JP2005049144A - Radiation measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress temporal deviation of counting rates by means of noise components, offset components, etc. and to simultaneously monitor radiations different in energy. <P>SOLUTION: According to this radiation measuring method, γ rays 12 from a negative electrode of a Cd-Te semiconductor detector (detection element) 14 impressed with a voltage are inlet into a positive electrode, where an interaction between atoms constituting the semiconductor detector 14 and the γ rays 12 induces induced charge, and environmental radiation is measured from output pulses b of the induced charge. This method comprises a process for converting/amplifying the output pulses b into voltage pulses c proportional to the quantity of pulses, a process for acquiring differential pulses d by differentiating/shaping the voltage pulses c with a time constant smaller than the maximum move time of positive holes produced by an interaction between the γ rays 12 and the semiconductor detector 14, a process for acquiring count values by counting excessive pulse height values e when the pulse height values of differential pulses d are the excessive pulse height values e exceeding a threshold, and a process for monitoring counting rates calculated from the count values while issuing an alarm to give a caution to workers when the counting rates exceed a preset level. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a radiation measurement method for performing qualitative and quantitative analysis of radiation using a radiation detector, and in particular, X-rays and γ for continuously monitoring radiation intensity in buildings of nuclear facilities and radiation utilization facilities. The present invention relates to a radiation measurement method suitable for use in a radiation area monitor such as a line.
[0002]
[Prior art]
Examples of radiation monitoring equipment for continuously monitoring environmental radiation in a management area of a plant such as a nuclear power plant include an area monitor, a dust monitor, and a gas monitor.
[0003]
The area monitor is a monitor for continuously monitoring the dose equivalent rate and the count rate in the work environment for the purpose of reducing the exposure of radiation workers. The dose equivalent rate represents the radiation dose to the human body per unit time. If the dose equivalent rate or count rate exceeds a preset level, the area monitor warns the radiation worker.
[0004]
As a radiation detector for the area monitor, a semiconductor detector, a GM (Geiger Muller) counter, an ionization chamber detector, a NaI (Tl) scintillation detector, or the like is used. In addition, the area monitor can measure the energy and dose of radiation in the management area.
[0005]
The detection of radiation is performed by converting the energy of the radiation into an electric signal or the like. For this reason, the operation of the radiation detector depends on how the material of the detection elements constituting the radiation detector interacts with the radiation to be measured. In particular, γ-rays as radiation are high-energy electromagnetic waves resulting from the transition of the nucleus itself, and interact with each other inside the detection element to generate electron-hole pairs.
[0006]
A semiconductor detector as a radiation detector has a configuration in which a semiconductor crystal as a detection element is sandwiched between a pair of electrodes (anode and cathode). When γ rays are incident on the detection element, an induced charge is generated at the anode and the cathode, and is output as an output pulse to the outside of the semiconductor detector. The waveform of the output pulse varies depending on the position where the atoms constituting the semiconductor crystal collide with the γ-ray. In the semiconductor detector, since the energy gap is smaller than that of the insulator, it is known that the number of electrons transferred to the conduction band can be increased and the energy resolution is high.
[0007]
Generally, in an area monitor using a semiconductor detector, a pulse waveform is shaped so that the pulse wave height is proportional to the amount of charge with respect to time series, and then pulse wave height discrimination is performed. In pulse height discrimination, a pulse having a pulse height value equal to or higher than a threshold value is output. Next, when the peak value of the pulse height (pulse peak value) is equal to or greater than the threshold value, the counter counts the pulse peak value and monitors the count value as a time-series change or count value per fixed time. A pulse height distribution is created from the counting rate and monitored.
[0008]
Here, a CdTe semiconductor detector using CdTe (cadmium telluride) single crystal as a detection element constituting the semiconductor detector was simulated with high energy γ-rays. ¹³⁷ Simulated Csγ ray (661 keV) 12a and low energy γ ray ²⁴¹ An Amγ ray (60 keV) 12b is incident. Pulse waveform shaping is performed on the output pulse obtained from the CdTe semiconductor detector.
[0009]
Corresponds to low energy ²⁴¹ Since the collision probability between the Amγ ray 12b and the atoms constituting the CdTe single crystal increases, ²⁴¹ There is a high probability that the Amγ ray 12b loses all energy inside the CdTe single crystal and disappears. Therefore, ²⁴¹ The pulse of the Amγ ray 12b is ²⁴¹ The pulse peak value proportional to the energy of the Amγ ray 12b is shown.
