JPH11109036A - Alpha-radioactivity measurement method and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily and accurately measure the α-radioactivity of an α-contami nated measurement object in a high γ ray field. SOLUTION: A container 2 containing a light element is provided on the side of a measurement sample 1 containing an α radioactive material of a neutron detector 5, the light element inside the container 2 and α rays cause (α, n) reaction, a generated neutron is detected and the α-radioactivity is obtained. Without directly measuring the α rays, the neutron generated by the (α, n) reaction of gas containing the light element filled around and the αrays is measured and the α-radioactivity is obtained. Between the neutron detector and the measurement sample, a γ ray shielding material (lead, iron) is installed. A neutron detection part with an additional function capable of selecting the thickness of the neutron detector 5 (He-3 (5a), BF3, B-10 lined (5B), FC) and the γ ray shielding material (lead, iron and tungsten alloy) corresponding to γ ray intensity is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an α-radioactive substance which is capable of accurately measuring an α-radioactivity even when an object to be detected for which the α-radioactivity is detected emits strong γ-rays. The present invention relates to a measuring method and an apparatus.

[0002]

2. Description of the Related Art Nuclear fuel cycle facilities handle alpha radionuclides such as uranium, plutonium, americium and curium. For this reason, equipment and waste from factories that handle them may be contaminated with alpha radiation,
Wastes contaminated with α-radiation must be strictly managed.

[0003] In the nuclear fuel cycle facility, equipment,
It is necessary to detect whether or not α radioactivity is attached to wastes, etc., and if detected, it is necessary to take appropriate measures. In order to detect whether or not an α-radioactive substance is attached to a device or the like, a method in which an inspector surveys the surface of the device or the like with an α-ray survey meter is generally used.

A method for measuring α-activity is described in, for example,
As disclosed in Japanese Unexamined Patent Publication No. 265593, a measurement sample that emits α-rays is contained in a gas or liquid containing a light element having a high probability of causing an (α, n) reaction, and the (α, n) reaction is performed. A method of measuring the α-activity of a measurement sample by measuring the number of neutrons generated as a result of is known.

Further, as disclosed in, for example, Japanese Patent Application Laid-Open No. 4-50689, SF ₆ gas is filled in a container containing a measurement sample, and (α, n) An α-activity measurement method is known in which the number of neutrons generated by the reaction is measured, and the α-activity in the container is quantified. FIG. 5 is a sectional view showing a container portion of a conventional α-activity measuring apparatus, which is disclosed in Japanese Patent Application Laid-Open No. 4-50689.

In FIG. 5, an α-activity measuring device is a container lid.
A heater / cooler 96 is provided outside the container 91 which is kept airtight by 92.
A heat transfer tube 97 is drawn out of the heating / cooling device 96, and the heat transfer tube 97 is connected to a flexible tube 95 wound around the side of the container 91. The heating / cooling device 96, the thermal transfer tube 97, and the flexible tube 95 and the cooling means of the container 91 are constituted. A signal cable 90 is connected to the neutron detector 89.

In the α-radiation measuring apparatus having such a configuration, the procedure until the SF ₆ gas is introduced into the container 91 is as follows, with the container 91 filled with the SF ₆ gas.
Activate the cooling function. Then, a cooling medium flows from the heating / cooling device 96 through the heat transfer tube 97 to cool the container 91. The SF ₆ gas in the container 91 has a melting point (under pressure) of -50.8
° C and the rise point is about -63 ° C, so it easily liquefies or solidifies.

At this time, since the volume of SF ₆ shrinks, SF ₆ gas can be continuously fed into the container 91 via the SF ₆ supply pipe 93. Therefore, if the supply of SF ₆ gas is continued while cooling is continued, the density of SF ₆ in the container 91 can be increased. As the number of SF ₆ molecules increases, the number of (α, n) reactions generated also increases.

In this α-activity measuring apparatus, a neutron detector
The number of neutrons due to the (α, n) reaction detected by 89 becomes large enough to be distinguished from the background due to spontaneous fission, and the number of neutrons due to the (α, n) reaction is easily counted. α radioactivity can also be estimated more accurately.

In the conventional example, after the measurement of the number of neutrons by the (α, n) reaction is completed, when the heating function of the heating / cooling device 96 is operated, the heat medium is transferred from the heating / cooling device 96 to the heat transfer tube.
It flows through 97 and heats the container 91. As a result, the container
Since the liquefied or solidified SF ₆ in 91 returns to the original gas state, SF _{6 in} this gas state can be recovered through the SF ₆ recovery pipe 94.

[0011]

The detection of α-rays by a survey meter also senses γ-rays. Therefore, when a lot of βγ radioactive nuclides adhere to α-contaminated equipment, strong gamma-rays are emitted from the equipment. Is emitted, the detector is saturated by the γ-rays, and there is a problem that the α-rays cannot be measured.

On the other hand, in the α-ray measurement technique utilizing the (α, n) reaction, when the measurement sample emits strong γ-rays, the neutron detector is saturated by γ-rays, and neutrons cannot be measured. There is a problem that it becomes impossible to quantify α rays correctly.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. Even when a measurement sample which is α-contaminated in a high γ-ray field, that is, a measurement object emits high-intensity γ-rays, the measurement object An object of the present invention is to provide a method and an apparatus for measuring α-activity, which can quantify α-activity of an object with high accuracy and operability.

[0014]

According to the first aspect of the present invention, a gas containing a light element is filled in a container containing an object to be measured containing an α-radioactive substance, and an (α, n) reaction between the α-ray and the light element is performed. In the α-activity measuring method for measuring neutrons generated by the method and quantifying the α-activity, the container is provided with at least two types of neutron detectors having different allowable γ-ray intensities, and the at least two types of neutron detectors are provided. , A detector is selected in accordance with the γ-ray intensity of the object to be measured, and neutrons are measured by the selected detector to quantify α-activity.

