JP2015025740A - Radiation measurement device, measurement method, and measurement program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiation measurement technique in which a stable measurement performance is maintained without an increase in scale even in an environment where a use temperature condition changes.SOLUTION: A radiation measurement device 10 includes: a semiconductor detector 144 that moves electron/hole 12 which are generated by incidence of radiation 11 in mutually opposite directions along an electric field E; a reception unit 16 that receives a response signal of the electron/hole 12 which have moved to electrodes 15 (15a and 15b) that form electric fields; a database 17 that registers a control parameter which is generated on the basis of temperature dependent characteristics of the semiconductor detector 144; and a processing unit 18 that processes the response signal on the basis of the control parameter and derives an energy value of the radiation 11.

Description

  The present invention relates to a radiation measurement technique using a semiconductor detector.

As an example of a radiation detector, there is a scintillator type radiation detector that converts incident radiation into light with a scintillator and indirectly measures the light with a photodetector.
On the other hand, there is a semiconductor detector using germanium (Ge), silicon (Si), cadmium telluride (CdTe), and thallium bromide (TlBr).
Radiation detectors using these semiconductors are superior in detection sensitivity compared to scintillator systems because they measure incident radiation directly converted into electrical signals.

The principle of radiation detection by a semiconductor detector is that radiation is incident on the semiconductor, energy greater than the band gap is applied, and the generated electron / hole pair is moved to the electrode by a bias voltage to obtain an electrical signal. by.
A radiation detector using a compound semiconductor such as CdTe or TlBr can be used at room temperature and has a high density, and therefore can detect γ rays with high efficiency.

However, these compound semiconductors have a problem that the detection sensitivity varies due to changes in electron / hole mobility and lifetime depending on the environmental temperature.
In order to solve these problems, a technique has been disclosed in which an electronic cooler is provided around the radiation detector to keep the temperature of the radiation detector constant (Patent Document 1).

JP 2005-265859 A

As described above, by controlling the temperature of the radiation detector, the radiation can be measured with a constant radiation detection sensitivity.
However, since it is necessary to add a cooling device or a circuit for controlling the temperature of the radiation detector, there is a problem that the measuring device becomes large-scale.

  The present invention has been made in consideration of such circumstances, and provides a radiation measurement technique capable of maintaining stable measurement performance without increasing the scale even in an environment where the operating temperature conditions change. With the goal.

  In the radiation measurement apparatus according to the present invention, a semiconductor detector that moves electrons / holes generated by incidence of radiation in opposite directions along an electric field, and the electrons / positive holes that are moved to an electrode that forms the electric field. A receiver for receiving a response signal of the hole; a database for registering a control parameter created based on a temperature-dependent characteristic of the semiconductor detector; and an energy value of the radiation by processing the response signal based on the control parameter And a processing unit for guiding.

  The present invention provides a radiation measurement technique that maintains stable measurement performance without increasing the scale even in an environment in which the operating temperature conditions change.

1 is a block diagram showing a first embodiment of a radiation measuring apparatus according to the present invention. (A) (B) The schematic of the semiconductor detector applied to each embodiment. The graph which shows the response signal of the electron / hole which moved to the electrode of a semiconductor detector. The graph which shows the relationship of the control parameter (applied voltage) with respect to temperature in 1st Embodiment. (A) The graph which shows the energy of the radiation which injected discretely with respect to time, (B) The graph which classify | categorizes into a some group based on an energy value, and shows the count value of each group. (A) Graph showing energy spectrum distribution of radiation (γ rays) at T = T1, (B) Graph showing energy spectrum distribution of radiation (γ rays) at T = T2 (> T1). The block diagram which shows the measuring device of the radiation which concerns on 2nd Embodiment or 3rd Embodiment. The graph which shows the relationship of the control parameter (sensitivity correction coefficient) with respect to temperature in 2nd Embodiment. The graph which shows the relationship of the control parameter (integration time) with respect to temperature in 3rd Embodiment. The block diagram which shows the measuring device of the radiation which concerns on 4th Embodiment.

(First embodiment)
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
As shown in FIG. 1, the radiation measuring apparatus 10 (hereinafter simply referred to as “measuring apparatus 10”) according to the first embodiment causes electrons / holes 12 generated by the incidence of radiation 11 to move along an electric field E. A semiconductor detector 14 that moves in the opposite direction, a receiver 16 that receives a response signal (FIG. 3) of the electrons / holes 12 that have moved to the electrodes 15 (15a, 15b) that form the electric field E, and a semiconductor detector A database 17 for registering control parameters (FIG. 4) created based on the temperature dependence characteristics of 14, and a processing unit 18 for processing the response signal (FIG. 3) based on the control parameters to derive the energy value of the radiation 11. It is equipped with.

