Experimental calibration of matching foils for avoiding thermal neutron flux perturbation

An experimental calibration of flux perturbation has been made with specially prepared neutron detecting foils producing only negligible perturbation in the thermal flux in a graphite medium. The foil material was composed of a 99.8% D₂O solution of MnSO₄. The manganese in the MnSO₄ served as the activating substance. The detecting foils were so prepared as to possess a moderating ratio equal to that of the medium. The calibration was made near the matching point, with foils of various concentrations of manganese, ranging from 1.39 to 13.9 Mn-mg/cc. The results of experiment indicated that the perturbation near the matching point was fairly insensitive to manganese concentration. The matching concentration was determined graphically. (author)