B(E1) Strengths from Coulomb Excitation of 11Be

The $B$(E1;$1/2^+\to1/2^-$) strength for $^{11}$Be has been extracted from intermediate energy Coulomb excitation measurements, over a range of beam energies using a new reaction model, the extended continuum discretized coupled channels (XCDCC) method. In addition, a measurement of the excitation cross section for $^{11}$Be+$^{208}$Pb at 38.6 MeV/nucleon is reported. The $B$(E1) strength of 0.105(12) e$^2$fm$^2$ derived from this measurement is consistent with those made previously at 60 and 64 MeV/nucleon, i n contrast to an anomalously low result obtained at 43 MeV/nucleon. By coupling a multi-configuration description of the projectile structure with realistic reaction theory, the XCDCC model provides for the first time a fully quantum mechanical description of Coulomb excitation. The XCDCC calculations reveal that the excitation process involves significant contributions from nuclear, continuum, and higher-order effects. An analysis of the present and two earlier intermediate energy measurements yields a combined B(E1) strength of 0.105(7) e$^2$fm$^2$. This value is in good agreement with the value deduced independently from the lifetime of the $1/2^-$ state in $^{11}$Be, and has a comparable p recision.Comment: 5 pages, 2 figures, accepted for publication in Phys. Lett.

Decay path measurements for the 2.429 MeV state in 9Be: Implications for the astrophysical a+a+n reaction

An experiment was performed at the Australian National University to study the 9Be(6Li,6Li)9Be*++n reaction. This experiment was designed to study the breakup of 9Be, in an attempt to quantify the contribution played by the 5He+ and 8Be2++n channels for the low lying excited states. This information is required in order to resolve uncertainties in the ++n 9Be reaction rate in high-energy and neutron-rich astrophysical environments such as supernovae. Angular correlation measurements have been used to deduce that the 2.429 MeV state breaks up almost exclusively via the 8Be2+ channel. This method of identifying the break-up channel resolves the problem of distinguishing between the 8Be2+ and 5Heg.s. channels which are kinetically identical at this excitation energy

Decay studies for states in 9 Be up to 11 MeV: Insights into the n + 8 Be and α + 5 He cluster stucture

An experiment was performed to study the Be9(Li6,Li6)Be9* →α+α+n reaction. This experiment was designed to study the breakup of Be9 in an attempt to quantify the breakup yield for each of the decay channels (n+ Be8 g.s,n+ Be8 2+, and α+ He5 g.s) fro

Breakup reaction studies of 10Be and 10,11B using a 10Be beam

The structure of 10Be has been investigated by inelastic scattering to states above the breakup threshold using the reaction 12C(10Be,10Be* → 6He+4/He)12C at Ebeam=302 MeV. Excited states in 10Be were observed at 9.6±0.1 and 10.2±0.1 MeV. No evidence was observed for the population of the 4 + member of the ground-state band of 10Be indicating the shell-model-like structure of the ground state. In addition, the decay of 8Be, 10B, and 11B, populated in the two-neutron, proton pickup, breakup and 1p pickup reactions, was reconstructed through the detection of coincident 4He+4He, 4He+6Li, and 4He+7Li particles. Cross sections for the formation of the 8Be, 9Be, 10B, and 11B were also deduced. Contrary to expectations, the two-neutron removal results in the production of 8Be predominantly (80%) in the first excited (2+) state. This suggests that dynamical excitations play an important role in the neutron removal process.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Breakup reaction studies of 10Be and 10,11B using a 10Be beam

The structure of 10Be has been investigated by inelastic scattering to states above the breakup threshold using the reaction 12C(10Be,10Be* → 6He+4/He)12C at Ebeam=302 MeV. Excited states in 10Be were observed at 9.6±0.1 and 10.2±0.1 MeV. No evidence was observed for the population of the 4 + member of the ground-state band of 10Be indicating the shell-model-like structure of the ground state. In addition, the decay of 8Be, 10B, and 11B, populated in the two-neutron, proton pickup, breakup and 1p pickup reactions, was reconstructed through the detection of coincident 4He+4He, 4He+6Li, and 4He+7Li particles. Cross sections for the formation of the 8Be, 9Be, 10B, and 11B were also deduced. Contrary to expectations, the two-neutron removal results in the production of 8Be predominantly (80%) in the first excited (2+) state. This suggests that dynamical excitations play an important role in the neutron removal process.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

1n and 2n Transfer With the Borromean Nucleus 6He Near the Coulomb Barrier

Angular distributions for 1n and 2n transfer are reported for the He6+Cu65 system at Elab=22.6MeV. For the first time, triple coincidences between α particles, neutrons, and characteristic γrays from the targetlike residues were used to separate the co

High-energy two-neutron removal from Be10

A kinetically complete measurement of the C12(Be10, α+α+n) and (Be10, α+α) reactions has been performed at a beam energy of 30 MeV/nucleon. The charged beam velocity particles were detected in an array of Si-CsI detectors placed at zero degrees, and the neutrons in an 81-element neutron array. The coincident detection of the final-state particles, produced in the breakup of Be10, allowed the reconstruction of the excitation energy in the Be8 and Be9 systems. States in Be8 were identified, in particular the ground and first-excited states; and in Be9, states at 1.68, 2.43, and (2.78, 3.05) MeV were observed. The population of these levels, in particular the 2.43 MeV 5/2- level, suggests that collective excitations play an important role in the neutron removal process. Distorted wave Born approximation and Glauber-type calculations have been used to model the direct neutron removal from the Be10 ground state and the two-step removal via inelastic excitations of the Be10(2+) and Be9(5/2-) excited states. © 2005 The American Physical Society.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Neutron removal and cluster breakup of 14B and 14Be

Measurements of the neutron removal and cluster breakup cross sections for the neutron-rich nuclei 14Be and 14B have been performed at 34.4 and 40.8 MeV/nucleon, respectively. Enhancement of the first chance cluster breakup cross section for 14Be compared to that of 14B provides evidence for a well-developed He cluster structure of the ground state of 14Be. Measurements of both the cross sections and decay-particle velocities suggest that multistep processes play an important role in the excitation and decay of both 14B and 14Be.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Evidence of a (1d 5/2) 2 component to the 12Be ground state

Data have been obtained on exclusive single neutron knockout cross sections from 12Be to study its ground state structure. The cross sections for the production of 11Be in its ground state (1/2 +) and first excited state (0.32 MeV, 1/2 -) have previously been measured, indicating a strong (2s 1 2) 2 component to the 12Be ground state. In the present experiment, performed at the GANIL laboratory, cross sections for the first (0.32 MeV, 1/2 -) and second (1.78 MeV, 5/2 +, unbound) excited states in 11Be were measured, which gives information on the admixture of (1p 1 2) 2 and (1d 5 2) 2 components in the ground state of 12Be. A fragmentation beam of 12Be of ∼10000 pps (95% pure) was incident on a carbon target at 41 MeV/u. The beam particles were tracked onto the target, and their energies were measured event-by-event. The beam-like residues were measured in a position sensitive telescope mounted at zero degrees, and neutrons were measured in the DéMoN array. The 1/2 - state of 11Be was identified by measuring coincident 320 keV γ-rays, using four NaI detectors. Full kinematic reconstruction of unbound states in 11Be was performed using coincident neutrons and 10Be ions. Detailed simulations were performed in order to interpret the data, and spectroscopic factors were calculated, using preliminary single particle removal cross sections calculated using a Glauber model. © 2005 American Institute of Physics.SCOPUS: cp.pinfo:eu-repo/semantics/publishe