JP2002328173A - Radiation measuring method and radiation measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize the improvement of time stability of an ordinary temperature semiconductor detector by simple monitoring and a resetting device. SOLUTION: This radiation measuring device using the semiconductor detector 1 is provided with a means 4 for observing a drift amount of an output signal of the semiconductor detector; a means 5 for comparing the drift amount with a predetermined threshold value; and a means 6 for resetting the drift on the basis of the relation between the drift amount and the threshold value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation measuring apparatus using a normal temperature semiconductor detector, and more particularly to a radiation measuring apparatus which resets a drift of an output signal of a normal temperature semiconductor detector and enables continuous operation for a long time. About.

[0002]

2. Description of the Related Art In normal temperature semiconductors such as CdTe and CZT, when radiation enters a crystal, electron pairs (electrons and holes) having a charge amount proportional to the energy of the incident radiation are generated. The room temperature semiconductor detector measures the energy of incident radiation by applying an electric field to the semiconductor and collecting the electron pairs.

In such a room-temperature semiconductor radiation detector, generally, since the mobility of charges in a crystal is small, charges are trapped by crystal defects or the like with the passage of time, and space charges are formed. If the junction between the electrode formed on the room temperature semiconductor crystal and the room temperature semiconductor to apply an electric field is a Schottky junction, the electric field inside the crystal is distorted by this space charge, and the signal from the room temperature semiconductor detector is low. It has the drawback that it drifts to the energy side and correct energy information cannot be obtained for a long time.

FIG. 11 shows a conventional example. In FIG.
The signal of the room temperature semiconductor detector 1 is amplified by the charge-sensitive preamplifier 2, and the signal from the charge-sensitive preamplifier 2 is subjected to wave height analysis by the multiplex wave height analyzer 3.

FIG. 12 shows a spectrum of a multiple height analyzer when measured by the conventional radiation measuring apparatus shown in FIG. As shown in FIG. 12, the spectrum immediately after the application of the voltage drifts to the low energy side with the passage of time. Therefore, FIG.
However, a stable spectrum cannot be obtained over a long period of time with the conventional radiation measuring apparatus shown in FIG.

[0006]

By the way, in the above-described wave height analysis of a normal temperature semiconductor radiation detector, space charge is formed in the semiconductor with the passage of time, and the internal electric field is distorted. Has shifted to the low energy side, and there has been a disadvantage that a stable spectrum cannot be obtained for a long time.

The present invention has been made in view of such circumstances, and has as its object to provide a radiation measuring method and a radiation measuring apparatus using a semiconductor detector capable of obtaining a stable spectrum for a long time. And

[0008]

According to a first aspect of the present invention, there is provided a method for measuring radiation using a semiconductor detector, the method comprising: measuring a drift amount of a signal output from the semiconductor detector; And the threshold value obtained in advance, or the correlation between the installation condition of the semiconductor detector and the reset execution time obtained in advance, when the drift amount exceeds the threshold value or every time a predetermined time elapses. And a radiation measurement method characterized by resetting a drift.

According to a second aspect of the present invention, in the radiation measuring method according to the first aspect, the drift amount of the semiconductor detector output signal includes a change with time of a leak current, a distribution of a slope of a rising edge of the semiconductor detector output signal, and a semiconductor detection. A radiation measurement method, wherein the estimation is performed based on at least one of the maximum values of the rising slope of the detector output signal.

According to a third aspect of the present invention, in the radiation measuring apparatus using the semiconductor detector, means for observing a drift amount of the output signal of the semiconductor detector and means for comparing the drift amount with a predetermined threshold value. And a means for resetting the drift based on the relationship between the amount of drift and the threshold value.

According to a fourth aspect of the present invention, in a radiation measuring apparatus using a semiconductor detector, a means for setting a time for performing a reset according to installation conditions of the apparatus, and an output signal of the semiconductor detector at regular intervals are provided. Means for resetting the drift.

According to a fifth aspect of the present invention, there is provided a radiation measuring apparatus, as means for resetting the drift according to the third or fourth aspect, further comprising means for irradiating light having energy corresponding to the band gap of the semiconductor. I will provide a.

