"Beta decay spectroscopy of 81Zn from an isotopically pure radioactive beam"
Miguel Madurga, University of Tennessee
(id #42)
Seminar: YesPoster: No
Invited talk: No
The beta decay of the neutron rich N=51 nucleus 81Zn was investigated in order to establish the ground state configuration of 81Zn and the excited states in the N=50 isotone 81Ga. The high detection efficiency digital beta/gamma spectroscopy setup at the HRIBF (Oak Ridge) was used. The isotopically pure radioactive beam of 81Zn obtained by means of high resolution isobar separator was critical for the success of this measurement.
The selectivity of beta decay allowed us to investigate the spin assignment of 81Zn ground state. The systematics observed in the first 1/2+ state in N=51 istotones suggested some scenarios were the 81Zn ground state spin is 1/2+ instead of conventionally expected 5/2+ [1], an effect observed in Hartree-Fock calculations [2]. The beta decay branching ratio observed in our work strongly suggests a 5/2+ assignment for the 81Zn g.s. This result is supported by our shell model calculation of the 81Zn excited states. Our predicted 5/2+ g.s. for N=50 isotones implies large g.s. branching ratio and thus short half-lifes for these important r-process nuclei.
In this work we present the first observation of high energy states in 81Ga, strongly populated in the beta decay of 81Zn, indicating allowed Gammow-Teller transitions. Similar Gamow-Teller transitions have been previously observed in the decay of 83Ge into the N=50 isotone 83As, explained as exciations of the N=40 core [3]. The evolution of core excitations in N=50 isotones indicates a strengthening of the N=40 subshell closure in neutron rich nuclei. This result, combined with the observed weakening of the N=50 shell closure [4], suggests a preponderance of the N=40 over the N=50 shell closure in the 78Ni region.
[1] D. Verney et al., Phys. Rev. C 76, 05432 (2007)
[2] J. Winger et al., Phys. Rev. C 81, 044303 (2010)
[3] J. Winger et al. Phys. Rev. C 38, 285 (1988)
[4] T. Rzaca-Urban et al., Phys. Rev. C 76, 027302 (2007)
The selectivity of beta decay allowed us to investigate the spin assignment of 81Zn ground state. The systematics observed in the first 1/2+ state in N=51 istotones suggested some scenarios were the 81Zn ground state spin is 1/2+ instead of conventionally expected 5/2+ [1], an effect observed in Hartree-Fock calculations [2]. The beta decay branching ratio observed in our work strongly suggests a 5/2+ assignment for the 81Zn g.s. This result is supported by our shell model calculation of the 81Zn excited states. Our predicted 5/2+ g.s. for N=50 isotones implies large g.s. branching ratio and thus short half-lifes for these important r-process nuclei.
In this work we present the first observation of high energy states in 81Ga, strongly populated in the beta decay of 81Zn, indicating allowed Gammow-Teller transitions. Similar Gamow-Teller transitions have been previously observed in the decay of 83Ge into the N=50 isotone 83As, explained as exciations of the N=40 core [3]. The evolution of core excitations in N=50 isotones indicates a strengthening of the N=40 subshell closure in neutron rich nuclei. This result, combined with the observed weakening of the N=50 shell closure [4], suggests a preponderance of the N=40 over the N=50 shell closure in the 78Ni region.
[1] D. Verney et al., Phys. Rev. C 76, 05432 (2007)
[2] J. Winger et al., Phys. Rev. C 81, 044303 (2010)
[3] J. Winger et al. Phys. Rev. C 38, 285 (1988)
[4] T. Rzaca-Urban et al., Phys. Rev. C 76, 027302 (2007)
