Shielding of Neutrons from 80-MeV Alpha-Particle Bombardment of Tantalum

The angular distribution, yield, spectra, and attenuation of fast neutrons from the alpha-particle bombardment of a thick elemental tantalum target have been measured. Data obtained by using threshold energy detectors and thermal-neutron detectors were reduced to neutron spectra with the computer program FLUXPOS. Thermal-neutron activation foils were placed in the shielding at 6-in. intervals to determine the neutron attenuation profiles at 0, 75, and 90° from the target. Data show that the neutron spectral slope becomes steeper and the relaxation length (1/e attenuation thickness) decreases with increasing angle.