Measured limits on radiation damage from low-energy atomic electrons emitted in nuclear beta decay

Electrons with kinetic energy greater than 10 eV can damage a single strand of DNA, while those with greater than 25 eV can damage both strands. Nuclear beta decay changes the electric charge in the nucleus, so bound atomic electrons of the parent atom can be emitted depending on their wavefunction overlap with an electron unbound from the progeny. The typical kinetic energies predicted by calculations of this sudden approximation are similar to the atomic binding energies. We laser-trap and cool ³⁷K, and collect electrons in coincidence with emitted positrons to a position-sensitive microchannel plate detector. using a uniform 150 V/cm electric field. We find we can model the resulting position spectra with existing calculations

using the sudden approximation, letting us deduce the energy spectra. We find the fraction of shakeoff electrons with energies > 10 eV to be 0.105 +--0.025, and > 25 eV to be 0.041+-0.011. Despite the tightly localized energy deposition from shakeoff electrons, as anticipated they would not contribute much radiation damage compared to MeV-energy beta's.