JP2015099015A - Radiation detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiation detector capable of measuring low dose with a simple structure.SOLUTION: The radiation sensor is structured including: a sealed space in which a pair of electrodes is disposed and filled with a radiation detecting gas; and insulator layers of a dielectric material formed to cover the electrodes. The radiation sensor is configured to measure radiation in the following two steps; i.e.: a radiation detection period T1, in which a voltage is applied across the pair of electrodes to accumulate electric charge on the insulator layers by means of entering radiation; and a radiation measurement period T2 in which, after the radiation detection period, a voltage biased inversely to the voltage which is applied across the electrodes in the radiation detection period, is applied to the electrodes to discharge and measure the radiation. After the radiation measurement period, a reset period is set for discharging to adjust the electric charge on the insulator layers.

Description

  The present invention relates to a radiation detection apparatus that detects radiation by collecting electrons and ions of gas ionized by radiation.

  This type of radiation detection device has a cathode and an anode in a gas-sealed container, applies a voltage between them, and collects electrons and ions of the gas ionized by radiation to the electrode to detect radiation. .

  A voltage / electrode configuration that does not amplify the gas ionization signal due to radiation due to the voltage applied between the cathode and anode is called an ionization chamber. A device with a voltage / electrode configuration is called a proportional coefficient method.

  Conventionally, a radiation detection apparatus has a thin anode disposed at the center of a cylindrical container sealed as a cathode, and an ionized gas obtained by adding an organic gas to, for example, argon (Ar) gas is enclosed in the container. It is comprised by. In this radiation detection apparatus, the radiation ionizes the ionized gas in the container and moves by the electric field applied between the cathode and the anode. At this time, electrons cause avalanche particularly near the anode, and radiation is counted as a large pulse signal.

Detection is performed by changing the type of ionized gas depending on the energy of radiation, such as X-rays and γ-rays. That is, for low energy X-rays, a gas with a large absorption coefficient and a large atomic number is used. On the other hand, neutrons do not ionize the gas, so helium (which causes charged particles by causing a nuclear reaction with the neutrons) the He ₃₎ and 3 and those using boron fluoride (BF ₃₎ gas such as, boron 10 (B ₁₀₎ and uranium 235 (U ₂₃₅₎ or the like is applied to the container used as a cathode, where converted into charged particles In addition, there is a configuration in which detection is performed by the same ionizing action (see, for example, Patent Documents 1, 2, and 3).

Japanese Patent Laid-Open No. 07-169438 JP 2002-181948 A Japanese Patent Laid-Open No. 2002-14171

  An object of the present invention is to provide a radiation detection apparatus capable of measuring a low dose with a simple configuration under such circumstances.

  In order to solve such a problem, the present invention forms an insulator layer made of a dielectric material so as to enclose a gas for radiation detection in a sealed space in which a pair of electrodes are arranged, and to cover the electrodes. The radiation sensor is configured, and at the time of radiation measurement, a voltage is applied between the pair of electrodes and a radiation detection period in which charges are accumulated on the insulator layer by incident radiation, and after the radiation detection period A radiation measurement period in which discharge is generated by applying a voltage reverse to the voltage applied to the electrode during the radiation detection period; and a discharge for adjusting the charge on the insulator layer after the radiation measurement period. And a reset period for generating radiation, and the radiation is measured by the radiation detection period and the radiation measurement period.

  According to the present invention, in the radiation detection period, the amount of charge accumulated in the insulator layer according to the radiation dose is used to measure the amount of voltage drop at the start of discharge. It is possible to realize a radiation detection apparatus that can measure and can measure a low dose with a simple configuration.

Sectional drawing which shows the sensor part of the radiation detection apparatus by one embodiment of this invention The figure for demonstrating the principle of operation of the radiation detection apparatus by this invention In the radiation detection apparatus according to the present invention, a voltage waveform diagram showing applied voltages in a radiation detection period and a measurement period Voltage waveform diagram for explaining a radiation measurement cycle in the radiation detection apparatus according to the present invention. The figure for demonstrating the measurement cycle of a radiation in the radiation detection apparatus by this invention The disassembled perspective view which shows the sensor part of the radiation detection apparatus by other embodiment of this invention.

  Hereinafter, a radiation detection apparatus according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view showing a schematic configuration of a sensor portion of a radiation detection apparatus according to an embodiment of the present invention.

