Neutron and Gamma-Ray Spectra from a Variety of Materials Bombarded with 14-MeV Neutrons

Measurements of the neutron and gamma-ray leakage spectra from 15 spherical target assemblies (carbon, nitrogen, H₂O, C₂F₄, aluminum, silicon, titanium, iron, copper, tantalum, tungsten, gold, lead, ²³²Th, and ²³⁸U) pulsed with 14-MeV neutrons were made using time-of-flight techniques. The spheres were ∼30 g/cm² thick to maximize the gamma-ray leakage per central source neutron. Among all the materials studied, silicon shows the highest conversion factor (∼2 γMeV/n), and lead the lowest (0.31 γMeV/n). Monte Carlo neutron-photon transport calculations were done using the TART and SANDYL codes, with the ENDL and ENDF/B-V libraries. Comparisons with the neutron measurements confirm earlier results, where both libraries reproduced the leakage spectra for most of these materials reasonably well. The gamma spectra calculated with ENDL give a fair representation of the measurements, with the exception of the initial calculations for ¹⁶O(H₂O) and ¹⁹F(C₂F₄), where serious discrepancies are found. Improvements were obtained for ¹⁶O after a re-evaluation of the neutron-induced cross sections based on more recent microscopic experimental data. This was also the case for ¹⁹F, where the calculations now overestimate the measurements by 30%. Calculations with the ENDF/B-V are lower than the experimental measurements for most of the materials.