[0010]
On the other hand, it corresponds to high energy ¹³⁷ Since the collision probability between the Csγ ray 12a and the atoms constituting the CdTe single crystal is low, ¹³⁷ After the Csγ ray 12a imparts a part of energy to the inside of the semiconductor crystal, the probability that it is emitted from the CdTe single crystal without disappearing is increased. Therefore, ¹³⁷ The pulse of the Csγ ray 12a is ¹³⁷ Rather than showing a pulse peak value proportional to the energy of the Csγ ray 12a, a continuous distribution is shown on the low peak side with reference to the pulse peak value when all the energy is applied inside the CdTe single crystal.
[0011]
afterwards, ¹³⁷ Csγ ray 12a, ²⁴¹ When the pulse peak value of each pulse of the Amγ ray 12b is equal to or greater than the threshold value, the pulse peak value is counted. Then, a pulse wave height distribution obtained from a count rate which is a count value per fixed time is created. (For example, see Patent Document 1.)
[0012]
FIG. 7 is a graph showing the pulse height distribution of the spectrum in the conventional radiation measuring means.
[0013]
As in the spectrum shown in FIG. 7, gamma rays with different energies ( ¹³⁷ Csγ ray 12a, ²⁴¹ In order to obtain the pulse height distribution of the Amγ ray 12b) at the same time, a low energy with a small pulse peak value is obtained. ²⁴¹ A threshold value is set to the pulse height value of the pulse height discriminator so that the Amγ ray 12b can be measured.
[0014]
On the other hand, there is a method of continuously monitoring the energy of γ rays with a pulse height analyzer, and there is a multi-channel pulse height analyzer as the pulse height analyzer. In this multichannel pulse height analyzer, the number of electrical signals accumulated in each channel can be monitored as a histogram by discriminating each energy (channel) from γ rays detected by a semiconductor detector.
[0015]
Multi-channel pulse height analysis can analyze the intensity of radiation at each wavelength of γ-rays, measuring the qualities of nuclides (energy of radiation) from the wavelengths, and quantifying the nuclides (radiation dose) from the intensity of radiation it can.
[0016]
[Patent Document 1]
Japanese Examined Patent Publication No. 3-75833 (pages 2 to 4, FIGS. 3 and 5)
[0017]
[Problems to be solved by the invention]
With conventional radiation measurement means, it corresponds to low energy ²⁴¹ By using a threshold value that enables measurement of the Amγ ray 12b, ²⁴¹ Amγ ray 12b, equivalent to high energy ¹³⁷ Csγ ray 12a is measured. Therefore, as shown in FIG. ¹³⁷ The pulse peak value of the Csγ ray 12a is concentrated near the threshold value. Therefore, it is strongly influenced by the noise component of the circuit system included in the pulse, the gain of the noise component, the offset component, and the like. A slight change in the noise component, the gain of the noise component, and the offset component causes a large change (shake) in the count value near the threshold value. That is, ¹³⁷ When monitoring the count rate of the Csγ ray 12a, the count rate displayed on the indicator greatly fluctuates in time and becomes unstable due to temporal fluctuations of the noise component, the gain of the noise component, and the offset component.
[0018]
In addition, the γ-ray area monitor measures γ-rays emitted from unknown sources, ¹³⁷ Csγ ray 12a, ²⁴¹ It is desirable that γ rays other than the Am γ ray 12b can be measured and monitored without distinction. However, since the pulse wave height distribution of the spectrum shown in FIG. 7 is strongly affected by the noise component, the gain of the noise component, and the offset component, ²⁴¹ Count rate of Amγ ray 101 ¹³⁷ The count rate of Csγ rays 12a cannot be monitored simultaneously.
[0019]
In addition, after a single gamma ray is detected by the semiconductor detector, a short period of time, that is, a dead time (ie, dead time), from the pulse height analysis by A / D conversion and the data analysis to the end of the recording operation. Dead time). Even if another gamma ray at the next timing is detected within this dead time, this gamma ray is counted off. In particular, data collection of random events, such as when environmental radiation is continuously monitored in a management area of a plant such as a nuclear power plant, it is necessary to prevent counting down during dead time.
