Generation of shielding data for neutron radiation produced by heavy ions

Abstract

The operation of heavy ion accelerators is unavoidably associated with the production of ionizing radiation. Neutron and gamma radiation is released when the impinging ions interact with nuclei of target materials. Consequently the architectural shielding design has to meet the requirements for a sufficient shielding design. The aim of this work is the provision of attenuation data for normal concrete on the basis of double differential source distributions (solid angle, energy) of released neutron radiation, the dominating radiation component for ions in the energy range to be considered here. For this purpose attenuation data for mono-energetic neutron radiation in a spherical geometry were computed using the radiation transport code FLUKA in an energy range from 100 keV to 3 GeV for a depth in the spherical concrete shielding from 1.5 m to 8 m. Measured or calculated double differential neutron yields serve as source terms. The mono-energetic attenuation curves can then be multiplied with the source strength of the corresponding energy bin. A superposition of all neutron energy specific attenuation curves delivers the total dose as a function of the shielding thickness for each angular range provided by the source data. Examples will be given for resulting attenuation curves with the input of measured and calculated double differential neutron yields. This arithmetical procedure can be a useful tool for example for facilities operating heavy ion accelerators with a large variety of ion-target combinations in a wide energy range. Comprehensive data bases for sources distributions are now available which make the shielding planning of these kinds of facilities easier.