States In 11B Research Articles

2α + t Cluster Structure in 11B

Structures of excited states in 11B are investigated with a method of β – γ constraint antisymmetrized molecular dynamics in combination with the generator coordinate method. Various cluster structures are suggested in excited states. For negative-parity states, we suggest a band with a 2α + t cluster structure. This band starts from the \({3/2^{-}_{3}}\) state and can correspond to the experimental band observed recently. We find that the feature of the \({3/2^{-}_{3}}\) is quite similar to the \({0^{+}_{2}}\) state in 12C.

Structure of Be Hyper Isotopes

The low-lying level structure of \({^{10}_\Lambda{\rm Be}}\) and \({^{12}_\Lambda{\rm Be}}\) has been studied by using the antisymmetrized molecular dynamics for hypernuclei (HyperAMD). In these hypernuclei, it is interesting to reveal the changes of excitation spectra by adding Λ hyperon, because the ground and low-lying states with different deformation coexist in 9Be and 11Be. Based on the HyperAMD calculation, it is found that the first excited state 1/2+ of 9Be is shifted up by about 700 keV in \({^{10}_\Lambda{\rm Be}}\) . In \({^{12}_\Lambda{\rm Be}}\) , the parity-inverted ground state of 11Be is reverted by adding Λ hyperon. In this article, we discuss the reason for these structure changes related to the coexistence of ground and low-lying states with different deformation.

The electron scattering form factor of 10B, 32S and 48Ca nuclei

Longitudinal and transverse electron scattering form factors and transition probabilities have been calculated for different states in 10B, 32Sc and 48Ca nuclei, where a microscopic theory is employed to include the effect of high configuration outside the model space, which is called the core-polarization (CP) effect. The Cohen–Kurath interaction for p-shell, the universal sd of Wildenthal interaction for sd-shell and the GXFP1 interaction for fp-shell are used with the Michigan three-range Yakawa (M3Y) effective NN interaction and modified surface delta interaction as a residual interaction for the CP calculations. The calculation is performed using the shell model codes CPM3Y and NuShell. The radial wave function for the single-particle matrix elements have been calculated with the Skyrme–Hartree Fock, harmonic oscillator potential and Wood Saxson potential to calculate the single-particle wave function. The inclusion of CP effects modifies the form factors markedly and describes the experimental data very well in the momentum transfer dependence.

α+α+t cluster structures and Hoyle-analogue states in 11B

The structures of 11B are studied with the 2α+t orthogonality condition model (OCM) for exploring Hoyle-analogue states in 11B.

Cluster states in 11B, 11C and 8He and their similarity to12C

We discuss cluster structures of 11B(11C) and 8He. The nB(3/2−3) is found to have a well developed 2α + t-cluster structure whose features are similar to those of the 12C(O+2). The ground and excited states of 8He were also investigated. Dineutron correlations at the surface of 8He are analyzed. The mechanism of dineutron correlations at a nuclear surface is also discussed.

Neutron knockout ofBe12populating neutron-unbound states inBe11

Neutron-unbound resonant states of 11Be were populated in neutron knock-out reactions from 12Be and identified by 10Be-n coincidence measurements. A resonance in the decay-energy spectrum at 80(2) keV was attributed to a highly excited unbound state in 11Be at 3.949(2) MeV decaying to the 2+ excited state in 10Be. A knockout cross section of 15(3) mb was inferred for this 3.949(2) MeV state suggesting a spectroscopic factor near unity for this 0p3/2- level, consistent with the detailed shell model calculations.

Interaction of α particles with 6Li and 7Li nuclei at low energies

The reaction of radiation capture (α, γ) on 7Li and 6Li nuclei, which is of importance in dt-plasma diagnostics, was studied. It was shown that the cross-section resonant structure of the (α, γ) reaction on 7Li and 6Li nuclei is determined by the structural features of the excited states of 11B and 10B nuclei, which have narrow α widths.

