Neutron skyshine from proton cyclotron and electron synchrotron

The dose distribution and the spectrum variation of neutrons due to the skyshine effect have been measured with various detectors in the environment surrounding the proton cyclotron and the electron synchrotron. The neutrons were produced from the carbon beam stopper bombarded by 52-MeV proton and extracted upward from the rectangular opening in the concrete shield of the cyclotron, and the neutrons were produced from the iron yoke magnet absorbed the 650-MeV electron beam and leaked from the concrete shield of the synchrotron ring. The dose distribution and the spectra of neutrons on the outer surface of the concrete shield were also measured in order to get information on the skyshine source. The experimental data were analyzed with two Monte Carlo codes, MMCR-2 and SKYSHINE-II, with the result that the calculated results are in good agreement with the experiment. These experiments are very unique since the neutron skyshine from the actual accelerator building was measured and the energy spectrum and dose distributions of the neutron source were clarified. (author)