The semiconductor detector 14 includes a semiconductor 13 such as TlBr, Si, CdTe, or GaAs that can be used at room temperature, an electrode 15 (15a, 15b) that forms an electric field E in the semiconductor 13 by an applied voltage of a power supply 22, and a substrate. Yes.
As the semiconductor 13, a semiconductor 13 that generates electrons / holes 12 when radiation 11 such as α rays, β rays, γ rays, and other charged particles is incident is applied.

When the energy of the incident radiation 11 exceeds the band gap of the semiconductor 13, the number of electrons / holes 12 corresponding to the magnitude of this energy is generated.
The generated electrons / holes 12 are separated by the electric field E formed according to the applied voltage of the power source 22 and moved to the electrodes 15 (15a, 15b) in the opposite directions.

An electric field E having a magnitude proportional to the applied voltage of the power source 22 is formed in the semiconductor 13 sandwiched between the electrodes 15 (15a, 15b).
The optimum value of the applied voltage is determined by the type and shape of the semiconductor 13, but is set in a range that is sufficient to move the generated electrons / holes 12 to the electrode 15 and does not cause dielectric breakdown.
For example, in the case of 1 mm thick TlBr, it is about 50V to several hundreds V.

As shown in FIG. 2A, in the semiconductor detector 14, the periphery of the semiconductor 13 and the electrodes 15 (15a, 15b) disposed at both ends thereof is covered with an insulator 31.
The insulator 31 is applied by applying a coating material so as to cover the periphery of the integrated body of the semiconductor 13 and the electrode 15 (15a, 15b) and then solidifying it.
Thus, by covering the semiconductor 13 and the electrode 15 (15a, 15b) with the insulator 31, it is possible to suppress the leakage current and increase the applied voltage. For reasons that will be described later, it corresponds to a wider environmental temperature. be able to.
The wiring extending from the electrode 15 (15a, 15b) passes through the insulator 31 and communicates with the connector 32.

As another example, as shown in FIG. 2B, the semiconductor detector 14 has a plurality of semiconductors 13 in which electrodes 15 (15a, 15b) are arranged at both ends arranged in an array, and the periphery thereof is opened. The structure covered with the shield 33 having the portion 34 can also be taken.
The shield 33 is made of a material capable of shielding radiation, and for example, a metal such as tungsten, lead, gold, iron, or a material containing these is applied.
In the semiconductor detector 14 shown in FIG. 2B, the temperature sensor 21 is provided inside the shield 33, but it may be provided outside the shield 33.
The temperature sensor 21 can employ various temperature measurement methods such as a thermocouple, a rapid temperature resistance pair, and a semiconductor type, and is disposed in the vicinity of the semiconductor detector 14 to measure the ambient temperature. It is desirable to accurately reflect the actual temperature of the vessel 14.

Returning to FIG. 1, the description will be continued.
An electric field E formed in the semiconductor 13 causes the electrons / holes 12 to move, and the charge amount Q induced in the electrode 15 is expressed by the following equation (1).
Q = n · e ₀ · exp (− | z−Z | / μτE) (1)

Here, e ₀ is the elementary quantity of electricity, n is the number of electrons / holes 12 generated by the incident radiation 11, and shows a larger value as the energy of the radiation 11 is higher. | z−Z | corresponds to the distance from the generation position of the electron / hole 12 to the electrode 15. μ and τ indicate mobility and lifetime, respectively, and are values that vary depending on the type and temperature of the semiconductor 13.

As apparent from the equation (1), the amount of charge Q moving to the electrode 15 depends on the mobility μ, the life τ, and the electric field E as well as the energy of the incident radiation 11.
And, as the mobility μ and the lifetime τ are longer and the electric field E is larger, the variation depending on the generation position of the electron / hole 12 is reduced, and the charge amount Q depending only on the energy of the incident radiation 11 is measured. Can do.

However, the electric field E has an upper limit of a level at which dielectric breakdown does not occur, and the mobility μ and the life τ have the property of changing according to the environmental temperature.
For this reason, when the temperature of the semiconductor detector 14 changes, the charge amount Q transferred to the electrode 15 per energy of the incident radiation 11 also changes.

The graph of FIG. 3 shows the waveform received by the receiver 16 after the amplifier 23 amplifies the response signal of the electron / hole 12 that has moved to the electrode 15.
As shown in FIG. 3, the waveform of the response signal is such that when the voltage V of the power source 22 is constant and the temperature T of the semiconductor detector 14 is the low temperature T ₁ , the response signal waveform is higher than the high temperature T _2. Observed sharply.

