On an unverified nuclear decay and its role in the DAMA experiment

Understand

The rate of the direct decay of 40K to the ground state of 40Ar through electron capture has not been experimentally reported.

• Aside from its inherent importance for the theory of electron capture as the only such decay known of its type (unique third-forbidden), this decay presents an irreducible background in the DAMA experiment.
• We find that the presence of this background, as well as others, poses a challenge to any interpretation of the DAMA results in terms of a Dark Matter model with a small modulation fraction.
• A 10ppb contamination of natural potassium requires a 20% modulation fraction or more.