[0020]
In addition, when the pulse wave height distribution is monitored simultaneously with the pulse count rate, the dead time of the measurement circuit system becomes longer than when only the pulse count rate is monitored. Therefore, the measurement accuracy of γ rays becomes a problem.
[0021]
The present invention has been made in consideration of the above-described circumstances, and provides a radiation measurement method capable of suppressing temporal fluctuations in the count rate due to noise components, offset components, and the like, and simultaneously monitoring radiations having different energies. The purpose is to do.
[0022]
[Means for Solving the Problems]
In order to solve the above-described problem, the radiation measurement method according to the present invention configures the detection element by applying a voltage to a detection element having an anode and a cathode so that radiation is incident from the cathode of the detection element. Measurement of environmental radiation from an output pulse, which is the sum of an induced charge electron pulse induced at the anode and an induced charge hole pulse induced at the cathode due to the interaction between the atom and the radiation. In the method, a first step of converting and amplifying the output pulse into a voltage pulse proportional to a pulse amount, and a time constant smaller than a maximum movement time of holes generated by the interaction between the radiation and the detection element A second step of differentially shaping the voltage pulse to obtain a differential pulse, and a pulse height value of the differential pulse is a super pulse peak value exceeding a threshold value, And having a third step of measuring the radiation by obtaining a count value by counting the super pulse peak value.
[0023]
In the radiation measurement method according to the present invention, radiation is incident from the cathode of the detection element by applying a voltage to the detection element having an anode and a cathode, and the atoms constituting the detection element and the radiation In a radiation measurement method for measuring environmental radiation from an output pulse that is a sum of an electron pulse of induced charge induced in the anode by interaction and a hole pulse of induced charge induced in the cathode, the output pulse is A first step of converting and amplifying the voltage pulse proportional to the pulse amount, and differential shaping the voltage pulse with a time constant smaller than the maximum movement time of holes generated by the interaction between the radiation and the detection element. A second step of obtaining a differential pulse, and if the pulse peak value of the differential pulse is a super pulse peak value exceeding a threshold value, the super pulse peak value is -A third step of converting the pulse peak value of the differential pulse into a digital pulse peak value, and a fourth step of measuring radiation by calculating the digital pulse peak value to obtain a calculated value. It is characterized by having.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of a radiation measurement method according to the present invention will be described with reference to the accompanying drawings.
[0025]
In the accompanying drawings, the same constituent elements are denoted by the same reference numerals, and redundant description is omitted.
[0026]
FIG. 1 is a schematic view showing a first embodiment of radiation measuring means used in the radiation measuring method of the present invention.
[0027]
In the radiation measuring means 11 in FIG. 1, incident radiation, for example, γ-ray 12 of an unknown radiation source causes an interaction to generate carriers (electrons (−) and holes (+)), A radiation detector (detecting element) that generates an output pulse b of induced charge, for example, a CdTe (cadmium telluride) semiconductor detector 14, and a voltage proportional to the pulse amount of the output pulse b by integrating the generated output pulse b The preamplifier 15 having a high input impedance to be converted / amplified into the pulse c, the capacitance (C) and the resistor (R) of the capacitor, the decay time of the voltage pulse c output from the preamplifier 15 is shortened, and the differential pulse d And a differential pulse shaping circuit 16 for obtaining.
[0028]
Further, when the pulse peak value of the differential pulse d is the super pulse peak value e exceeding the pulse threshold value, the pulse peak discriminator 17 that outputs the super pulse peak value e that is a timing signal, and the super pulse peak value and a counter 18 that counts e to obtain a count value.
[0029]
The CdTe semiconductor detector 14 simulates γ rays 12 of an unknown radiation source, for example, high energy γ rays 12. ¹³⁷ Csγ ray (661 keV) 12a is incident. The CdTe semiconductor detector 14 includes a CdTe single crystal (not shown) as a detection element, and the CdTe single crystal is sandwiched between a pair of electrodes (anode and cathode) not shown. The sum of the electron pulse b1 due to the induced charge induced at the anode and the hole pulse b2 due to the induced charge induced at the cathode can be output to the preamplifier 15 as the output pulse b.
