Multiscale time-bin analysis of delayed gamma-ray spectra of fission products

Abstract

The present work provides an analysis scheme of delayed gamma-ray spectra based on multiscale time-bin measurements in order to draw conclusions on the association of observed gamma-lines to certain nuclides, especially following the fission process to serve nuclear safeguards and security. The provided time-bin analysis scheme focuses on estimating post-irradiation decays of fission products with interfering gamma-ray lines having energies within the resolution of the used gamma detector. Being a source of deviation, instead of the fixed values of cooling time before each measurement, pinning down the accurate time for each time-bin that should be assigned to each radionuclide in each measurement had been determined independently. This scheme had enabled multiscale of the time-bin analysis ranging from a minute to hours. Experimental measurements were carried out on a natural uranium dioxide sample irradiated in a mixed field of water moderated neutrons. A stable neutron flux from a 5 Ci Am-Be source was used. Results showed great potential for the use of identification and assessment of the contents. The multiscale time-bin analysis scheme was able to resolve the 74 keV gamma-band to obtain the cross-section for 238U(n,γ)239U reaction, the 884.09 keV gamma-line of 134I/ 134Te, the 306.8 keV gamma-line from 101Tc/101Mo, and the 658 keV gamma-line of 97Nb/97Zr. Time-bin analysis showed that 134I, 101Tc, and 97Nb are not, by themselves, primary fission products, but rather they are the daughters of their high-yield parent fission products (134Te, 101Mo, and 97Zr). In the article, the mathematics of the proposed multiscale time-bin analysis is thoroughly outlined.