A new neutron spectrometer with narrow acceptance diagram

Abstract

A new instrument for spectrometry of neutrons has been designed. The original design scheme which is distinct from the widely spread Bonner type neutron spectrometer is used. Main difference is in angular selectivity that is absent in a Bonner spectrometer. Helium counters of thermal neutrons SNM-18 surrounded by a screen and moderator layers for various ranges of neutron energy are used as detectors. The protection from thermal neutrons en- sures the complete shielding of the counters from selected directions that has allowed creating of a spectrometer ac- cepting radiation only from the given direction. Due to using of a detector set with different moderator thickness the energy diapason of a spectrometer spreads from a thermal range up to hundreds MeV. The important feature of the instrument is its angular directivity: the angle of acceptation does not exceed 30-40 degrees. Construction of the spec- trometer (with the detailed representation of all materials which are included in it) has been simulated on GEANT-4 package. This has allowed us to investigate the instrument response to neutrons and other particles of various ener- gies from 0.1 eV up to 300 MeV. The working experimental model of a spectrometer is manufactured and its calibra- tion is carried out. Technical data of the instrument appeared in the consent with calculated. Measuring of the thermal neutron intensity at the ground has shown a significant anisotropy of neutron flux. Determination of a neutron spec- trum over all the indicated energy diapason requires a solution of an inverse problem, i.d. deconvolution.