Use of Mohr's Salt for High Level Gamma Dosimetry (Up to 108 Gy)

Abstract

Fricke's dosemeter, which has been used for many years as a transfer dosemeter for doses up to 400 Gy employs Mohrs salt Fe(SO4)2(NH4)26H2O in an ultra-pure solution. The originality of the method proposed is that the salt is irradiated in the solid state. Spectrophotometrc measurements are then made on the absorption peak (345 nm) of a solution of this salt in 0.1 N hydrochloric acid. The solution is more and more diluted as the dose increases in order to remain always under conditions where the Beer-Lambert law is applicable. Two series of experiments are described. In the first series, a 60Co source was used to irradiate small plastic containers filled with powdered Mohr salt. In the second series, 3 mm diameter glass tubes filled with powder were irradiated using a fuel element source (fuel elements from the OSIRIS reactor) which enabled very high integrated doses to be reached. The decaying fission products of this latter irradiator required regular determinations of the corresponding dose rates during irradiation. Alanine ESR dosimetry was used for this purpose. The method proposed is simple, cheap and accurate. A comparison with single crystal LiF measurements is made.