title: Radical formation in lithium formate EPR dosimeters after irradiation with protons and nitrogen ions.
abstract: Radical formation in polycrystalline lithium formate monohydrate after irradiation with gamma rays, protons and nitrogen ions at room temperature was studied by continuous-wave electron paramagnetic resonance (EPR) spectroscopy. The linear energy transfer (LET) of the various radiation beams was 0.2, 0.7-3.9 and 110-164 keV/microm for gamma rays, protons and nitrogen ions, respectively. Doses between 5 and 20 Gy were given. The EPR reading (the area under the EPR absorption resonance) increased linearly with dose for all types of radiation. As the LET increased, the relative effectiveness (the EPR reading per dose relative to that for gamma rays) decreased, while the EPR line width increased. Track structure theory and modeling of detector effectiveness predicted the dosimeter response observed after proton and nitrogen-ion irradiation. A semi-empirical line broadening model including dipolar spin-spin interactions was developed that explained the dependence of the line width on LET. The findings indicate that the local radical density in lithium formate is increased after high-LET irradiation.
authors.affiliation: Department of Medical Physics, The Norwegian Radium Hospital, Oslo University Hospital, Oslo, Norway.
authors.forename: Einar
authors.initials: E
authors.lastname: Waldeland
authors.forename: Eli Olaug
authors.initials: EO
authors.lastname: Hole
authors.forename: Bo
authors.initials: B
authors.lastname: Stenerlöw
authors.forename: Erik
authors.initials: E
authors.lastname: Grusell
authors.forename: Einar
authors.initials: E
authors.lastname: Sagstuen
authors.forename: Eirik
authors.initials: E
authors.lastname: Malinen
mesh_terms: D017357:Cyclotrons; D004307:Dose-Response Relationship, Radiation; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D005561:Formates; D005720:Gamma Rays; D018499:Linear Energy Transfer; D009590:Nitrogen Radioisotopes; D011522:Protons; D011874:Radiometry / Q000379:methods; D013548:Sweden
chemical_list: D005561:Formates; D009590:Nitrogen Radioisotopes; D011522:Protons; C030544:formic acid