Environmental neutron spectrum outside the LLL high-intensity 14-MeV neutron facility

The Lawrence Livermore Laboratory has been developing several methods for estimating neutron energy spectra in the field. This work has been motivated by the desire to: (1) verify calculations of spectra and dose to personnel in the environment of neutron sources, (2) provide appropriate calibration factors for dosimeters and dose-rate meters used in the field, and (3) provide physics data for the design of improved neutron shielding around some of our sources. Two approaches were explored. Bonner-sphere measurements were made using various foil-moderator and detector-moderator configurations. In addition, high-resolution measurements were made over a restricted energy range using proton recoil spectrometers including NE 213 liquid scintillators and hydrogen proportional counters. A field measurement using the latter technique is described.