An Investigation of the Protons, Deuterons and Tritons from the Bombardment of⁹Be with 5.7 MeV³He

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

“…In that study it was concluded that the allowed transition to the 3/2 + state at 9.87 MeV was alone responsible for the delayed alphas. Alburger et al also made a couple of observations regarding the shape of the 9.87 MeV peak, namely that the width observed in β decay is significantly larger than that observed in scattering and reaction experiments [9][10][11][12][13], and that there are signs of an * jonas.refsgaard@kuleuven.be 11 Be. Each level is labelled by its energy in MeV relative to the 11 B ground state as well as its spin and parity, J π .…”

“…Halo nuclei form a class of clusterised nuclear systems characterised by having one or two nucleons in very extended orbitals around the remaining nucleons. The 11 Be ground state is a typical example of a halo system and is well described as a 10 Be core coupled to an s-wave halo neutron [1]. The halo structure influences the fundamental properties of this state, which furthermore has the unusual spin and parity J π = 1/2 + [2], contrary to the 1/2 − designation which would be expected from the shell model.…”

“…The halo structure influences the fundamental properties of this state, which furthermore has the unusual spin and parity J π = 1/2 + [2], contrary to the 1/2 − designation which would be expected from the shell model. This has an important impact on the β decay from 11 Be to 11 B (see Figure 1), where the lowest four levels have negative parity. The transitions to these levels are therefore all first-forbidden and strongly suppressed.…”

“…Also, the allowed transitions to the 6.79 MeVand 7.98 MeV-states are quite slow, with log(f t) values of 5.94 and 5.58, respectively. The hindrance of these transitions not only results in 11 Be having an unusually long half-life (13.81 s [3]), but also leads to a relative enhancement of branches with a small Q β . This has recently allowed the detection of the rather exotic β − p decay branch [4] and it makes 11 Be ideal for studying the hypothesised dark decay of the neutron [5,6].…”

“…We describe a measurement of the shape and normalisation of the β-delayed α spectrum from 11 Be. The experimental technique involves implanting 11 Be ions in a finely segmented Si-detector and counting the implantations and decays.…”