KR20010086670A - Multi-Functional Gamma Radiation Spectrometer and Detection Method Theirof - Google Patents

Abstract

PURPOSE: A device for analyzing radioactive gamma nuclide and a measuring method thereof are provided to analyze a small amount of radioactivity existing in a sample to be measured through installing an auxiliary detector. CONSTITUTION: An HPGe detector(1) is installed at a center. A vacuum chamber(18) filled with Si(Li) detector is located on the HPGe detector. The HPGe detector and the Si(Li) detector are covered by NaI(Tl) detectors. A cooling rod(3) of the HPGe detector is withdrawn from lower portions of the NaI(Tl) detectors. Herein, the cooling rod is stored in a liquid nitrogen container for cooling the HPGe detector. A plastic scintillation detector(28) is installed at an outer portion of a low level radioactivity shielding body of surrounding the HPGe detector, the Si(Li) detectors, and the NaI(Tl) detector. Then, the plastic detector is covered by an ordinary radioactive shielding body. The Si(Li) detector is inserted to an upper plate of the vacuum chamber for connecting cables. High voltage is supplied to the Si(Li) detector through the cables, and a signal from the Si(Li) detector is transferred to outside through the cables. A vacuum valve is arranged on the upper plate of the vacuum chamber for maintaining vacuum state of the vacuum chamber by using a vacuum hose. The vacuum hose and the cables are connected to outside through a gap between the NaI(Tl) detector and the HPGe detector.

Description

Multi-Functional Gamma Radiation Spectrometer and Detection Method Theirof}

The present invention is configured to analyze a small amount of radioactivity present in a sample to be measured by installing a secondary detector around a device for determining a radionuclide and radioactivity by measuring a gamma ray of a radioactive sample (hereinafter referred to as a gamma nuclide analyzer). The present invention relates to a gamma nuclide analyzer and a measuring method using an auxiliary detector.

More specifically, the apparatus of the present invention is a device related to HPGe detectors (1 to 10), devices related to Si (Li) surface barrier detectors (11 to 19, 9, 41), and devices related to NaI (Tl) scintillation detectors (20 to 20). 27, 9), plastic scintillation detector related devices (28-33, 9) and analysis module (43). Compton reduction technology, spacecraft impact reduction technology, Charged particle-gamma simultaneous measurement technology is applied.

The present invention is a means for measuring a trace amount of radioactivity using a gamma nucleus analyzer. In the related art, a device and a measurement method for reducing compton scattering or cosmic effect are applied to a gamma nucleus analyzer (LLKiang et al, Nuclear Instruments and Methods in Physics Research A327, 1993, 427-432) and Reeves (JHReeves et al, PNL-SA-14316), but have not been applied to the simultaneous measurement of charged particle-gamma.

Since the technique of the present invention can be used alone or in combination, it can optionally be used for the precise analysis of trace radionuclides.

The present invention improves the measurement performance of a gamma nucleus analyzer by simultaneously applying a device related to compton scattering reduction, spacecraft influence reduction, and charged particle-gamma simultaneous measurement to a gamma nuclide analyzer.

Detectors and related devices used in gamma nuclide analyzers should be made of materials with low radioactivity.

1 is a schematic representation of an apparatus associated with the operation of an HPGe detector

2 is a schematic representation of an apparatus associated with the operation of a Si (Li) surface barrier detector.

3 is a schematic representation of an apparatus associated with the operation of a NaI (Tl) scintillation detector;

4 is a schematic diagram of an apparatus associated with the operation of a plastic flash detector;

5 is a schematic diagram of a Compton scattering reduction device using a NaI (Tl) scintillation detector

6 is a schematic diagram of an apparatus for shielding a spacecraft using a plastic scintillation detector;

7 is a diagram illustrating a result of simultaneous measurement of gamma rays

8 shows Compton scattering reduction measurement results.

9 is a view showing the results of spacecraft shield measurement

10 is a cross-sectional view in which a Si (Li) surface barrier detector is installed in a NaI (Tl) scintillation detector and an HPGe detector.

11 is a sectional view in which a Si (Li) surface barrier detector, a NaI (Tl) scintillation detector and a plastic scintillation detector are installed in the overall system.

