Neutron Penetration through Iron and Concrete Shields with the Use of 22.0- and 32.5-MeV Quasi-Monoenergetic Sources

Abstract

For the first time, spectra in the range of 34 MeV down to 0.4 eV for neutrons that penetrated through iron and concrete shields were measured with the use of quasi-monoenergetic sources generated from a [sup nat]Li(p,n)Be reaction. The source neutrons were produced by the bombardment of 35- and 25-MeV protons on a 2-mm-thick natural lithium target and were measured by the time-of-flight method. The neutrons that penetrated through the shields were measured by an NE-213 scintillator, a proton recoil proportional counter, and a spherical multimoderator spectrometer, i.e., the Bonner Ball, and were analyzed to energy spectra by the unfolding methods. The attenuations of a peak fluence, a total fluence, and a dose equivalent were also analyzed. Monte Carlo calculations using the MORSE-CG code were carried out with the multigroup cross-section library DLC-119/HILO86 and the original version, DLC-87/HILO, to evaluate the cross sections by comparison with the measurement. The results of the calculation indicated the following. On the whole, the calculated neutron spectra agreed with the experimental spectra above 10 odd MeV but gave an underestimation below that value. The peak fluence attenuation length for 22-MeV neutrons that penetrated through the iron shield was overestimated by DLC-87 but corrected bymore » DLC-119. The dose-equivalent attenuation lengths almost agreed with the measurement for the concrete shield. On the other hand, those for the iron shield were underestimated.« less