High resolution measurement of tagged two-neutron energy and angle correlations in Cf252 (sf)

Abstract

Background: Spontaneous fission events emit prompt neutrons correlated with one another in emission angle and energy. Purpose: We explore the relationship in energy and angle between correlated prompt neutrons emitted from 252 Cf spontaneous fission. Methods: Measurements with the Chi-Nu array provide experimental data for coincident neutrons tagged with a fission chamber signal with 10 o angular resolution and 1 ns timing resolution for time-of-flight energy calculations. The experimental results are compared to simulations produced by the fission event generators CGMF, FREYA, and MCNPX-POLIMI IPOL(1)=1. Results: We find that the measurements and the simulations all exhibit anisotropic neutron emission, though differences exist between fission event generators. Conclusions: This work shows that the dependence of detected neutron energy on the energy of a neutron detected in coincidence, although weak, is non-negligible,indicating that there may be correlations in energy between two neutrons emitted in the same fission event.

Scission Neutrons in Spontaneous and Neutron-Induced Fission: Effect on Prompt Fission Neutron Spectra

“…If, for example with this harder neutron spectrum from Pu-Be, a greater cross talk correction is applied, then the angular correlation corrected for this effect would reduce the curves at the very forward and very backward correlation and then the mid -range angles would appear to have more events, which could be interpreted as scission neutrons. (Note: this consultant has had experience with crosstalk of neutron detectors [Schuster 2019] and can say with confidence that it is "tricky business" and deserves extensiv e Monte Carlo modelling where even the uncertainties in the input nuclear data need to be included. )…”

Development of a liquid scintillator based active fission target for FIPPS

“…One limiting aspect of such studies, especially when investigating isotopes with small fission yields, is the γ-ray background originating from β decays of radioactive fission products, particularly compromising the quality of the coincidence energy spectra. In the past fission tagging devices have been developed for measurements of fission and neutron capture cross sections of actinides [9][10][11], fission γ-ray calorimetry [12,13] and measurements of fission neutron distributions [14,15]. The direct detection of one or both fission fragments has been achieved e.g.…”

“…The direct detection of one or both fission fragments has been achieved e.g. with fission ionization chambers [9,14], parallel plate avalanche counters [10,12], Micromegas [11], scintillating gases [15] or thin scintillating films [13]. Although the fission tagging detectors have been versatile for fission studies, they are not suitable for γ-ray spectroscopy due to the long flight-path of the fission fragments, causing Doppler shifts of the emitted γ rays.…”