  As shown in FIG. 1, the first sensor substrate 1 and the second sensor substrate 2 are arranged to face each other with a predetermined interval with a spacer 3 made of glass interposed therebetween, and the first sensor substrate 1 and the second sensor substrate 2. A sealed space 5 is formed by sealing between the substrate 1 and the second sensor substrate 2 and the spacer 3 with a sealing material 4. The sealed space 5 includes He, Ne, Ar, Kr, and Xe that are ionized by radiation A such as X-rays and γ-rays transmitted through the first sensor substrate 1 and the second sensor substrate 2. One or more selected gases are enclosed, thereby constituting a radiation sensor. In addition, organic gas etc. are contained in the gas ionized by radiation as needed.

  In the first sensor substrate 1 and the second sensor substrate 2, electrodes 8 and 9 made of Ag are formed on insulating substrates 6 and 7 that can transmit radiation made of soda glass, respectively. Insulating layers 10 and 11 made of a lead-free dielectric material are formed on the insulating substrates 6 and 7 so as to cover them.

Here, as the lead-free dielectric material that does not contain lead constituting the insulator layers 10 and 11, bismuth oxide (Bi ₂ O ₃ ), zinc oxide (ZnO), and boron oxide (B ₂ O ₃ ) are mainly used. The main components are silicon oxide (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ), calcium oxide (CaO), strontium oxide (SrO), barium oxide (BaO), molybdenum oxide (MoO ₃ ), oxidation A lead-free glass dielectric material constituted by containing tungsten (WO ₃ ), cerium oxide (CeO ₂ ) or the like is used.

  A dielectric material powder is prepared by pulverizing a dielectric material composed of these composition components with a wet jet mill or a ball mill so that the average particle diameter is 0.5 μm to 2.5 μm. And a binder component are well kneaded with three rolls to produce a dielectric layer paste for die coating or printing. The binder component is terpineol or butyl carbitol acetate containing 1% to 20% by weight of ethyl cellulose or acrylic resin. In addition, dioctyl phthalate, dibutyl phthalate, triphenyl phosphate and tributyl phosphate are added to the paste as needed, and glycerol monooleate, sorbitan sesquioleate, homogenol (Kao Corporation) as a dispersant. The printability may be improved by adding a phosphoric ester of an alkyl allyl group or the like.

  The dielectric paste thus produced is printed by screen printing or die coating and dried, and then fired at 550 ° C. to 590 ° C., which is slightly higher than the softening point of the dielectric material. 10 and 11 are formed. In addition, about the film thickness of the insulator layers 10 and 11, about 40 micrometers is preferable.

  Next, the detection operation principle of the radiation detection apparatus according to the present invention will be described with reference to FIG.

  First, as shown in FIG. 2A, a voltage of several hundred volts is applied to the radiation sensor shown in FIG. 1 such that the electrode 8 side of the first sensor substrate 1 is positive and the electrode 9 side of the second sensor substrate 2 is negative. To do. When radiation A enters in this state, the gas in the sealed space 5 of the radiation sensor is ionized, and electron / ion pairs are generated.

  As shown in FIG. 2B, the generated electrons and ions are applied between the electrode 8 of the first sensor substrate 1 and the electrode 9 of the second sensor substrate 2 of the radiation sensor. As a result, negative charges are accumulated on the insulator layer 10 side of the first sensor substrate 1 and positive charges are accumulated on the insulator layer 11 side of the second sensor substrate 2. At this time, charges are only accumulated in the insulator layer 10 of the first sensor substrate 1 and the insulator layer 11 of the second sensor substrate 2, and no current flows.

  The period shown in FIGS. 2A and 2B is a radiation detection period, and the insulator layer 10 of the first sensor substrate 1 and the insulator layer of the second sensor substrate 2 according to the amount of incoming radiation. Therefore, a difference occurs in the amount of electric charge accumulated in 11.

  Next, when measuring the detected radiation dose, as shown in FIG. 2 (c), the electrode 8 side of the first sensor substrate 1 is minus, as shown in FIG. 2 (a), and the second sensor substrate. A reverse bias voltage of several hundred volts is applied so that the second electrode 9 side is positive, and a discharge is generated between the first sensor substrate 1 and the second sensor substrate 2. At this time, a low voltage is applied according to the amount of charge accumulated in the insulator layer 10 of the first sensor substrate 1 and the insulator layer 11 of the second sensor substrate 2, that is, the amount of radiation detected in the radiation detection period. Discharging starts. By measuring the voltage drop at the start of discharge, the radiation dose detected in the radiation detection period can be measured.

