Structural and statistical aspects of extensive level schemes from (N,γ) and transfer reactions

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Abstract
The very precise spectrometers for (n,γ) and (n,e) reactions at the ILL, Grenoble, and the high resolution Q3D spectrograph at the Munich Tandem Accelerator yield very detailed information on nuclear transitions and excitations. These results allow the establishment of level schemes which are rather complete in a given spin and energy region and which contain frequently more than 70 levels with spin and parity information. Recently the nuclei 20F, 24 Na, 28Al, 36Cl, 40K, 41K, 42K, 114Cd, 134Cs, 155Sm, 154Eu, 155Gd, 161Dy, 163Dy and several actinide nuclei have been investigated. The limits of this method and the possibilities to identify nuclear structures will be discussed. In particular the mixing of single particle and vibrational excitations in deformed nuclei will be treated. A statistical analysis of these extensive level schemes gives information on the level density, on the strength of gamma transitions and on gamma multiplicities of levels. A systematic survey of gamma multiplicities of low spin levels shows that these multiplicities increase only slowly after the first 20 levels while the spread seems to decrease. Level density parameters for the constant temperature and Bethe formulae are determined. These formulae reproduce nicely the experimental level densities. The distribution of the E1 and M1 strength of primary transitions is compared with theoretical predictions. The energy dependence of dipole transitions in the Cl and K isotopes agrees better with an E3 proportionality than with E5 observed for heavier nuclei. Non‐statistical distribution of M1 strength in the sd shell nuclei was seen and might be explained by nuclear structure effects.

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