Measurement of 75As(n,2n) cross section in well-defined spectrum of LR-0 special core

The article describes measurement of the 75As(n,2n)74As reaction rate in a well-defined reactor spectrum of a special core assembled in the LR-0 reactor. It presents a comparison of this value with results of calculations. The reaction rate is derived from activity of 74As which is determined using gamma spectrometry of an irradiated As2O3 sample. The resulting value averaged in reactor spectrum is 77.0 ± 3.9 μb. This cross section is important as it is included as neutron flux monitor in the International Reactor Dosimetry and Fusion File. The calculations were carried out with the MCNP6 code using ENDF/B-VII.0, ENDF/B-VII.1 JEFF-3.1, JEFF-3.2, JENDL-3.3, JENDL-4, ROSFOND-2010 and CENDL-3.1 nuclear data libraries. The comparison between calculation and experiment shows very good agreement. The relative difference between calculation and experiment is lower than the related uncertainty in all cases. The discrepancy is even below 1% with ENDF/B-VII.1 and JEFF-3.2.