  More specifically, at the end of the accumulation period, which is a radiation detection period, a certain amount of charge having a polarity opposite to the applied voltage proportional to the radiation dose is accumulated on the surfaces of the insulator layers 10 and 11. In order to measure this electric charge, when a bias voltage opposite to the accumulation period is applied between the electrodes 8 and 9, an electric field corresponding to the applied voltage + accumulated voltage (voltage due to accumulated charge) is applied to the gas space. Since discharge occurs at a lower voltage than when there is no stored voltage, the stored voltage can be measured by measuring the voltage difference.

For example, if the applied voltage V ₀ , the storage voltage V, and the discharge start voltage are Vf, Vf = V ₀ + V. By increasing the applied voltage V ₀ in a staircase shape or a pulse shape, the timing at which the discharge occurs can be changed to discharge light emission or If observed with a current signal or the like, V ₀ can be measured. Since Vf is a value determined by the structure and gas composition, the accumulated voltage V can be obtained. Further, the accumulated voltage V is known from the capacitance C of the insulator layers 10 and 11 and the accumulated charge Q according to the relationship of Q = CV, the dielectric material forming the insulator layers 10 and 11, the thickness, and the electrode shape. Since the capacity can be calculated, the accumulated charge Q proportional to the radiation dose can be obtained.

  As described above, in the radiation detection apparatus according to the present invention, the first sensor substrate 1 and the second sensor substrate 2 are disposed in a sealed space 5 formed so as to face each other with a predetermined interval therebetween. The first sensor substrate 1 and the second sensor substrate 2 of the radiation sensor include electrodes 8 on insulating substrates 6 and 7 that can transmit radiation, respectively. 9 and forming the insulator layers 10 and 11 made of a dielectric material on the insulating substrates 6 and 7 so as to cover the electrodes 8 and 9, and in the radiation detection period, The first sensor substrate 1 and the second sensor substrate are obtained by utilizing the amount of charge accumulated in accordance with the radiation dose in the insulator layer 10 of the first sensor substrate 1 and the insulator layer 11 of the second sensor substrate 2. Radiation measurement that generates electric discharge between In the period, by measuring the voltage drop amount of starting discharge, it is capable of measuring the amount of radiation detected by the radiation detection period.

  FIG. 3 is a voltage waveform diagram showing applied voltages in a radiation detection period and a measurement period in a radiation detection apparatus according to another embodiment of the present invention. In FIG. 3, 21 is a voltage waveform applied to the electrode 8 side of the first sensor substrate 1 as shown in FIG. 2A, and 22 is the electrode 9 side of the second sensor substrate 2 on the radiation A incident side. It is a voltage waveform applied to. T1 is a radiation detection period, and T2 is a radiation measurement period.

  As enclosed by the frame line in FIG. 3, in the present embodiment, in the radiation measurement period T2, the radiation measurement period T1 and the electrode 8 of the first sensor substrate 1 and the electrode 9 of the second sensor substrate 2 are Is configured to apply ramp voltage waveforms 21a and 22a in which the voltage gradually changes when a reverse bias voltage is applied. That is, in the radiation measurement period T2, the voltage waveform 21 applied to the electrode 8 side of the first sensor substrate 1 is applied with the ramp voltage waveform 21a in which the voltage gradually decreases and becomes a negative potential, and the radiation A is incident. As for the voltage waveform 22 applied to the electrode 9 side of the second sensor substrate 2 that is the side, a ramp voltage waveform 22a is applied in which the voltage gradually rises and becomes a positive potential.

  As described above, in the radiation measurement period T2, when a voltage having a reverse bias to that of the radiation measurement period T1 is applied to the electrode 8 of the first sensor substrate 1 and the electrode 9 of the second sensor substrate 2, the voltage gradually increases. By applying the changing ramp voltage waveforms 21a and 22a, as described in FIG. 2, when measuring the accumulated radiation dose by measuring the voltage when the discharge occurs, the steep pulse waveform By controlling the slope of the ramp voltage waveform, it is possible to easily and accurately measure the discharge generation voltage as compared with the case of measuring by applying a voltage. In addition, the ramp voltage waveform is a waveform whose voltage value changes with the application time, so the voltage at which the discharge occurs can be measured by converting it to the application time, and the detection result can be displayed digitally. The circuit configuration can be easily realized.

  4 and 5 are diagrams for explaining a measurement cycle of the radiation detection apparatus according to the present invention. FIG. 4 is a voltage waveform diagram showing an applied voltage in the measurement cycle of the radiation detection apparatus according to the present embodiment. FIG. It is the schematic for demonstrating operation | movement of the radiation detection apparatus in the measurement cycle. In FIG. 5, (1) to (9) indicate concepts of states corresponding to (1) to (9) in FIG.

