Neutron and gamma-ray spectra from /sup 232/Th, /sup 235/U, /sup 238/U, and /sup 239/Pu after bombardment with 14-MeV neutrons. [Stilbene, NE-213]
The 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 /sup 232/Th, /sup 235/U (with radii of 0.7 and 1.5 mfp), /sup 238/U (with radii of 0.8 and 2.8 mfp), and /sup 239/Pu (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 with 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 approx. 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 discrepancy observed for the neutrons between 0.9 and 10 MeV is 30%. The notable exception is /sup 232/Th, where calculations carried out with the ENDF/B-IV underestimate by a factor of 2 the neutron emission between 5 and 10 MeV. The gamma-ray emission calculations were carried out only with ENDL, because of its overall better representation of the neutron measurements; ENDL overestimates the gamma-ray production, with discrepancies ranging between 5 and 20%. However, use of the measured detector efficiency would reduce the maximum discrepancy to < 13%. To facilitate the use of the neutron data for calculational purposes by other laboratories, an experimental one-dimensional neutron energy spectrum is given for each measurement. 10 figures, 7 tables.
- Research Organization:
- Univ. of California, Livermore
- OSTI ID:
- 5702760
- Journal Information:
- Nucl. Sci. Eng.; (United States), Vol. 72:1
- Country of Publication:
- United States
- Language:
- English
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