[0030]
The voltage pulse c output from the preamplifier 15 is a pulse that decays exponentially and relatively slowly. As the preamplifier 15, a charge sensitive type amplifier such as a pulsed light reset method or a transistor reset method is used.
[0031]
The differential pulse shaping circuit 16 is a differential circuit that differentially shapes the voltage pulse c with a required time constant in order to shorten the decay time of the pulse.
[0032]
Next, the operation of the radiation measurement unit 11 will be described.
[0033]
A voltage is applied to the anode and cathode of the CdTe semiconductor detector 14 provided in the radiation measuring means 11 to generate an electrostatic field.
[0034]
When a voltage is applied to the CdTe semiconductor detector 14, an unknown source γ ray 12, for example, a high-energy γ ray 12 is simulated from the cathode of the CdTe single crystal to which the voltage is applied to the CdTe single crystal. ¹³⁷ Csγ ray (661 keV) 12a is incident. Atoms constituting the CdTe single crystal; ¹³⁷ Carriers (electrons (−), holes (+)) are generated by the interaction with the Csγ ray 12a. Since a voltage is applied to the CdTe single crystal, electrons generated inside the CdTe single crystal move (drift) to the anode and holes move to the cathode, respectively.
[0035]
Here, the atoms constituting the CdTe single crystal and ¹³⁷ Interaction with Csγ ray 12a is incident ¹³⁷ Depending on the energy of the Csγ ray 12a, this occurs in the entire range inside the CdTe single crystal.
[0036]
Equivalent to high energy ¹³⁷ When the Csγ ray 12a is incident, the collision probability with the atoms constituting the CdTe single crystal is lowered. Therefore, ¹³⁷ While the Csγ ray 12a interacts with the atoms constituting the CdTe single crystal one or more times by one or more times of collision, the Csγ ray 12a enters the position relatively far from the cathode (position near the anode). Loss all or part of the energy.
[0037]
Next, electrons generated at the interaction position drift to the anode and holes drift to the cathode, respectively. As a result, an electron pulse b1 as an induced charge is generated at the anode and a hole pulse b2 as an induced charge is generated at the cathode. The output pulse b is the sum of the electron pulse b1 and the hole pulse b2, and corresponds to high energy. ¹³⁷ In the Csγ ray 12a, since the interaction position is close to the anode, the drift distance of the holes to the cathode is increased, and the contribution of the hole pulse b2 is increased.
[0038]
Therefore, ¹³⁷ Since the Csγ ray 12a interacts at a position near the anode, the output pulse b obtained from the CdTe semiconductor detector 14 is output as an output pulse b having a long rise time, the contribution of the hole pulse b2 being the main component. .
[0039]
An output pulse b, which is the sum of the electron pulse b1 from the anode and the hole pulse b2 from the cathode, is output to the preamplifier 15 and amplified by the preamplifier 15.
[0040]
The voltage pulse c which is an output signal from the preamplifier 15 is ¹³⁷ Each time the Csγ ray 12a is incident, it is output to the differential pulse shaping circuit 16 as a stepped waveform with a gradual attenuation that rises stepwise.
[0041]
In the differential pulse shaping circuit 16, the input voltage pulse c is differentially shaped with a required time constant.
[0042]
Next, a method for setting a required time constant will be described.
[0043]
High energy ¹³⁷ When the Csγ ray 12a interacts at a position near the anode, the pulse amount of the output pulse b obtained from the CdTe semiconductor detector 14 is mainly composed of the contribution of the hole pulse b2, and therefore the output pulse b having a long rise time. Is output as
[0044]
Here, the maximum movement time t of holes having a long time as a drift time _MAX Is determined by the thickness d of the CdTe single crystal, the mobility of holes (value specific to the substance of the CdTe single crystal) m, and the applied voltage E.
[Expression 1]
t _MAX = D / m / E
It can be expressed as.
[0045]
In the differential pulse shaping circuit 16, the output pulse b has a required time constant, for example, the maximum movement time t of holes. _MAX Differential shaping with a shorter time constant. That is, ¹³⁷ The voltage pulse c of the Csγ ray 12a is equal to the rise time (0 to t) due to the hole drift time. _MAX ) Is removed and differential shaping is performed. In addition, a result is obtained that the degree of decrease in the pulse peak value becomes more conspicuous as the position of the interaction is closer to the anode.
