IOP PUBLISHING PHYSICS IN MEDICINE AND BIOLOGY Phys. Med. Biol. 52 (2007) 5219–5230 doi:10.1088/0031-9155/52/17/008 Improvement of ESR dosimetry for thermal neutron beams through the addition of gadolinium M Brai 1,3 , M Marrale 1,3 , G Gennaro 1 , A Bartolotta 2,3 , M C D’Oca 2 and G Rosi 4 1 Dipartimento di Fisica e Tecnologie Relative, Universit` a di Palermo, Viale delle Scienze, Edificio 18, 90128 Palermo, Italy 2 Dipartimento Farmacochimico, Tossicologico e Biologico, Universit` a di Palermo, via Archirafi 32, 90123 Palermo, Italy 3 Unit` a CNISM, Palermo and Gruppo V Sezione INFN, Catania, Italy 4 Centro di Ricerche ENEA, Casaccia, Rome, Italy E-mail: marrale@difter.unipa.it Received 31 January 2007, in final form 8 June 2007 Published 15 August 2007 Online at stacks.iop.org/PMB/52/5219 Abstract In this paper, the addition of gadolinium is proposed as a useful tool to enhance the electron spin resonance (ESR) sensitivity of organic compounds to thermal neutrons. The target of this work is the detection, through the ESR technique, of the thermal neutron fluence in a mixed field of photons and neutrons. Gadolinium was chosen because it has a very high capture cross section to thermal neutrons; its nuclear reaction with thermal neutrons induces complex inner shell transitions that generate, besides other particles, Auger electrons, which in turn release their energy in the neighborhood (only several nanometers) of the place of reaction. Gadolinium was added to two organic molecules: alanine and ammonium tartrate. The main result obtained was a greater neutron sensitivity for dosimeters with gadolinium than for those without gadolinium for both organic molecules used. Since a dosimeter pair is required to discriminate between the two components of a mixed field, we studied the response of each dosimeter pair irradiated in a mixed field. Through a blind test we verified the usefulness of this dosimetric system and we obtained an estimate of the fluence in the mixed field with a relative uncertainty of 3%, when the pair composed of an alanine dosimeter and a dosimeter with alanine and gadolinium is used. 1. Introduction Neutron applications to tumor radiotherapy are of great clinical and research interest since the discovery of the neutron by Chadwick in 1962. In fact, fast neutron radiotherapy was 0031-9155/07/175219+12$30.00 © 2007 IOP Publishing Ltd Printed in the UK 5219