JP2014174073A - Radiation counter and radiation counting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiation counter which has a simple configuration and easily differentiates radiation and noise.SOLUTION: Phases of a pulse signal a being a detection signal of a first photodiode, a pulse signal b being a detection signal of a second photodiode, and a pulse signal c being a detection signal of a third photodiode are compared. In the case where phases of all pulse signals match as in (3), the signals are determined as noise, and when pulse signals with different phase exit as in (1)(2), the signals are determined as radiation. Without using a device such as a noise sensor and an impact sensor, radiation and noise are differentiated only by photodiodes to make it possible to count radiation.

Description

  The present invention relates to a radiation counter device and a radiation counting method, and more particularly to a technique for removing noise such as vibration, shock, and external radio waves.

There is a growing need for radiation counter devices, particularly personal simplified radiation counters. Such a radiation counter device is known, for example, as disclosed in Japanese Patent Application Laid-Open No. 2007-289514 (Patent Document 1).
Since a simple radiation counter is easily affected by vibration, shock, and external radio waves, there is a possibility that a non-radiation counter is erroneously counted, so that noise countermeasures are a major issue.
Examples of commonly used radiation sensors include an ion chamber for high dose rate measurement and a Nai scintillation detector for low dose rate measurement.

JP 2007-285951 A

The technique described in Patent Document 1 includes a noise sensor that detects electromagnetic noise and an impact sensor that detects an impact for noise suppression. Accordingly, since a plurality of different sensor devices are required, there is a problem that the cost becomes high and the processing is complicated because the calculation for canceling the noise using the output signal of the noise sensor or the impact sensor is required. It was.
Moreover, although an ion chamber and a Nai scintillation detector as a radiation sensor have high accuracy, they are expensive and large-sized ones used in nuclear power plants and the like, and are difficult to use in individuals and small organizations. There was a problem.
The present invention has been made in view of the above circumstances, and provides a radiation counter apparatus and a radiation counting method capable of discriminating radiation and noise using only a photodiode without providing a plurality of different devices.

The invention according to claim 1 is a plurality of photodiodes, a plurality of charge amplifiers provided for each of the photodiodes for converting charges generated by the photodiodes into voltages,
Provided for each charge amplifier, a plurality of comparators for converting a voltage converted by the charge amplifier into a pulse signal, and a pulse signal converted by each comparator are inputted, and a radiation dose is identified by identifying a radiation signal and noise. And a control circuit for calculating a radiation counter.

  The invention according to claim 6 is a radiation counting method of a radiation counter device comprising a plurality of photodiodes, the step of converting the charges generated by the plurality of photodiodes into a voltage, and the pulse of the converted voltage. A radiation count comprising: a step of converting into a signal; and a step of inputting a pulse signal corresponding to the plurality of the converted photodiodes, and identifying a radiation signal and noise to calculate a radiation dose. A method is provided.

  According to the present invention, radiation and noise can be identified without providing a plurality of different sensor devices.

It is a block diagram which shows schematic structure of the conventional radiation counting device. It is the whole apparatus block diagram which showed the internal structure of the control circuit in FIG. It is a time chart which shows the signal of the principal part of FIG. It is a block diagram showing a schematic structure of a radiation counting device which is one embodiment concerning the present invention. It is a time chart for performing the operation | movement of FIG.

<Description of background technology>
First, background technology will be described to facilitate understanding of the present invention. FIG. 1 is a block diagram of a general radiation counter device, FIG. 2 is an overall device configuration diagram showing an internal configuration of a control circuit in FIG. 1, and FIG. 3 is a time chart showing signals of essential parts of FIG.

  The apparatus shown in FIG. 1 includes a radiation sensor 100, a noise sensor 200, an impact sensor 300, and a control circuit 400. This radiation sensor 100 detects external radiation and outputs a signal A. The noise sensor 200 detects an external electromagnetic wave and outputs a signal B. The impact sensor 300 detects vibration and impact and outputs a signal C. The signal A, the signal B, and the signal C are connected to the control circuit 400, respectively.

FIG. 2 is an overall device configuration diagram showing an internal configuration of the control circuit 400 shown in FIG. In FIG. 2, the control circuit 400 includes a signal conversion unit 410, a signal conversion unit 420, a signal conversion unit 430, a radiation counter 700, and a calculator 800.
The signal conversion unit 410 includes a charge amplifier 411 and a comparator 412, receives the signal A output from the radiation sensor 100, amplifies the signal by the charge amplifier 411, and amplifies the voltage of the signal D by the comparator 412. The voltage is compared with the voltage, and when the voltage of the signal D exceeds the reference voltage, the pulse signal G corresponding to the signal component is output.