  As shown in FIGS. 4 and 5, in the radiation detection apparatus according to the present invention, one cycle of radiation measurement includes a radiation detection period T1, a radiation measurement period T2, and a reset period T3.

  In the initial detection period (1) of the radiation detection period T1, only a voltage of several hundred volts is applied so that the electrode 8 side of the first sensor substrate 1 is positive and the electrode 9 side of the second sensor substrate 2 is negative. Since no radiation is incident on the radiation sensor, the insulator layers 10 and 11 of the first sensor substrate 1 and the second sensor substrate 2 are not charged with radiation. is there.

  When radiation A enters in the middle of the detection period (2), the gas in the sealed space 5 of the radiation sensor is ionized to generate electron / ion pairs, and the electrodes 8 and 2 of the first sensor substrate 1 are generated. The negative electric charge is gradually accumulated on the insulator layer 10 side of the first sensor substrate 1 by the electric field applied between the electrode 9 of the sensor substrate 2 and the insulation of the second sensor substrate 2. Positive charges are gradually accumulated on the body layer 11 side. Further, when radiation A enters in the middle of the detection period (3), electric charges are added and accumulated in the insulator layer 10 of the first sensor substrate 1 and the insulator layer 11 of the second sensor substrate 2. Is done.

  At the end of the detection period (4), the charge proportional to the incident radiation dose is accumulated in the insulator layer 10 of the first sensor substrate 1 and the insulator layer 11 of the second sensor substrate 2.

  Next, in the initial measurement period (5) of the radiation measurement period T2 for measuring the detected radiation dose, the electrode 8 side of the first sensor substrate 1 is minus, and the electrode 9 side of the second sensor substrate 2 is plus several hundred volts. The reverse bias voltage is applied. At this time, ramp voltage waveforms 21a and 22a are applied.

  Thereafter, in the middle period (6) of the measurement period, discharge is generated by an electric field of applied voltage + accumulated voltage (voltage due to accumulated charge). As described above, at this time, discharge occurs at a lower voltage than in the case where there is no accumulated voltage. Therefore, the accumulated voltage corresponding to the accumulated radiation dose can be measured by measuring the voltage difference. In the latter part (7) of the measurement period in which the measurement is completed, a positive charge is accumulated on the insulator layer 10 side of the first sensor substrate 1 by the discharge generated in the middle part (6) of the measurement period, and the second Negative charges are accumulated on the insulator layer 11 side of the sensor substrate 2.

  Therefore, after the radiation measurement period T2 ends, a reset period T3 is provided to return the charge in the radiation sensor to the initial state of the radiation detection period T1. At the time of resetting (8) in the reset period T3, the insulator layer 10 of the first sensor substrate 1 is set by setting the electrode 8 of the first sensor substrate 1 and the electrode 9 of the second sensor substrate 2 to the ground potential. And a minute discharge corresponding to the charge accumulated in the insulator layer 11 of the second sensor substrate 2 occurs, and after resetting (9), the insulator layer 10 and the second layer of the first sensor substrate 1 of the radiation sensor The charges accumulated in the insulator layer 11 of the sensor substrate 2 are erased and the initial state is restored. That is, during the reset period T3, a charge adjustment discharge is generated for adjusting the charges of the insulator layers 10 and 11 of the first sensor substrate 1 and the second sensor substrate 2 to the state before the radiation enters. It is a period to let you.

  The above operation is one measurement cycle.

  Here, in this measurement cycle, it is desirable that the radiation detection period T1 in one cycle for measuring radiation is variable in radiation dose. When the radiation dose is large, the accumulation period is shortened to reduce the accumulated amount. Is good. Conversely, in the case of a low dose, by increasing the accumulation period as much as possible, the incident radiation increases and the sensitivity is improved. The variable period is, for example, several hundreds μs to several hundreds. The radiation measurement period T2 is preferably about several tens of μs to several ms.

  FIG. 6 is an exploded perspective view showing another example of a sensor portion in a radiation detection apparatus according to another embodiment of the present invention. In the embodiment shown in FIG. 6, a plurality of sensor portions are formed, and the sensor portions are two-dimensionally arranged in a matrix with m columns and n rows.