According to a sixth aspect of the present invention, as means for irradiating light of energy corresponding to the band gap of the semiconductor according to the seventh aspect, a scintillator which emits light at an energy wavelength corresponding to the band gap and an emission wavelength band are limited. Provided is a radiation measurement device including a filter.

According to a seventh aspect of the present invention, in the radiation measuring apparatus according to the first or second aspect, before resetting the drift, there is provided means for switching in advance the outputs of a plurality of flat detectors. Provided is a radiation measurement apparatus characterized by the following.

According to the present invention, the following effects can be obtained. That is, by observing the drift amount of the semiconductor detector output signal, comparing the drift amount with a predetermined threshold, and resetting the drift, the drift is reset when the drift amount exceeds the threshold. It is possible to obtain a stable output for a long time.

A stable output can be obtained over a long period of time by setting the time for resetting according to the installation conditions of the apparatus and resetting the drift of the semiconductor detector output signal at regular intervals. By measuring the temperature of the installation location and calculating the time for performing the reset from the measured temperature from the correlation obtained in advance, it is possible to obtain a stable output with respect to the temperature change of the installation location.

The drift amount of the output signal of the semiconductor detector can be estimated by measuring the leak current of the semiconductor detector and monitoring the change over time of the leak current. By monitoring the rising edge of the semiconductor detector output signal,
The drift amount of the semiconductor detector output signal can be estimated from the obtained semiconductor detector signal rising portion. By monitoring the maximum value of the slope of the rising edge of the output signal of the semiconductor detector, the drift amount of the output signal of the semiconductor detector can be estimated from the change with time of the maximum value of the slope.

By irradiating light of energy corresponding to the band gap of the semiconductor, space charges formed in the semiconductor detector can be reset. By providing a scintillator that emits light at an energy wavelength corresponding to the band gap and a filter that limits the emission wavelength band, light corresponding to the band gap can be irradiated according to the incidence of radiation. By previously switching the outputs of a plurality of detectors provided in a plane before resetting the drift, a plurality of detectors arranged in a plane with a substantially same spatial position with respect to the measurement target can be obtained. The detector output can be switched prior to reset to reduce or eliminate dead time due to reset.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

First Embodiment (FIG. 1) FIG. 1 shows an apparatus configuration according to a first embodiment. As shown in FIG. 1, in the apparatus of the present embodiment, a semiconductor detector 1, a charge-sensitive preamplifier 2, a multiplex height analyzer 3, a drift monitoring means 4, and a comparator 5 are sequentially connected.
Is input to the drift reset means 6, and a reset command for the semiconductor detector is output.

The semiconductor detector 1 is, for example, CdTe, CZT
The signal of the semiconductor detector 1 is amplified by a charge-sensitive preamplifier 2, and the signal from the charge-sensitive preamplifier 2 is subjected to wave height analysis by a multiplex wave height analyzer 3.

The drift amount of the output signal from the semiconductor detector 1 is obtained by the drift monitoring means 4. The comparator 5 compares the calculated drift amount with a predetermined threshold value, and when the drift amount exceeds the threshold value, the semiconductor detector output signal drift is reset by the drift reset means 6. You. Note that estimation of a drift value and the like in the present embodiment are the same as those in the second embodiment described below, and will be described in the second embodiment.

According to the above-described first embodiment, the change over time of the semiconductor detector 1 is monitored and the change over time can be reset, so that a stable spectrum can be obtained for a long time. Become.

Second Embodiment (FIGS. 2 to 6) FIG. 2 shows an apparatus configuration according to a second embodiment. As shown in FIG. 2, in the apparatus of the present embodiment, a semiconductor detector 1, a charge-sensitive preamplifier 2, and a multiplex height analyzer 3 are sequentially connected to obtain an analysis value. On the other hand, a reset time determining means 7 is provided, and the set value from the reset time determining means 7 is input to the drift reset means 6, and a reset command for the semiconductor detector is output.

In this embodiment, the reset time determining means 7
In the above, the reset time is set according to the condition of the installation place of the apparatus, and the drift of the output signal of the semiconductor detector is reset by the drift reset means 6 at regular intervals.

FIG. 3 is an explanatory diagram of the reset time determining means 7 for setting the reset time. In FIG. 3, there is generally a certain correlation between the drift amount of the semiconductor detector output per unit time and the temperature, as indicated by the temperature on the horizontal axis and the drift amount per unit on the vertical axis. That is, as the temperature increases, the drift amount per unit time increases.