According to the first aspect of the present invention, the neutron detectors arranged around the container containing the gas to be measured and the gas containing the light element have different allowable gamma dose rates or allowable gamma ray intensities. Then, an appropriate neutron detector is selected according to the gamma dose rate or intensity of the object to be measured, neutrons are measured, and α radioactivity is obtained from the obtained neutron count. Even if a ray is emitted, it is possible to measure neutrons with high accuracy and obtain α-activity.

According to a second aspect of the present invention, a first neutron is used by using two or more kinds of gases containing at least two kinds of light elements, first filling the first gas containing the first light element into the container. Counting, then filling the vessel with a second gas containing a second light element, measuring a second neutron count, and further counting the third and subsequent light elements containing the third and subsequent light elements. When a gas is also used, the container is filled with the gas sequentially, and the third and subsequent neutron counts are measured. The obtained neutron count and the neutron collection of the (α, n) reaction of the α radionuclide are obtained. The α activity of each α radionuclide is determined using the ratio.

According to the second aspect of the present invention, the neutron yield of the (α, n) reaction is specific to each element, so that two or more gases containing at least two types of light elements are used. Each gas is filled in a container, the neutron count is measured, the obtained neutron count rate is obtained, and the neutron yield of the α radionuclide (α, n) reaction to be obtained is used to obtain each α. The α activities of the radionuclides are determined, and these are integrated to determine the total α activities.

For example, when obtaining the radioactivity of two kinds of α radionuclides, an object to be measured is put in a gas containing two kinds of light elements, and the neutron counting rate in each case is measured. In this way, the unknown is two α-radioactive activities, and the neutron count rate, the neutron yield and the proportionality constant of each (α, n) reaction of each α-radionuclide are known numbers, and Is obtained.

This solution is easily obtained. The α activities of the two nuclides to be determined are required. Accordingly, since the α activity of each α radionuclide can be obtained with high accuracy, the total α activity can be obtained with high accuracy by integrating them.

According to a third aspect of the present invention, a container containing an object to be measured containing an α-radioactive substance is filled with a gas containing a light element,
In an α-activity measurement method for measuring neutrons generated by an (α, n) reaction between an α-ray and a light element to quantify α-activity, in addition to the neutron measurement values, the α-activity is determined from the history of the measurement object. The α radioactivity is determined using the abundance ratio of the α radionuclide in the object to be measured and the neutron yield data of the (α, n) reaction of the light element of the α radionuclide.

According to the third aspect of the present invention, the neutron yield of the (α, n) reaction differs depending on the α-radionuclide. Neutron yield containing information on the abundance ratio of α radionuclides by multiplying the abundance ratio of α radionuclide by the neutron yield data of (α, n) reaction of each α radionuclide with light element Since the rate is determined, the α activity can be measured with high accuracy.

According to a fourth aspect of the present invention, a container containing an object to be measured containing an α-radioactive substance is filled with a gas containing a light element,
In the α-activity measurement method for measuring neutrons generated by the (α, n) reaction between α-rays and light elements to determine α-activity, in addition to the neutron measurement values, the γ-ray spectrum measurement and the neutron simultaneous measurement are used. The α radioactivity is determined using the abundance ratio of the α-radiation nuclide in the measured object and the neutron yield data of the (α, n) reaction of the light element of the α-radionuclide.

According to the invention of claim 4, in addition to the neutron counting circuit system, a neutron coincidence counting circuit system and a γ-ray spectrum measuring circuit system are provided, and based on the measurement results, U, Pu and Am isotopes, Cm- The ratio of 244 is determined, and these ratios are multiplied by the neutron yield data of each α radionuclide (α, n) reaction, and the integrated data is used as a correction factor.
α radioactivity can be measured accurately.

According to a fifth aspect of the present invention, there is provided a container containing an object to be measured containing an α-radioactive substance and filled with a light element gas, a table having a small surface area for mounting the object to be measured, a neutron moderator,
At least two types of neutron detectors with different allowable γ-ray intensity, neutron counting circuit system, γ dose rate meter, data processing computer, processing program for calculating α radioactivity from neutron counting, depending on γ dose rate of the measurement object And a processing program for selecting a neutron detector.

According to the fifth aspect of the present invention, the neutron detectors arranged around the container containing the gas to be measured and the gas containing the light element have different allowable gamma dose rates or allowable gamma ray intensities. Then, an appropriate neutron detector is selected according to the gamma dose rate or intensity of the object to be measured, neutrons are measured, and α radioactivity is obtained from the obtained neutron count. Even if a ray is emitted, it is possible to measure neutrons with high accuracy and obtain α-activity.

The invention according to claim 6 is a container containing an object to be measured containing an α-radioactive substance and filled with a light element gas, a table having a small surface area for mounting the object to be measured, a neutron moderator, and an allowable γ. At least two kinds of neutron detectors having different line intensities, a neutron counting circuit system, a first logic pulse signal after detecting a neutron signal, and a second logic pulse delayed in time from the first logic pulse signal A pulse signal generator that generates a signal, first and second counters that operate in response to a logical pulse signal from the signal generator, γ-ray spectrum measuring means, and a data processing computer; Using the neutron count data counted by the first and second counters, the γ-ray spectrum measurement data, and the neutron yield data of the (a, n) reaction of the light element, α release from the neutron count rate is performed. It is characterized by having a processing program for calculating a conversion factor to the shooting power.

