Quasiparticle spectra near the yrast line

A description of high-spin phenomena in atomic nuclei is presented from both the experimental and theoretical points of view. The characteristic features of collective nuclear motion, such as rotational bands, band crossings, and backbending, as well as noncollective aspects, like high-spin isomers and irregular decay patterns, are discussed in detail. Recent achievements of the cranking model including the independent quasiparticle and the shell correction methods are reviewed. Changes in the structure of nuclei excited up to the highest possible angular momenta are analyzed; in particular, angular momentum alignment effects, shape changes, possible phase transitions, and sudden rearrangements in the single-particle structure are discussed. Phenomena related to the nuclear quasicontinuum spectra are also examined.

High-spin phenomena in atomic-nuclei

Developing the Recoil Distance Doppler-Shift technique towards a versatile tool for lifetime measurements of excited nuclear states

Spectroscopic properties of fission isomers

The Cranked Shell Model (CSM) interprets the rotational bands of deformed nuclei as configurations of quasiparticles moving in a rotating potential. The most important consequences of this independent particle picture, such as the additivity of the aligned angular momentum, the grouping of band crossings around characteristic frequencies and the oscillating strength of band mixing seem to be born out by the data on i13/2 neutron aligned bands. The alignment process in the other high spin orbitals, as h11/2-, h9/2-, i13/2-proton and j15/2-neutron are surveyed. The available data are compatible with the CSM-predictions. At the highest angular momenta high spin orbitals from the adjacent shells (specially i13/2-protons) enter the yrast region. An analysis of rotational bands in terms of aligned and collective angular momentum indicates a reduced collective part in the presence of aligned quasiparticles. The relation to γ-γ correlation experiments is discussed.

http://iopscience.iop.org/article/10.1088/0031-8949/24/1B/034/pdf

Spin Alignment in Heavy Nuclei

Discrete yrast transitions from states with spins up to $I=38$ have been observed in $^{158}\mathrm{Er}$ via the reaction $^{122}\mathrm{Sn}(^{40}\mathrm{Ar}, 4n\ensuremath{\gamma})$ In addition to the pronounced backbend at $I=14$ and the upbend at $I=28$ previously known, the start of a third yrast discontinuity at $I=38$ is indicated Candidates for the $I=40$ state are suggested and possible causes of the yrast discontinuity are discussed

https://escholarship.org/content/qt74d9b09s/qt74d9b09s.pdf?t=p0llnz

Second Discontinuity in the Yrast Levels of Er 158

Multiplicities as a function of ..gamma..-ray energy have been measured for continuum ..gamma..-ray spectra produced in argon reactions at several bombarding energies on various targets. With the heavier systems there exist regions in the spectra that have particularly high multiplicities which can be associated with the yrast (collective) cascade. The results suggest that the angular momentum in the ..gamma..-ray cascade is limited by ..cap alpha.. emission for Z approximately-less-than 60 and by fission for Z approximately-greater-than 60.

/pdf/energy-dependent-multiplicities-of-continuum-gamma-rays-2v33q285il.pdf

Energy-dependent multiplicities of continuum. gamma. rays

Gamma-ray multiplicities have been measured as a function of the light-fragment atomic number Z{sub 3} for the above reactions. The events associated with sequential fission of the heavy fragment were distinguished from binary events by means of a triple coincidence. The failure of the measured y-multiplicities for deep-inelastic collisions to rise with decreasing Z{sub 3}, according to the rigid-rotation limit, appears more likely to be associated with a selective population of the low Z fragments by the lower {ell}-waves rather than to an incomplete relaxation of the rotational energy.

/pdf/evidence-for-angular-momentum-fractionation-in-86kr-induced-15fbgk3tkc.pdf

EVIDENCE FOR ANGULAR MOMENTUM FRACTIONATION IN 86Kr-INDUCED REACTIONS ON 107,109Ag, 165Ho AND 197Au

Measurements of lifetimes and feeding times for high spin states in 156Dy

Multiplicities as a function of $\ensuremath{\gamma}$-ray energy have been measured for continuum $\ensuremath{\gamma}$-ray spectra produced in argon- and calcium-induced reactions. A peak sometimes occurs in the multiplicity spectrum, indicating a correlation between $\ensuremath{\gamma}$-ray energy and multiplicity (spin). This correlation can be explained by rotational motion of the nucleus, suggesting basically prolate nuclear shapes. Absence of structure in the multiplicity spectrum is interpreted to indicate noncollective motion, and hence spherical or oblate shapes.

/pdf/nuclear-shapes-at-high-angular-momentum-52rycsk3nv.pdf

M. M. Aleonard

Papers

Second Discontinuity in the Yrast Levels of Er 158

Energy-dependent multiplicities of continuum. gamma. rays

EVIDENCE FOR ANGULAR MOMENTUM FRACTIONATION IN 86Kr-INDUCED REACTIONS ON 107,109Ag, 165Ho AND 197Au

Measurements of lifetimes and feeding times for high spin states in 156Dy

Nuclear shapes at high angular momentum