β-decay matrix elements from the study of asymmetric emission from polarised nuclei: γ-tagging – a new method for complex β-decay

Abstract: A new method is introduced designed to facilitate study of matrix elements in complex β-decay through the measurement of asymmetric β-emission from a low-temperature polarised source. The method involves coincident detection of the β-emission with subsequent γ-transitions to tag the β-spectrum component. The method is demonstrated by application to the decay of ¹⁴⁰La.