Nuclear structure south-east of 48Ca and upwards in spin in the 208Pb region

 

Rafal Broda

 

Niewodniczanski Institute of Nuclear Physics PAN, Krakow    Poland

 

For the last two decades binary reactions taking place in heavy-ion collisions at energies exceeding by 10 to 30% the Coulomb barrier were used to perform spectroscopic study of nuclei that are not accessible in standard fusion evaporation reactions. The present development of such study will be illustrated by the most recent results obtained for few nuclei in the doubly-magic 48Ca and 208Pb regions.

The investigation of the 48K [1] and 49K [2] isotopes will be discussed to show more advanced techniques used to study exotic neutron-rich nuclei of previously completely unknown structure. This study used the data obtained in three experiments.  Two of them were performed at the LNL Legnaro using the PRISMA-CLARA spectrometer.  They provided an initial identification of gamma rays and exploited plunger technique to determine lifetimes of few excited states. The third experiment was performed with the Gammasphere detector array at the Argonne NL and used the standard thick target gamma coincidence method. The obtained results revealed an evolution of nuclear structure with the increase of neutron-richness and provided an experimental input to improve shell model theoretical calculations in the region.

In the 208Pb region the level structures extending up to the record I=30 spin range values were established for the hard-to reach 204Tl [3] and 203Hg [4] nuclei.  The advanced analysis of  multifold gamma coincidences measured with the Gammasphere array for the 208Pb + 330 MeV 48Ca colliding system exploited the presence of several isomeric states to achieve the high detection sensitivity in selected regions of the level schemes.  The established level structures arising from the coupling of available proton and neutron holes show spectacular agreement with the shell model calculation results.  The experimental level scheme established for the 204Tl isotope extends far beyond the presently available shell model calculations and states located in the highest part clearly involve high-spin 208Pb core excitations.  In both the 204Tl and 203Hg nuclei strongly populated yrast states were located just above the highest spin-isomers and could be safely identified with the 3- lowest excitation of the core.  The observed energies of these states reinforce a simple additivity rule governing the coupling of states with maximally aligned valence particles and holes with the octupole vibration of the 208Pb core [5].

 

[1] W. Królas et al., Phys. Rev. C84, 064301 (2011).

[2] R, Broda et al., Phys. Rev. C82, 034319 (2010).

[3] R. Broda et al., Phys. Rev. C84, 014330 (2011).

[4] B. Szpak et al., Phys. Rev. C83, 064315 (2011).

[5] M. Rejmund et al., Eur. Phys.J. A8, 161 (2000).