"Investigating isomers in heavy neutron-rich nuclei populated in relativistic projectile fragmentation of 238U"
Michael Bowry, University of Surrey
(id #132)
Seminar: NoPoster: Yes
Invited talk: No
Investigating isomers in heavy neutron-rich nuclei populated in relativistic projectile fragmentation of 238U
M Bowry1, Zs Podolyák1, S Pietri2, J Kurcewicz2, M Bunce1, P H Regan1, F Farinon2, H Geissel2,
C Nociforo2, A Prochazka2, J Gerl2, I Kojouharov2, H Schaffner2, N Kurz2, H Weick2, E T Gregor2,
A M Denis Bacelar3, A M Bruce3, G F Farrelly1, N Alkhomashi1, N Al-Dahan1 et al.
1 University of Surrey, Guildford, Surrey GU2 7XH, United Kingdom
2 GSI, Planckstrasse 1, D - 64291 Darmstadt, Germany
3 University of Brighton, Brighton BN2 4GJ, United Kingdom
A relativistic, high intensity beam of 238U ions (Energy/Nucleon = 1 GeV) with an intensity of 2x109 ions per 'spill', provided by the SIS synchrotron at the Helmholtz Centre for Heavy Ion Research (GSI , Darmstadt, Germany) was fired at a 1.6 g/cm2 9Be target to create radioactive beams of neutron-rich nuclei far from stability. The experiment was performed in October 2009. The aim was to produce a variety of new isotopes of mass number A ~ 200 via the fragmentation of the initial, stable 238U beam upon the target. The GSI Fragment Separator (FRS), operated in achromatic mode, was used to select and identify nuclei of interest preceding implantation in a stopper at the final focal position, whereupon the nuclei are stopped completely. Gamma-ray transitions de-exciting isomeric states were detected with high resolution with the high efficiency RISING array of 15 High-Purity Germanium cluster detectors surrounding the stopper. The technique is sensitive to isomeric decays with half-lives of between 100 nanoseconds and 1 millisecond [1].
Relativistic projectile fragmentation reactions have proved to be a powerful method in populating neutron-rich nuclei. The present study complements previous experiments using a 208Pb beam, which provided a large amount of data regarding several new exotic neutron-rich isotopes[2].
Results from two FRS settings will be presented. Our 'exotic' FRS setting focused on nuclei around 200Os (Z=76) and the data analysis is still ongoing. Interest in this region is driven by the need to test and improve theoretical models, particularly those regarding the ground-state shapes of these heavy nuclei, a variety of which are known to exist with increasing mass and proximity to the N = 126 neutron shell closure. For example, from the observation of excited states in 198Os it was concluded that this nucleus is oblate deformed [3].
Another setting was used to select and transmit nuclei located much closer to stability through the FRS. Information on new isomeric states in three nuclei, 195Au, 201Tl and 215Rn was obtained.
Results on isomeric states in the A~200 region will be presented. The obtained experimental level schemes will be compared with theoretical calculations and systematics.
[1] Pietri, S et al, Acta Phys. Pol. B 38, 1255 (2007).
[2] Steer, S J et al, Int. J. Mod. Phys. E 18, 1002 (2009).
[3] Podolyák, Zs et al, Phys. Rev. C 79
M Bowry1, Zs Podolyák1, S Pietri2, J Kurcewicz2, M Bunce1, P H Regan1, F Farinon2, H Geissel2,
C Nociforo2, A Prochazka2, J Gerl2, I Kojouharov2, H Schaffner2, N Kurz2, H Weick2, E T Gregor2,
A M Denis Bacelar3, A M Bruce3, G F Farrelly1, N Alkhomashi1, N Al-Dahan1 et al.
1 University of Surrey, Guildford, Surrey GU2 7XH, United Kingdom
2 GSI, Planckstrasse 1, D - 64291 Darmstadt, Germany
3 University of Brighton, Brighton BN2 4GJ, United Kingdom
A relativistic, high intensity beam of 238U ions (Energy/Nucleon = 1 GeV) with an intensity of 2x109 ions per 'spill', provided by the SIS synchrotron at the Helmholtz Centre for Heavy Ion Research (GSI , Darmstadt, Germany) was fired at a 1.6 g/cm2 9Be target to create radioactive beams of neutron-rich nuclei far from stability. The experiment was performed in October 2009. The aim was to produce a variety of new isotopes of mass number A ~ 200 via the fragmentation of the initial, stable 238U beam upon the target. The GSI Fragment Separator (FRS), operated in achromatic mode, was used to select and identify nuclei of interest preceding implantation in a stopper at the final focal position, whereupon the nuclei are stopped completely. Gamma-ray transitions de-exciting isomeric states were detected with high resolution with the high efficiency RISING array of 15 High-Purity Germanium cluster detectors surrounding the stopper. The technique is sensitive to isomeric decays with half-lives of between 100 nanoseconds and 1 millisecond [1].
Relativistic projectile fragmentation reactions have proved to be a powerful method in populating neutron-rich nuclei. The present study complements previous experiments using a 208Pb beam, which provided a large amount of data regarding several new exotic neutron-rich isotopes[2].
Results from two FRS settings will be presented. Our 'exotic' FRS setting focused on nuclei around 200Os (Z=76) and the data analysis is still ongoing. Interest in this region is driven by the need to test and improve theoretical models, particularly those regarding the ground-state shapes of these heavy nuclei, a variety of which are known to exist with increasing mass and proximity to the N = 126 neutron shell closure. For example, from the observation of excited states in 198Os it was concluded that this nucleus is oblate deformed [3].
Another setting was used to select and transmit nuclei located much closer to stability through the FRS. Information on new isomeric states in three nuclei, 195Au, 201Tl and 215Rn was obtained.
Results on isomeric states in the A~200 region will be presented. The obtained experimental level schemes will be compared with theoretical calculations and systematics.
[1] Pietri, S et al, Acta Phys. Pol. B 38, 1255 (2007).
[2] Steer, S J et al, Int. J. Mod. Phys. E 18, 1002 (2009).
[3] Podolyák, Zs et al, Phys. Rev. C 79