Therefore, in the present embodiment, the reset time is determined from the measured temperature and reset is performed within a range that does not affect the required accuracy of the apparatus from the correlation. The means 4 for observing the drift amount in FIG. 1 shown in the first embodiment described above and FIG.
This will be described with reference to (a) to (c).

As for drift monitoring, when there is no change in the surrounding radiation, the drift amount can be estimated from the history of the spectrum. However, in actual operation, the surrounding radiation changes, and it may be difficult to estimate the amount of drift from the history of the spectrum.

FIG. 4A is a diagram for explaining a method of monitoring a leak current and estimating a drift amount. A proportional correlation is observed between the leak current shown on the horizontal axis and the drift amount shown on the vertical axis in FIG. Based on this correlation, an allowable leakage current range is obtained from a drift amount that does not hinder the required accuracy of the device, and the drift amount can be monitored by monitoring the leak current.

Next, means for monitoring the rising portion of the output signal of the semiconductor detector and estimating the drift amount will be described with reference to FIG. As shown in FIG. 4B, the rise of the output signal of the semiconductor detector is generally caused by a signal due to the movement of electrons, a component in which the signal due to the movement of holes overlaps (a fast component indicated by a solid line), and A subsequent component (slow component indicated by a broken line) due to the movement of only holes.

The slope of the rise of these signals is proportional to the intensity of the electric field applied to the crystal. When drift occurs, a space charge that cancels the electric field applied in the crystal is formed, and therefore, the rising slope of the signal becomes small as shown in FIG. Therefore, by monitoring the slope distribution of the semiconductor detector output signal,
The drift amount can be estimated.

FIG. 4C is an explanatory diagram of a method of monitoring the rising portion of the output signal of the semiconductor detector.
As described above with reference to FIG. 4B, it is possible to estimate the drift amount by monitoring the distribution of the slope of the output signal of the semiconductor detector, but the mobility of the holes depends on the formation of space charges. And the slope of the signal is
It is considered that the inclinations are variously distributed as shown in FIG. Therefore, by monitoring the maximum value of the gradient distribution, it is possible to effectively monitor the change in the electric field in the crystal. Then, the drift of the semiconductor detector output can be estimated by a simple process. The drift amount can be monitored by monitoring the drift of the output signal of the standard source using the standard source.

Next, the drift reset means 6 of the semiconductor detector output signal in the configuration shown in FIGS. 1 and 2 will be described with reference to FIG.

For resetting the drift, a means for relaxing the space charge is required, and the high voltage power supply of the semiconductor detector is turned off.
F is conceivable. FIG. 5 is a schematic diagram of resetting the drift by irradiating light with energy corresponding to the band gap of the semiconductor as a method of relaxing space charge without turning off the high-voltage power supply. As shown in FIG. 5, since the mobility of electric charge is low in a normal-temperature semiconductor, the electric charge is trapped in a level between the valence band and the conduction band.

When the junction between the semiconductor crystal and the electrode is a Schottky junction, the trapped charge is not relaxed, and the space charge is formed in the crystal, thereby distorting the internal electric field and causing drift of the output signal. To mitigate this space charge,
Light with a wavelength having energy equivalent to the band gap of a semiconductor is irradiated. For example, when the semiconductor is CdTe, the light may be emitted from a light-emitting diode (for example, GaAlAs) in an infrared region that has a band gap of 1.47 keV and emits light at substantially the same energy wavelength.

The trapped charges are excited to the conduction band by the irradiated light, the space charges disappear, and the drift phenomenon is reset. According to this method, space charge can be alleviated without having to turn off the high-voltage power supply of the detector.

Next, a method of irradiating light with energy corresponding to the band gap of the semiconductor will be described with reference to FIG. As a method of irradiating light corresponding to the band gap, irradiation of light from a light emitting diode or the like can be considered.
In many cases, a light source such as a light emitting diode requires a power supply, but a method that does not require a power supply is also possible. FIG. 6 is a schematic diagram showing a case where light is emitted using a scintillator that emits light at a wavelength of energy corresponding to the band gap of the semiconductor and a filter that limits the emission wavelength band. As shown in FIG. 6, the scintillator emits light due to the incidence of radiation, the emission wavelength is limited by a filter that limits the emission wavelength, and the space charge can be reset in the same manner as in the principle shown in FIG. That is, the use of the scintillator has the advantage that the drift can be reset without using a power supply.

