MONTE CARLO SIMULATIONS OF THE RESPONSE OF ESR DOSIMETERS TO NEUTRON BEAMS

Electron Spin Resonance (ESR) spectroscopy is extensively used in gamma photon dosimetry.It relies on the detection of the signal from free radicals (paramagnetic species) produced aftersample irradiation. Organic materials, such as alanine and ammonium tartrate, are widely usedfor dosimeter preparation, thanks to the good photon sensitivity and tissue equivalence of suchcompounds. However, the low neutron cross section of their nuclei does not make them suitablefor neutron dosimetry.Thanks to its very high neutron capture cross section and to the high Linear Energy Transferof released particles, even small additions of gadolinium will yield large sensitivity enhancementsof the dosimeters. However, its high atomic number strongly reduces the dosimeter tissue equivalence.Our recent results have shown, both experimentally and computationally (through MonteCarlo simulations), how the ESR response depends on additive concentration, for organic dosimetersadded with gadolinium oxide and exposed to mixed fields of thermal neutrons and gammaphotons. Since Monte Carlo simulations have proved to be a valuable tool for describing theneutron energy released inside the dosimeter, we have decided to extend our computational investigationto neutron beams with composite energy spectra and different irradiation setups, in orderto simulate real Neutron Capture Therapy conditions. The Monte Carlo results presented here willbe useful for planning our future experiments.