Calculating the Linear Energy Transfer Distribution in Radiobiological Experiments on the U400M Cyclotron

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Abstract: Radiobiological experiments with the irradiation of various biological samples by nuclei from boron to neon with a primary energy of 30-50 MeV/nucleon are performed on the U400M cyclotron of the Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research. The linear energy transfer (LET) of the nuclei in samples is calculated using the code Lise++. For reducing the energy of nuclei and increasing their LET, aluminum filters with different thickness are placed before samples. The presence of filters and other absorbers before a sample results in the production of secondary charged particles whose LET may strongly differ from the LET of primary nuclei of the beam. This also affects the accuracy of calculating the absorbed dose. For this reason, detailed calculations of particle fields in samples are performed using the Monte Carlo code for radiation transport in matter PHITS 3.20 for several variants of sample irradiation with thick absorbers before samples. The calculated LET distributions are analyzed and compared with the calculations using the code Lise++.