TIME-DEPENDENT FAST NEUTRON AND SECONDARY GAMMA RAY SPECTRUM MEASUREMENTS IN CONCRETE. VOLUME II.
Final rept. 1 Mar 68-15 Nov 69,
GULF GENERAL ATOMIC INC SAN DIEGO CALIF
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An experimental method was developed for studying simultaneously fast-neutron transport and secondary gamma-ray production and transport in shields. An electron linear accelerator Linac was used to produce intense 50-nsec pulses of photo-neutrons. These neutrons streamed down an evacuated 52-meter long drift tube to strike concrete slabs up to 40 in. thick. A 5 in. by 5 in. cylindrical NE-213 scintillator was positioned behind the concrete slabs to detect both fast neutrons and secondary gamma rays produced in the concrete by n, x gamma and n, gamma reactions. Three parameters time, pulse-height, and neutrongamma-ray identification were recorded for each detection event. Fast neutrons and gamma rays produced by n, x gamma reactions were recorded for times 0.87 to 2.84 microsec corresponding to incident neutron energies 1.8 to 20 MeV. Capture gamma rays were detected for times up to 1500 microsec after the Linac pulse. Pulse-height spectra were binned according to time for neutrons and gamma rays. Then, for each time interval, these pulse-height spectra were unfolded to produce time-dependent fast-neutron 2.0 E 20 MeV and gamma ray 0.8 E 9.0 MeV energy spectra. Thirty-group P3S16Lobatto 1DF neutron transport calculations were performed, and results were compared with measured leakage neutron energy spectra. Author
- Nuclear Radiation Shielding, Protection and Safety