A simple estimate of the lead thickness of the enclosure for synchrotron radiation experiments

•A simple method to estimate shielding thicknesses for photon beam lines is given.•At energies below the pair production threshold fluorescence and scattering dominate.•The derived expression assuming isotropic secondary radiation can be factorized.•This clarifies the influence of the various factors and enables spread sheet calculation.•No buildup factors are required because always the minimal absorption is used.

A simple estimate for the thickness of the shielding of photon beam lines with energies below the pair production threshold has been developed. In this energy range scattering and fluorescence are the main sources of secondary radiation. In the low energy regime up to about 150 keV fluorescence dominates. This justifies the assumption of an isotropic radiation field allowing the derivation of a simple expression in which the influence of the various parameters like energy bandwidth or distance from the primary beam become clearly visible. Furthermore the simplicity of this expression allows the generation of a spread shield calculation resulting in a simple estimate of shielding thicknesses.