Here, the Y value (response signal) in the graph of FIG. 3 corresponds to the current value input to the receiving unit 16 at each time point.
Therefore, the time integral value of the waveform of the response signal corresponds to the charge amount Q of the ionized electron / hole 12, that is, the energy of the incident radiation 11.

The graph of FIG. 4 shows the relationship of the control parameter (applied voltage V) of the power source 22 with respect to the temperature signal T measured by the temperature sensor 21.
The database 17 a holds control parameters created in advance based on the temperature dependence characteristics of the semiconductor detector 14.
In other words, the correlation between the mobility μ and the lifetime τ in the above equation (1) is converted into data, and the relationship between the measured temperature T and the applied voltage V at which μτE is constant is derived by simulation or experiment and registered in the database 17a. To do.

The graph of FIG. 4 exemplifies the case where TlBr is used as the semiconductor 13, but it is known that the mobility μ of the TlBr rapidly decreases when the temperature becomes 30 ° C. or higher.
A TlBr element is used at a thickness of 1 mm and a temperature range of 0 to 50 ° C., and a maximum voltage of 300 V that can be applied at a temperature of 50 ° C. at which the mobility μ decreases most is a reference.
The control parameter is set so that the applied voltage V tends to decrease as the mobility μ increases, that is, the temperature T decreases.
Thus, the control parameter in the first embodiment is the applied voltage V of the power source 22 that causes the electrode 15 to form the electric field E that is uniquely set for the given temperature T.

Returning to FIG. 1, the description will be continued.
The voltage processing unit 18 a acquires the applied voltage V corresponding to the temperature signal T measured by the temperature sensor 21 from the database 17 a, sets the power source 22, and forms an electric field E on the electrode 15.
As a result, as shown in FIG. 3, the broad-shaped response waveform represented by the alternate long and short dash line at the applied voltage V ₁ at the high temperature T ₂ is indicated by the solid line by setting the applied voltage V ₂ (> V ₁ ). Sharpen like a waveform.

Therefore, by appropriately selecting the applied voltage V, the response signal to the radiation 11 having the same energy can be made constant in the peak value H (maximum value) without depending on the temperature of the semiconductor detector 14.
For this reason, in the first embodiment, the energy of the incident radiation 11 can be determined based on the peak value H (maximum value) of the response signal.
Therefore, the voltage processing unit 18a processes the response signal (FIG. 3) based on the control parameter, and converts it into a radiation energy value.

As shown in the graph of FIG. 5A, the energy of the incident radiation 11 is discretely measured with respect to time.
As shown in FIG. 5B, the counting unit 19 (FIG. 1) classifies the response signals of the radiation 11 into a plurality of groups based on the energy values of FIG. 5A, and calculates the count values of each group. To derive.
A known method such as Wilkinson method, successive approximation type, flash ADC type, or Time over Threshold Method can be applied to count the response signal with respect to this energy value.

FIG. 5B is a schematic graph for explaining the energy spectrum of radiation, but the actual energy spectrum distribution of γ-rays further narrows the range of the radiation energy of the group in which the radiation is counted. As shown in FIG.
Here, the graph of FIG. 6A shows the count value with respect to the energy of the γ rays incident at the temperature T = T ₁ and the applied voltage V = V ₁ .
On the other hand, the graph of FIG. 6B shows the count value for the energy of the γ-rays incident at the temperature T = T ₂ (> T ₁ ) and the applied voltage V = V ₁ .

Thus, when the temperature T rises, the peak of the energy spectrum of γ rays shifts to the lower energy side, and the intensity decreases and is observed.
As described based on FIG. 3, this is because the peak value H of the response signal of the electron / hole 12 decreases as the temperature increases.
Therefore, in the environment of temperature T = T ₂ (> T ₁ ) (FIG. 6B), by setting the applied voltage V = V ₂ (> V ₁ ), the γ rays shown in FIG. Energy spectrum distribution is obtained.

In the first embodiment, by controlling the applied voltage V based on the temperature T of the semiconductor detector 14 measured by the temperature sensor 21, the reproducibility of the radiation energy spectrum distribution measurement is not affected by the environmental temperature. Can be improved.
Moreover, by covering the periphery of the semiconductor detector 14 with the insulator 31, the breakdown voltage can be increased and the upper limit of the adjustment range of the applied voltage V can be expanded.