According to the invention of claim 6, in addition to the neutron counting circuit system, a neutron coincidence counting circuit system and a γ-ray spectrum measuring circuit system are provided, and the U, Pu and Am isotopes, Cm- The ratio of 244 is determined, and these ratios are multiplied by the neutron yield data of each α radionuclide (α, n) reaction, and the integrated data is used as a correction factor.
α radioactivity can be measured accurately.

According to a seventh aspect of the present invention, the gas containing the light element to be filled in the container is Li, Be, B, C, O,
A gas containing at least one element of F, Ne, Na, Ng, and Al, and the gas to be filled in the container is SF ₆ , chlorofluorocarbon, BF ₃ , CF ₄ , C ₂ F ₂ , N ₂
It is characterized by comprising at least one of F ₃ and CHF ₃ .

According to the invention of claim 7, as the gas containing the light element to be filled in the container together with the object to be measured, a gas containing an element having a high probability of causing the (α, n) reaction is selected and used. As a result, the number of neutrons generated can be increased, and the α radioactivity can be measured with high measurement accuracy.

According to the eighth aspect of the present invention, a γ-ray shielding material made of a substance having a small neutron shielding effect and a large γ-ray shielding effect is selected according to the type of the detector, and a γ-ray shielding material made mainly of iron or lead is used. It is characterized by using a line shielding material.

According to the eighth aspect of the present invention, the neutron has good permeability and the γ-ray has a high intensity so that a predetermined neutron detector can measure even an object emitting a stronger γ-ray. Since a gamma ray shielding material mainly composed of lead or iron with a high shielding effect is installed around the neutron detector, it is possible to measure neutrons with high detection efficiency, and to accurately measure alpha radioactivity .

A ninth aspect of the present invention provides a pressure gauge for measuring the pressure of a gas containing a light element filled in a container for accommodating the object to be measured containing the α-radioactive substance, the measured pressure data and the pre-measured reference pressure. It is characterized by comprising a processing program for obtaining a correction coefficient for a change in gas pressure from data, and a means for removing impurity gas mixed with a gas containing a light element during a measurement operation. The invention according to claim 10 is characterized in that the object to be measured and the neutron detector are provided with means for relatively rotating.

An eleventh aspect of the present invention relates to an α-ray source whose radioactivity intensity is calibrated, a storage container for the α-ray source, means for contacting or separating the α-ray source and a gas containing a light element in the container, And a processing program for calculating a sensitivity variation correction coefficient from count data obtained by measuring neutrons generated as a result of the (α, n) reaction of light elements in the gas and a reference value.

A neutron source having a calibrated neutron generation intensity, a storage container for the neutron source, means for installing and removing the neutron source in a container for storing the object to be measured, and a neutron source, A processing program for calculating a correction coefficient for sensitivity fluctuation from neutron count data and a reference value resulting from the installation is provided.

The invention of claim 13 is characterized in that the first neutron counting data measured in a state where the gas containing the light element in the container is discharged and the second neutron counting data measured in a state where the light element gas is filled in the container. It is characterized by comprising a processing program for using the neutron count data, subtracting the first neutron count data from the second neutron count data, and calculating α-activity from the obtained neutron count data.

According to the ninth to thirteenth aspects of the present invention, a pressure gauge for correcting pressure fluctuation of the light element gas filled in the container,
A processing program to subtract the neutron background,
Standard α-ray source and its handling mechanism to correct the fluctuation of neutron count generated by (α, n) reaction, neutron source and its handling mechanism to correct fluctuation of sensitivity of neutron detection system, radioactivity distribution Is provided with means for relatively rotating the object to be measured or the neutron detector in order to reduce the influence of, the α-radioactivity can be measured accurately.

The invention according to claim 14 is a means for outputting the measured α-radioactivity and γ-dose rate, a mechanism for attaching a sheet on which the output result is described to a measurement object, α-radioactivity and γ
Means for classifying and transporting the destination of the measurement object according to the intensity of the dose rate, means for generating an alarm when the value exceeds a predetermined range, and a gas leak detector, α dust monitor, gas leak It is characterized in that a means for generating an alarm when a measured value of the detector and the α-activity measuring device exceeds a reference value is provided.

According to the fourteenth aspect of the present invention, since an alarm device and a device for transporting an object to be measured are provided when the measured value of the α-activity or the nuclide monitor exceeds the reference value, the α-activity can be reduced with good operability. Can be measured. The neutron detector is selected according to the γ-ray charge rate or intensity of the measurement object, so the neutron detector uses a neutron detector with an appropriate detection efficiency without saturating with strong γ-rays and making measurement impossible. Alpha radioactivity can be quantified well.

Further, since lead or iron having good neutron permeability and high γ-ray shielding effect is installed around the neutron detector, the intensity of γ-rays can be reduced without reducing the intensity of neutrons. Since neutrons can be measured specifically, α radioactivity can be quantified accurately.

Further, even if the pressure of the gas fluctuates due to the provision of a pressure gauge for the gas containing the light element and the generated intensity of the (α, n) neutrons changes, the neutron intensity is measured using the pressure measured by the pressure gauge. Can be corrected and accurate measurement can be performed.
In addition, since a handling mechanism is provided for installing an α-ray source such as Am-241 in a container containing a gas containing a light element, the neutron is set at a predetermined position inside, and the neutron is measured. Compared with the values, data for correcting the fluctuation of the light element gas concentration and the neutron detection efficiency can be obtained, and as a result, the measurement accuracy is improved. In addition to this, the measurement accuracy is improved by providing a neutron source handling mechanism, a rotating mechanism of the object to be measured, a means for correcting the conversion constant by means for obtaining the abundance ratio of α-radionuclide in the object to be measured, and the like.

