International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

For unfolding neutron spectra at physical accelerator facilities in a very wide energy range, Bonner multi-sphere spectrometers are effectively used. Such spectrometers consist of a thermal neutron detector placed in spherical polyethylene moderators of various diameters which are characterized by certain sensitivity functions. The report proposes an approach to optimizing the choice of the number and size of spheres for conducting rational measurements and subsequent unfolding of neutron spectra using Tikhonov’s regularization method. Our approach is based on the use of weighting factors in the regularization functional, built on the condition numbers of the Gram matrix of the set of sensitivity functions. The effectiveness of the approach is demonstrated using the spectral unfolding of reference neutron fields of the JINR Phasotron.

A dose assessment of external neutron irradiation at high-energy accelerating complexes, where neutron energy can be in a wide range of 10-8 to 103 MeV, is important for staff radiation safety. In this case, Bonner multi-sphere spectrometers can be used to register the neutron flow. The work proposes a method for unfolding the neutron spectrum by Bonner spectrometer readings, based on the use of the detector sensitivity functions as the basic functions of decomposition of the spectrum under consideration. To find the decomposition coefficients, the system of integral Fredholm equations of the 1st kind is used. From a mathematical point of view, this problem is the illposed one and is solved numerically using the A.N. Tikhonov regularization method. According to the received energy spectrum of neutrons, an assessment of the dose of irradiation is made at the detection locations. The results of unfolding the neutron spectrum at the JINR Phasotron and the dose to its personnel are presented.