9 - 26 - 2006 Energy and Width of 11 B ( 1 / 2 + , T = 3 / 2 )

I find that data for the reaction 10Be(p, γ) can be reasonably well described with a 1/2+ resonance whose width is 640 keV, rather than the accepted 210 keV. Disciplines Physical Sciences and Mathematics | Physics Comments Suggested Citation: Fortune, H.T. (2006). Energy and Width of 11B(1/2+, T = 3/2). Physical Review C 74, 034328. © 2006 American Physical Society http://dx.doi.org/10.1103/PhysRevC.74.034328 This journal article is available at ScholarlyCommons: http://repository.upenn.edu/physics_papers/204 PHYSICAL REVIEW C 74, 034328 (2006) Energy and width of 11B(1/2+, T = 3/2) H. T. Fortune Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA (Received 12 June 2006; published 26 September 2006) I find that data for the reaction 10Be(p, γ ) can be reasonably well described with a 1/2+ resonance whose width is 640 keV, rather than the accepted 210 keV. DOI: 10.1103/PhysRevC.74.034328 PACS number(s): 21.10.Pc, 24.30.−v, 25.20.Lj, 27.20.+n The energy and width of the lowest T = 3/2 state in 11B [1] is a matter of some debate [2,3]. This state should be the analog of the 1/2+ ground state (g.s.) of 11Be, and should have the isospin structure (1/3) 10Be×p + (2/3)10B(0+, T = 1) × n. The proton width of the analog in 11B can be computed from p = C2S sp, where C2 = 1/3, S should be the same as in 11Be; and sp, as computed in a potential model, is about 2.4 MeV [2] for a state at the supposed position of 11B(1/2+, T = 3/2). If the (d, p) spectroscopic factor of 11Be(g.s.) is anywhere near the value 0.7–0.8 commonly found [4], this state should, therefore, have a width of about 600 keV, whereas the value in the compilation [1] is barely 1/3 of that. Listed in Table I are the compiled values of energy and width of the supposed analogs of the first two states of 11Be, together with results from two experiments [5,6]. At least two other experiments [7,8] provide similar data for the 1/2– state, but not for the 1/2+. The 1/2–, T = 3/2 assignment [7] is from the reaction 13C(p,3He) in comparison with 13C(p, t). The 1/2+ state was not observed in that reaction, and should not have been, because it contains a 2s1/2 nucleon that is absent in the 13C target. Primary evidence for the J , T assignment for the lower level comes from the reaction 10Be(p, γ ), which yielded the assignment [6] J = 1/2+(3/2+), T = 3/2, with the energy and width as given in Table I. The authors of Ref. [6] also observed a higher resonance that they took to be the 1/2–, and a structure near Ex = 12.17 MeV that they were unable to distinguish as an actual state or a 10B∗ + n threshold-opening feature. I set out to determine whether those data could accommodate a 1/2+ state of much larger width. In the calculations, the 1/2– width was held fixed at the compiled value of 200 keV, and the position was allowed to vary only slightly from the compiled energy. For the 1/2+ state, the energy was allowed to vary slightly, but whatever the energy, the energy-dependent width was constrained at the values p(E) = C2S sp(E), where S = 0.75, and sp(E) came from a potential-model calculation. For each state, the resonance cross section was computed as σ (E) = N k2 ( E + 11.228 MeV E0 + 11.228 MeV )3 ( p (E − E0) + 2 p/4 )