[0041]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) (Corresponding to Claims 5 and 8 to 12) FIG. 1 is a configuration diagram showing an example of an α-activity measuring apparatus of the present invention.

The measurement sample 1 of the measurement object to which the α-radionuclide is attached is placed in a closed vessel 2 and placed on a stand 3 made of, for example, a thin pipe and having only a small surface area structural material. By reducing the surface area in this way, the area of the surface where the (α, n) reaction between the α radionuclide attached to the surface of the measurement sample 1 and the gas containing the light element is prevented is reduced as much as possible, and the measurement accuracy is improved. Is what you do. If the obstructed area is large, the amount of unmeasured α-radionuclide increases and the measurement accuracy decreases. Here, the table 3 on which the measurement sample 1 is placed is installed, but a mechanism for holding the measurement sample 1 from the side, above, or from above may be used instead of the table 3.

A neutron moderator 4 is provided around the container 2, and a neutron detector 5 is used as a neutron detector 5 in the neutron moderator 4.
A three detector 5a and a B-10 lined counter 5b are provided. In addition, at least two types of neutron detectors having different allowable γ-ray intensities such as a BF3 detector, a fission counter, a scintillator, and a semiconductor detector with Li can be selected and installed.

Here, the characteristics of the three types of detectors described below will be briefly described. First, in order of neutron detection efficiency, the He-3 detector 5a, B-10 lined counter 5b, and fission counter Become. However, in the descending order of the allowable γ-ray intensity, a fission counter, a B-10 lined counter 5b, and a He-3 detector 5a are used.

From the above-described characteristics, the measurement sample 1 having a low neutron intensity usually has a high detection efficiency of He-3.
Although the detector 5a is used alone, this detector has an allowable γ
Since the line intensity is low, measurement cannot be performed if a measurement sample having a slightly higher γ-ray intensity is targeted. In addition, in anticipation of such a situation, if the B-10 lined counter 5b having a high allowable γ-ray intensity is used in advance, the detection efficiency is low, so that a long time measurement is necessary to obtain sufficient counting statistical accuracy. , Processing capacity is reduced.

Therefore, as in the present embodiment, a gamma dose rate meter 6 is installed near the container 2 containing the measurement sample 1, the gamma ray intensity of the measurement sample 1 is measured, and according to the gamma ray intensity. , Allowable γ
Select an appropriate neutron detector with high neutron detection efficiency within the line intensity and measure neutrons. Then, it is possible to measure neutrons with high detection efficiency even with a measurement sample that emits a strong γ-ray, which was not measured by the conventional technique.

Although the neutron detector 5 is arranged around the measurement sample 1 in FIG. 1, when the neutron detector 5 is arranged around a part of the periphery, the measurement sample 1 and the neutron detector 5 are arranged. 5
A means for relatively rotating. If you do so,
Since the neutrons are detected from each direction of the measurement sample 1, the distance from the neutron detector 5 is averaged, so that even if the deposition of the α radionuclide is in a non-uniform distribution, it is possible to accurately measure the α radioactivity. it can.

An air or light element gas discharge pipe 7, a light element gas supply pipe 8, a pressure balancing valve 9, and a pressure gauge 10 are provided on an upper lid 16 for sealing the container 2. The air or light element gas discharge pipe 7 is connected to a vacuum pump 11 via valves 17 and 21, connected from the vacuum pump 11 to a gas purification filter via valves 22 and 25, and further connected to a gas purification filter 12. From the light element gas supply tank via the valve 34
Connected to 13. The light element gas supply pipe 8 also continues to the compression pump 14 and the filter 15 and is connected to the light element gas supply tank 13. Reference numeral 36 in FIG. 1 denotes an α-ray dust monitor.

Here, after the measurement sample 1 is placed in the container 2, the upper lid 16 of the container 2 is closed and sealed. Since the container 2 is evacuated to a vacuum level and a gas having a pressure higher than the atmospheric pressure is put in the container 2, it is necessary to have a pressure-resistant structure.

A method for measuring the α-activity of a sample to be measured with the α-activity measuring apparatus having such a configuration will be described. First, an operation of discharging the air inside the container 2 is performed.
Close valves 9, 18, 19, 20, 25, and close valves 17, 2
Release 1,22,23,24. In this state, the vacuum pump 11
Is operated, the air in the container 2 is sucked by the vacuum pump 11 and released to the atmosphere through the valve 24. A pressure gauge indicates that air has been discharged from the container 2 and has reached a predetermined pressure.
When confirmed at 10, the valves 17, 21, 22, and 24 that have been opened are closed.

Next, an operation of filling the inside of the container 2 with a gas containing a light element is performed. Valves 9, 17, 26, 32, 34 are closed and valves 18, 19, 27, 28, 29, 30, 31, 33, 35 are open. When the compression pump 14 is operated in this state, the light element gas in the light element gas storage tank 13 is supplied to the container 2 through the filter 15 and the compression pump 14. When it is confirmed by the pressure gauge 10 that the inside of the container 2 has reached a predetermined pressure, the compression pump 14 is stopped, and the valves 18, 27, 28, 3
0, 31, and 33 are closed.

Here, as an example, the gas purification filter 12 is used as a means for removing impurities in the light element gas.
Although the filter 15 for purifying light element gas is used, other separation means such as a permselective membrane may be used instead of the filters 12 and 15.

A container 2 containing a measurement sample 1 and He
-3 detector 5a and B-10 lined counter 5b, if a γ-ray shielding material is used in consideration of the thickness in accordance with the allowable γ-ray intensity of each detector, it has γ-ray resistance and neutron detection. Since neutrons can be measured under conditions of high efficiency, α radioactivity can be measured with high accuracy.

