The use of gadolinium for ESR dosimetry

Abstract

The application of gadolinium to sensitize Electron Spin Resonance (ESR) dosimeters is reviewed. This nucleus is chosen because it has very good features in interacting with ionizing radiations. In particular, it has a very high capture cross section for thermal neutrons which favors the interactions of these particles within the detector; moreover, the charged secondary particles released after neutron interactions (mainly Auger and internal conversion electrons) are able to release their energy close the gadolinium site and, therefore, inside the sensitive volume of the detector. Consequently, the addition of gadolinium inside ESR dosimeters produces a significant enhancement of thermal neutron sensitivity. Furthermore, the presence of gadolinium can improve the sensitivity to photons because its high atomic number (Z_Gd=64) increases the effective cross photon section of the detectors. However, it must be taken into account for medical dosimetric application of Gd-added dosimeters that the tissue equivalence is heavily reduced. In this work, the response of ESR dosimeters added with gadolinium after irradiation to various radiation beams (such as 60Co gamma photons, thermal neutrons, protons) is described. Monte Carlo simulations able to theoretically model the effects of gadolinium on the ESR dosimeter sensitivity are reported along with the comparison of these computational results with the experimental ones.