Low excitation structure of 10B probed by scattering of electrons and of 197 MeV polarized protons

Differential cross section and analyzing power data from 197 MeV ( p → , p ′ ) scattering and longitudinal and transverse form factors for electron scattering to low lying states in 10B have been analyzed as tests of the structure of the nuclear states when they are described using a no-core ( 0 + 2 ) ℏ ω shell model. While the results obtained from the shell model clearly show the need of other elements, perhaps three-body forces, to explain the observed spectrum, the reasonable level of agreement obtained in the analyses of the scattering data suggest that the wave functions from our shell model with only a two-body potential are credible through the volume of the nucleus. Any changes to the wave functions with the introduction of additional terms in the shell model Hamiltonian, therefore should be relatively minor.

Evidence of a new state in 11Be observed in the 11Li β-decay

Coincidences between charged particles emitted in the β-decay of 11Li were observed using highly segmented detectors. The breakup channels involving three particles were studied in full kinematics allowing for the reconstruction of the excitation energy of the 11Be states participating in the decay. In particular, the contribution of a previously unobserved state at 16.3 MeV in 11Be has been identified selecting the α+He7→α+He6+n channel. The angular correlations between the α particle and the center of mass of the 6He+n system favors spin and parity assignment of 3/2− for this state as well as for the previously known state at 18 MeV.

Kinematic identification of the $ \beta$ t branch in the decay of 11Li

The -delayed 8 Li + t branch of the 11Li decay was identified via kinematical analysis of the charged particles observed in coincidence. The back-to-back events observed in a narrow angular acceptance were compared to a Monte Carlo simulation. The 8 Li + t sum energy spectrum was fitted assuming that the decay occurs through an intermediate state in 11Be . The resulting energy centroid and full-width half maximum for the intermediate state are 18.35(30)MeV and 1.5(4)MeV, respectively. The -delayed 8 Li + t branching ratio obtained from the coincidence spectrum, BR t = 0.93(8)×10-4 , is in agreement with previous measurements but more precise.

CLUSTER STATES IN13CAND11B

The cluster structures of the excited states in11B and13C were discussed by measuring the isoscalar monopole strengths in the inelastic α scattering at Eα= 388 MeV . It was found that the [Formula: see text], [Formula: see text], and [Formula: see text] states in13C are candidates for the α cluster states with a 3α + n molecular configuration.

Ab InitioMany-Body Calculations ofn−H3,n−He4,p−He3,4, andn−Be10Scattering

We develop a new ab initio many-body approach capable of describing simultaneously both bound and scattering states in light nuclei, by combining the resonating-group method with the use of realistic interactions, and a microscopic and consistent description of the nucleon clusters. This approach preserves translational symmetry and Pauli principle. We present phase shifts for neutron scattering on 3H, 4He, and 10Be and proton scattering on 3,4He, using realistic nucleon-nucleon potentials. Our A=4 scattering results are compared to earlier ab initio calculations. We demonstrate that a proper treatment of the coupling to the n-10Be continuum is successful in explaining the parity-inverted ground state in 11Be.

Study of β-delayed 3-body and 5-body breakup channels observed in the decay of 11Li

The β-delayed charged particle emission from 11Li has been studied with emphasis on the three-body n α 6He and five-body 2 α3n channels from the 10.59 and 18.15 MeV states in 11Be. Monte Carlo simulations using an R-matrix formalism lead to the conclusion that the A He resonance states play a significant role in the break-up of these states. The results exclude an earlier assumption of a phase-space description of the break-up process of the 18.15 MeV state. Evidence for extra sequential decay paths is found for both states.

Neutron Emission Profile of d-Be Reaction with Low-energy Deuteron Beam for Accelerator Neutron Source

The neutron emission profile of the 9Be(d,n)10B nuclear reaction using a low-energy deuteron beam (300 keV) was examined to develop an accelerator neutron source for boron neutron capture therapy (BNCT). The gamma rays corresponding to the transition from excited levels of 10B were measured using a high-purity Ge detector. By analyzing the gamma-ray yields, the transition probability to each excited state of 10B was determined and the neutron yields for the individual energies were evaluated. The emission of the 3.8 MeV neutron was approximately 42% of the total emission, and other neutron emissions from 1.1 to 4.5 MeV were clearly specified. A neutron moderator assembly using heavy water (D2O) or Be metal was designed in order to obtain thermal neutrons from the d-Be reaction with high efficiency. The simulations of neutron transport in the assembly were performed using the Monte Carlo code MCNP4C. Thermal, epithermal, and fast neutron fluxes were calculated as a function of the moderator thickness. The experimentally evaluated neutron emission property was reflected in the simulation. The results indicate that the use of the D2O moderator is suitable for thermal neutron production and shielding of fast neutrons rather than that of Be.

