Spectroscopy along the proton drip line

This page describes the spectroscopic studies along the proton drip line One of the goals is to determine the limits of the number of protons and neutrons that can be found inside the nucleus. It is also of interest to study the possible new phenomena in nuclear structure caused by the large excess off protons.

The RITU separator has been extensively employed in spectroscopic studies along the proton drip line. Both the delayed spectroscopy, using the GREAT array placed at the focal plane of RITU, and prompt spectroscopy, using the JUROGAM II array placed around the target position of RITU have been used in these studies.

At and beyond the drip line the main problem is how to produce satisfactory amounts of nuclei to obtain spectroscopic information. Only few events are enough to define the ground state properties of a nucleus, however it is of importance to obtain information of the excited states as well to make any conclusions about the nuclear structure. For these studies, state-of-the-art systems are needed.    

The N = Z = 50 shell closure is one of the ultimate goals for such studies. For example above 100Sn spectroscopic studies have been performed for 110Xe [1] and 109I [2]. Enhanced collectivity arising from n-p interaction is suggested based on results obtained from these works and when compared to the level systematic obtained from the heavier isotopes. 

Above the shell closure N = 82 (and Z = 72) four new proton emitters have been identified using the RITU separator. The proton-decay properties have been measured for the first time for 159Re [3], 164Ir [4], 170Au, and 176Tl [5]. In many cases the decay properties were measured also for the heavier odd-Z proton emitters with much improved statistics.

The main area in our studies at the drip line have been the very neutron-deficient nuclei above the Z = 82 shell closure. Even though the proton emitters have not yet been reached in these studies, many delayed and prompt spectroscopic studies have been performed at and beyond the proton drip line for bismuth [6], astatine [6-10], and francium [11] isotopes. The down sloping intruder states, the shape coexistence and the onset of deformation as function of decreasing neutron number and the fact that the odd-Z nuclei become proton unbound provides an interesting domain for these studies.

  1. M. Sandzelius et al., Phys. Rev. Lett. 99, 022501 (2007)
  2. M. Petri et. al., Phys. Rev. C 76, 054301 (2007)
  3. D. T. Joss et. al., Phys. Lett. B 641, 34 (2006)
  4. H. Kettunen et. al., Acta. Phys. Pol. B 32, 989 (2001)
  5. H. Kettunen et. al., Phys. Rev. C 69, 054323 (2004)
  6. M. Nyman, Research Report No. 12 (2009)
  7. H. Kettunen et. al., Eur. Phys. J A 16, 457 (2003)
  8. H. Kettunen et. al., Eur. Phys. J A 17, 537 (2003)
  9. K. Andgren et al., Phys. Rev. C 78, 044328 (2008)
  10. U. Jakobsson et. al., Phys. Rev. 82, 044302 (2010)
  11. J. Uusitalo et. al., Phys. Rev. C 71, 024306 (2005)