The above description (process for obtaining the spectral distribution of FIG. 6) is an example in which the radiation is counted by finely dividing the range of radiation energy.
As another embodiment, the count unit 19 sets a wide energy range for counting radiation and derives a count value of a response signal having an energy value exceeding a threshold value.
That is, the display unit 24 may function to display the count number of the radiation 11 having an energy value larger than a predetermined value.
In addition, the range of energy from which the count value is derived may be set not only as a lower limit threshold but also as an upper limit threshold.

(Second Embodiment)
As shown in FIG. 7, the radiation measuring apparatus 10 according to the second embodiment acquires, as the processing unit 18, a sensitivity correction coefficient (control parameter) corresponding to the temperature signal T measured by the temperature sensor 21 from the database 17b. And a waveform processor 18b for correcting the peak value of the response signal.
7 that have the same configuration or function as those in FIG. 1 are denoted by the same reference numerals, and redundant description is omitted.

In the second embodiment, as shown in FIG. 8, a sensitivity correction coefficient uniquely set for a given temperature T is used as a control parameter.
As described above, the peak value H of the waveform of the response signal received by the receiving unit 16 varies depending on the temperature even if the energy of the radiation 11 incident on the semiconductor detector 14 is constant.
Therefore, in the second embodiment, the energy of the radiation 11 is converted by multiplying the peak value H (H1, H2) of the response signal by the sensitivity correction coefficient.

The graph of FIG. 8 exemplifies the case where TlBr is used as the semiconductor 13. However, in the range of 0 to 50 ° C., TlBr has a peak value of the response signal at around 10 to 20 ° C. even when the applied voltage is constant. Is known to be maximized.
Therefore, the sensitivity correction coefficient is based on the peak value at 50 ° C. at which the sensitivity of the response signal is the lowest, and the data for the target temperature range so that the product of the peak value of the response signal is constant for the same energy. And is registered in the database 17b.
In the second embodiment, based on the temperature T of the semiconductor detector 14 measured by the temperature sensor 21, the sensitivity correction coefficient is multiplied by the peak value of the response signal, so that the radiation energy is not affected by the environmental temperature. The reproducibility of spectrum distribution measurement can be improved.

(Third embodiment)
As shown in FIG. 7, the radiation measuring apparatus 10 according to the third embodiment has, as the processing unit 18, an integration time t (t ₁ , t ₂ ; FIG. 3) corresponding to the temperature signal T measured by the temperature sensor 21. A waveform processing unit 18c that acquires (control parameter) from the database 17c and integrates the response signal is provided.
7 that have the same configuration or function as those in FIG. 1 are denoted by the same reference numerals, and redundant description is omitted.

In the third embodiment, as shown in FIG. 9, an integration time uniquely set for a given temperature T is used as a control parameter.
If the energy of the radiation 11 incident on the semiconductor detector 14 is constant, the area (time integral value) of the response signal (FIG. 3) received by the receiving unit 16 is not dependent on the temperature for the above-described reason. handle.
Therefore, in the third embodiment, the energy of the radiation 11 is converted based on the integrated value of the response signal.

As the waveform processing unit 18c (FIG. 7), an analog circuit configured by a differential integration circuit or the like, or a digital circuit configured by a high-speed AD converter or a digital integrator is applied.
When the waveform processing unit 18c is configured by an analog circuit, the integration time t (FIG. 3) of the response signal can be adjusted by changing the resistance value and the capacitance.

When the waveform processing unit 18c is configured by a digital circuit, the sampling clock is set so that at least 10 sampling points are obtained within the integration time t set from the rising edge of the response signal.
Then, the added value of the Y values sampled within the integration time t set from the rise of the response signal is made to correspond to the radiation energy value.

The amount of charge detected from the semiconductor detector 14 is expressed as an integral value of the waveform of the response signal. When the temperature of the semiconductor detector 14 changes, the waveform width of the response signal changes.
In particular, when the mobility μ is greatly changed compared to the lifetime τ as in the case of a TlBr detector or the like, the waveform width increases as the temperature rises. Therefore, if the integration time is made constant, the energy is estimated to be small.
Therefore, by setting the integration time t according to the temperature T measured by the temperature sensor 21, the energy of radiation can be measured with high reproducibility without depending on the environmental temperature.

(Fourth embodiment)
As shown in FIG. 10, the radiation measuring apparatus according to the fourth embodiment has a configuration in which the temperature sensor 21 in FIG. 7 is omitted.
In the fourth embodiment, a sensitivity correction coefficient uniquely determined with respect to the waveform width of the response signal (FIG. 3) is used as the control parameter.
Thereafter, as in the second embodiment, the waveform processing unit 18d acquires a sensitivity correction coefficient corresponding to the measured waveform width from the database 17d, and corrects the peak value of the response signal.
The waveform width handled in the waveform processing unit 18d is a half width derived from the response signal received by the receiving unit 16.

