R. J. Howerton

Measurements and calculations of the leakage multiplication from hollow beryllium spheres

Using the Pulsed-Sphere Method, the leakage spectra from hollow Be spheres of 4.5, 13.8 and 19.9 cm thickness have been measured. The predicted copious production of epithermal and thermal neutrons from the 13.8 and 19.9 cm spherical shells has been verified. A quantitative comparison of measured and calculated time-of-arrival count spectra over the energy range from thermal to ..integral.. 15 MeV indicates that the ENDL-84 library overestimates the leakage spectra between 2 and 10 MeV and in the epithermal and thermal energy regions. In the remaining regions, the leakage spectra are underestimated. Because of the above compensation the inferred leakage multiplication for the 19.9 cm Be is ..integral.. 3% higher than calculations. In the case of the 13.8 cm Be, the compensation is less exact and the inferred leakage multiplication is ..integral.. 9% higher than calculations.

Neutron and Gamma-Ray Spectra from 232Th, 235U, 238U, and 239Pu After Bombardment with 14-MeV Neutrons

AbstractThe neutron and gamma-ray leakage spectra from pulsed spheres having a radius equal to 1.0 mean-free-path (mfp) for 14-MeV neutrons in 232Th, 235U (with radii of 0.7 and 1.5 mfp), 228U (with radii of 0.8 and 2.8 mfp), and 239Pu (with radii of 0.7 and 1.25 mfp) were measured by using time-of-flight techniques. The neutron spectra were measured between 0.9 and 15 MeV using stilbene and NE-213 scintillators. For the gamma rays, the electron recoil spectra were measured between 0.35 and 8 MeV with the NE-213 detector only. Pulse-shape discrimination and flight paths of ∼10 m were used in these measurements. The measured spectra are compared with calculations carried out with TARTNP, a coupled neutron-photon Monte Carlo transport code. The Lawrence Livermore Laboratory ENDL (neutron and photon cross sections) and ENDF/B-IV libraries were used in these calculations.In the region between 10 and 15 MeV, the calculated neutron spectra are in good agreement with the measurements (±5%). The maximum discrepan...