Clarification of large-strength transitions in the β decay of Be11

Abstract

The shape and normalisation of the β-delayed α spectrum from 11 Be was measured by implanting 11 Be ions in a segmented Si detector. The spectrum is found to be dominated by a well-known transition to the 3/2 + state at Ex = 9.87 MeV in 11 B. A significant increase in the observed decay strength towards the higher end of the Q β window means, however, that the 9.87 MeV state cannot alone be responsible for the transition. Using the R-matrix framework we find that the inclusion of an extra 3/2 + state at Ex = 11.49(10) MeV is required in order to obtain a satisfactory description of the spectrum. Both states show large widths towards α decay, exhausting significant fractions of the Wigner limit, a typical signature of α clusterisation. The observed Gamow-Teller strength indicate large overlaps between the two states and the ground state of 11 Be.

Search for beta-delayed proton emission from $$^{11}$$Be

“…The basic idea is as in the earlier experiments [6,7] to collect 11 Be samples, determine their intensity on-line via the γ-decays and measure the amount of produced 10 Be via a subsequent accelerator mass spectrometry (AMS) step. Samples collected at different settings of the ISOLDE mass separator allow checking the reproducibility of the result as well as testing for different sources of contamination.…”

“…This process is only allowed for a few neutron-rich nuclei and was predicted [4] to have a very small branching ratio even for the most promising case, that of 11 Be. The first experiments [5,6,7] to look for this decay focussed on detecting the final nucleus 10 Be rather than the emitted proton. In the latest of these [7] evidence for the decay was found with an intensity 8.3 (9) • 10 −6 , orders of magnitude above the preceeding theoretical prediction of 3.0•10 −8 [4].…”

“…An overview of the current state of knowledge on the beta decay of 11 Be was given in [6]. A recent experimental a email:kvr@phys.au.dk result [10] clarified the situation for the beta-delayed αdecay branch of 11 Be.…”

Convenient Location of a Near-Threshold Proton-Emitting Resonance in B11

“…Moreover, a close-lying broad J π = (3/2 + ) alpha-decaying state has been suggested in Ref. [19] to explain the β-delayed α spectrum from 11 Be.…”

“…The nearby J π = (3/2 + ) excitation discussed in Ref. [19], on the other hand, alpha decays. A candidate for this resonance could be, e.g., the predicted 3/2 + 4 state, which weakly couples to oneneutron and one-proton reaction channels.…”