  In the fourth embodiment, the information on the waveform width of the response signal is used as information in place of the temperature T of the semiconductor detector 14 to improve the reproducibility of the radiation energy spectrum distribution measurement without being affected by the environmental temperature. it can.

  According to the radiation measuring apparatus of at least one embodiment described above, the operating temperature condition is obtained by processing the response signal by the control parameter created based on the temperature dependence characteristic of the semiconductor detector and deriving the energy value of the radiation. Even in an environment where the temperature changes, stable measurement can be performed without increasing the scale.

Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, changes, and combinations can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.
The components of the radiation measurement apparatus can also be realized by a processor of a computer and can be operated by a radiation measurement program.

  DESCRIPTION OF SYMBOLS 10 ... Radiation measuring device, 11 ... Radiation, 12 ... Electron / hole, 13 ... Semiconductor, 14 ... Semiconductor detector, 15 (15a, 15b) ... Electrode, 16 ... Receiver (response signal), 17 (17a, 17b, 17c, 17d) ... database, 18 (18a) ... processing unit (voltage processing unit), 18 (18b, 18c, 18d) ... processing unit (waveform processing unit), 19 ... counting unit, 21 ... temperature sensor, 22 DESCRIPTION OF SYMBOLS ... Power supply, 23 ... Amplifier, 24 ... Display part, 31 ... Insulator, 32 ... Connector, 33 ... Shielding body, 34 ... Opening part, E ... Electric field.

Claims (10)

A semiconductor detector that moves electrons / holes generated by incidence of radiation in opposite directions along the electric field;
A receiver for receiving a response signal of the electrons / holes moved to the electrode forming the electric field;
A database for registering control parameters created based on the temperature-dependent characteristics of the semiconductor detector;
And a processing unit that processes the response signal based on the control parameter and derives an energy value of the radiation. The radiation measurement apparatus according to claim 1,
The control parameter is a parameter that causes the electrode to form an electric field that is uniquely set for a given temperature,
The radiation processing apparatus, wherein the processing unit processes the response signal by acquiring the control parameter corresponding to the measured temperature signal and forming the set electric field on the electrode. The radiation measurement apparatus according to claim 1,
The radiation measurement apparatus is characterized in that the energy of the radiation is converted based on a peak value of the response signal. The radiation measurement apparatus according to claim 3,
The control parameter is a sensitivity correction coefficient that is uniquely set for a given temperature,
The radiation measurement apparatus, wherein the processing unit acquires the sensitivity correction coefficient corresponding to the measured temperature signal and corrects the peak value of the response signal. The radiation measurement apparatus according to claim 1,
The energy of the radiation is converted based on an integral value of the response signal,
The control parameter is an integration time uniquely set for a given temperature,
The radiation measurement apparatus, wherein the processing unit acquires the integration time corresponding to the measured temperature signal and integrates the response signal. The radiation measurement apparatus according to claim 3,
The control parameter is a sensitivity correction coefficient uniquely determined for the waveform width of the response signal,
The radiation measurement apparatus, wherein the processing unit acquires the sensitivity correction coefficient corresponding to the measured waveform width and corrects the peak value of the response signal. The radiation measurement apparatus according to any one of claims 1 to 6,
A radiation measuring apparatus, further comprising: a counting unit that classifies the response signals into a plurality of groups based on the energy value and derives a count value of each group. The radiation measurement apparatus according to any one of claims 1 to 6,
The radiation measuring apparatus, further comprising: a counting unit that derives a count value of the response signal in which the energy value exceeds a threshold value. Moving electrons / holes generated by radiation incident on the semiconductor detector in opposite directions along the electric field;
Receiving the response signal of the electrons / holes transferred to the electrode forming the electric field;
Registering control parameters created based on temperature dependent characteristics of the semiconductor detector in a database;
Processing the response signal based on the control parameter to derive an energy value of the radiation, and a method for measuring radiation. On the computer,
Moving electrons / holes generated by radiation incident on the semiconductor detector in opposite directions along the electric field,
Receiving the response signal of the electrons / holes transferred to the electrode forming the electric field;
Registering a control parameter created based on the temperature-dependent characteristics of the semiconductor detector in a database;
A step of processing the response signal based on the control parameter to derive an energy value of the radiation is executed.

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