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). •Gaseous fission products have been produced through neutron irradiation of highly-enriched uranium at NPL.•A high-resolution beta-gamma coincidence detection system has been used to measure the gaseous fission products.•This paper compares the expected isotopic activity ratios from nuclear decay-ingrowth calculations with measurements.•The 135Xe half-life was determined through measurement and is in excellent agreement with the literature value.