Cluster states in 11B and 13C

The cluster structures of the excited states in 11B and 13C were discussed by measuring the isoscalar monopole strengths in the inelastic α scattering at Eα = 388 MeV. It was found that the 1/22−, 1/23−, and 1/24− states in 13C are candidates for the α cluster states with a 3α + n molecular configuration.

Study of β-delayed charged particle emission of 11Li: evidence of new decay channels

The break-up of the 18.2 MeV state in 11Be was studied in a 11Li β-decay experiment. We report here on the study of the dominating breakup channels involving na6He or 3n2α in the final state, with special emphasis dedicated in this contribution to the three-particle channel. The two emitted charged particles were detected in coincidence using a highly segmented experimental set-up. The observed experimental energy-vs-energy scatter plot indicates a sequential breakup where nuclei of mass 4, alpha particles, and mass 7, 7He, are involved. A Monte-Carlo simulation of the sequential channel, 11Be* → α + 7He → nα6He was performed and compared to the experimental data and to a simulation of the direct break-up of the 18.2 MeV state nα6He by phase space energy distribution. The energy-versus-energy plot are explained by the sequential simulation but not by the phase space simulation.

Three-body cluster state in 11B

The cluster structures of the excited states in 11B are studied by analyzing the isoscalar monopole and quadrupole strengths in the 11B(d,d′) reaction at E d = 200 MeV . The excitation strengths are compared with the predictions by the shell-model and antisymmetrized molecular-dynamics (AMD) calculations. It is found that the large monopole strength for the 3 / 2 3 − state at E x = 8.56 MeV is well described by the AMD calculation and is an evidence for a developed three-body 2 α + t cluster structure.

Formula omitted] strengths from Coulomb excitation of 11Be

The B(E1;1/2+→1/2−) strength for 11Be 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 Be11+Pb208 at 38.6 MeV/nucleon is reported. The B(E1) strength of 0.105(12) e2 fm2 derived from this measurement is consistent with those made previously at 60 and 64 MeV/nucleon, in 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) e2 fm2. This value is in good agreement with the value deduced independently from the lifetime of the 1/2− state in 11Be, and has a comparable precision.

Investigation of the reaction mechanism for the four-particle photodisintegration of a carbon nucleus

The four-particle photodisintegration of a carbon nucleus in the reactions 12C(γ, p)3H2α and 12C(γ, n)3H2α is investigated by a method that employs a diffusion chamber in a magnetic field. It is shown that these reactions proceed according a sequential-type scheme: excited states of 11B and 11C nuclei decay to weakly excited states of 8Be, 7Li, and 7Be nuclei. It is concluded that nucleons are knocked out from the s shell. In the excitation curve for the 2α system in the reaction 12C(γ, p)3H2α, a resonance is found between the maxima corresponding to the ground and the first excited state of the 8Be nucleus, and this resonance is identified as a ghost anomaly. The branching fractions of the decay modes are determined. The angular distributions of nucleons in the reaction c.m. frame are measured. The energy dependence of the asymmetry coefficient for the angular distributions is obtained. A fast increase in this coefficient is observed in the energy range 38–40 MeV. It is concluded that the asymmetry coefficient depends on the excitation energy of the final nucleus in the region of intermediate photon energies.

2α + t cluster state in11B

The cluster structures of the excited states in11B are studied by analyzing the isoscalar monopole and quadrupole strengths in the11B (d,d′) reaction at Ed= 200 MeV . The excitation strengths are compared with the predictions by the shell-model and antisymmetrized molecular-dynamics (AMD) calculations. It is found that the large monopole strength for the [Formula: see text] state at Ex= 8.56 MeV is well described by the AMD calculation and is an evidence for a developed 2α + t cluster structure.