Dipole transition strengths and level densities inA≤80odd-odd nuclei obtained from thermal neutron capture

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Abstract
Level densities and primary E1 and M1 transition strengths recently obtained from extensive studies in fifteen light and medium odd-odd nuclei (20≤A≤80) are analyzed. The level densities are parametrized in terms of the constant temperature Fermi gas and the Bethe formulae; both models provide equally good fits to the experimental results. Empirical relationships between their parameters and simple expressions for the extension of level densities and γ-ray strength functions into the region of noncomplete level schemes are proposed. For nuclei with A≳46 the E1 strengths agree very well with the predictions of the electric giant dipole resonance model; for the lighter nuclei the E1 strengths are stronger than the giant dipole resonance prediction because of direct neutron capture. The observed mass and energy dependence of M1 strengths seems to indicate some influence of the magnetic giant dipole resonance; however, the M1 spectra are strongly structured by nonstatistical effects, in particular in the sd shell.

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