12 is a photograph of an analysis module for analyzing and processing a signal generated by a detector

<Description of the symbols for the main parts of the drawings>

1: HPGe detector 2: Preamplifier 3: Cooling rod

4: liquid nitrogen 5: liquid nitrogen communication 6: high voltage supply

7: amplifier 8: ADC 9: computer

10: power supply 11: vacuum pump 12: surface barrier detector

13: aluminum film 14: sample holder 15: high voltage supply

16: Preamplifier 17: Amplifier 18: Vacuum Room

19: ADC 20: NaI (Tl) annular detector 21: NaI (Tl) cylindrical detector

22, 22a to 22g: photomultiplier tube 23: photomultiplier tube

24: high voltage supply 25: high voltage supply 26: amplifier

27: ADC 28, 28a ~ 28l: plastic flash detector

29: high voltage supply 30: high voltage supply 31: high voltage supply

32: amplifier 33: ADC 34: sample

41: vacuum hose 42: cable

The apparatus of the present invention is an apparatus for detecting GaG nuclides (1 to 10) and an auxiliary detector used to improve the performance of the gamma nucleus analyzer. 9, 41, NaI (Tl) scintillation detector related devices 20 to 27, 9, plastic scintillation detector related devices 28 to 33, 9, and an analysis module (see Fig. 12).

The HPGe detector 1 is a device for detecting gamma rays emitted from radioactive samples. The HPGe detector 1 uses a cooling rod 3 in the liquid nitrogen cylinder 5 filled with the liquid nitrogen 4, and then cools it for about 6 hours. When a high voltage is applied to the cooled HPGe detector 1 by the high voltage supply 6, a current signal is generated in the HPGe detector 1 and amplified by passing through the preamplifier 2 supplied with power to the power supply 10. The current signal generated by the preamplifier 2 is amplified by a voltage signal through the amplifier 7, and converted into a digital signal through the ADC 8 and input to the computer 9. By converting the magnitude of the signal input to the computer 9 into gamma ray energy, the type and radioactivity of the gamma ray emitting nuclide can be determined.

The Si (Li) surface barrier detector 12 is a device for detecting charged particles such as alpha particles, beta particles, and protons emitted from radioactive samples. Since charged particles easily lose energy in the air, the space between the radioactive sample and the detector must be vacuumed. Therefore, the radioactive sample and the Si (Li) detector 12 are put in the vacuum chamber 18 and the air is removed by the vacuum pump 11 and then measured. When the high voltage generated from the high voltage supply 15 is supplied to the Si (Li) detector 12 through the preamplifier 16, a current signal is generated every time charged particles enter the Si (Li) detector 12. Amplified by a preamplifier 16, then amplified by a voltage signal via an amplifier 17, converted into a digital signal by the ADC 19, and input to the computer 9; The computer 9 determines the type of charged particle emitting nuclide by converting the magnitude of the input signal into charged particle energy. The Si (Li) surface barrier detector 12 is also used for simultaneous measurement of charged particle-gamma radiation as an auxiliary detector of a multifunctional gamma nuclide analyzer.

The NaI (Tl) scintillation detector is a device for detecting compton scattered gamma rays in the HPGe detector (1). Since the NaI (Tl) scintillation detector is more efficient around the HPGe detector 1, the HPGe detector 1 is inserted into one hole of the hollow cylindrical NaI (Tl) annular detector 20, and the opposite side The rod-shaped NaI (Tl) cylindrical detector 21 was inserted into the hole, and the NaI (Tl) scintillation detector was manufactured to surround the HPGe detector 1 as much as possible.

The NaI (Tl) annular detector 20 is supplied with a high voltage from the high voltage supply 24, and the NaI (Tl) cylindrical detector 21 is operated by being supplied with a high voltage from the high voltage supply 25. When the compton scattered gamma ray enters the NaI (Tl) annular detector 20, the generated current signal is amplified through the seven photomultiplier tubes 22a to 22g and input to the amplifier 26. When the compton-scattered gamma ray enters the NaI (Tl) cylindrical detector 21, the generated current signal is amplified through the photomultiplier tube 23, amplified by a voltage signal in the amplifier 26, and then the ADC 27 ) Is converted into a digital signal and input to the computer 9. This NaI (Tl) detector is used for compton scattering gamma ray reduction as an auxiliary detector of the multifunctional gamma nuclide analyzer.