[0046]
The differential pulse d subjected to differential shaping by the differential pulse shaping circuit 16 shown in FIG. 1 is output to the pulse height discriminator 17.
[0047]
In the pulse height discriminator 17, if the peak (pulse peak value) of the pulse height of the differential pulse d is the super pulse peak value e exceeding the threshold value, the super pulse peak value e as a timing signal is sent to the counter 18. Output. Here, the threshold value is the number of atoms constituting the CdTe single crystal. ¹³⁷ It refers to a limit dose that can cause interaction with the Csγ ray 12a, and is arbitrarily set.
[0048]
In the counter 18, the pulse height discriminator 17 counts the super pulse peak value e exceeding the threshold value. The count rate (count value / time), which is the count number of the superpulse peak value e per unit time, is an index of the radiation measurement amount, and is monitored via an indicator. The count rate is displayed by an indicator, and when the count rate exceeds a preset level, an alarm is issued to warn the radiation worker.
[0049]
Furthermore, in the radiation measuring means 11 shown in FIG. ¹³⁷ Similar to the monitor of the Csγ ray 12a, the low energy γ ray 12 was simulated. ²⁴¹ The Amγ ray (60 keV) 12b can be monitored.
[0050]
Corresponds to low energy ²⁴¹ When the Amγ ray 12b is incident from the cathode of the CdTe single crystal to which a voltage is applied, the probability of collision with atoms constituting the CdTe single crystal increases. Therefore, ²⁴¹ The Amγ ray 12b interacts once by colliding with the atoms constituting the CdTe single crystal once, and loses all of the energy at a position relatively near the cathode (position away from the anode) and disappears. .
[0051]
Next, electrons generated at the interaction position drift to the anode and holes drift to the cathode, respectively. As a result, an electron pulse b1 as an induced charge is generated at the anode and a hole pulse b2 as an induced charge is generated at the cathode. Corresponds to low energy ²⁴¹ In the Amγ ray 12b, since the interaction position is close to the cathode, the drift distance of electrons to the anode is increased, and the contribution of the electron pulse b1 is increased.
[0052]
Therefore, ²⁴¹ When the Amγ ray 12b interacts at a position near the cathode, the pulse amount of the output pulse b obtained from the CdTe semiconductor detector 14 is mainly composed of the contribution of the electron pulse b1, so that the output pulse b having a short rise time is obtained. Is output.
[0053]
Corresponds to high energy measured by the radiation measuring means 11 ¹³⁷ Csγ ray 12a, equivalent to low energy ²⁴¹ In the Amγ ray 12b, there is a difference in the position of interaction depending on the energy. Therefore, a difference occurs in the time (drift time) until the electrons generated at the interacted position reach the anode. Similarly, holes generated at the interacted positions also have a difference in drift time depending on energy.
[0054]
FIG. 2 is a graph showing the pulse height distribution of the spectrum in the radiation measuring means 11.
[0055]
The spectrum shown in FIG. 2 shows a pulse wave height distribution according to a count rate which is a count value per unit time. The count value is obtained by the operation of the radiation measuring means 11 shown in FIG. ¹³⁷ Csγ ray 12a, ²⁴¹ In the case of a super differential pulse e in which the pulse peak value of each differential pulse d of the Amγ line 12b exceeds a threshold value, it is obtained by counting the super pulse peak value e as a timing signal.
[0056]
The pulse wave height distribution shown in FIG. 2 corresponds to higher energy than the conventional pulse wave height distribution shown in FIG. ¹³⁷ It can be seen that the change in the count rate near the threshold value of the Csγ ray 12a is reduced. In the differential pulse shaping circuit 16, the voltage pulse c is converted into the maximum hole movement time t. _MAX The differential shaping is performed with a shorter time constant, and after the rising time of the output pulse b whose main component is the hole pulse b2 (0 to t _MAX ) Has been removed.
[0057]
FIG. ¹³⁷ It is a graph which shows the fluctuation rate of the pulse peak value of the differential pulse in the Csγ ray 12a as a time series transition.
