Cosmic-ray neutron spectrometry by solid state detectors

Extensive data have been gathered since the early 1990s on the response of different detectors based on the registration of neutron- induced fission in bismuth, gold, tantalum by the spark replica counter and the thin film breakdown counter. These detectors make it possible to exploit the excellent characteristics of the fission reactions in bismuth, gold and tantalum for the measurements of high- energy neutrons. Most of the investigations have been carried out at the quasi-monoenergetic neutron beam facility at The Svedberg Laboratory-TSL of the Uppsala University in cooperation with the Khlopin Radium Institute (KRI). The responses of different fission detectors in the intermediate range of neutron energy (35-180 MeV) have been evaluated: a region where the predictive power of available nuclear reaction models and codes is not reliable yet. For neutron energy greater than 200 MeV, the fission-detector responses have been derived from the data of the proton fission cross-sections. Finally, by using the ratio of the responses of these detectors, a simple and accurate way to evaluate the spectrum hardness can be obtained, thus providing a tool to obtain spectral information needed for neutron dosimetry without the need to know the entire spectrum. The experimentally measured spectra obtained to-date have different shapes and they are also different from those calculated. In this paper, a new approach will be reported to analyse the existing spectra by using response ratios of different detectors. Preliminary data have been already obtained for the high-energy neutron spectrum from the CERN concrete facility.