Plastic flash detectors are devices that detect charged particles in spacecraft. The plastic scintillation detector is installed at the outermost side, and the more surrounding the entire measuring device, the better the measurement efficiency. Therefore, two plastic flash detectors were installed at the top and two at the bottom and eight at the bottom. The plastic flash detectors 28a and 28b at the upper end are supplied with a high voltage from the high voltage generator 31, and the plastic flash detectors 28c to 28j at the side are supplied with a high voltage from the high voltage generator 30, and the plastic flash detectors at the lower end are provided. 28k and 28l operate by receiving a high voltage from the high voltage generator 29. When radiation is incident on the plastic scintillation detectors 28a to 28l, the generated current signal is amplified by the preamplifier, amplified by the amplifier 32 again to a voltage signal, and then converted into a digital signal by the ADC 33 to be converted into a computer 9) is analyzed. This plastic scintillation detector is used as a secondary detector of the multifunctional gamma nuclide analyzer and is used to reduce spaceship effect.

The following describes the configuration and installation of the gamma nuclide analyzer.

<HPGe Detector, Si (Li) Detector, NaI (Tl) Detector>

The HPGe detector 1 is installed at the innermost side. Above the HPGe detector is placed a vacuum chamber 18 containing a Si (Li) surface barrier detector 12. The HPGe and Si (Li) detectors are covered with NaI (Tl) detectors 20 and 21 and only fall out. You can come out. Underneath the NaI (Tl) detector, the cold rods (3) of the HPGe detector emerge, and all but the cold rods are surrounded by a low-level radiation shield. The cooling rods serve to cool the HPGe detector in the liquid nitrogen passage (5).

<Plastic Detector>

The plastic scintillation detector 28 is installed outside the low level radiation shield surrounding the HPGe detector, the Si (Li) detector and the NaI (Tl) detector. The plastic detector is again surrounded by a normal radioactive shield.

<Installation of Si (Li) Detector>

As shown in Fig. 2, the Si (Li) detector 12 is screwed onto the plate above the vacuum chamber 18. The BNC connector is installed on the vacuum plate, and the cable 42 is connected to the outside of the shield. This cable supplies a high voltage to the Si (Li) detector and transmits the signal generated by the Si (Li) detector to the outside.

A vacuum valve is attached to the vacuum chamber and a vacuum hose 41 is connected thereto to extract air from the vacuum chamber to maintain the vacuum chamber in a vacuum state.

The vacuum hose and the cable are connected to the outside in the shape as shown in FIG. 10 by a gap between the NaI (Tl) annular detector 20 and the HPGe detector 1 of FIG. If all of the installation is configured as shown in FIG.

The following describes the use of the gamma nuclide analyzer through the examples.

<Example 1>

Radioactivity measurement of a sample that emits gamma radiation puts the sample on top of the HPGe detector (1) and operates the measuring devices (1, 2, 6 to 10), for example assuming that Co-60 is present in the sample at 10,000 Bq. , Co-60 contains 10,000 × 0.9986 = 9,986 1173 keV energy gamma rays per second with a branching rate of 0.9986. If the measuring efficiency of the HPGe detector (1) is 5%, the HPGe detector (1) emits gamma rays. 9,986 × 5% = 499.3 gamma rays per second, equivalent to 5% of, are detected. The signal generated by the HPGe detector is amplified by the preamplifier (2) and the amplifier (7) and converted into a digital signal by the ADC (8), indicating that 499.3 gamma rays of 1173 keV energy are detected by the computer.

The computer confirms that 499.3 gamma rays of 1173 keV energy are measured per second, and divides the measured values by the branching rate and the measurement efficiency and analyzes that Co-60 of 499.3 ÷ 5% ÷ 0.9986 = 10,000Bq exists.

Si (Li) surface barrier detectors, NaI (Tl) scintillation detectors and plastic scintillation detectors are also analyzed for radioactivity in the same way.

