Radiation protection problems at compact cyclotrons for medical and other use

an outline summary is given of five years' experience at the compact cyclotron CV-28 of the Juelich Nuclear Research Center, studying certain aspects of radiation protection. With regard to shield design, experiments with concrete showed a) The worst case target is beryllium b) γ-radiation is sufficiently reduced by the neutron shield c) The neutron yield of gas targets (14-MeV-deuterons on CO2- or CO-targets) and accordingly the equivalent dose rate behind thick shields only amounts to about 20% of the respective values for the beryllium target. With regard to induced activity, special attention was given to air contamination in the cyclotron target room, and the limitations of theoretical models for its evaluation. With regard to personnel exposures, the following conclusions were drawn: a) collective doses increased during the period 1972-1977 of introduction and test of new methods for the production and manufacture of short-lived radionuclides. These could be lowered with increasing experience, improvements in radiation protection and automation of experimental procedures. b) Average annual body doses never exceeeded 10% of permissible dose values. c) The average specific dose could be lowered to 0.23 mrem.mCi-1 (whole body) and 6.6 mrem.mCi-1 (hands), respectively. Constructional materials are also considered for target and beam tube, and shield Typical decay curves are shown for the dose rate of the target case surface and typical γ-spectrometric valuation of the shield. (U.K.)