Quenching of gA deduced from the β-spectrum shape of 113Cd measured with the COBRA experiment

A dedicated study of the quenching of the weak axial-vector coupling strength g(A) in nuclear processes has been performed by the COBRA collaboration. This investigation is driven by nuclear model calculations which show that the beta-spectrum shape of the fourfold forbidden non-unique decay of Cd-113 strongly depends on the effective value of g(A). Using an array of CdZnTe semiconductor detectors, 45 independent Cd-113 spectra were obtained and interpreted in the context of three nuclear models. The resulting effective mean values are (g) over bar (A)(ISM) = 0.915 +/- 0.007, (g) over bar (A)(MQPM) = 0.911 +/- 0.013 and (g) over bar (A)(IBFM-2) = 0.955 +/- 0.022. These values agree well within the determined uncertainties and deviate significantly from the free value of g(A). This can be seen as a first step towards answering the long-standing question regarding quenching effects related to g(A) in low-energy nuclear processes. (C) 2019 The Author. Published by Elsevier B.V.