Quasi-continuum Lifetimes With GRETINA

Leo Kirsch, University of California, Berkeley

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 56Fe(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 method1 and the two-step cascade method developed by Wiedeking et al.2

1Guttormsen, M. et. al., Radiative strength functions in 93-98Mo, Phys. Rev. C, 71(4):044307, 2005.
2Wiedeking, M., et. al., Low-Energy Enhancement in the Photon Strength of 95Mo, 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