Low-lying neutron unbound states inBe12

Abstract

The neutron decay of an unbound resonance in 12 Be has been measured at 1243±21 keV decay energy with a width of 634±60 keV. This state was populated with a one-proton removal reaction from a 71 MeV/u 13 B beam incident upon a beryllium target. The invariant mass reconstruction of the resonance was achieved by measuring the daughter fragment in coincidence with neutrons. Despite being above the 2n separation energy, the state decays predominantly by the emission of one neutron to 11 Be, setting an upper limit on the branching ratio for the two-neutron decay channel to 10 Be of less than 5%. From the characteristics of the population and decay of the resonance, it is concluded that this state cannot correspond to the previously observed state at 4580±5 keV.

Selective population of unbound states in 10Li

“…More information is available in Ref. [37], which used the same experimental setup but a different secondary beam.…”

“…Initially, a single energy-dependent, = 1, Breit-Wigner lineshape [37,38] was used to fit the data. The minimization procedure pushed the width of the resonance to unphysical values and was unable to reproduce the experimental distribution (confidence of ∼3.5σ ).…”

Two-neutron sequential decay ofO24

“…In this analysis, we require D 12 > 50 cm, and V 12 > 12 cm/ns which is the beam velocity. This technique has been used in several measurements of two-neutron unbound nuclei to discriminate against 1n scatter [11,13,23,[32][33][34][35][36][37]. To further enhance the 2n signal, an additional threshold of 5 MeVee is applied to every hit recorded in MoNA-LISA.…”

Search for unboundBe15states in the3n+Be12

“…The first attempt to experimentally observe 15 Be was performed using a two-proton removal from a 17 C beam [8]. The ground state of 17 C has been shown to have a 3/2 + spin and parity [9] and the reaction used * anthony. Shell model calculations predict a large spectroscopic overlap (1.27 for ℓ = 2) between the predicted 3/2 + state and the first excited 2 + state in 14 Be [8].…”

“…Applying a multiplicity-one restriction to a two-body decay energy spectrum enhances the signal from single neutron decays. To reduce cross-talk from multiple scattering between scintillator bars in MoNA, causality requirements were applied to the three-body decay energy spectrum [4,5,[15][16][17]. The causality requirements used here restrict the first two hits to have velocities greater than 10 cm/ns and the distance between hits to be greater than 30 cm.…”