Monte Carlo simulation of the energy released by neutrons on organic compounds for EPR dosimetry

In this work we report the analyses of the energy released per unit mass in organic compounds used for EPR dosimetry exposed to neutron beams in order to predict the increase in dose achievable by addition of gadolinium (Gd) inside the pellets. In particular, Monte Carlo (MC) simulations were carried out for alanine, ammonium tartrate and phenolic compounds irradiated with neutron beams with different energy spectra at various depths inside a water phantom. The addition of gadolinium increases sensitivity of these dosimeters to neutrons thanks to the high gadolinium cross section for neutron capture and to the large number of secondary particles (mainly Auger and internal conversion electrons) which are able to release energy inside the sensitive material layers. For small depths in water phantom and low energy neutron spectra the increase in dose due to gadolinium is large. The enhancement is smaller in case of epithermal neutron beam, whereas the increase in dose for fast neutrons is less than 50%. The sensitivity improvements for the various compounds considered were compared. In particular, the sensitivity enhancements were calculated for each neutron energy range (therrmal, epithermal and fast neutrons). The results are explained and discussed on the basis of the compositions of the compounds considered. All results here found suggest that considered organic compounds added with ggadolinium could be fruitfully used for dosimetric applications in Neutron Capture Therapy.