Third Embodiment (FIG. 7) FIG. 7 shows an apparatus configuration according to a third embodiment. As shown in FIG. 7, the device of this embodiment is basically the same as that of the first embodiment, and includes a semiconductor detector 1, a charge-sensitive preamplifier 2, a multiplex height analyzer 3, and a drift monitoring means 4. , The comparator 5 is sequentially connected, the result of comparison in the comparator 5 is input to the drift reset means 6, and a reset command for the semiconductor detector is output.

In this embodiment, a plurality of ordinary temperature semiconductor detectors 1 to 1 ′ are installed in a plane, and the signals of the ordinary temperature semiconductor detectors 1 to 1 ′ are charged-sensitive. It passes through a changeover switch 8 connected to the former stage of the die preamplifier 2. The individual signals passing through the changeover switch 8 are input to the charge-sensitive preamplifier 2, and the signal amplified by the charge-sensitive preamplifier 2 is subjected to wave height analysis by the multiplex wave height analyzer 3.

In this embodiment having such a structure,
As in the first embodiment described above, the drift amount is obtained by the drift monitoring means 4 for observing the drift amount of the semiconductor detector output signal, and the drift amount obtained by the comparator 5 is compared with a predetermined threshold value. The drift can be reset by the drift reset means 6 of the semiconductor detector output signal when the threshold value is exceeded.

In the present embodiment, the changeover switch 8 is provided after the normal temperature semiconductor detectors 1 to 1 'and before the charge-sensitive preamplifier 2, but the present invention is not limited to this. It is also possible to provide a charge-sensitive preamplifier in the same number as that described above, and to provide a changeover switch 8 at the subsequent stage.

Fourth Embodiment (FIGS. 8 and 9) FIG. 8 shows an apparatus configuration according to a fourth embodiment. As shown in FIG. 8, this embodiment is basically based on the configuration of FIG. 2 shown in the second embodiment, and is a case where a plurality of ordinary temperature semiconductor detectors 1 to 1 ′ are applied.

That is, in the present embodiment, as shown in FIG. 8, signals of a plurality of normal-temperature semiconductor detectors 1 to 1 ′ arranged in a plane are transferred via a changeover switch 8 to a charge-sensitive preamplifier. 2, the signal from the charge-sensitive preamplifier 2 is subjected to wave height analysis by a multiplex wave height analyzer 3.

In this case, in this embodiment, a reset time determining means 7 for setting a reset time according to the condition of the installation place is installed, and the reset time is set in the reset time determining means 7, and the drift reset is performed at regular time intervals. The drift of the semiconductor detector output signal is reset by the means 6.

In this embodiment, similarly to the second embodiment, the reset execution time is set in accordance with the installation conditions of the apparatus, and the drift of the semiconductor detector output signal is reset at regular time intervals. A stable output can be obtained for a long time.

Incidentally, as described in the third embodiment, the changeover switches 8 may be provided after the charge-sensitive preamplifier provided in the same number as the semiconductor detectors.

FIG. 9 is an explanatory diagram of a method of switching the detector output before resetting the drift.
FIGS. 7A and 7B show states viewed from different sides.

As shown in these figures, a changeover switch 8 is connected to a plurality of semiconductor detectors arranged in a plane, and when the observed drift amount exceeds a threshold value, or when a predetermined reset is performed. When the time has elapsed, the detector 1 is switched by the changeover switch 8 immediately before resetting the drift of the detector 1.
By switching the detector 1 by the changeover switch 8, the dead time of measurement can be reduced or eliminated.

The changeover switches 8 may be provided at the subsequent stage of the charge-sensitive preamplifier 2 provided in the same number as the number of the detectors 1.

FIG. 10 shows a case where the drift of the output of the semiconductor detector is reset by irradiating light corresponding to the band gap of the semiconductor in each of the above embodiments, as compared with the case of FIG. 12 of the conventional example. 3 shows a spectrum of a multi-wave height analyzer.

