International comparison of activity measurements of 133Xe

Production and measurement of fission product noble gases

Gaseous fission products have been produced via thermal neutron irradiation of a highly-enriched uranium target and extracted using a custom gas processing system for measurement on a prototype, high-resolution β - γ coincidence detection system. The gas was extracted and measured in two stages in order to measure the prompt and β^--delayed fission products. This paper presents an overview of the system used to produce gaseous fission products, and the results of the advanced coincidence spectrometry techniques used to identify and quantify decays from the radionuclides produced, including the noble gases ⁸⁵Kr, ^85mKr, ⁸⁸Kr, ¹³³Xe, ¹³⁵Xe, ^133mXe and ^135mXe, as well as ¹³³I and ⁸⁸Rb. The measurements were validated by determination of the nuclear decay half-lives, specifically for the ground state decay of ¹³⁵Xe, which was found to be 9.15(49) hours and consistent with the literature value. This work demonstrates the UK capability to produce gaseous radionuclides for quality assurance and calibration purposes in Radionuclide Laboratories supporting the Comprehensive Nuclear-Test-Ban Treaty (CTBT).

Experimental facility for the production of reference atmosphere of radioactive gases (Rn, Xe, Kr, and H isotopes)

Radioactive gases are of great interest for environmental measurements and can be distinguished in two categories. The natural radionuclides such as the isotopes of radon (²²²Rn and ²²⁰Rn), and the anthropogenic radionuclides coming from fission products (isotopes of Xe and ⁸⁵Kr) and activation products (³H and ³⁷Ar). Gas monitoring in the environment is an important issue for radioprotection and for the Comprehensive Nuclear-Test-Ban Treaty (CTBT), which both require metrological traceability of these gases. For this purpose, two gas chambers, of 42 L and 125 L, have been conceived and built at the LNE-LNHB to produce reference atmospheres of various gas mixtures. These chambers were created in order to provide any radioactive gas atmosphere with a wide range of activity concentrations (Bq·m^-3 to MBq·m^-3). The goal of this setup is to be representative of the different environmental conditions for detector qualification and to perform studies of radioactive gas absorption in materials of interest. As a result, the 2 chambers used in this experimental facility are designed to work from vacuum pressure to atmospheric pressure, with a constant activity concentration for any radioactive gas, and under dry to high humidity conditions. It can also be used in a static mode, in which the activity concentration will follow the radioactive decay of the gas. In this paper, the characterization of the chambers will be discussed. These two chambers are combined with different primary standards established by the LNE-LNHB. As the production of the reference atmosphere depends on the primary standard method, we present the details for each atmosphere production, which require a well-known volume, pressure or a direct activity concentration measurement.