Multi-quasiparticle sub-nanosecond isomers in W-178

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Sánchez-Tembleque Verbo, Victor
Vedia Fernández, María Victoria
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Elsevier Science BV
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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(Ce) scintillator detectors of the NuBall array at the ALTO facility in Orsay, France. The half-lives of these states only became experimentally 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. The measured half-lives are 476(44)ps and 275(65)ps for the I-pi = 11(-) and 12(+) states, 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. (C) 2019 The Author(s). Published by Elsevier B.V.
© 2019 The Author(s). Published by Elsevier B.V. Artículo firmado por 36 autores. Funding support is acknowledged from the UK Science and Technology Facilities Council under grant numbers ST/L005743/1 and ST/P005314/1, as well as the BMBF under grants NuSTAR.DA 05P15RDFN1, and 05P19PKFNA. This work was also supported by the Spanish gouvernment projects FPA2015-65035-P and RTI2018-098868-B-I00, as well as the project B2017/BMD-3888 PRONTO-CM. P.H. Regan acknowledges support from the UK Department of Business, Energy and Industrial Strategy (BEIS) via the Natioanl Measurement System (NMS). R.L. Canavan acknowledges support from the BEIS, and ENSAR2 transnational access funding from the European Commission.
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2207 Física Atómica y Nuclear