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Purpose:Boron Neutron Capture Therapy (BNCT) is a special kind of particle therapy, based on the neutron induced fission of the boron isotope 10B [1]. We have performed dosimetry experiments on the mixed neutron and gamma fields at the TRIGA Mark II research reactor in Mainz. Commonly, dosimetry in such fields is realized by foil activation and ion chambers [2]. Here we investigate alanine as an easier and more robust alternative dosimeter.Methods:We have performed four phantom experiments at the TRIGA Mark II research reactor in Mainz [3], in a predominantly thermal neutron field with a strong gamma component. All alanine pellets irradiated are manufactured and read out at the National Physical Laboratory (NPL), United Kingdom [4]. To predict the dose and its components for each pellet, the Hansen & Olsen detector response model [5] is applied along together with FLUKA [6].Results:The measured dose response of all pellets could be reproduced by calculations within a uncertainty of 5 %. For all experiments three dose components have been separated. A proton dose is generated in the 14N(n,p)14C reaction. Secondary gammas are generated by various (n,γ) reactions, dominated by the 2.2 MeV photon from neutron capture of hydrogen. The primary gamma dose deposited originate from the reactor core itself.Conclusion:Alanine dosimeters are suitable of measurements in mixed neutron fields and the alanine response in thermal neutron fields can be fully understood by the used interpretation model. In further experiments the dosimeters will be exposed to higher neutron energies, which are more typical for BNCT treatments.References:[1] Barth, R.F; 2009: Boron neutron capture therapy at the crossroads: Challenges and opportunities. Applied Radiation and Isotopes 67, 3-6.[2] Rogus, R.D.; Harling, O.K.; Yanch, J.C.; 1994: Mixed field dosimetry of epithermal neutron beams for boron neutron capture therapy at the MITR‐II research reactor. Medical Physics 21, 1611-1626.[3] Hampel, G.; Blaickner, M.; Knorr,J.; Kratz, J.V.; Lizón Aguilar, A.; Minouchehr, S. et al.; 2009: Irradiation facility at the TRIGA Mainz for treatment of liver metastases. Applied Radiation and Isotopes 67, 238-241.[4] Sharpe, P.; Sephtan, J.; 2000: An automated system for the measurement of alanine/EPR dosimeters. Applied Radiation and Isotopes 52, 1185-1188.