Calculated neutron spectra from 9Be(α, n) sources

Abstract

The neutron spectra from 9Be(α, n) sources are calculated for the α emitters 241Am, 210Po,and 239Pu. For a Pu–Be source, peaks are found at neutron energies of 0.75, 1.20, 2.10, 3.15, 4.95, 6.50, 7.75, and 9.65 MeV. Similar peak positions are found for sources made with 241Am and 210Po. The effect of the α-energy losses in the α-emitting material is studied by means of a simple model consisting of clusters of the α-emitting material embedded in a matrix of beryllium. For sources composed of clusters of AmBe13 or PuBe13 in beryllium, the changes in shape of the neutron spectrum are minor as the cluster size is increased from 0.5 to 20 μ. However, for sources consisting of clusters of Pu and Am or Po embedded in beryllium, the spectrum is considerably distorted as the cluster size is varied from 0.5 to 10 μ. The neutron yield per 106 α particles is calculated for sources having Am, Po, or Pu clusters ranging in size from 0 to 20 μ and AmBe13 or PuBe13 clusters ranging from 0 to 40 μ. The percentage of neutrons below 1.5 MeV including the contribution from the multiparticle reaction 9Be(α, αn)8 Be is estimated to be 16% for an AmBe13 type of source and 12% for a PuBe13 type of source, each with a cluster size of 0.5 μ.