Collective Band Structure and Origin of Enhanced <span class="aps-inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>E</mi><mn>1</mn><mn></mn></math></span> Decays in <span class="aps-inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mmultiscripts><mrow><mi mathvariant="normal">O</mi></mrow><mprescripts></mprescripts><mrow></mrow><mrow><mn>18</mn></mrow><mrow></mrow><mrow></mrow></mmultiscripts></mrow></math></span>

M. Gai; S. L. Rugari; R. H. France, III; B. J. Lund; Z. Zhao; D. A. Bromley; B. A. Lincoln; W. W. Smith; M. J. Zarcone; Q. C. Kessel

doi:10.1103/PhysRevLett.62.874

Collective Band Structure and Origin of Enhanced $E 1$ Decays in ${}^{18}O$

M. Gai, S. L. Rugari, R. H. France, III, B. J. Lund, Z. Zhao, D. A. Bromley, B. A. Lincoln, W. W. Smith, M. J. Zarcone, and Q. C. Kessel

Phys. Rev. Lett. 62, 874 – Published 20 February 1989

Abstract

The weak $4_{2}^{+}$ → $2_{3}^{+}$ transition in ${}^{18}O$ was observed with a branching ratio (0.30±0.08)%, using the ${}^{14}C (α, γ) {}^{18}O$ radiative-capture reaction at $E_{α} = 1.14$ MeV. The corresponding $B (E 2 : 4_{2}^{+} \to 2_{3}^{+}) = 5.7 \pm 1.9$ Weisskopf unis appears noncollective, and serves as a crucial test of microscopic models predicting collective band structures and enhanced $E 1$ decays in ${}^{18}O$ ; it is smaller by a factor of 3-8 than predictions of such models, and cannot be reproduced by the well-established coexistence model for ${}^{18}O$ , suggesting that our understanding of collective motion in light nuclei is incomplete. We review recent suggestions for extending coexistence models.