Measurements of $$^{233}$$U$$(\text {n}_{\text {th}},\text {f})$$ fission product mass yields with the LOHENGRIN recoil mass spectrometer

Abstract

Numerous measurements of fission product yields were performed since the discovery of the nuclear fission process. However, more precise and reliable fission product yields are requested. Lack of covariance matrices make difficult to use it for specific application purposes such as the propagation uncertainty of decay heat. In this work, we propose to measure independently the fission product mass yields for the whole heavy peak (including the symmetric mass region) for the 233 U(n th , f) reaction. Both average values and experimental covariance is provided. The fission product mass yields are measured with the LOHEN-GRIN recoil mass spectrometer of the ILL using an ionization chamber located at the focal plane. A new procedure of data taking has been developed in order to minimize the biases. Concretely several ionic charges and kinetic energy distributions have been measured for each mass. Particular attention has been considered in the monitoring of the target time evolution. Additional corrections were necessary in the symmetry mass region due to contaminants coming from the LOHENGRIN recoil mass spectrometer. A complex Monte Carlo analysis has been developed in order to better propagate all the uncertainties. The fission product mass yields of the 233 U(n th , f) and its associated covariance matrix has been produced. An overall good agreement has been observed with ENDF/B-VIII.0 in contrast with the JEFF-3.3 evaluation. A precision around 2% for the heavy peak has been measured. The experimental covariance matrix was also computed. In the symmetry mass region, two components were observed in the kinetic energy distribution. One of this component was considered as an artifact and was ruled-out.

Measurement of the fission yield of 136Cs in the 239Pu(nth,f) reaction

“…A brief reminder of the analysis is described hereafter. All the details can be found in [6,7]. Several steps are necessary to estimate an independent fission yield with the LOHENGRIN spectrometer:…”

“…A weighted average was computed by using the correlation matrix between all estimates. All details are available in [6]. Moreover, in this work we measured independent fission yields Y(A, Z).…”

Covariance analysis of 235U(nth,f) independent and cumulative fission yields: Propositions for JEFF4

“…4). There is not model input in this analysis and the correlation matrix come from the competition of the positive component of systematic uncertainties and the negative component due to the self-normalization [13].…”

New measurement of the235U(nth,f) fission yields and development of a Time of Flight line at the LOHENGRIN spectrometer

“…Indeed such a device would allow the determination of the velocity of fission products, which is different for the contaminant and the symmetric mass. In a recent analysis for the 233 U(n th ,f) reaction yield measurement [4], a correction for this effect has been applied. It turns out that the low energy component in the symmetric masses kinetic energy distributions is only due to contamination, based on theoretical arguments.…”