Hyperfine Interactions

, Volume 223, Issue 1, pp 137-146

First online:

Decay spectroscopy of neutron-rich nuclei with A ≃ 100

  • G. LhersonneauAffiliated withGANIL Email author 
  • , B. PfeifferAffiliated withMainz University
  • , K.-L. KratzAffiliated withMainz University

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We review structure data obtained by decay spectroscopy of neutron-rich nuclei of mass close to 100. Emphasis is put on the contribution of experiments at IGISOL in the nineties. They confirmed the earlier postulated shape coexistence in the fast shape-transition region between N = 58 (spherical ground states and low collectivity) and N = 60 (strong axial deformation). A detailed spectroscopic study of the A = 99 chain established the upper-Z limit of the N = 56 shell closure region with 99Nb, owing to striking similarities with 97Y. A consequence of the N = 56 closure is that the s 1/2 odd-neutron becomes the ground state of the most neutron-rich N = 57 isotones, starting with 99Mo, instead of the degenerated d 5/2 and g 7/2 subshells familiar in the tin region. Consequences on the change of spin on astrophysical r-process calculations are briefly discussed. Finally, we say a few words about neutron-rich rhodium and palladium isotopes near the neutron midshell where regular and intruder states coexist very close to each other.


Gamma transitions and level energies 90 ≤ A ≤ 149 PACS Nuclear structure models and methods