Further, although not shown, an α-ray source whose radioactivity intensity has been calibrated is transferred into the container 1, and the α-ray emitted by this source and the light element in the gas react with each other (α, n). If the neutrons resulting from the occurrence of the neutrons are measured and the sensitivity fluctuation is corrected based on the obtained neutron count data, the α radioactivity can be obtained with high accuracy.

Further, if a neutron source whose neutron generation intensity is calibrated instead of the α-ray source is measured and the neutron count is used to correct the sensitivity fluctuation, the α-radioactivity can be accurately corrected. Can be requested.

(Second Embodiment) (Claims 4, 5, and 6)
FIG. 2 is a configuration diagram showing an example of a measurement system of the α-activity measuring apparatus of the present invention. A He-3 detector 37, a B-10 lined counter 38, a fission counter tube 39, a Ge detector 40, a gamma dose rate meter 41, and a measurement circuit system for them are provided.

Signals generated by detecting three neutrons by three He-3 neutron detectors 37 arranged around a container for storing radioactive substances are supplied to a preamplifier 42a, an amplifier 42b,
The signal is input to a gate generator 44 via an SCA (single channel analyzer) 43.

Similarly, a gate generator 46 and counters 47a, 47 connected to the assumed system of the B-10 lined counter 38.
b, a gate generator connected to the measurement system of the fission counter 39
48 and counters 49a and 49b also include a gate generator 44 and counters 45a and 45b connected to the measurement system of the He-3 detector 37.
Performs the same operation as.

The operation of the gate generator 44 and the counters 45a and 45b will be described taking the case of the He-3 detector 37 as an example. The gate generator 44 generates a logic pulse that keeps the counter 45a in the measurement state from several tens microseconds to 1 msec immediately after detecting the arbitrary neutron signal. Also,
Since the output terminal of the gate generator 44 and the input terminal of the gate of the counter 45b are electrically connected to each other, a logic pulse signal generated by the gate generator 44 for, for example, 1 msec after detection of the arbitrary neutrons for 1 msec. Is input to the gate of the counter 45b, and neutrons in the meantime are counted.

Here, the neutrons counted by the counter 45a are assumed immediately after arbitrary neutrons are measured.
There is a high probability of detecting time-correlated neutrons such as spontaneous fission neutrons emitted at the same time two to three. of course,
During this time, randomly generated neutrons without time correlation generated in the (α, n) reaction are also detected as statistical phenomena.

On the other hand, the neutrons counted by the counter 45b have passed 1 ms after the measurement of any neutrons, so that spontaneous fission neutrons having a time correlation have already been attenuated.
As a result, most neutrons generated randomly are detected.
Therefore, subtracting the count of the counter 45b from the count of the counter 45a results in a value correlated with the spontaneous fission neutrons.

In the present embodiment, a counter is used to measure neutrons having a time correlation, but a means for measuring a time change of the count may be used instead of the counter. For example, a multi-channel analyzer (MC
Use A) to use its multi-channel scaling function. The neutron measurement by the counters 45a and 45b is repeatedly performed until sufficient counting statistical accuracy is obtained.

Next, the Ge detector 40, the preamplifier 42a,
The gamma-ray spectrum of the measurement sample (waste) is measured by the high-voltage power supply 50, the amplifier 42b, and the MCA (multi-channel analyzer) 51, and the measurement data is analyzed by the computer 52, and the U-235, U-238, Pu- 238, Pu-239,
The gamma ray intensity of Pu-241 and Am-241 isotopes is determined, and the abundance ratio of these nuclides is calculated. This abundance ratio is used for obtaining α radioactivity from neutron counting to improve accuracy.

The gamma dose rate meter 41 and its measuring circuit 53 are
Depending on the γ-ray intensity of the measurement sample, an appropriate neutron detector 37,
In order to select 38 and 39, it is installed near the measurement sample and γ
This is for measuring the line intensity.

(Third Embodiment) (Claims 1, 3,
4 and 13) FIG. 3 is a flowchart showing an example of the measurement operation of the α-activity measurement method according to the third embodiment.

In order to determine the α radioactivity, four measurements are performed: total neutron counting measurement 55, background measurement 61 of total neutron counting, neutron simultaneous counting measurement 57, and gamma ray spectrum measurement 58.

First, in the first neutron counting measurement 55, a container containing a measurement sample is filled with a gas containing a light element. Here, as an example, the container is filled with SF6 gas, 54 Total neutron counting measurement to measure the number of neutrons
Do 55. Then, Pu-240, Pu-242, Cm
Total neutron intensity of spontaneous fission neutrons such as −244
56 and (α, n) generated by the (α, n) reaction between α ray and F
A neutron count of 60 is obtained.

Second Total Neutron Counting Background Measurement 61
Then, after discharging SF6 gas from the container 59, the background measurement 61 of the total neutron counting is performed, the background neutron intensity 62 is obtained, and the other neutron counting other than the reaction (α, n) which is the background neutron is performed. Get 63. Here, when the count 63 of the other neutrons is subtracted 64 from the count 60 of the (α, n) reaction and the other neutrons, a count 65 of the neutrons generated in the (α, n) reaction with F is obtained.

In the third simultaneous neutron counting measurement 57, the intensity 66 of the neutrons having a time correlation emitted from the container is measured, and the count 67 of the spontaneous fission neutrons is obtained. This count becomes information 68 on the abundance ratio of Pu-240, Pu-242, and Cm-244.

