Dosimetric properties of neutron beams from the D-D reaction in the energy range from 6.8 to 11.1 MeV

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Abstract
The tissue kerma in air, the tissue dose at maximum build-up, the relative depth dose on the central axis and dose build-up characteristics were measured for neutrons produced by 6.8, 8.9 and 11.1 MeV deuterons on deuterium. Neutron beams were produced by a variable-energy cyclotron with a fully stopping deuterium gas target 20 cm long. Measurements were made in a 11.1 cm .times. 11.1 cm field 126 cm from the target entrance window. Dose rate apparently increased rapidly with energy from 0.07 rad min-1 .mu.A-1 at 6.8 MeV to 0.35 rad min-1 .mu.A-1 at 11.1 MeV. The entrance dose was about 50% of the dose maximum for each bombarding energy. The depth of the 95% dose level in the build-up region increased from 50 mg cm-2 at 6.8 MeV to 90 mg cm-2 at 11.1 MeV. Penetration was independent of the bombarding energy in the region investigated. Attenuation of the total dose to 50% of the maximum occurred at 10.2 .+-. 0.1 g cm-2 for all 3 bombarding energies. The dose at the maximum is typically 14% higher than the tissue kerma in air.