Angular distribution measurement of gamma rays from inelastic neutron scattering on 56Fe at the nELBE time-of-flight facility

Mirco Dietz,Stefan E Müller,Tamás Szücs,Daniel Bemmerer,Ronald Schwengner,Toni Kögler,Arnd R Junghans,Louis Wagner,Marcell P Takacs,Roland Beyer,Stefan Gohl,Ralph Massarczyk,Andreas Wagner

doi:10.1051/epjconf/201714611040

Mirco Dietz, Stefan E Müller + Show 11 more

Open Access

https://doi.org/10.1051/epjconf/201714611040

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Abstract

Inelastic neutron scattering from 56 Fe was studied at the n ELBE time-of-flight facility. The incoming neutron energy ranges from 100 keV to 10 MeV in the fast neutron spectrum, where high precision nuclear data are needed. A detector setup has been installed to investigate the γ-ray angular distributions. It contains five HPGe and five LaBr3 detectors positioned at 30, 55, 90, 125 and 150 degrees relative to the beam axis. The intrinsic and the neutron induced background from the setup was subtracted by cyclical measurements with and without the natural Fe-target. Corrections for extended source efficiency and gamma-self-absorption, inside the target, were done using GEANT4 simulations. The angular distributions measured with the HPGe detectors are compared with earlier data. High neutron energy resolution up to a few keV was obtained with the LaBr3 detectors due to their much better time resolution.

Highlights

The fast neutron generator at Argonne National Laboratory provided quasi-monoenergetic neutrons from 7Li( p, n) with an energy resolution of about 50 keV
The incoming neutron energy ranges from 100 keV to 10 MeV in the fast neutron spectrum, where high precision nuclear data are needed
The angular distribution Wn can be determined in a relative measurement, because all detectors measure at the same time and in that way Wn is independent from the neutron flux in contrast to the single detector measurement of Smith [3]

Summary

Introduction

The fast neutron generator at Argonne National Laboratory provided quasi-monoenergetic neutrons from 7Li( p, n) with an energy resolution of about 50 keV. This anisotropy can influence the γ -ray production cross section, if not taken into account as a correction in a partial cross section measurement, e.g., taken at an angle of 125◦. The inelastic scattering cross section on 56Fe shows resonant structures below the second excited state. High-resolution measurements of the γ -ray angular distribution are required to match the resolution of the inelastic scattering cross section measurements e.g., [4] and [5]

Time-of-flight facility nELBE

Data analysis

Setup for angular distribution measurement

Results

Correction of partial cross sections for γ -Ray angular distribution

Conclusion