Systematics of the K = 8 - isomeric decay in the N=74 isotones: a study of the lighter 128 Xe isotone † School of Engineering, University of Brighton Brighton, BN2 4GJ, UK Nico Orce Alison Bruce email: [email protected] Acknowledgements
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†School of Engineering, University of Brighton Brighton, BN2 4GJ, UK
Nico Orce Alison Bruce
email: [email protected]
A. Emmanouilidis†, L. Frankland†, A.P. Byrne1, G.D. Dracoulis1,
J. Hazel1, T. Kibedi1, P.M. Walker2, Z. Podolyak2, M. Camaaño2,
H. El-Masri2, C. Pearson2, C. Wheldon3 and D.M. Cullen4
1Department of Nuclear Physics, The Australian National University, Canberra, ACT 0200, Australia
2Department of Physics, University of Surrey, Guildford, GU2 5XH, UK
3Department of Physics, University of Liverpool, Liverpool, L69 7ZE, UK
4Department of Physics and Astronomy, University of Manchester, Manchester, M13 9PL, UK
•The observed E1 transition from the K = 8- isomeric state to the 8+ state of the yrast band (assumed to have K=0) is seven times K-forbidden and should be rigorously hindered. However, such an E1 transition has been observed in 138Gd, 136Sm, 134Nd, 132Ce and 130Ba but not yet in 128Xe.
• Indeed, these E1 decays are observed to have greater reduced hindrance values ( f= (T1/2 / T1/2w )1/ , where = K-) as the proton number decreases (see right), which may indicate some collective or pairing effects.
• This contradiction with that which is theoretically predicted has been explained by A.M. Bruce et al. (Phys. Rev. C, 1997. volume 55, p.620.) on the basis of a two-band mixing calculation.
No link between the K= 8- isomeric state and the yrast band has been observed in 128Xe
• Due to this increase in energy, for the first time in the N=74 isotone region the K=8-isomeric state in 128Xe is above the 7- and 6- states of a negative parity sideband. Therefore, it preferentially decays to these negative parity states since the reduced transition probability for the M1 transition is twice as large as for the competing E1 transition