The use of small MnSO4-baths for calibration of neutron sources

The uncertainty of neutron source strength determination by means of the Mn55-activation in aqueous MnSO4-baths is principally determined by two kinds or errors: the uncertainties of the correction factors to be applied for all kind of fast, intermediate and thermal neutron losses by nuclear reactions and by leakage, and the experimental errors in determining the Mn55-concentration and finally the Mn56-saturation activation. With decreasing source strength the experimental error increases and determines often the uncertainty of the result. The situation can be improved by decreasing the bath size, which increases the specific activation. However, at the same time the neutron-loss correction and its uncertainty increases. Systematic experimental studies have been performed on the Mn55-activation in different sized spherical and a large size cylindrical bath, with varying Mn55-concentration, using AmBe-neutron sources with varying source strengths. The Mn56-activity is measured by a NaJ(TL) crystal dipped into the bath. The experimental results of bath activation were compared with computer data based on calculations with the one dimensional multigroup code ANISN. A quantitative error analysis was applied to determine the crucial uncertainties of the technique as a function of neutron source strength