[0058]
FIG. 3 simulates high energy gamma rays 12 ¹³⁷ For the Csγ line 12a, the pulse peak value of the differential pulse d is measured, and the time-series transition of the fluctuation rate (pulse peak value of the differential pulse d / threshold value) is shown. That is, the pulse peak value of the differential pulse d having a variation rate of 1 or more is counted as the super pulse peak value e because the pulse peak value is equal to or greater than the threshold value. The variation rate is shown as a time-series transition from the start of operation when the conventional radiation measurement means and the radiation measurement means 11 shown in FIG. 1 are operated with the same environmental radiation.
[0059]
Like the variation rate shown in FIG. 3, the maximum hole movement time t in the differential pulse shaping circuit 16 of the radiation measuring means 11. _MAX When the voltage pulse c is differentially shaped using the time constant as a time constant, the fluctuation of the pulse peak value of the differential pulse d near the threshold value (variation rate = 1) decreases.
[0060]
On the other hand, like the spectrum of FIG. ²⁴¹ In the pulse wave height distribution of the Amγ ray 12b, it can be seen that there is almost no reduction in the change in the count rate. The fact that there is almost no change in the counting rate corresponds to low energy ²⁴¹ This is because the Amγ ray 12b interacts with the position in the vicinity of the cathode, particularly at the cathode surface, so that the decrease in the charge of the output pulse b in which the hole pulse b2 is a small component hardly affects the count rate.
[0061]
When the radiation measuring means 11 shown in FIG. 1 is used, the differential pulse shaping circuit 16 changes the voltage pulse c to the maximum hole movement time t. _MAX Differential shaping with a shorter time constant. Therefore, it corresponds to high energy ¹³⁷ When the Csγ ray 12a is incident, the temporal fluctuation of the count rate can be suppressed by noise components, offset components, and the like. Also, ¹³⁷ Csγ ray 12a and ²⁴¹ The Amγ ray 12b can be monitored simultaneously.
[0062]
In the radiation measuring means 11 shown in FIG. 1, the sum of the electron pulse b1 obtained from the anode provided in the CdTe semiconductor detector 14 and the hole pulse b2 obtained from the cathode is the pulse of the output pulse b of the induced charge. However, only the hole pulse b2 obtained from the cathode may be used as the pulse amount of the output pulse b of the induced charge.
[0063]
FIG. 4 is a schematic view showing a second embodiment of the radiation measuring means used in the radiation measuring method of the present invention.
[0064]
The γ rays 12 of the unknown radiation source are incident on the radiation measuring means 11A in FIG.
[0065]
The radiation measuring means 11A collects an A / D converter 22 for digitally converting the pulse peak value of the differential pulse d output from the differential pulse shaping circuit 16 and an A / D converted digital pulse peak value g. And an arithmetic unit 23 for performing arithmetic processing.
[0066]
The A / D converter 22 is equipped with a gate (not shown), and switches between coincidence and anti-coincidence by a switch. The A / D converter 22 to which the differential pulse d as an input signal is input operates with the super pulse peak value e output from the pulse peak discriminator 17.
[0067]
In the pulse height discriminator 17 shown in FIG. 4, when the super pulse peak value e exceeding the threshold value is generated, the pulse height discriminator 17 outputs the super pulse peak value e. Using the super pulse peak value e as a trigger, the differential pulse shaping circuit 16 outputs a differential pulse d to the A / D converter 22, and the A / D converter 22 converts the pulse peak value of the differential pulse d into a digital pulse peak value. converted to g. The reason why the differential pulse d is digitally converted by using the superpulse peak value e as a trigger is to prevent digital conversion from being performed on the differential pulse d having a pulse height less than the threshold value. This is for the purpose of preventing the contamination and reducing the conversion load. The digital pulse peak value g is an index of the radiation measurement amount.
[0068]
Further, as described in the radiation measuring means 11 shown in FIG. 1, the superpulse peak value e from the pulse height discriminator 17 to the A / D converter 22 becomes a stable output signal.
[0069]
In the calculator 23, calculation processing is performed on the digital pulse peak value g input from the A / D converter 22. Then, the digital pulse peak value g is counted to obtain an operation value that is digital data.
[0070]
Furthermore, wave height analysis, time distribution measurement, and the like can be performed from the calculated values obtained by the calculator 23.
[0071]
When the radiation measuring means 11A shown in FIG. 4 is used, the differential pulse shaping circuit 16 causes the voltage pulse c to be the maximum hole movement time t. _MAX Differential shaping with a shorter time constant. Therefore, when γ rays 12 corresponding to high energy are incident, temporal fluctuations in the count rate can be suppressed by noise components, offset components, and the like. Moreover, the gamma rays 12 with different energies can be monitored simultaneously.
