Measurement of Prompt Fission Neutron Spectrum of Neptunium-237 for 0.62 MeV Incident Neutrons

Abstract

The prompt fission neutron spectrum of ²³⁷Np induced by 0.62 MeV neutrons has been measured by using a Time-of-Flight (TOF) method with a heavily shielded NE213 scintillator. The 4.5 MV Dynamitron accelerator of Tohoku University was used to produce pulsed neutrons. The sample used was NpO₂ powder enclosed in a stainless steel container.

The fission spectrum data were obtained in the energy range from 0.8 to 12 MeV. Best fit parameters to the experimental data have been derived for the Maxwellian and the Watt type distribution functions.

The Maxwellian temperature T_m of the present work was 1.28±0.04 MeV. It is smaller than the Maxwellian temperature of 1.38 MeV given by JENDL-3.2, but is consistent with that derived by the Howerton-Doyas formula on the relation between the average energy or Maxwellian temperature and the average number of prompt fission neutrons . The measured spectrum is well described in terms of the Watt distribution, X_w = C_w sinh exp(–1.01E).

KEYWORDS:

• neptunium 237
• prompt fission neutron spectrum
• measurement
• MeV range 01–10
• incident energy
• Time-of-Flight method
• NE213 scintillator
• Maxwellian temperature
• Watt distribution