As shown in FIG. 10, in the case of the present invention, the spectrum immediately after voltage application drifts to the low energy side with the passage of time, whereas the spectrum is shifted to the high energy side by light irradiation. I have. Therefore,
According to the present invention, it is possible to improve the time stability of a room-temperature semiconductor detector and obtain a stable spectrum over a long time, as compared with the conventional radiation measuring apparatus shown in FIG. It has been recognized.

[0052]

As described in detail above, according to the present invention, a simple monitoring and resetting device can improve the time stability of a room-temperature semiconductor detector, and is a practically extremely effective radiation measuring device. And the device can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a radiation measuring apparatus according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram showing a radiation measurement device according to a second embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a method for determining a reset time according to an installation environment of an apparatus according to a second embodiment of the present invention.

FIGS. 4A, 4B, and 4C are explanatory diagrams showing a method for observing a drift amount according to a second embodiment of the present invention.

FIG. 5 is an explanatory view showing a drift reset method of a conductor detector according to a second embodiment of the present invention.

FIG. 6 is an explanatory view showing a method of irradiating light according to a band gap using a scintillator according to a second embodiment of the present invention.

FIG. 7 is a configuration diagram showing a radiation measuring apparatus according to a third embodiment of the present invention.

FIG. 8 is a configuration diagram showing a radiation measurement device according to a fourth embodiment of the present invention.

FIGS. 9A and 9B are explanatory diagrams showing a method for switching the output of a detector before resetting according to a fourth embodiment of the present invention.

FIG. 10 is a diagram showing an example of drift reset of an output of a semiconductor detector due to light irradiation.

FIG. 11 shows a conventional example.

FIG. 12 is a graph showing an example of a semiconductor detector drift phenomenon.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor detector 2 Charge sensitive preamplifier 3 Multi-wave height analyzer 4 Drift monitoring means 5 Comparator 6 Drift reset means 7 Reset time determination means 8 Changeover switch

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Mikio Izumi 2-1 Ukishima-cho, Kawasaki-ku, Kawasaki-ku, Kanagawa Prefecture Inside the Toshiba Hamakawasaki Plant (72) Inventor Akira Yuzuki 1-Toshiba-cho, Fuchu-shi, Tokyo Toshiba Fuchu Works (72) Inventor Soichiro Morimoto 8 Shinsugita-machi, Isogo-ku, Yokohama-shi, Kanagawa Prefecture F-term in Toshiba Yokohama Works Co., Ltd. 5F088 AB09 BA10 JA17 KA02 KA06 LA07

Claims (7)

[Claims] 1. A method for measuring radiation using a semiconductor detector, wherein a relationship between a drift amount of a signal output from the semiconductor detector and a predetermined threshold value, or a predetermined installation of the semiconductor detector is provided. A radiation measurement method, wherein the drift is reset based on a correlation between a condition and a reset execution time when the drift amount exceeds a threshold value or every time a predetermined time elapses. 2. The radiation measuring method according to claim 1, wherein the drift amount of the output signal of the semiconductor detector includes a change with time of a leak current, a distribution of a slope of a rise of the output signal of the semiconductor detector, and a slope of a rise of the output signal of the semiconductor detector. A radiation measurement method which estimates based on at least one of the maximum values. 3. A radiation measuring apparatus using a semiconductor detector, a means for observing a drift amount of an output signal of the semiconductor detector, a means for comparing the drift amount with a predetermined threshold, and a threshold for the drift amount. Means for resetting the drift based on the relationship with the value. 4. A radiation measuring apparatus using a semiconductor detector, wherein: means for setting a time for performing resetting according to the installation conditions of the apparatus; and means for resetting a drift of an output signal of the semiconductor detector at regular intervals. A radiation measuring device comprising: 5. A radiation measuring apparatus according to claim 3, further comprising means for irradiating light having energy corresponding to the band gap of the semiconductor, as the means for resetting the drift according to claim 3 or 4. 6. A means for irradiating light of energy corresponding to a band gap of a semiconductor according to claim 7, comprising a scintillator which emits light at an energy wavelength corresponding to the band gap and a filter which limits a light emission wavelength band. Characteristic radiation measurement device. 7. The radiation measuring apparatus according to claim 1, further comprising means for switching in advance the outputs of a plurality of planar detectors before resetting the drift. .