EXPERIMENTAL METHODS

Transcription

1 S. H. Liu, 1 J. H. Hamilton, 1 A. V. Ramayya, 1 A. Covello, 2 A. Gargano, 2 N. Itaco, 2 Y. X. Luo, 1,3 J. O. Rasmussen, 3 S. J. Zhu, 4 J. K. Hwang, 1 A.V.Daniel, 1,5 G.M.Ter-Akopian, 5 Y. Oganessian 5, N. J. Stone, 6,7 J. R. Stone 7 1. Vanderbilt University 2. University of Napoli, Complesso Universitario di Monte San Angelo 3. Lawrence Berkley National Lab 4. Tsinghua University 5. Joint Institute for Nuclear Reaction 6. University of Tennessee 7. Oxford University

2 EXPERIMENTAL METHODS Lawrence Berkeley National Laboratory. Gammasphere Detector Array with 101 Comptonsuppressed Ge Detectors. 252 Cf Source of 62 µci, stopped in iron foils. Total of 5.7x10 11 triple and higher fold γ γ γ coincidence events (in cube). Triple coincidence data were sorted into 64 two dimensional histograms corresponding to the 64 angle bins for the angular correlation studies.

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5 134 I 133 I I 135 I I 82

6 134 I

7 134 I ν(h11/2) π(g7/2) 3 π(g7/2) 2 (2d5/2) 1 See Liu et al, PRC 79, (2009) and Coraggio et al. PRC 80, (R) (2009) for details in experiment and theory, respectively.

8 N=84 Isotones: 137 I and 139 Cs 137 I : 3 new levels with 4 new transitions. 139 Cs: 10 new levels with 18 new transitions.

9 Spin-parity Assignment in 139 Cs J Π = 7/2 + for the ground state [1]. J Π of the excited levels, determined by measuring γ-γ angular correlations and the ICC of the kev transition. Cascade (kev) A exp 2, A exp 4 A the 2, A the 4 (Q->Q) > (1), -0.01(2) > (1), 0.00(2) 0.10, > (2), -0.02(3) 0.10, > (3), -0.01(4) 0.10, > (2), 0.01(3) 0.10, > (4), -0.00(7) 0.10, 0.0 α T (236.9)=0.086(12): M1/E2 mixture. Multipolarities: (M1/E2, δ= or -0.07(2) ), 475.3(E2), 428.2(E2), 740.4(E2), 727.9(E2), 601.6(E2), 544.4(E2) and 589.8(E2). [1] Table of Isotopes, 8th ed., edited by R. B. Firestone and V. S. Shirley (Wiley: New York, 1996).

10 Shell-Model Calculations for 137 I and 139 Cs 137 I: 3 valence protons and 2 neutrons beyond 132 Sn. 139 Cs: 5 valence protons and 2 neutrons beyond 132 Sn. 132 Sn as a closed core, valence protons in 0g 7/2, 1d 5/2, 3/2, 1s 1/2, 0h 11/2 and neutrons in 0h 9/2, 1f 7/2, 5/2, 2p 3/2, 1/2, 0i 13/2, the two-body effective interaction derived from the CD-Bonn nucleon-nucleon potential [1], 5 valence-proton and 6 valence-neutron energies taken from the experimental spectra of 133 Sb and 133 Sn except πs 1/2 and νi 13/2 levels [1], OSLO shell model code [2]. [1] L. Coraggio, A. Covello, A. Gargano, and N. Itaco, Phys. Rev. C 72, (2005). [2] T. Engeland, The Oslo shell-model code, unpublished,

11 Shell-Model Calculations for 137 I and 139 Cs Reproduce the level pattern rather well up to 29/2 + in both nuclei. 137 J π E exp E J π E exp E I calc calc 139 Cs 7/ / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / δ the (595.4)= -3.6, close to , favoring E2. Large discrepancy at high spin may reflect limits of chosen model space. See Liu et al. PRC 80, (2009)

12 Spin-parity Assignments in N=83 isotones: 135 Te, 136 I, 137 Xe, 138 Cs

13 Spin-parity Assignments in N=83 isotones: 135 Te, 136 I, 137 Xe, 138 Cs The shell-model calculations performed using the OXBASH computer code [1]. [1] B. A. Brown, et al., The computer code OXBASH, MSU-NSCL, Report No. 524.

14 Spin-parity Assignments in N=83 isotones: 135 Te, 136 I, 137 Xe, 138 Cs

15 Spin-parity Assignments in N=83 isotones: 135 Te, 136 I, 137 Xe, 138 Cs

16 g-factor of the 15/2 state in 137 Xe The fission fragments implanted and stopped in the iron foils, subject to the hyperfine fields (B HF ) caused by their implantation in substitutional sites in the iron lattice. It becomes possible for us to carry out angular correlation measurements to determine the g-factors of long-lived states by using the integral perturbed angular correlation (IPAC) technique. The result of the rotation of the implanted nucleus about the B HF is an attenuation of the expected angular correlation coefficients.

17 g-factor of the 15/2 state in 137 Xe

18 g-factor of the 15/2 state in 137 Xe E2 E2 E2 G 2 =0.072/0.102=0.71(7), B HF (Xe)=73(8) T [1], Lifetime calc =0.6 ns g =0.26(5) [1] G. N. Rao, Hyperfine Interact. 26, 1119 (1985). Shell-model calculations, g calc =0.31. See Liu et al. PRC 81, (2010) for more details in shell-model calculations.

19 Summary Level scheme of 134 I was identified for the first time and reproduced by shell-model calculations. N=84 isotones 137 I and 139 Cs were re-investigated and level patterns were predicted by shell-model calculations up to 29/2 +. Spin-parities of levels in N= Te, 136 I, 137 Xe, 138 Cs were assigned based on angular correlation measurements, confirmed by shell-model calculations. g-factor of the 15/2 state in 137 Xe was determined, consistent with the calculated value from shellmodel calculations.