Mechanisms in knockout reactions

We report the first detailed study of the relative importance of the stripping and diffraction mechanisms involved in nucleon knockout reactions, by the use of a coincidence measurement of the residue and fast proton following one-proton knockout reactions. The measurements used the S800 spectrograph in combination with the HiRA detector array at the NSCL. Results for the reactions Be9(C9,B8+X)Y and Be9(B8,Be7+X)Y are presented and compared with theoretical predictions for the two reaction mechanisms calculated using the eikonal model. The data show a clear distinction between the stripping and diffraction mechanisms and the measured relative proportions are very well reproduced by the reaction theory. This agreement adds support to the results of knockout reaction analyses and their applications to the spectroscopy of rare isotopes. © 2009 The American Physical Society.link_to_subscribed_fulltex

Particle decay of Be12 excited states

The breakup of E/A=50 MeV Be12 fragments following inelastic scattering off of hydrogen and carbon target nuclei has been studied. The breakup channels α+He8, He6+He6, t+Li9, and p+Li11 were observed. Two doublets at excitation energies of 12.8 and 15.5 MeV were found for the α+He8 channel. A low-energy shoulder in the excitation-energy spectra at 10.2 MeV indicates one or more additional states. This work could not confirm the presence of He6-He6 rotational structure reported by Freer [Phys. Rev. C 63, 034301 (2001)], although possible peaks at excitation energies of 13.5 and 14.5 MeV were found for He6+He6 decay. Significant structure is observed in the excitation-energy spectrum for p+Li11 at 25-30 MeV which maybe associated with T=3 analog states. © 2007 The American Physical Society.link_to_subscribed_fulltex

Investigation of particle-unbound excited states in light nuclei with resonance-decay spectroscopy using a Be12 beam

Resonance-decay spectroscopy is used to study particle-unbound excited states produced in interactions of E/A=50 MeV Be12 on polyethylene and carbon targets. The particle-unbound states are produced in a variety of reaction mechanisms, ranging from projectile fragmentation to proton pickup. New proton-decaying excited states are observed in Li9(E*=14.1±0.1 MeV, Γ=207±49 keV) and Be10(E*=20.4±0.1 MeV, Γ=182±74 keV). In addition a new α-decaying state is observed in B13(E*=13.6±0.1 MeV, Γ≤320 keV). Also found was a Be8 state with E*=23 MeV, Γ=616±30 keV, which decays to the p+3H+α channel. Correlation between the fragments indicates that the decay is initiated by a proton emission to the 4.63-MeV state of Li7 and the spin of the state is J>2. A second T=2 state was confirmed in B12 at 14.82 MeV, which decays to the p+11Be, 3H+9Be, and α+8Li channels. Its width was found to be Γ≤100 keV and its spin is consistent with Jπ=2+. © 2008 The American Physical Society.link_to_subscribed_fulltex

The high resolution array (HiRA) for rare isotope beam experiments

The High Resolution Array (HiRA) is a large solid-angle array of silicon strip-detectors that has been developed for use in a variety of nuclear structure, nuclear astrophysics and nuclear reaction experiments with short lived beta-unstable beams. It consists of 20 identical telescopes each composed of a thin (65 μ m) single-sided silicon strip-detector, a thick (1.5 mm) double-sided silicon strip-detector, and four CsI(Tl) crystals read out by photodiodes. The array can be easily configured to meet the detection requirements of specific experiments. To process the signals from the 1920 strips in the array, an Application Specific Integrated Circuit (ASIC) was developed. The design and performance characteristics of HiRA are described. © 2007 Elsevier B.V. All rights reserved.link_to_subscribed_fulltex

Double isobaric analog of 11Li in 11B

The ground state of 11Li is the preeminent example of a two-neutron-halo nucleus and is part of an isobaric sextet. Another member of this sextet, the double isobaric analog of 11Lig .s. in 11B, has been identified in the 12Be(p,2n)11B reaction. The state was discovered through its two-proton decay branch. From detected 2p+9Li events, its excitation energy was determined to be 33.57(8) MeV using the invariant mass method. With the known masses of 11Li and its isobaric analog state in 11Be, three members of the same sextet have measured masses for the first time, permitting the masses of the remaining members to be extrapolated using the isobaric multiplet mass equation. All members of this multiplet are expected to have a two-nucleon halo structure and this was found consistent with the evolution of the mass across the sextet. The momentum correlations of the detected protons were found to have both "diproton" and "cigar" components. © 2012 American Physical Society.link_to_subscribed_fulltex

Ground-state proton decay of Br69 and implications for the se68 astrophysical rapid proton-capture process waiting point

We report on the first direct measurement of the proton separation energy for the proton-unbound nucleus Br69. Bypassing the Se68 waiting point in the rp process is directly related to the 2p-capture rate through Br69, which depends exponentially on the proton separation energy. We find a proton separation energy for Br69 of Sp(Br69)=-785-40+34keV; this is less bound compared to previous predictions which have relied on uncertain theoretical calculations. The influence of the extracted proton separation energy on the rp process occurring in type I x-ray bursts is examined within the context of a one-zone burst model. © 2011 American Physical Society.link_to_subscribed_fulltex

Ground-State Proton Decay of 69Br and Implications for the 68Se Astrophysical Rapid Proton-Capture Process Waiting Point

We report on the first direct measurement of the proton separation energy for the proton-unbound nucleus 69Br. Bypassing the 68Se waiting point in the rp process is directly related to the 2p-capture rate through 69Br, which depends exponentially on the proton separation energy. We find a proton separation energy for 69Br of Sp(69Br)=-785-40+34  keV; this is less bound compared to previous predictions which have relied on uncertain theoretical calculations. The influence of the extracted proton separation energy on the rp process occurring in type I x-ray bursts is examined within the context of a one-zone burst model