The signal conversion unit 420 includes a charge amplifier 421 and a comparator 422, receives the signal B output from the noise sensor 200, amplifies the signal by the charge amplifier 421, and a voltage of the amplified signal E by the comparator 422 The voltage is compared with the voltage, and when the voltage of the signal E exceeds the reference voltage, the pulse signal H corresponding to the signal component is output.
The signal conversion unit 430 includes a charge amplifier 431 and a comparator 432, receives the signal C output from the impact sensor 200, amplifies the signal by the charge amplifier 431, and amplifies the voltage of the signal F by the comparator 432. The voltage is compared with the voltage, and when the voltage of the signal F exceeds the reference voltage, the pulse signal I corresponding to the signal component is output.

The radiation counter 500 receives the pulse signal G and counts radiation.
The noise counter 600 receives the pulse signal H and counts noise signals.
The impact counter 700 receives the pulse signal I and counts the impact signal.
The arithmetic unit 800 is a general microprocessor that repeatedly executes a program every cycle. The outputs of the radiation counter 500, the noise counter 600, and the impact counter 700 are input, the counts indicated by the radiation counter 700 are referred to every cycle, and when the change is recognized, the radiation dose is calculated. The radiation dose is calculated while canceling the noise signal and the shock signal by the algorithm of
FIG. 3 is a timing chart showing an example of the signals A to I in FIG.

<Best Mode for Carrying Out the Invention>
The conventional radiation counter apparatus described above can remove noise, but as described above, different sensor devices such as a radiation sensor, a noise sensor, and an impact sensor are required.
FIG. 4 is a schematic block diagram of a radiation counter device according to an embodiment of the present invention.
FIG. 5 is a time chart for explaining the operation of FIG.
In FIG. 4, a charge amplifier 2A. 2B and 2C are basically the same as the operation of the charge amplifier 411 in FIG. 2, and the operations of the comparators 3A, 3B and 3C are basically the same as the operation of the comparator 412 in FIG. Is omitted.

  Hereinafter, the radiation counter device of the present embodiment will be described with reference to FIG. The radiation counter device of this example includes first to third photodiode units 1A, 1B, and 1C, and first to second photodiodes that convert output signals from these photodiode units 1A, 1B, and 1C into pulse signals, respectively. Three comparators 3A, 3B, and 3C, and a control circuit 4 that receives the output pulses from these comparators 3A, 3B, and 3C, identifies radiation and noise, and calculates the radiation dose.

  The photodiode units 1A, 1B, and 1C are charge amplifiers 2A, 2B, and 2C that convert electric charges into voltages, amplify them, and supply them to the comparators 3A, 3B, and 3C, respectively. Have The silicon semiconductor radiation detection element is preferably constituted by a silicon avalanche photodiode. When there is a large electric field in the semiconductor, electrons generated by photon collision are accelerated, and collide with other semiconductor atoms to eject a plurality of electrons. The electrons ejected here are accelerated by the electric field and collide with other semiconductor electrons to further eject electrons. The phenomenon in which electrons that move through this chain explosively increase is called avalanche multiplication. The avalanche photodiode is a photodiode whose light receiving sensitivity is increased by using avalanche multiplication.

  That is, the silicon avalanche photodiode is a high-speed, high-sensitivity photodiode that utilizes an internal amplification action that occurs when a reverse voltage is applied. It is possible to measure weak signals compared to PIN photodiodes. In an environment where the signal is weak, the influence of noise becomes large, so the effect of the present embodiment becomes more prominent. In the case of a simple radiation counter device, the basic principle of this embodiment is the same even if the following photodiode is used.

A PN photodiode has the most basic structure in which a photoelectric conversion part is formed by a P layer of 1 μm or less on the light receiving surface side and an N layer on the substrate side, and the neutrality of the P layer and the N layer by the energy of light. Electrons generated in the region (depletion layer) flow to the N layer and holes flow to the P layer.
A PIN photodiode has a structure in which an I-type semiconductor is sandwiched between PN junctions. Since the depletion layer becomes larger when a reverse voltage is applied by sandwiching the I layer, high-speed response characteristics can be obtained. Sensitivity is better than PN photodiode.
When the photodiode detects radiation, a charge is generated on the bonding surface, but the generation of the charge is very small in a very short time. Silicon avalanche photodiodes can measure weak signals at a higher speed, with higher sensitivity than PN photodiodes and PIN photodiodes, so that this embodiment can be used even in consideration of the S / N ratio with noise. It is suitable to adopt.

  The thicknesses of the sensitive portions of the silicon semiconductor radiation detection elements included in the photodiode portions 1A, 1B, and 1C may be the same as or different from each other. That is, the sensitivity of the photodiodes included in the radiation detectors 1A, 1B, and 1C may be the same or different. If they are the same, only the phases of the pulse signals can be compared, and if they are different, it becomes easier to detect radiations having different intensities and times.

  The photodiode portions 1A, 1B, and 1C are provided with gamma ray adjustment plates 1GA, 1GB, and 1GC, respectively. The gamma ray adjusting plate has a function of adjusting gamma ray energy and gamma ray flux incident on the photodiode radiation detector, and is made of lead, iron, aluminum or the like and has a function of attenuating gamma rays. Since the gamma ray adjusting plate has different gamma ray energy and force for attenuating the flux depending on its thickness, the thickness can be set according to the level of the energy region to be measured. The thicknesses of the gamma ray adjustment plates 1GA, 1GB, 1GC of the photodiode portions 1A, 1B, 1C may be the same or may be changed little by little. If they are the same, only the phases of the pulse signals can be compared, and if they are different, it becomes easier to detect radiations having different intensities and times.

