NEUTRON ATTENUATION THROUGH IRON LAYER IN LIGHT WATER.

The thermal neutron attenuation through iron layer bounded by light water was measured in the HTR experimental pool for six cases in which the iron layers had thickness ranging from 2 cm to 20 cm.In order to obtain the removal cross section of iron from measurements of neutron flux with and without iron layer, the following corrections were made.(1) The geometrical correction of the distance between source and shielding plate to account for the use of reactor core instead of fission plate as neutron source.(2) The correction for the effect of the difference between incident neutron spectrum on iron layer and fission neutron spectrum, obtained from the differrence of mean energy between these spectra and the energy dependence of the total cross section of iron.With these corrections, the removal cross section of iron was determined to be Σr=0.165±0.006 cm-1.This method should be applicable to other cases where a reactor is similarly used for the determination of removal cross section.The measured cross section of iron layers thinner than 10 cm was about 6% larger than similar layers of 1520 cm.