IMPROVEMENT OF ESR DOSIMETRY FOR THERMAL NEUTRON BEAMS THROUGH THE ADDITION OF GADOLINIUM

In this paper the addition of gadolinium nucleus is proposed as useful tool to enhance the ESR sensitivity of organic compounds to thermal neutrons. The target of this work is the detection of the thermal neutron fluence in a mixed field of photons and neutrons through the ESR technique. The gadolinium nucleus was chosen because it offers a very high capture cross section to thermal neutrons (255000 barns). The nuclear reaction with neutron induces complex inner shell transitions that generate, besides the other particles, also some Auger electrons which release their energy in the neighborhood (only several nanometers) of the reaction place. Two organic compounds were doped with gadolinium: the alanine and the ammonium tartrate. The main result is a greater neutron sensitivity for the dosimeters with gadolinium than for those without gadolinium for both the organic compounds used. Because the use of a dosimeter pair is required to discriminate the two components of the mixed field, we studied the response of each dosimeters pair to the mixed field. Through a blind test we tested the goodness of this dosimetric system and we obtained an estimate of the fluence in the mixed field with maximum uncertainty of 3% using the dosimeters pair of alanine and alanine with gadolinium.