Background: The understanding and description of forbidden decays provides interesting challenges for nuclear theory. These calculations could help to test underlying nuclear models and interpret experimental data.Purpose: Compare a direct measurement of the 138 La β-decay Q value with the β-decay spectrum end-point energy measured by Quarati et al. using LaBr3 detectors [Appl. Radiat. Isot. 108, 30 (2016)]. Use new precise measurements of the 138 La β-decay and electron capture (EC) Q values to improve theoretical calculations of the β-decay spectrum and EC probabilities.Method: High-precision Penning trap mass spectrometry was used to measure cyclotron frequency ratios of 138 La, 138 Ce and 138 Ba ions from which β-decay and EC Q values for 138 La were obtained.Results: The 138 La β-decay and EC Q values were measured to be Q β = 1052.42(41) keV and QEC = 1748.41(34) keV, improving the precision compared to the values obtained in the most recent atomic mass evaluation [Wang, et al., Chin. Phys. C 41, 030003 (2017)] by an order of magnitude. These results are used for improved calculations of the 138 La β-decay shape factor and EC probabilities. New determinations for the 138 Ce 2EC Q value and the atomic masses of 138 La, 138 Ce, and 138 Ba are also reported. Conclusion:The 138 La β-decay Q value measured by Quarati et al. is in excellent agreement with our new result, which is an order of magnitude more precise. Uncertainties in the shape factor calculations for 138 La β-decay using our new Q value are reduced by an order of magnitude. Uncertainties in the EC probability ratios are also reduced and show improved agreement with experimental data.

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The spin and parity dependent nuclear level densities (NLD) are calculated for medium-heavy nuclei using shell model techniques. The NLD are used to calculate cross sections and reaction rates of interest for nuclear astrophysics and nuclear energy applications. We investigate a new approach of describing the shell model NLD via a constant temperature parametrization. This approach provides new information about the effects of symmetries on the temperature of the low-lying nuclear states, and it is shown to be more versatile for applications