"New, high-lying isomers in the proton-particle three-neutron-hole nucleus 206Bi "
Natalia Cieplicka, IFJ PAN
(id #175)
Seminar: NoPoster: Yes
Invited talk: No
N. Cieplicka1, B. Fornal1, R. Broda1, C. J. Chiara2,3, M.P. Carpenter2, R.V.F. Janssens2, W. Królas1,
T. Pawłat1, W. B. Walters3, J. Wrzesiński1, S. Zhu2
1) Institute of Nuclear Physics, Polish Academy of Sciences, Kraków
2) Physics Division, Argonne National Laboratory, Argonne, IL, USA
3) Department of Chemistry and Biochemistry, University of Maryland, College Park, MD, USA
The 206Bi nucleus is a one-proton-particle, three-neutron-hole system with respect to the doubly magic 208Pb core. Its low-energy structure arises from 1p-3h couplings involving 1h9/2, 2f7/2, and 1i13/2 proton particles, and 3p1/2, 2f5/2, 3p3/2, and 1i13/2 neutron holes. The 206Bi ground state, with spin-parity J^pi=6+, is of pi h9/2 ni (f5/2)-1 character, with the isomeric (T1/2=7.7 mi s) J^pi=4+ member of thepi h9/2 ni (p1/2)-1 multiplet lying only 60 keV above it. At higher excitation energies, two other isomeric states have been identified in an earlier study with the 205Tl(alfa,n gamma) reaction[1]. These are the 10- state at 1045 keV with T1/2=0.89 ms and an assigned pi h9/2 ni (i13/2)-1 configuration, and the 15+ excitation at 3147 keV, with a 15.6 ns half-life of
pi h9/2 ni (p1/2)-1(i13/2)-2 character. The highest yrast states known thus far in 206Bi, i.e., 17+ and 18+ levels at 3604 and 4305 keV have been located in the 205Tl(alfa,n gamma) work as well.
An experiment performed recently at Argonne National Laboratory, USA, in which gamma rays emitted during reactions induced by a 76Ge beam on a thick 208Pb target were measured with the Gammasphere array, showed that deep-inelastic processes populate relatively high-spin states in nuclei located “north-west” of 208Pb. One of the intense products was 206Bi.
We analyzed the spectra of delayed gamma rays (emitted between beam bursts separated by ca. 410 ns) by requiring coincidences with the known 206Bi yrast transitions. A series of higher-lying gamma rays, deexciting two previously unknown 206Bi isomers, have been found. Inspection of the double gates set on these newly discovered transitions, allowed us to extend the 206Bi level scheme up to an isomeric level located at approximately 10 MeV.
We have been able to propose spin and parity assignments for the new states, based on their decay pattern and on comparisons with the shell model calculations. The yrast excitations located at energies up to approx. 7 MeV can be described in terms of the 1p-3h couplings. Higher lying yrast states, including the two new isomers, probably involve neutron excitations across the N=126 shell gap. These will be discussed as originating from proton-particle, neutron-particle, and four neutron-hole couplings.
[1] T.Lonnroth, L.Vegh, K.Wikstrom, B.Fant, Z. Phys. A287, 307 (1978).
T. Pawłat1, W. B. Walters3, J. Wrzesiński1, S. Zhu2
1) Institute of Nuclear Physics, Polish Academy of Sciences, Kraków
2) Physics Division, Argonne National Laboratory, Argonne, IL, USA
3) Department of Chemistry and Biochemistry, University of Maryland, College Park, MD, USA
The 206Bi nucleus is a one-proton-particle, three-neutron-hole system with respect to the doubly magic 208Pb core. Its low-energy structure arises from 1p-3h couplings involving 1h9/2, 2f7/2, and 1i13/2 proton particles, and 3p1/2, 2f5/2, 3p3/2, and 1i13/2 neutron holes. The 206Bi ground state, with spin-parity J^pi=6+, is of pi h9/2 ni (f5/2)-1 character, with the isomeric (T1/2=7.7 mi s) J^pi=4+ member of thepi h9/2 ni (p1/2)-1 multiplet lying only 60 keV above it. At higher excitation energies, two other isomeric states have been identified in an earlier study with the 205Tl(alfa,n gamma) reaction[1]. These are the 10- state at 1045 keV with T1/2=0.89 ms and an assigned pi h9/2 ni (i13/2)-1 configuration, and the 15+ excitation at 3147 keV, with a 15.6 ns half-life of
pi h9/2 ni (p1/2)-1(i13/2)-2 character. The highest yrast states known thus far in 206Bi, i.e., 17+ and 18+ levels at 3604 and 4305 keV have been located in the 205Tl(alfa,n gamma) work as well.
An experiment performed recently at Argonne National Laboratory, USA, in which gamma rays emitted during reactions induced by a 76Ge beam on a thick 208Pb target were measured with the Gammasphere array, showed that deep-inelastic processes populate relatively high-spin states in nuclei located “north-west” of 208Pb. One of the intense products was 206Bi.
We analyzed the spectra of delayed gamma rays (emitted between beam bursts separated by ca. 410 ns) by requiring coincidences with the known 206Bi yrast transitions. A series of higher-lying gamma rays, deexciting two previously unknown 206Bi isomers, have been found. Inspection of the double gates set on these newly discovered transitions, allowed us to extend the 206Bi level scheme up to an isomeric level located at approximately 10 MeV.
We have been able to propose spin and parity assignments for the new states, based on their decay pattern and on comparisons with the shell model calculations. The yrast excitations located at energies up to approx. 7 MeV can be described in terms of the 1p-3h couplings. Higher lying yrast states, including the two new isomers, probably involve neutron excitations across the N=126 shell gap. These will be discussed as originating from proton-particle, neutron-particle, and four neutron-hole couplings.
[1] T.Lonnroth, L.Vegh, K.Wikstrom, B.Fant, Z. Phys. A287, 307 (1978).
