Monoenergetic neutrons from the 9Be(p,n)9B reaction induced by 35, 40 and 45-MeV protons

Abstract

The 9Be(p,n)9B reaction was simulated and experimentally conducted in order to test the feasibility of producing monoenergetic neutrons at high energies, for potential uses in various applications. Two distinct peaks of monoenergetic neutrons, well separated by ∼2.4 MeV, were obtained by bombarding a 0.25-mm thick beryllium target with proton beams. For 35, 40 and 45-MeV protons, the corresponding centroid energies of the neutron peaks were (i) 29.4 and 31.8 MeV, (ii) 34.5 and 36.8 MeV, and (iii) 39.7 and 42.0 MeV, respectively. Two approaches were employed for experimental confirmation of the simulated neutron spectra: verification of the known values of the threshold energies of particular (n,xn) reactions, and measurement of the 209Bi(n,4n)206Bi reaction cross section. For verifying the monoenergetic neutrons through the threshold energies, samples of 93Nb, 63Cu and 209Bi were irradiated with neutrons produced by 35, 40 and 45-MeV protons. The measured gamma-ray spectra from the neutron-irradiated samples confirmed the formation of 90Nb, 60Cu and 204Bi radioisotopes and therefore provided evidence that 93Nb(n,4n)90Nb, 63Cu(n,4n)60Cu, and 209Bi(n,6n)204Bi reactions were induced, respectively, by neutrons of 31.8, 36.8, and 42.0 MeV, which are just above the ‘effective’ threshold energies of the respective (n,xn) reactions. In addition, the cross sections of the 209Bi(n,4n)206Bi reaction were measured at 29.4, 31.8, 34.5, 36.8, 39.7 and 42.0 MeV. These newly measured cross sections are close to those predicted by the EAF-2010 and TALYS libraries, which also indirectly verifies the simulated neutron monoenergies. The present studies show that the simulated monoenergetic neutrons can be experimentally reproduced, and their energies can be tailored for applications which require monoenergetic neutrons of different energies.