Internal bremsstrahlung in beta decays

This study investigates the effect of partially absorbed internal bremsstrahlung photons on the shape of beta spectra, a scenario more akin to experimental reality than the usual assumptions of either full absorption or complete loss. To this end, two theoretical models of the internal bremsstrahlung process were implemented in a custom program: the historical KUB model and a more advanced QED model that includes Coulomb and recoil corrections. Both were validated against experimental data across various atomic numbers. Geant4 simulations were next developed to model internal bremsstrahlung emission during beta decay events for two realistic experimental setups, considering a well-suited radionuclide for each. Results showed a minimal impact on the beta spectrum of ⁹⁹Tc when measured with a cryogenic detector, and a modest but discernible effect at high energy for ³²P when measured with silicon detectors. Sensitivity of the spectrum shape to internal bremsstrahlung effect would require the measurement of approximately 10⁹ events for ⁹⁹Tc and 10⁸ events for ³²P, making experimental detection of this effect challenging. Despite this, the study offers a flexible methodology for assessing spectrum distortions due to internal bremsstrahlung in future experiments involving other radionuclides and detection systems.