In the fourth γ-ray spectrum measurement 58, the γ-ray peak is analyzed, and U-235, U-238, Pu-238, P
peak γ-ray intensity of u-239, Pu-241 and Am-241 69
Is required. Using these results, the α activity 71 of the six nuclides can be obtained by calculating the α activity 70.

Here, the obtained Pu-238, Pu-239
, Pu-241 data, the Pu-240, P-241 data are obtained from the representative Pu isotope ratio data prepared in advance.
The radioactivity 72 of u-242 is calculated. Then, the radioactivity data 72 of Pu-240 and Pu-242 are converted to Pu-24.
The radioactivity 73 of Cm-244 is obtained by subtracting from the information 68 on the abundance ratio of 0, Pu-242 and Cm-244.

Further, the Cm-244 radioactivity 73 determined here
And U-235, U-238, Pu-238, Pu-239, Pu
-241 and Am-241 radioactivity 71, the abundance ratio 74 of each of these α radionuclides was determined, and this abundance ratio was used to calculate the data of the neutron yield 75 of (α, n) of F of each α radionuclide. Multiply,
By integrating these, a relational count 76 between the neutron generation rate and the α activity of the measurement sample is obtained.

The coefficient thus obtained, that is, the relationship 76 between the neutron generation rate and the α activity, is obtained by calculating the conversion constant from the (α, n) neutron count 65 to the α activity 77 with F obtained by measurement. Since it is used as a correction coefficient, the measurement accuracy of the α radioactivity 77 is improved.

Although the decay of α-activity in the light element gas is not described here, the α-activity and neutrons in the gas are naturally taken into account in consideration of the concentration and stopping power of the constituent elements of the gas. The function of the number of occurrences has been determined.

Here, the abundance ratio of α radionuclide in the measurement sample was obtained by neutron coincidence measurement and γ-ray spectrum measurement, but the abundance ratio data of α radionuclide obtained from the history of the measurement sample was used. Also, as described above,
If 77 is obtained, α-activity 77 can be obtained with high accuracy.

(Fourth Embodiment) (corresponding to claim 14) FIG. 4 is a block diagram showing an example of the α-radioactivity measuring apparatus of the present invention. The measurement sample 78 is placed in a container 79 together with a gas containing a light element, and the γ dose rate and neutrons are measured by a γ dose rate meter 80 and a plurality of neutron detectors 81. As a result, γ
The dose rate and alpha activity are obtained. Then, these data are compared with the predetermined reference range,
If it is out of the range, an alarm is generated by the alarm device 82. On the other hand, the γ dose rate and the α activity amount are output to a sheet by the γ dose rate and the α activity amount output means 83, and the sheet is
It is automatically attached to the measurement sample 78 by the attaching mechanism 84. The measurement sample 78 on which the sheet is stuck is transferred to the transfer destination classifying means 85, where the transfer destination is determined according to the γ dose rate or the α activity, and the transfer destination is classified by the transfer destination classification means 85. The measurement samples classified here are conveyed by the conveyor-type conveyance system 86 to the determined destination. In FIG. 4, 87 is a measurement circuit system, and 88 is a data processing computer.

(Fifth Embodiment) (Corresponding to Claims 2 and 7) In a container containing a measurement sample containing an α-radioactive substance, (α,
n) When a light element gas containing a light element having a large neutron yield of the reaction is filled, a large amount of neutrons are generated. Therefore, by measuring the number of the neutrons, the α radioactivity can be measured.

With respect to the neutron yield of the (α, n) reaction,
Matsunobu, Hiroyuki, et al., "Databook for calculating neutron yield from (α, n) reaction and spontaneous fission" JAERI
1324 (1992).

As an example, Am-241 and the light element (α,
n) The neutron yield of the reaction is as follows. H-He-Li 2.41E-06 n / α Be 7.93E-05 n / α B 2.04E-05 n / α C 1.09E-07 n / α N 0.00E + 00 n / α O 6.58E-08 n / α F 1.02E-05 n / α Ne 9.52E-07 n / α Na 2.13E-06 n / α Mg 1.33E-06 n / α Al 7.28E-07 n / α Si 1.20E-07 n / α

From this, it can be seen that the light elements other than H, He and N have a relatively high neutron yield of the (α, n) reaction. Therefore, Li, Be, B, C, O, F, N
e, Na, Mg, Al, Si A light element gas containing at least one kind of light element is filled in a container, and a measurement sample is placed in the container, whereby an (α, n) reaction occurs in the container. Since neutrons are generated, α-activity can be determined by measuring the neutrons.

Here, when attention is paid to an element having a higher neutron yield, the elements are B and F. Therefore, gases containing these elements, that is, SF6, Freon, BF3
, CF4, C2 F2, NF3 and CHF3, many (.alpha., N) reactions occur and many neutrons are generated. Therefore, these gases are combined with the light element gas (α,
n) When used for α radioactivity measurement for measuring neutrons by reaction, neutron counting accuracy is improved, and measurement accuracy is improved.

Next, two or more kinds of gases containing at least two kinds of light elements are used, each gas is filled in a container, the neutron count is measured, and the ratio of the obtained neutron count is used. The quantification of Noh is described below.

From the above literature, U-235, Pu-239,
And Cm-244 as examples, the (α, n) of Li, B, and F
The neutron yield data for the reaction, together with the ratio to Cm-244, is set forth below.

