Internal Bremsstrahlung emission during 32P decay

The aim of this work is to experimentally investigate the role of Internal Bremsstrahlung (IB) in the decay of 32P, a pure β-emitter with end-point energy of 1.71 MeV and half-life of 14.28 days. IB is a continuous electromagnetic radiation occurring in β-decay, that had been widely studied in the past years. Its contribution, even if appreciable, is neglected in Monte Carlo (MC) simulation as well as in dosimetric and radiation protection calculations. Ionization current measurements were carried out using a well ionization chamber and compared with MC simulations, performed in the GAMOS (GEANT4-based Architecture for Medicine-Oriented Simulations) framework. Two experimental data sets of 32P IB spectra, taken from the literature, were used to model the IB photon spectral distribution and to include IB emission as an additional source term in MC calculation. Without IB, MC simulations underestimate up to about −18% the measured exposure, whereas the inclusion of IB according to either of the two spectra lead to differences of +2% or +8%. Consequently, the IB process is relevant for high-energy pure β-emitters such as 32P, and its contribution should be considered in all the dosimetric and radioprotection calculations.