Investigation of neutron activation of ⁹³Nb for a determination of the weak axial vector coupling constant from the ⁹⁴Nb beta-decay spectral shape

The effective value of the weak axial vector coupling constant g_A in nuclear β-decay is of significant theoretical interest and is particularly important for calculations of nuclear matrix elements for neutrinoless double β­-decay. Recent theoretical studies have shown that g_A can be determined by comparing the shape of calculated and experimental β-decay spectra that, for certain nuclides such as ⁹⁴Nb, are sensitive to g_A. We are performing preliminary studies for a measurement of the ⁹⁴Nb β-decay spectrum. This includes studying the production of ⁹⁴Nb via the ⁹³Nb(n,γ)⁹⁴Nb reaction using an Am-Be neutron source. Using a Ge detector, we have studied the γ-ray spectra of activated ⁹³Nb samples. Initial findings indicate that the ⁹³Nb(n,2n)⁹²Nb reaction dominates over ⁹³Nb(n,γ)⁹⁴Nb due to the small neutron capture cross-section of ⁹³Nb. The decay of ¹⁸²Ta was also observed, consistent with neutron activation of ¹⁸¹Ta impurities in our sample. Results for neutron flux calibration of our Am-Be source using the ⁹²Nb and ¹⁸¹Ta data, and prospects for performing a measurement of the ⁹⁴Nb β-decay spectral shape will be discussed.