Shielding Experiments at High Energy Accelerators of Fermilab (III): Neutron Spectrum Measurements in Intense Pulsed Neutron Fields of The 120-GeV Proton Facility Using A Current Bonner Sphere Technique

Neutron energy spectra behind iron and concrete shields have been measured at the anti-proton production target station in Fermi National Accelerator Laboratory to provide shielding benchmark data of neutrons produced from 120-GeV proton induced reaction. To measure neutron spectra in the radiation bursts accompanied by the injection of intense pulsed proton beam into the target, we have developed a current readout technique of a multi-moderator spectrometer. We employed a pair of BF 3 proportional counters filled with different 10 B isotope enrichment gases, nat BF 3 (18% enrichment) and 10 BF 3 (96% enrichment) and used them as current readout ionization chambers to avoid signal pile-up problem. The spectrometer is aimed to discriminate neutrons from other particles such as -rays and muons incoming in short bursts by subtracting results of the nat BF 3 counter from that of the 10 BF 3 counter. The neutron spectrum obtained with the present technique is generally consistent with results of neutron-induced activation measurements