Multi-quasiparticle sub-nanosecond isomers in 178W

We report on the first measurement of the half-lives of K(pi) = 11- and 12+ four-quasiparticle states in the even-even nucleus W-178. The sub-nanosecond half-lives were measured by applying the centroid shift method to data taken with LaBr3 scintillator detectors of the NuBall array at the ALTO facility in Orsay, France. The half-lives of these states only became accessible by the combination of several experimental techniques - scintillator fast timing, isomer spectroscopy with a pulsed beam, and the event-by-event calorimetry information provided by the NuBall array as a whole. The measured half-lives are 476(44)ps and 275(65)ps for the I(pi) = 11- and 12+, respectively. The decay transitions include weakly hindered E1 and E2 branches directly to the ground-state band, bypassing the two-quasiparticle states. This is the first such observation for an E1 transition. The interpretation of the small hindrance hinges on mixing between the ground-state band and the t-band.

RUDIGIER Matthias;  WALKER P.M.;  CANAVAN Rhiann;  PODOLYAK Z.;  REGAN P. H;  SÖDERSTRÖM P.A.;  LEBOIS M.;  WILSON J. N.;  JOVANCEVIC Nikola;  BLAZHEV A.;  BENITO J.;  BOTTONI S.;  BRUNET M.;  CIEPLICKA-ORYNCZAK N.;  COURTIN S.;  DOHERTY D.T.;  FRAILE L.M.;  HADYNSKA-KLEK K.;  HEINE M.;  ISKRA L.W.;  JOLIE J.;  KARAYONCHEV V.;  KENNINGTON A.;  KOSEOGLOU P.;  LOTAY G.;  LORUSSO G.;  NAKHOSTIN M.;  NITA C.;  OBERSTEDT Stephan;  QI Liqiang;  RÉGIS J.M.;  SÁNCHEZ-TEMBLEQUE V.;  SHEARMAN R.;  WITT W.;  VEDIA V.;  ZELL K.O.; 

2020-02-03

ELSEVIER SCIENCE BV

JRC117359

0370-2693 (online),   

https://publications.jrc.ec.europa.eu/repository/handle/JRC117359,   

10.1016/j.physletb.2019.135140 (online),