[Triumf-seminars] TRIUMF Seminar today at 11:00

[TRIUMF Seminars]

Date/Time: Thu 2013-09-19 at 11:00

Location:  Auditorium          

Speaker:   Sam Tabor (Florida State University)

Title:     Isospin Purity around the N=Z Line

Abstract: Superallowed Fermi beta decay provides an excellent tool for locating and quantifying isobaric analog states.   The beta decay of radioactive 55Cu (TZ=-3/2) (Jpi = 3/2-) was observed to 55Ni (TZ=-1/2) in an FSU led experiment at NSCL.   N and Z identified implants were correlated with betas and gammas using a DSSD Ge planar detector and the SEGA Ge gamma detector array.  They reveal that the analog of the T=3/2 ground state of  55Cu  is split in 55Ni, in agreement with previous suggestions for  55Co (TZ=+1/2).   Shell model calculations for 55Ni using the GXPF1 interaction predict that the 8th T=1/2  3/2- state lies within 60 keV of the lowest T=3/2 state before mixing.  This strengthens the suggestion that the analog state is split by an “accidental” degeneracy.   The GXPF1 calculation also gives good predictions for the Gamow-Teller decays to the two states.  The remaining Fermi strengths to the analog doublet in 55Cu after subtraction of the much weaker predicted G-T contributions combined with the observed 20 keV separation show that a rather small mixing matrix element and somewhat closer unmixed energy spacing can account for the observed strong isospin mixing.   Our reinterpretation of the A=23 system implies that a quite similar  situation can account for large mixing of that analog state as well.  Other systematics around N=Z will be discussed.

Stimulants available 15 minutes before the talk.

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