Pb-210 in volume samples: self-attenuation and scattering problems.

In this work we study the effect of the matrix of the source on the spectrum and on the full energy peak efficiency for low energy photons. Using realistic simulations carried out with PENELOPE 2018, including detector resolution, we show that small angle Compton scattering does contribute to the peak count rate, implying the dependence of the matrix effects on the linear attenuation coefficient μ and also on the scattering cross section. We show that the effect of Compton scattering can be removed from the apparent peak, resulting a "clean" peak depending only on μ. We apply the procedure for the evaluation of μ on the basis of uncollimated transmission measurements and subsequently use it for the calculation of self-attenuation corrections. We analyze measurements carried out in IFIN-HH in the context of an intercomparison exercise.