Neutron yield of (α, n) reaction of Li U-235 7.14E-09 n / α 0.2% Pu-239 1.30E-06 n / α 32.7% Cm-244 3.97E-06 n / α 100.0 Neutron yield of (α, n) reaction of% B U-235 9.62E-06 n / α 41.1% Pu-239 1.71E-05 n / α 73.1% Cm-244 2.34E-05 n / α 100.0% F Neutron yield of (α, n) reaction of U-235 2.86E-06 n / α 21.2% Pu-239 7.28E-06 n / α 53.9% Cm-244 1.35E-05 n / α 100.0%

As a first measurement sample, U-235 and Pu-
Assume a measurement sample containing 239. In this case, first, L
When a measurement sample is put in a gas containing i, neutrons are generated in accordance with the neutron yields of U-235 and Pu-239 in the table. Therefore, the neutron counting rate is measured. Next, when this measurement sample is put in a gas containing B, U-235 and P
u-239 generates neutrons because it generates neutrons according to the yields in the table. Then, the neutron counting rate is represented by the following two equations.

Nl = K · (Ylu · Au + Ylp · Ap) Nb = K · (Ybu · Au + Ybp · Ap) Nl: Neutron counting rate in case of gas containing Li K: Proportional constant Ylu: Li of U-235 Neutron yield of α, n) reaction Au: radioactivity of U-235 Neutron yield of (α, n) reaction of Li of Ylp: Pu-239 Ap: radioactivity of Pu-239 Nb: of gas containing B Neutron yield Yneu: neutron yield of (α, n) reaction of B of U-235 Ybp: neutron yield of (α, n) reaction of B of Pu-239

The unknowns are Au and Ap, and the other are real numbers different from 0 instead of 0. Since there are two equations,
The unknowns Au and Ap can be determined. That is,
The radioactivity of U-235 and Pu-239 can be determined.

In addition, U-235, Pu-239,
When Cm-244 is contained, a measurement sample is put in a gas containing Li, B, and F, and the neutron counting rate is measured for each. Then, in the same manner as described above, three equations are obtained with three unknown α radioactivity. In this case, a solution is obtained by a normal operation.

Therefore, U-235, Pu-239, Cm
An alpha activity of -244 is required. As described above, when each neutron counting rate is measured using a gas containing at least two or more types of light elements, the radioactivity is determined for each α-radioactive substance, so that the α-radioactivity is measured with high accuracy. be able to.

[0090]

According to the present invention, even when the object to be measured is α-contaminated in a high γ-ray field and emits high-intensity γ-rays, the α-radiation of the object to be measured can be accurately and operably controlled. Radioactivity can be measured.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of an α-activity measuring apparatus according to the present invention.

FIG. 2 is a configuration diagram showing a second embodiment of the α-activity measuring apparatus according to the present invention.

FIG. 3 is a flowchart showing a measuring procedure of the α-activity measuring apparatus according to the present invention.

FIG. 4 is a configuration diagram showing a third embodiment of the α-activity measuring apparatus according to the present invention.

FIG. 5 is a vertical cross-sectional view showing a partial block diagram of a conventional α-activity measuring apparatus.

[Explanation of Signs] 1 ... measurement sample (measurement object), 2 ... container, 3 ... stand, 4 ...
Neutron moderator, 5 neutron detector, 5a He-3 detector, 5b B-10 lined counter, 6 γ dose rate meter,
7 ... air or light element gas discharge pipe, 8 ... light element gas supply pipe, 9 ... valve for pressure balance, 10 ... pressure gauge, 11 ...
Vacuum pump, 12… Filter for gas purification, 13… Light element gas supply tank, 14… Compression pump, 15… Filter, 16… Top cover, 17-35… Valve, 36… α-ray dust monitor, 37… He
-3 detector, 38: B-10 lined counter, 39: fission counter, 40: Ge detector, 41: gamma dose rate meter, 42a: preamplifier, 42b: amplifier, 43: SCA, 44, 46, 48 ... gate generator, 45a, 45b, 47a, 47b , 49a, 49b ... counter, filled 50 ... high voltage power supply, 51 ... MCA, 52 ... calculator, 53 ... measuring circuit system, the SF ₆ gas 54 ... container, 55 ... Total neutron counting measurement, 56: total neutron intensity, 57: neutron coincidence measurement, 58: γ-ray spectrum measurement, 59: SF ₆ gas is discharged from the container, 60: (α, n) with F and other neutrons , 61 ... background measurement of total neutron counting, 62 ... background neutron intensity, 63 ... other neutron counting, 64 ... subtraction processing, 65 ... (α, n) neutron counting with F, 66 ... time Correlated neutron intensity, 67: counting of spontaneous fission neutrons, 68: Pu-240, Pu-242,
Information on the abundance ratio of m-244, 69 ... U-235, U-238, P
γ-ray peaks of u-238, Pu-239, Pu-241 and Am-241, 70 ... α radioactivity calculation, 71 ... U-235, U-238,
Pu-238, Pu-239, Pu-241, Am-241 radioactivity, 72 ... Pu-240, Pu-242 radioactivity, 73 ... Cm-
244 Radioactivity, 74: abundance ratio of each α radionuclide, 75: (α, n) neutron yield of each α radionuclide, 76: Relationship between neutron generation rate and α radioactivity, 77… α radioactivity, 78 ... measurement sample, 79 ... container, 80 ... gamma dose rate meter, 81 ... neutron detector, 82 ... alarm device, 83 ... output means, 84 ... sticking mechanism, 85 ... destination classification means, 86 ... transport system, 87 ... Measurement circuit system, 88 ... Data processing computer.

