Probing configuration mixing in 12Be with Gamow-Teller transition strengths

• Published in: Physical review letters Vol. 108; no. 12; p. 122501
• Main Authors: Meharchand, R, Zegers, R G T, Brown, B A, Austin, Sam M, Baugher, T, Bazin, D, Deaven, J, Gade, A, Grinyer, G F, Guess, C J, Howard, M E, Iwasaki, H, McDaniel, S, Meierbachtol, K, Perdikakis, G, Pereira, J, Prinke, A M, Ratkiewicz, A, Signoracci, A, Stroberg, S, Valdez, L, Voss, P, Walsh, K A, Weisshaar, D, Winkler, R
• Format: Journal Article
• Language: English
• Published: United States 23.03.2012
• ISSN: 1079-7114
• DOI: 10.1103/PhysRevLett.108.122501

We present a novel technique for studying the quenching of shell gaps in exotic isotopes. The method is based on extracting Gamow-Teller (ΔL=0, ΔS=1) transition strengths [B(GT)] to low-lying states from charge-exchange reactions at intermediate beam energies. These Gamow-Teller strengths are very sensitive to configuration mixing between cross-shell orbitals, and this technique thus provides an important complement to other tools currently used to study cross-shell mixing. This work focuses on the N=8 shell gap. We populated the ground and 2.24 MeV 0+ states in 12Be using the 12B(1+) (7Li, 7Be) reaction at 80  MeV/u in inverse kinematics. Using the ground-state B(GT) value from β-decay measurements (0.184±0.007) as a calibration, the B(GT) for the transition to the second 0+ state was determined to be 0.214±0.051. Comparing the extracted Gamow-Teller strengths with shell-model calculations, it was determined that the wave functions of the first and second 0+ states in 12Be are composed of 25±5% and 60±5% (0s)4(0p)8 configurations, respectively.