Internal Bremsstrahlung: A process to be considered for a realistic study of exposure to high-energy beta emitters.

A process usually neglected in the Beta decay is the Internal Bremsstrahlung (IB), a weak continuous energy electromagnetic radiation associated with Beta emission. Despite this phenomenon is not kept into account in the conventional estimate of the absorbed dose due to the exposure to beta emitter radionuclides, we recently found that such contribution appears worthy of consideration. We implemented different models for the IB spectral distribution in Monte Carlo (MC) codes to simulate the absorbed dose whether or not the IB photon emission is present. Then, at the Institute of Radiation Physics (IRA) in Lausanne, we carried out radiometric measurements aimed at identifying the most proper spectral distribution, by comparing MC simulations with experimental results for high-energy beta emitters such as 90Y and 32P. These studies show that the inclusion of IB photons allows achieving a reasonable agreement with measurements, indicating the most reliable model to adopt for the IB spectral distribution, and also confirming the need to include this process in MC simulations.