JP2010249753A - Method for analyzing transuranium element contained in substance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable nondestructive plutonium measurement with a high degree of accuracy through LX-ray measurement of a transuranium element, and to allow discrimination and separation of Am-241 from plutonium isotopes through energy differentiation. <P>SOLUTION: A method for analyzing a transuranium element contained in a substance includes the steps of: detecting LX-rays radiated along with alpha collapse from a transuranium contained in a substance by using a microcalorimeter of a superconducting phase transition edge thermometer type; and carrying out direct measurement of plutonium isotopes through energy differentiation. For example, discrimination and separation of Am-241 from plutonium isotopes are carried out by measuring LX-rays of 10 to 20 keV with a resolution of 100 eV or lower. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for directly analyzing a transuranium element in a substance using a superconducting phase transition edge thermometer type microcalorimeter.

  Plutonium is an α-ray emitting nuclide, and usually plutonium analysis is performed by measurement by α-ray measurement. However, α rays have a low ability to penetrate a substance, and the attenuation of energy by the substance is large. Therefore, it is practically impossible to measure α rays emitted from plutonium existing in the substance from the outside. In addition, the α-ray measurement may be affected by radon progeny nuclides of natural radioactive materials. Therefore, when plutonium is quantified by α-ray measurement, it is performed exclusively by chemical destruction analysis.

  By the way, a trace amount of KX rays and LX rays are emitted from the transuranium element with α decay. In particular, plutonium isotopes have a relatively high emission rate of 10 to 20 keV LX rays. Although LX rays are low energy, they can be measured to some extent from the outside of the material. Therefore, LX rays measurement using a semiconductor detector has been performed on plutonium in the human lung, which has been impossible to analyze destructively. Yes.

  However, for the plutonium LX-ray measurement, the semiconductor detector has insufficient energy resolution. Incidentally, since the energy resolution of the semiconductor detector depends on the energy gap width of the semiconductor, the theoretical limit value is about 240 eV, and about 400 eV in a normal product. Therefore, the detection limit is high, and it is also disturbed by LX rays from Am-241 generated by the radiation decay of Pu-241. Specifically, the energy of LX rays of plutonium isotopes is 13.6 keV, 17.4 keV, and 20.5 keV, whereas the energy of LX rays of Am-241 is 13.9 keV, 17.8 keV, And 20.8 keV. Therefore, plutonium isotopes and Am-241 cannot be discriminated and separated by plutonium LX-ray measurement using a semiconductor detector.

  In recent years, a superconducting phase transition edge sensor (TES) microcalorimeter has been developed as a radiation analyzer with energy resolution superior to that of semiconductor detectors. It has become possible (see Patent Document 1). A microcalorimeter is a device that measures the temperature rise caused by radiation incident on an object (absorber) being absorbed by the absorber and becomes heat, and determines the energy that the radiation has from the temperature rise. Usually, since the temperature rise due to radiation absorption is slight, it is measured with a highly sensitive thermometer. As a thermometer, a method using a change in electric resistance is generally used, and in particular, a TES type using a rapid change in resistance value from normal to superconductivity of a material has attracted attention.

  Although such a TES type micro calorimeter is used for elemental analysis and impurity inspection, there is no example in which LX rays (10 to 20 keV) of transuranium elements such as plutonium are analyzed. Therefore, actual measurement data of the plutonium isotope LX-ray emission rate has not been obtained, and it has not been proved that the plutonium isotope and Am-241 can be discriminated and separated. This is because a TES type micro calorimeter for the purpose of LX ray analysis of transuranium element has not been developed.

JP 2008-14775 A

  The problem to be solved by the present invention is that it is possible to perform LX-ray measurement of a transuranium element and to measure plutonium with high accuracy and non-destructiveness. Another problem to be solved by the present invention is to identify and separate plutonium isotopes and Am-241 by energy discrimination.

  The present invention uses a superconducting phase transition thermometer type (TES type) microcalorimeter to detect LX rays radiated from α-ray decay from superuranium elements in a substance and perform energy discrimination. This is a method for analysis of transuranium elements in substances that directly measure plutonium isotopes. Thus, the main feature of the present invention is that the TES type micro calorimeter is used as the LX ray detector.

  The method for analyzing a transuranium element of the present invention uses a TES microcalorimeter to detect LX rays emitted from a transuranium element in a substance along with α-ray decay and perform energy discrimination to thereby detect plutonium isotopes. Therefore, plutonium and Am-241 mixed in the nuclear fuel material can be discriminated and separated. In addition, plutonium can be measured directly without interference from natural radon progeny. These enable high-sensitivity measurement and non-destructive analysis of plutonium by LX-ray measurement.

Therefore, the method of the present invention is
(1) Collection of basic academic data such as LX-ray emission rate of transuranium elements (2) Evaluation of transuranium elements in facilities or environmental samples (3) Evaluation of human plutonium content (4) In waste Useful for evaluation of transuranium elements.