  In the figure, a is a pulse signal that is the output of the comparator 3A, b is a pulse signal that is the output of the comparator 3B, and c is a pulse signal that is the output of the comparator 3C.

<Operation of the embodiment>
The control circuit 4 receives the pulse signals a, b, and c output from the comparators 3A, 3B, and 3C shown in FIG. 5 and compares the phases of the three systems of pulse signals.
As shown in FIG. 5 (3), when all the photodiodes detect a pulse having the same phase, it is highly possible that the noise is a shock or the like, and the noise is determined to be noise.
In other words, because one radiation is a point with no area, it can only be detected by one photodiode, so that all photodiodes detected a pulse with the same phase, not noise but noise such as shock and electromagnetic waves. It is thought that.

  Conversely, as shown in FIG. 5A, when all the photodiodes detect pulse signals having different phases, it is considered that each photodiode independently detects radiation.

As shown in FIG. 5 (2), when the pulse signals a and b having the same phase and the pulse signal c having the different phases are detected, it may be determined how to judge by experiment or simulation. When present, there is a possibility that two photodiodes detect two radiations at the same time. Furthermore, since pulse signals having different phases are detected, there is a high possibility of radiation instead of noise. Now consider radiation.
Such a phase comparison circuit can be constructed by a hardware logic circuit, but generally, sampling is performed, and the temporal position of the pulse signal is written in a memory and compared by software.

  Although the method for calculating the radiation dose from the detected pulse signal is not described in detail, the conventional radiation counter device as shown in FIG. 1 has to calculate the noise component in consideration of the noise component. According to the embodiment, since noise is ignored in advance, there is an effect that the calculation is simplified.

As mentioned above, although embodiment of this invention was described, this invention is not limited to these, The invention described in the claim and its equal range are included.
The claims appended at the time of filing this application will be appended below.

<Appendix>
[Claim 1]
A plurality of photodiodes;
A plurality of charge amplifiers that are provided for each of the photodiodes and convert charges generated by the photodiodes into a voltage;
A plurality of comparators provided for each of the charge amplifiers for converting a voltage converted by the charge amplifier into a pulse signal;
A control circuit for inputting a pulse signal converted by each comparator, calculating a radiation dose by identifying a radiation signal and noise, and
A radiation counter device comprising:
[Claim 2]
The radiation control apparatus according to claim 1, wherein the control circuit regards radiation as a radiation when the phases of at least two pulse signals output from the plurality of comparators are different.
[Claim 3]
2. The radiation counter device according to claim 1, wherein the control circuit regards as noise when the phases of a plurality of pulse signals output from the plurality of comparators all coincide.
[Claim 4]
4. The radiation counter device according to claim 1, wherein the photodiode is a silicon avalanche photodiode.
[Claim 5]
The radiation counter device according to claim 1, wherein the photodiode includes a gamma ray adjustment plate.
[Claim 6]
A radiation counting method of a radiation counter device comprising a plurality of photodiodes,
Converting charges generated by the plurality of photodiodes into a voltage;
Converting the converted voltage into a pulse signal;
Inputting pulse signals corresponding to the converted plurality of photodiodes, identifying radiation signals and noise, and calculating a radiation dose;
A radiation counting method comprising:

1A, 1B, 1C ... Photodiode part 2A, 2B, 2C ... Charge amplifier 3A, 3B, 3C ... Comparator 4 ... Control circuit 1GA, 2GA, 3GA ... Gamma ray adjustment version

Claims (6)

A plurality of photodiodes;
A plurality of charge amplifiers that are provided for each of the photodiodes and convert charges generated by the photodiodes into a voltage;
A plurality of comparators provided for each of the charge amplifiers for converting a voltage converted by the charge amplifier into a pulse signal;
A control circuit for inputting a pulse signal converted by each comparator, calculating a radiation dose by identifying a radiation signal and noise, and
A radiation counter device comprising:   The radiation control apparatus according to claim 1, wherein the control circuit regards radiation as a radiation when the phases of at least two pulse signals output from the plurality of comparators are different.   2. The radiation counter device according to claim 1, wherein the control circuit regards as noise when the phases of a plurality of pulse signals output from the plurality of comparators all coincide.   4. The radiation counter device according to claim 1, wherein the photodiode is a silicon avalanche photodiode.   The radiation counter device according to claim 1, wherein the photodiode includes a gamma ray adjustment plate. A radiation counting method of a radiation counter device comprising a plurality of photodiodes,
Converting charges generated by the plurality of photodiodes into a voltage;
Converting the converted voltage into a pulse signal;
Inputting pulse signals corresponding to the converted plurality of photodiodes, identifying radiation signals and noise, and calculating a radiation dose;
A radiation counting method comprising:

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