Spectrometry of 50 and 100 MeV quasi monochromatic neutron fields with extended range Bonner spheres

Abstract

Quasi monochromatic neutron fields (QMN) from 50 to 180MeV are produced at TSL, The Svedberg Laboratory (Uppsala University, Sweden) by exploiting the 7Li(p,n) reaction in the forward direction. The energy distribution of these fields includes a main high-energy peak, with a few MeV width, superposed to a low-energy tail having its maximum in the tens of MeV region. Because this low-energy tail can be as important as 50% or more in terms of neutron fluence, the knowledge of its energy distribution is essential to completely characterize the QMN neutron fields. This is especially needed when QMN fields are used to irradiate devices with non-zero response to low-energies.This work presents the complete neutron spectrometry, from thermal energies up to the nominal peak energy, of the 50 and 100MeV QMN fields produced at TSL. This was done by means of two extended range Bonner Sphere Spectrometer (ERBSS) relying on different central detectors and independently calibrated. In spite of its known limitations such as the poor energy resolution, this spectrometer is still the only one capable to simultaneously respond to all energies of interest. Significant outcomes of this work are the neutron spectra and the determination of spectrum-integrated quantities such as the total fluence and the peak fluence.