[0072]
In the radiation measurement means 11A shown in FIG. 1, the sum of the electron pulse b1 obtained from the anode provided in the CdTe semiconductor detector 14 and the hole pulse b2 obtained from the cathode is the pulse of the output pulse b of the induced charge. However, only the hole pulse b2 obtained from the cathode may be used as the pulse amount of the output pulse b of the induced charge.
[0073]
FIG. 5 is a schematic view showing a third embodiment of radiation measuring means used in the radiation measuring method of the present invention.
[0074]
The γ rays 12 of the unknown radiation source are incident on the radiation measuring means 11B in FIG.
[0075]
The radiation measuring means 11A collects and calculates an A / D converter 22 that digitally converts the pulse peak value of the voltage pulse c output from the preamplifier 15 and an A / D converted digital pulse peak value g. And an arithmetic unit 23 that performs processing.
[0076]
In the pulse height discriminator 17 shown in FIG. 5, when the super pulse peak value e exceeding the threshold value is generated, the pulse height discriminator 17 outputs the super pulse peak value e. A voltage pulse c is output from the preamplifier 15 to the A / D converter 22 using the super pulse peak value e as a trigger, and the A / D converter 22 converts the pulse peak value of the voltage pulse c into a digital pulse peak value g. Is done.
[0077]
Further, as described in the radiation measuring means 11 shown in FIG. 1, the superpulse peak value e from the pulse height discriminator 17 to the A / D converter 22 becomes a stable output signal.
[0078]
In the calculator 23, calculation processing is performed on the digital pulse peak value g input from the A / D converter 22. Then, the digital pulse peak value g is counted to obtain an operation value that is digital data.
[0079]
Here, in general, the calculator 23 performs a calculation based on the detected energy information of the γ-ray 12. In order to increase the accuracy of the calculation performed by the calculator 23, it is necessary to know and distinguish the energy of the γ-ray 12 as clearly as possible, and it is desirable that the difference due to the energy of the pulse peak value is large. Therefore, the differential / shaped voltage pulse c from the preamplifier 15 is A / D converted rather than the differentiated pulse d differentiated / shaped by the differential pulse shaping circuit 16 of the radiation measuring means 11A shown in FIG. Is preferable. This is because the voltage pulse c has a greater difference due to the energy of the pulse peak value than the differential pulse d.
[0080]
When the radiation measuring means 11B shown in FIG. 5 is used, the differential pulse shaping circuit 16 causes the voltage pulse c to be the maximum hole movement time t. _MAX Differential shaping with a shorter time constant. Therefore, when γ rays 12 corresponding to high energy are incident, temporal fluctuations in the count rate can be suppressed by noise components, offset components, and the like. Moreover, the gamma rays 12 with different energies can be monitored simultaneously.
[0081]
FIG. 6 is a schematic view showing a fourth embodiment of radiation measuring means used in the radiation measuring method of the present invention.
[0082]
The γ rays 12 of the unknown radiation source are incident on the radiation measuring means 11C in FIG.
[0083]
Further, the radiation measuring means 11C collects and calculates an A / D converter 22 that digitally converts the pulse peak value of the voltage pulse c output from the preamplifier 15 and an A / D converted digital pulse peak value g. And an arithmetic unit 23 that performs processing.
[0084]
Further, a normalization processor 24 is provided for normalizing the calculation value i output from the calculator 23 by the count value h output from the counter 18.
[0085]
Since one γ-ray 12 is detected, digital conversion by the A / D converter 22 and calculation by the calculator 23 are performed, but there is a certain fixed time (dead time). If another γ ray 12 is detected by the CdTe semiconductor detector 14 during this dead time, the other γ ray 12 is counted off. In particular, in the collection of random events, such as when continuously monitoring environmental radiation, for example, gamma rays 12 in a controlled area of a plant such as a nuclear power plant, another gamma ray 12 incident during the dead time is used. It is necessary to prevent counting off.
[0086]
The normalization processor 24 normalizes the calculation value i, which is a digital signal output from the calculator 23 and having a dead time, with the count value h, which is an analog signal output from the counter 18 and has almost no dead time. Events during the dead time that are not included in the calculated value i can be corrected with the count value h, which is a true value.