1 is a schematic diagram of an analyzer used in the present invention. The top view of the TES type micro calorimeter. The spectrum which shows the example of the measurement result by a micro calorimeter. The spectrum which shows the example of the measurement result by a semiconductor detector.

  The present invention uses a TES-type microcalorimeter to detect LX rays radiated from α-ray decay from transuranium elements in a substance and perform direct discrimination of plutonium isotopes by performing energy discrimination. This is a method for analyzing transuranium elements in a characteristic substance. A typical example is a method for discriminating and separating plutonium isotopes from Am-241 by measuring 10 to 20 keV LX rays with a resolution of 100 eV or less.

  An example of the analyzer used in the present invention is shown in FIG. The microcalorimeter 10 includes an absorber 12 that absorbs LX rays, a thin film thermometer 14 whose resistance value changes due to heat generated by the absorber, and heat generated by the absorber 12 and the thin film thermometer 14 is cold stage ( The heat link 18 is configured to control the heat flow to escape to the heat bath 16. When the LX rays radiated from the sample material enter the absorber 12 and are absorbed, the temperature rises slightly. By measuring the temperature rise with the thin film thermometer 14, the energy of the LX rays can be found. This is the principle of measurement. The TES type utilizes a rapid change in resistance from normal to superconductivity as a highly sensitive thin film thermometer. The entire apparatus is cooled to about 100 mK by the cooling device 20, and the current flowing through the microcalorimeter is amplified as a magnetic field signal by the SQUID (superconducting quantum interference device) amplifier 24 via the input coil 22, and the electric signal by the amplifier 26. Converted to amplified. This signal is taken out, the energy is analyzed by the wave height analyzer 28, and the spectrum is displayed.

  Here, as the TES type micro calorimeter, for example, a superconducting thin film thermometer composed of two layers of Au / Ti and a structure in which an Au absorber laminated thereon is provided, and the film thickness of the Au absorber is 10 μm. Hereinafter, for example, it is preferable to set the thickness to about 5 μm.

  For the LX-ray measurement of plutonium isotopes, a TES-type microcalorimeter using a thin-film thermometer consisting of two layers of Ti and Au, which has been proven in X-ray measurement of several keV or less, was designed, fabricated and tested. . The TES type microcalorimeter 10 has a structure in which a thin film thermometer 14 and an Au absorber 12 are laminated on a SiNx film to be a heat link 18 as shown in FIG.

The thin film thermometer 14 is
Thickness: Au (120-70 nm) / Ti (40-50 nm)
・ Operating temperature: Tc = 190mK
・ Area: 500μm in length × 500μm in width
The portion of the Au absorber 12 is
・ Thickness: Au (5.0μm)
-Absorption rate of 20 keV photons: 50%
・ Area: 300μm in length × 300μm in width
It is.

  The measurement test of Pu-239 and Am-241 was carried out using the produced TES microcalorimeter for transuranium element LX-ray analysis. The measurement result (energy spectrum) is shown in FIG. A is the spectrum of Pu-239, and B is the spectrum of Am-241. The energy resolution of X-ray photons with an energy of 10 to 20 keV is about 50 to 60 eV, and it was confirmed that the energy discrimination between Pu-239 and Am-241 mixed in the nuclear fuel material was possible. In addition, since the resolution is high, plutonium can be identified with a small count, and high sensitivity can be realized. Thereby, nondestructive analysis by plutonium LX ray measurement becomes possible.

  Incidentally, with the energy resolution (about 400 eV) of the conventional semiconductor detector, it was impossible to discriminate between Pu-239 and Am-241. The measurement result (energy spectrum) by the semiconductor detector is shown in FIG.

  From these results, the development of new analysis and measurement technology can be expected by demonstrating the measurement of transuranium elements using a TES microcalorimeter, and it is also useful for the preparation of basic data such as LX-ray emissivity data.

10 Microcalorimeter 12 Absorber 14 Thin film thermometer 16 Cold stage (heat bath)
18 Thermal Link 20 Cooling Device 22 Input Coil 24 SQUID (Superconducting Quantum Interference Device) Amplifier 26 Amplifier 28 Wave Height Analyzer

Claims (3)

  Using a superconducting phase transition thermometer-type microcalorimeter, LX rays emitted from alpha uranium elements in materials are detected as a result of alpha ray decay, and plutonium isotopes are directly measured by energy discrimination. A method for analyzing transuranium elements in a substance.   The method for analyzing transuranium elements in a substance according to claim 1, wherein the plutonium isotope and Am-241 are discriminated and separated by measuring 10 to 20 keV LX rays with a resolution of 100 eV or less.   A superconducting thin film thermometer composed of an Au / Ti layer and an Au absorber laminated thereon, and a superconducting phase transition edge thermometer type micro structure having a structure in which the film thickness of the Au absorber is set to 5 μm The method for analyzing a transuranium element in a substance according to claim 1 or 2, wherein a calorimeter is used.

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