<Example 2>

In order to perform simultaneous beta-gamma measurement using the Si (Li) surface barrier detector 12 in the HPGe detector 1, the HPGe detector apparatuses 1 to 10 and the Si (Li) surface barrier detector apparatuses 11 to 11 19, 9 and 41 must be operated simultaneously and the computer is instructed to store the signal only when the signal is generated simultaneously by the HPGe detector 1 and Si (Li) detector 12.

In the measuring method, the measurement sample is placed in the sample holder 14, and the Si (Li) surface barrier detector 12 is placed in the vacuum chamber 18, and the vacuum chamber 18 is placed on the HPGe detector 1. If Co-60 is present in the sample at 10,000Bq, Co-60 emits beta particles and gamma rays simultaneously. Assuming that the measurement efficiency of the Si (Li) surface barrier detector 12 for beta particles emitted from Co-60 is 20%, the Si (Li) surface barrier detector 12 has 10,000 × 20% = 2,000 units per second. Beta particles are detected. As described above, the HPGe detector 1 detects 499.3 gamma rays of 1173 keV energy per second. That is, beta-gamma simultaneous measurement means that the beta particles are detected in the Si (Li) surface barrier detector 12 and the gag rays of 1173keV energy are detected in the HPGe detector 1, which is generated by the HPGe detector 1 in the computer. To accept the signal.

2,000 of the beta particles released from Co-60 of the sample are detected by the Si (Li) surface barrier detector 12 and the remaining 8,000 (80%) are lost. Only 20% of the signals generated in 1) are obtained and 499.3 × 20% = 99.86 signals accepted by the computer.

If the sample has a gamma-emitting nuclide other than Co-60, the measurement by the HPGe detector (1) also detects gamma rays of other nuclides in addition to the gamma-rays of Co-60. If traces of Co-60 are present and other nuclides dominate, then it is difficult to detect the gamma rays of Co-60. In this case, beta-gamma simultaneous measurement causes 80% signal loss. However, gamma rays from other nuclides do not coincide with beta particles or gamma rays of Co-60 and are not accepted by computers. That is, since only the radioactivity of Co-60 is measured, the radioactivity of Co-60 can be measured by preserving the loss by increasing the measurement time as much as the loss (80%) generated by simultaneous beta-gamma measurement.

<Example 3>

Compton scattering reduction measurement using a NaI (Tl) scintillation detector is measured by surrounding the HPGe detector (1) with NaI (Tl) annular detector 20 and NaI (Tl) cylindrical detector 21 as shown in FIG. The sample is placed on the HPGe detector (1). If 10,000 Bq of Co-60 is present in the sample, 499.3 per second, which is 5% of the gamma ray of 1173 keV energy emitted from Co-60, is detected by the HPGe detector (1). Many of the remaining 95% were incident on the HPGe detector 1 but exited by compton scattering without losing energy. These compton scattering gamma rays are recorded as any other energy in the gamma nucleus analyzer and accepted as background signals. This is called the Compton Contiguous Section, which increases the background of the radiometric system, making it difficult to analyze the radioactivity of the sample. Therefore, the signal measured by the HPGe detector at the same time when the signal is received by the NaI (Tl) scintillation detector is the background. Therefore, the signal is generated by the HPGe detector when the signal is received by the NaI (Tl) scintillation detector using the analysis module. By eliminating the signal, the background of the gamma nucleus analyzer is reduced to facilitate gamma nuclide analysis.

To reduce the Compton sequence appearing on a computer using a NaI (Tl) detector, operate the HPGe detector associated device (1-10) and the NaI (Tl) flash detector related device (20-27, 9) simultaneously. (9) A signal must be stored only when no signal is generated at the same time by the NaI (Tl) detector and the NaI (Tl) scintillation detector.

<Example 4>

To reduce the spaceship with the plastic flash detector, operate the HPGe detector related devices (1 to 10) and the plastic flash detector related devices (28 to 33, 9) at the same time, and then, whenever the computer generates a signal from the plastic flash detector, About several microseconds to about 100 microseconds). Do not store the signal from the HPGe detector.