  As shown in FIG. 6, the first sensor substrate 31 and the second sensor substrate 32 are opposed to each other with a predetermined interval with a cross-shaped spacer 33 made of glass interposed therebetween. A plurality of sealed spaces 34 are formed by sealing between one sensor substrate 31 and the second sensor substrate 32 and the spacer 33 with a sealing material (not shown). The sealed space 34 includes He, Ne, Ar, Kr, and Xe ionized by radiation A such as X-rays and γ-rays transmitted through the first sensor substrate 31 and the second sensor substrate 32. One or more selected gases are sealed, thereby forming a plurality of sensor portions 35.

  The first sensor substrate 31 and the second sensor substrate 32 are made of electrodes 38 and 39 on a plurality of lines made of Ag on insulating substrates 36 and 37 that can transmit radiation made of soda glass, respectively. Insulating layers 40 and 41 made of a lead-free dielectric material are formed on the insulating substrates 36 and 37 so as to cover the electrodes 38 and 39. The dielectric material and the formation method for forming the insulator layers 40 and 41 are the same as those in the embodiment shown in FIG.

  When measuring radiation using a radiation sensor configured by arranging a plurality of sensor units 35 in two dimensions in this way, a voltage waveform is sequentially applied to each sensor unit 35 in the measurement cycle shown in FIG. Thus, it is possible to measure similarly.

  In addition, as in the present embodiment, a plurality of sensor units 35 are two-dimensionally arranged in a matrix to constitute a sensor, thereby making it possible to measure a radiation dose difference due to a difference in position of the sensor unit 35. Measurement of the direction in which the radiation enters is also possible.

  Furthermore, the sensitivity as a radiation detection apparatus can be improved by adding the radiation doses detected by the plurality of sensor units 35.

  In the above description, each of the first sensor substrate and the second sensor substrate is an insulating substrate that can transmit radiation made of soda glass. However, glass, resin, or the like is used on the surface of the metal substrate. An insulating material may be used to form an insulating substrate, or at least one insulating substrate may be formed by forming an insulating material such as glass or resin on the surface of a metal substrate.

  As described above, in the radiation detection apparatus according to the present invention, the gas for radiation detection is sealed in the sealed space 5 in which the pair of electrodes 8 and 9 are arranged, and the dielectric material is used so as to cover the electrodes 8 and 9. Insulator layers 10 and 11 are formed to constitute a radiation sensor, and the radiation sensor accumulates electric charges on the insulator layers 10 and 11 by ions and electrons generated by ionizing a gas by radiation. And a radiation detection period T1 in which a charge is accumulated on the insulator layers 10 and 11 by radiation incident upon applying a voltage between the pair of electrodes 8 and 9 when measuring radiation, and After the radiation detection period, a radiation measurement period T2 in which discharge is generated by applying a voltage reverse to the voltage applied to the electrodes 8 and 9 during the radiation detection period, and after the radiation measurement period, the insulator layer 1 , And a reset period T3 for generating a discharge for adjusting the electric charge on 11, and measuring the radiation. In the radiation detection period, the radiation is accumulated in the insulator layer according to the radiation dose. By using the amount of charge and measuring the voltage drop at the start of discharge, the amount of radiation detected in the radiation detection period can be measured, and a radiation detector that can measure low doses with a simple configuration is realized. be able to.

  As described above, the present invention is a useful invention that can provide a novel radiation detection apparatus.

DESCRIPTION OF SYMBOLS 1,31 1st sensor board | substrate 2,32 2nd sensor board | substrate 3,33 Spacer 5,34 Sealed space 6,7,36,37 Insulating board | substrate 8,9,38,39 Electrode 10,11,40,41 Insulator layer 21, 22 Voltage waveform 21a, 22a Ramp voltage waveform T1 Radiation detection period T2 Radiation measurement period T3 Reset period

Claims (2)

A radiation detection gas is sealed in a sealed space in which a pair of electrodes are arranged, and an insulating layer made of a dielectric material is formed so as to cover the electrodes, and a radiation sensor is formed. A radiation detection period in which charges are accumulated on the insulator layer by incident radiation by applying a voltage between the pair of electrodes; and a voltage applied to the electrodes in the radiation detection period after the radiation detection period; Provides a radiation measurement period in which a reverse bias voltage is applied to generate a discharge, and a reset period in which a discharge for adjusting the charge on the insulator layer is generated after the radiation measurement period, and the radiation detection period A radiation detection apparatus configured to measure radiation according to a radiation measurement period. The radiation detection apparatus according to claim 1, wherein the reverse bias voltage applied during the radiation measurement period is a ramp voltage waveform.

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