Claims (14)

[Claims] 1. A container containing an object to be measured containing an α-radioactive substance is filled with a gas containing a light element, and neutrons generated by the (α, n) reaction between the α-ray and the light element are measured to determine α-activity. In the α-activity measurement method for quantifying the neutron detector, the container is provided with at least two types of neutron detectors having different allowable γ-ray intensities, and according to the γ-ray intensity of the object to be measured from among the at least two types of neutron detectors. A method for measuring α-activity, characterized in that a detector is selected by using the selected detector, neutrons are measured by the selected detector, and α-activity is quantified. 2. A composition containing at least two kinds of light elements.
First, a first gas containing a first light element is charged into the container, and a first neutron count is measured using at least one kind of gas.
Next, a second gas containing a second light element is filled in the container, a second neutron count is measured, and a third gas or a subsequent gas containing a third or later light element is also used. Is used to measure the neutron counts of the third and subsequent neutrons by sequentially filling the vessel with the gas, and using the obtained neutron counts and the neutron yield of the (α, n) reaction of the α radionuclide. 2. The method for measuring α-activity according to claim 1, wherein α-activity of each α-nuclide is determined. 3. A container containing an object to be measured containing an α-radioactive substance is filled with a gas containing a light element, and neutrons generated by the (α, n) reaction between the α-ray and the light element are measured to determine the α radioactivity. In the α radioactivity measurement method for quantifying the neutron, in addition to the neutron measurement value, the abundance ratio of the α radionuclide in the measurement object obtained from the history of the measurement object, and (α, n) Using the neutron yield data of the reaction, α
A method for measuring α-activity, characterized by determining radioactivity. 4. A container containing an object to be measured containing an α-radioactive substance is filled with a gas containing a light element, and neutrons generated by an (α, n) reaction between the α-ray and the light element are measured to obtain α-activity. In addition to the neutron measurement values, the a radionuclide abundance ratio in the measurement object obtained from the γ-ray spectrum measurement and the neutron simultaneous measurement and the (α) , N) A method for measuring α-activity, wherein α-activity is determined using neutron yield data of the reaction. 5. A container containing an object to be measured containing an α-radioactive substance and filled with a light element gas, a table having a small surface area for mounting the object to be measured, a neutron moderator, and at least two different allowable γ-ray intensities. Types of neutron detectors, neutron counting circuit system, gamma dose rate meter, data processing computer, processing program to calculate alpha radioactivity from neutron counting, processing to select neutron detector according to gamma dose rate of measurement object An α-activity measuring device characterized by comprising a program. 6. A container containing an object containing an α-radioactive substance and filled with a light element gas, a table having a small surface area on which the object is placed, a neutron moderator, and at least different allowable γ-ray intensities. Two types of neutron detectors, a neutron counting circuit system, and a pulse for generating a first logical pulse signal and a second logical pulse signal which is delayed in time from the first logical pulse signal after detecting a neutron signal A signal generator, first and second counters that operate in response to a logical pulse signal from the signal generator, γ-ray spectrum measuring means, and a data processing computer, wherein the data processing computer includes the first and second counters. Neutron count data, gamma-ray spectrum measurement data and light element (a,
n) An α-activity measuring device comprising a processing program for calculating a conversion factor from a neutron count rate to α-activity using neutron yield data of a reaction. 7. The gas containing a light element to be filled in the container is Li, Be, B, C, O, F, Ne, Na, N
g, made from a gas containing at least one element of Al, as a gas filled into the container, SF _6, fluorocarbons, BF _3, CF _4, at least one of _{C 2 F 2, NF 3,} CHF 3 6. The method according to claim 5, wherein
7. The α-activity measuring device according to any one of items 6 to 6. 8. A gamma ray shielding material made of a substance having a small neutron shielding effect and a large gamma ray shielding effect is selected according to the type of the detector, and a gamma ray shielding material made mainly of iron or lead is used. 7. The α-activity measuring apparatus according to claim 5, wherein 9. A pressure gauge for measuring a pressure of a gas containing a light element filled in a container for accommodating a measurement object containing the α-radioactive substance, and a gas pressure based on measured pressure data and pre-measured reference pressure data. 7. The α-radioactivity measuring apparatus according to claim 5, further comprising a processing program for obtaining a correction coefficient of fluctuation, and a means for removing impurity gas mixed with gas containing light elements during a measuring operation. 10. The α-radiation measuring apparatus according to claim 5, further comprising means for relatively rotating the object to be measured and the neutron detector. 11. An alpha source whose radioactivity intensity is calibrated,
A container for the α-ray source, means for contacting or separating the α-ray source and the gas containing the light element in the container, and neutrons generated as a result of the (α, n) reaction between the α-ray and the light element in the gas are measured. 6. A processing program for calculating a correction coefficient for sensitivity fluctuation from the count data obtained by the calculation and a reference value.
7. The α-activity measuring device according to any one of items 6 to 6. 12. A neutron source whose neutron generation intensity is calibrated, a storage container for the neutron source, means for installing or removing the neutron source in a container for storing the object to be measured, and installation of the neutron source 7. The α-activity measuring apparatus according to claim 5, further comprising a processing program for calculating a sensitivity fluctuation correction coefficient from the neutron count data and a reference value. 13. Use is made of first neutron count data measured in a state where a gas containing a light element in the container is discharged, and second neutron count data measured in a state where a light element gas is filled in the container. 7. The α-activity according to claim 5, further comprising a processing program for subtracting the first neutron count data from the second neutron count data and calculating the α-activity from the obtained neutron count data. measuring device. 14. A means for outputting the measured α-activity and γ-dose rate, a mechanism for attaching a sheet on which the output result is described to a measurement object, and the measurement according to the intensity of the α-activity and γ-dose rate Means for classifying and transporting the destination of the object,
Having a means for generating an alarm when the value exceeds a predetermined range, and an alarm when the measured value of the gas leak detector, α dust monitor, gas leak detector and α radioactivity measuring device exceeds the reference value. 7. An α-activity measuring apparatus according to claim 5, further comprising means for generating the α-activity.