Nuclear shapes from alpha–gamma-ray angular correlations

Abstract

The angular distribution of alpha particles with respect to the spin direction of the residual nuclei is used to probe the shapes of the emitting systems. Two compound systems have been studied: ' Yb and " Sn. Deformed emission shapes are required in order to understand the alpha-gamma correlations in the ' Yb system, but not for the " Sn compound system. These conclusions are identical to those reached by the study of giant resonances built on excited states for very similar systems.

Nuclear structure at high excitation energies

“…More than a decade ago, Gaardhoje et al [1] studied the shape of giant dipole resonance (GDR) built on excited states for ½¼ Sn and concluded that the data are consistent with a mostly spherical shape up to Ì ¾ ¼ MeV. A few years later Majka et al [2] reached a similar conclusion for ½½¼ Sn in a study of « -ray angular correlation measurements. Recently Bracco et al [10] have studied the dependence of the GDR width and angular distribution of the -rays as a function of temperature and spin for ½¼ ½½¼ Sn and concluded that due to thermal fluctuation effects the average deformation becomes very large at Ì ³ ¾ ¼ MeV and  ³ ¼ .…”

“…The partition function is given by  « Á ¿ ¾ Ì (2) where, corresponding to the laboratory Þ-axis cranking, the moment of inertia factor is given by…”

“…Also hot nuclei at low angular momenta can be produced in inelastic «-scattering type reactions. Since several years different isotopes of tin have been the subject matter of investigation of the change in quadrupole shape parameters ¬ and as a function of excitation energy (temperature, Ì ) and spin (Â) [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. From the many body mean field theories, like Hartree-Fock or Hartree-Fock-Bogoliubov, it is expected that with the increase of temperature even the deformed ground state (Ì ¼ ) shape would tend towards a spherical one [15].…”

Influence of nuclear deformation on the correlation of protons emitted from compound nuclei

“…One example is the recent investigation of ~-~ angular correlations in compound nucleus reactions [1]. In this contribution we present the first results from an experiment designed to study the angular correlation of two successively emitted protons measured in coincidence.…”

Defining a reaction plane in particle-fission correlation measurements

“…A variety of techniques have been employed in these studies. Some measurements have used the 7-ray hit pattern observed in a 4 rt spin spectrometer [1,2] to define an average spin orientation. Others have used fission fragments to determine the spin direction [3,4].…”