The measurement method is that when the spacecraft enters the gamma nucleus analyzer outside the plastic scintillation detector 28, a part of it enters the HPGe detector 1 and the computer 9 recognizes the signal of the HPGe detector 1, Will increase the background. The spacecraft emits a lot of radiation at the same time, some of which are detected by the plastic flash detector 28. If the computer ignores the signal of the HPGe detector 1 generated when the signal is detected in the plastic detector 28, the measurement background increased due to the spacecraft can be reduced, so that the spacecraft can be shielded using the plastic detector.

The devices associated with the HPGe detector are required for gamma nuclide analysis and should always be operated. Each measurement method using the remaining secondary detectors can be used with only one function or in combination. For example, only a spacecraft impact reduction device can be operated for gamma nuclide analysis, or compton scatter reduction and gamma-beta simultaneous measurements can be performed. The use of several functions enables precise measurement, but on the other hand, the measurement efficiency is lowered and the measurement time is longer. Which method should be combined depends on the radiometric sample to be analyzed.

In radiological measurement, measurement errors depend on the number measured or the measurement efficiency. Therefore, the more complex the measurement method is used, the smaller the measurement efficiency and the number of measurements and the greater the error. Therefore, the method of reducing the error by increasing the measurement time is taken. Since the propagation of the error is automatically calculated by these gamma nucleus analyzers, the operator's only task is to determine the measurement efficiency for each measurement method, and the measurement efficiency must be performed for each type of sample.

FIG. 7 shows gamma-ray spectra analyzed by computer for the case of simultaneous measurement of the gamma rays (coincidence spectrum) and the absence of (single spectrum). When the simultaneous measurement was not performed, the measurement background was 1/100 lower than when the simultaneous measurement was not performed. As a result, when the simultaneous measurement efficiency was 5%, the 1332 keV gamma ray was 5%.

8 shows a gamma ray spectrum analyzed by a computer with respect to the Compton scattering reduction (anticompton spectrum, black graph) and not (single spectrum, red graph). Compton scattering was reduced by about 1/10 in the middle part compared to the case where the Compton scattering cut was not made.

FIG. 9 shows gamma-ray spectra analyzed by a computer in the case of spacecraft effect reduction (anti-cosmic spectrum, red graph) and not (single spectrum, black graph). In the middle part, the background was reduced by half compared to the case where the spacecraft impact reduction was not done.

The present invention is applied to the apparatus of the present invention by using a small amount of radioactivity measuring technology that emits gamma rays by a conventional gamma nucleus analyzer, so that the gamma nucleus analyzer is present in a very small amount when there is a radionuclide that emits charged particles simultaneously with gamma rays. Radioactivity can also be analyzed. In addition to the existing Compton scattering reduction and spacecraft impact reduction functions, it is very easy to analyze trace radionuclides.

Claims (8)

