### Quasi-continuum Lifetimes With GRETINA

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Leo Kirsch, University of California, Berkeley
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This presentation explains a new experimental method to determine the absolute magnitude and energy dependence of the gamma-strength function employing an extension of the Doppler shift attenuation method in ^{56}Fe(p,p') using the GRETINA array coupled to a fast phoswich particle detector. The Gamma Ray Energy Tracking In-beam Nuclear Array (GRETINA) is an 1,152-segmented germanium detector array that has the capabilites to extract quasicontinuum lifetimes (QCτ) from miniscule Doppler shifts as a function of outgoing particle energy. High-resolution gamma-ray spectroscopy provide access to lifetimes of discrete nuclear excited states via changes in gamma-ray energy with angles respective to the initial nuclear recoil vector. Gates on the outgoing particle energy isolate events where decay from the QC precedes a low-lying discrete transition. This gives the recoiling excited nucleus more time to slow down and reduces Doppler shift of subsequent gamma rays. The relationship between QCτ and gamma-strength complements both the traditional Oslo method^{1} and the two-step cascade method developed by Wiedeking et al.^{2}
References:
^{1}Guttormsen, M. et. al., Radiative strength functions in ^{93-98}Mo, *Phys. Rev. C*, 71(4):044307, 2005.
^{2}Wiedeking, M., et. al., Low-Energy Enhancement in the Photon Strength of ^{95}Mo, *Phys. Rev. Lett.*, 108(16):162503, 2012.

**Abstract Author(s): **Leo Kirsch, L.A. Bernstein, A.O. Macchiavelli, D.G. Sarantites, H.L. Crawford, M. Cromaz, P. Fallon, C.M. Campbell