons are collected on the anode side (anode layer la side) and holes are collected on the cathode side (cathode layer 1c), so that a pulsed current flows through the semiconductor radiation detection element 1. As a result, the voltage between the resistor 2 and the semiconductor radiation detection element 1 changes in a pulsed manner, and this changes through the capacitor 3 to the preamplifier 4.
and is amplified by this preamplifier 4. This amplified signal is then given to a pulse height discrimination circuit 5, which discriminates and outputs an input signal exceeding a reference value given by a pulse height discrimination setter 6.

Use this to cut below the noise level.

Here, the semiconductor radiation detection element 1 has a property that when a bias voltage is applied between the intermediate layer 1b and the cathode layer 1c, the collection ratio of electron-hole pairs generated by the incident radiation changes depending on the bias voltage level. have.

In this device, the bias voltage applied between the intermediate layer 1b and the cathode layer IC is supplied by a periodic voltage generator 7 that periodically shows voltage changes according to a predetermined function.

As a result, the peak value of the output of the semiconductor radiation detection probe 1 changes as the voltage applied to the intermediate layer tb changes.

Normally, when the bias voltage applied between the intermediate layer 1b and the cathode layer 1c is increased to reduce the peak value of the detection output,
A pulse with a low wave height generated by interaction with low-energy radiation can be made lower than the discrimination voltage of the wave height discrimination circuit 6, and the signal can be cut by the wave height discrimination circuit 5.

Taking advantage of this, this device attempts to flatten the radiation detection characteristics by controlling the output of the semiconductor radiation detection probe 1. To this end, this device uses a periodic voltage generator 7 to periodically change the bias voltage applied between the intermediate layer tb and the cathode layer 1c.

This periodic change is optimal depending on the energy range to be measured and the semiconductor radiation detection element used, and an example is as shown in FIG.

That is, in FIG. 4, since the detection characteristic of the semiconductor radiation detector is as shown in a in FIG. 6, an example is shown in which a function approximating the characteristic curve a is used to correct this. In Figure 4, the repetition period of change is approximately 100 m5.
It is about ec.

When such a voltage that changes in a periodic manner is generated by the periodic voltage generator 7 and applied as a bias to the semiconductor radiation detector 1, the output shown in Fig. 5 is obtained, which is the detected output of radiation at the peak energy level. is suppressed, and the target pulse height can be cut by a predetermined proportion corresponding to the bias change generated by the periodic voltage generator 7.

In this way, by changing the bias voltage applied to the semiconductor radiation detector 1 according to an appropriate function, a
The detection characteristic can be changed from the characteristic of b to the characteristic of b.

In this way, this device improves the detection characteristics of the semiconductor radiation detector to desired characteristics by utilizing the fact that the detected energy characteristics can be changed by changing the bias voltage applied to the semiconductor radiation detector. It uses a periodic voltage generator that generates a periodic voltage that matches the detection characteristics of the semiconductor radiation detector, and changes the bias voltage applied to the semiconductor radiation detector by adjusting the speed of voltage change. This is how it was done.

Therefore, it is no longer necessary to use a metal cap to improve the detection characteristics of semiconductor radiation detectors as in the past. This makes it possible to deal with this problem only by adjusting the bias voltage.

In the embodiments described above, the bias voltage applied to the semiconductor radiation detector was applied between the intermediate layer tb and the cathode layer fc. However, configurations such as those shown in FIGS. 2 and 3 may also be used.

Figure m2 shows a configuration in which a periodic voltage generator 7 is attached between the anode layer 1a and the intermediate layer 1b of the semiconductor radiation detection element 1. In addition, FIG. 3 shows an anode 1 centered on the intermediate layer 1b.
a) This is a configuration in which a periodic voltage generator 7 is attached to both cathode ICs.

This arrangement exhibits the same effect as the configuration shown in FIG. 1 in that the collection of electron-hole pairs generated by interaction with radiation is controlled and the energy characteristics are improved.

It should be noted that the present invention is not limited to the embodiments described above and shown in the drawings, but can be implemented with appropriate modifications within the scope without changing the gist thereof.

[Effects of the Invention] As explained above, according to the present invention, the response characteristics to incident radiation can be improved simply by electrical adjustment according to the characteristics of the detection element, and flat detection characteristics can be achieved in any energy range. In addition to improving measurement accuracy, it is now possible to improve energy characteristics simply by electrically adjusting the characteristics of semiconductor radiation detection elements and changes over time after use. A radiation detection device that is easy to maintain and adjust can be provided.

[Brief Description of the Drawings] Fig. 1 is a block diagram showing one embodiment of the present invention, Figs. 2 and 3 are block diagrams showing other embodiments of the present invention, and Fig. 4 is a block diagram showing an embodiment of the present invention. Figure 5 is a diagram showing an example of the output voltage waveform of a periodic voltage generator, Figure 5 is a diagram showing an example of the detection output of a semiconductor radiation detection element, and Figure 6 is a characteristic example of the radiation energy output count rate of a general semiconductor radiation detection element. FIG. 1... Semiconductor radiation detection element, 2... Resistor, 3...
- Capacitor, 4... Preamplifier, 5... Wave height discriminator, 6... Wave height discrimination setting device, 7... Periodic voltage generator.

Claims (2)

[Claims] (1) In a radiation detection device using a semiconductor radiation detection element as a detection element, using a periodic voltage generation means that generates a periodic voltage that changes the voltage with predetermined change characteristics in accordance with the detection characteristics of the semiconductor radiation detection element, A radiation detection device characterized in that the generated periodic voltage is applied to the semiconductor radiation detection element as a bias voltage. (2) The periodic voltage generating means is characterized in that the rate of change of the generated voltage is set in accordance with the detection characteristics of the semiconductor radiation detection element so as to cut out many areas of the semiconductor radiation detection element where the response of radiation is high. The radiation detection device according to claim (1).