[0087]
When the radiation measuring means 11C shown in FIG. 6 is used, the differential pulse shaping circuit 16 causes the voltage pulse c to be the maximum hole movement time t. _MAX Differential shaping with a shorter time constant. Therefore, when γ rays 12 corresponding to high energy are incident, temporal fluctuations in the count rate can be suppressed by noise components, offset components, and the like. Moreover, the gamma rays 12 with different energies can be monitored simultaneously.
[0088]
In addition, when the radiation measuring unit 11C is used, the measurement value i and the calculation value i are measured in parallel, and the calculation value i having a dead time is normalized by the count value h. The measurement accuracy of the wave height analysis using the value i can be improved.
[0089]
In the radiation measuring means 11C shown in FIG. 6, it is desirable to use a method in which the pulse peak value of the voltage pulse c output from the preamplifier 15 is digitally converted by the A / D converter 22; A method of digitally converting the pulse peak value of the differential pulse d output from the circuit 16 by the A / D converter 22 may be used.
[0090]
【The invention's effect】
According to the radiation measurement method according to the present invention, temporal fluctuations in the count rate can be suppressed by noise components, offset components, and the like, and radiations having different energies can be monitored simultaneously.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a first embodiment of radiation measurement means used in the radiation measurement method of the present invention.
FIG. 2 is a graph showing a spectral pulse wave height distribution in the radiation measuring means.
[Fig. 3] ¹³⁷ The graph which shows the fluctuation rate of the pulse peak value of the differential pulse in Csγ rays as a time series transition.
FIG. 4 is a schematic diagram showing a second embodiment of radiation measuring means used in the radiation measuring method of the present invention.
FIG. 5 is a schematic view showing a third embodiment of radiation measuring means used in the radiation measuring method of the present invention.
FIG. 6 is a schematic view showing a fourth embodiment of radiation measuring means used in the radiation measuring method of the present invention.
FIG. 7 is a graph showing a pulse height distribution of a spectrum in a conventional radiation measuring means.
[Explanation of symbols]
11, 11A, 11B, 11C Radiation measurement means
14 CdTe semiconductor detector (detection element)
15 Preamplifier
16 Differential pulse shaping circuit
17 Pulse height discriminator
18 counter
22 A / D converter
23 Calculator

Claims (3)

By applying a voltage to a detection element having an anode and a cathode, radiation is made incident from the cathode of the detection element, and induced charges are induced in the anode by the interaction between the atoms constituting the detection element and the radiation. In a radiation measurement method for measuring environmental radiation from an output pulse that is the sum of an electron pulse of the above and a hole pulse of induced charge induced in the cathode,
A first step of converting and amplifying the output pulse into a voltage pulse proportional to the pulse amount;
A second step of differentially shaping the voltage pulse with a time constant smaller than the maximum movement time of holes generated by the interaction between the radiation and the detection element to obtain a differential pulse;
And a third step of measuring radiation by counting the superpulse peak value and obtaining a count value when the pulse peak value of the differential pulse is a superpulse peak value exceeding a threshold value. A radiation measurement method characterized by the above. By applying a voltage to a detection element having an anode and a cathode, radiation is made incident from the cathode of the detection element, and induced charges are induced in the anode by the interaction between the atoms constituting the detection element and the radiation. In a radiation measurement method for measuring environmental radiation from an output pulse that is the sum of an electron pulse of the above and a hole pulse of induced charge induced in the cathode,
A first step of converting and amplifying the output pulse into a voltage pulse proportional to the pulse amount;
A second step of differentially shaping the voltage pulse with a time constant smaller than the maximum movement time of holes generated by the interaction between the radiation and the detection element to obtain a differential pulse;
When the pulse peak value of the differential pulse is a super pulse peak value exceeding a threshold value, the pulse peak value of the differential pulse is converted into a digital pulse peak value using the super pulse peak value as a trigger. And the process of
And a fourth step of measuring radiation by calculating the digital pulse peak value to obtain a calculated value. The radiation measurement method according to claim 2, wherein the fourth step includes a step of digitally converting the pulse peak value of the voltage pulse into a digital pulse peak value by using the super pulse peak value as a trigger.

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