In measuring trace amount of radioactivity by gamma nuclide analyzer, HPGe detector related devices (1 to 10) for detecting gamma rays emitted from radioactive sample, alpha particles emitted from radioactive sample to improve the performance of gamma nuclide analyzer, Si (Li) surface barrier detector-related devices (11 to 19, 9, 41), which are auxiliary detectors for detecting charged particles such as beta particles and protons, and NaI for detecting compton scattered gamma rays in the HPGe detector (1). (Tl) scintillation detector related devices (20 to 27, 9), plastic scintillation detector related devices (28 to 33, 9) for detecting charged particles of a spacecraft, and an analysis module (see FIG. 12). Multifunctional Radioactive Gamma Nuclear Spectrometer The Si (Li) surface barrier type detector associated device (11 to 19, 9, 41) is provided with a sample holder (14), a Si (Li) detector (12), an aluminum film, and a vacuum pump (11). ), A high-voltage supply (15), a preamplifier (16), an amplifier (17), and a digital signal connected to a vacuum chamber (18) connected to a vacuum line, and connected to a Si (Li) detector (12) to amplify a voltage signal. A multifunctional radiogamma nuclide analyzer, characterized by consisting of a converting ADC (19), and a computer (9) for analyzing data. The NaI (Tl) scintillation detector associated apparatus 20 to 27, 9 has a NaI (Tl) cylindrical detector at a hole opposite to the HPGe detector 1 at one hole of the NaI (Tl) annular detector 20. The Na (TI) scintillation detector manufactured to enclose (21) the HPGe detector (1), and the NaI (Tl) annular detector 20 and the Na (TI) cylindrical detector 21 are supplied with a high voltage. (24) (25) and the amplifier (26) to be amplified through the photomultiplier tube (22a to 22g) when the compton scattered gamma ray is incident on the NaI (Tl) annular detector 20 and , The photon multiplier tube 23 for amplifying the generated current signal when the compton scattered gamma ray enters the NaI (Tl) cylindrical detector 21, an amplifier 26 for amplifying the voltage signal into a voltage signal, and a voltage signal Multifunctional radiogamma nuclide analyzer, characterized by consisting of an ADC (27) for converting the signal, and a computer (9) for analyzing the data The apparatus according to claim 1, wherein the apparatus related to the plastic flash detectors (28 to 33, 9) is provided with two plastic flash detectors arranged at two upper sides and two lower end portions at the upper end to cover the whole, and a plastic flash detector at the upper end ( 28a, 28b), high-voltage generators 31, 30, and 29 for supplying high voltages to the plastic flash detectors 28c-28j on the side and the plastic flash detectors 28k and 28l at the bottom, and the plastic flash detectors ( 28a to 28l), an amplifier 32 for amplifying a generated current signal through a preamplifier and then amplifying a voltage signal, an ADC 33 for converting a voltage signal into a digital signal, and analyzing data Multifunctional radiogamma nuclide analyzer, characterized by consisting of a computer (9) In measuring a small amount of radioactivity by a gamma nuclide analyzer, detecting a gamma ray detected in a radioactive sample by an HPGe detector associated device, and using a Si (Li) surface barrier detector associated device as an auxiliary detector. Detecting charged particles such as alpha particles, beta particles, protons, etc. emitted from the radioactive sample to improve the performance, and NaI (Tl) scintillation detector associated devices (20 to 27, 9) in the HPGe detector (1) Comprising the Compton scattered gamma rays, detecting the cosmic charged particles by the plastic scintillation detector associated device, and analyzing by the analysis module, gamma-charged particles, gamma-gamma simultaneous measurement, Multi-function radioactivity measuring method characterized by simultaneous or selective measurement of Compton scattering reduction measurement and spacecraft impact reduction measurement The radioactivity measurement by the Si (Li) surface barrier detector associated device as an auxiliary detector is performed by vacuuming the radioactive sample and the detector to detect charged particles such as alpha particles, beta particles, and protons emitted from the radioactive sample. Measuring air after removing air with a vacuum pump, supplying a high voltage generated from a high voltage supply to a Si (Li) detector through a preamplifier, and whenever charged particles are incident to the Si (Li) detector. After the current signal is generated and amplified in the preamplifier, the amplifier is amplified to a voltage signal, the ADC converts the voltage signal into a digital signal and converts the magnitude of the signal input into the computer into charged particle energy to form charged particle energy. Multi-function radioactivity measuring method characterized in that simultaneously and measuring the charged particle-gamma The radioactivity measurement by the NaI (Tl) scintillation detector related device comprises: receiving a high voltage from the NaI (Tl) annular detector and the NaI (Tl) cylindrical detector by a high voltage supply, and the NaI (Tl) annular detector. When the Compton-scattered gamma ray is incident to the generated current signal is amplified through seven photomultiplier tube and input to the amplifier, and when the Compton-scattered gamma ray is incident on the NaI (Tl) cylindrical detector, the generated current signal is Amplified by the photomultiplier tube and amplified by the amplifier again to a voltage signal, and analyzed by an analysis module which reduces the compton scattered gamma rays using the voltage signal, and converts the ADC into a digital signal and inputs it into a computer. Multifunctional radioactivity measuring method characterized in that the radioactivity is measured by reducing the Compton scattering The method of claim 5, wherein the detection of charged particles of the spacecraft by the plastic flash detector is characterized in that the plastic flash detector at the top, side and bottom receive high voltage from each of the high voltage generators, and the current generated when radiation is incident on the plastic flash detector. The signal is amplified by the preamplifier and amplified by the amplifier to the voltage signal again, using the voltage signal to analyze the effect of the spacecraft by the analysis module, and the ADC converts the voltage signal into a digital signal to radiate the spacecraft Multifunctional radioactivity measuring method characterized by measuring by reducing the impact