States Of 8Be Research Articles

A new particle-hole approach to collective states

The relevance of the particle-hole space is demonstrated by showing that in some commonly used formalisms the first excited state lies entirely within the particle-hole space generated from the correlated ground state. This property is proved for several cases of angularmomentum projection — projected Hartree-Fock method (PHF) — and for the generator coordinate method in the Gaussian overlap approximation, while in other cases it has been verified only numerically. A new method is presented for the approximate calculation of energies and transition amplitudes of particle-hole excited states. Only hermitian one-body operators are used to generate the excited states. The two-body density matrix of a correlated state approximating the ground state is required as input data. The formula is tested on the 2 + and 3 − states of 8Be and 12C by using the PHF ground state. Where comparison is possible the method gives better agreement with PHF and experiment than the extended random-phase approximation.

A study of excited states of5He by the7Li (d, α)5He-reaction

The interactions of deuterons with7Li, in which two α-particles and a neutron are produced in the final state are studied atEd=1.2 MeV. The dual parameter α-α coincidence spectrum was analyzed with a search program. The results indicate two excited states of5He: One at excitation energy 2.9±0.1 MeV and with a reduced width of γ2=1.1±0.4 MeV, and the other at 4.8±0.4 MeV, with γ2=0.9±0.4 MeV. No contributions of sequential decay through the 4+ state in8Be or direct three body decay was observed.

Proton nuclear reaction cross sections in carbon and the12C(p,p'3α) reaction mechanism at 13 MeV

The mechanism of the 12C(p,p'3 alpha ) reaction at 13 MeV is found to involve the ground state of 8Be and the ground state of 9B in 24% of the events, and the 8Be ground state alone in 51% of the events. The remaining 25% of the events show no clear evidence of levels in intermediate nuclei. The cross section for this reaction is 154 mb.

Formula omitted] four-body break-up and states in 9Be

The four-body break-up d+ 11B → α+n reaction has been studied by simultaneous detection of α-α and α-n coincidences at two bombarding energies, 10.425 and 12.0 MeV, in order to obtain information about the decay properties of the excited states in 9Be. Measured spectra reveal the importance of sequential decay mechanisms in the reaction. The decay structure of low-lying levels in 9Be has been discussed.

Isospin mixing of the first [formula omitted] states in 9Be and 9B

Contribution of Coulomb interaction to the isospin mixing in J π = 3 2 − states of 9Be and 9B has been calculated. It was found that this contribution only could not account for the measured widths for the first T = 3 2 analogue states. Importtance of a charge-dependent nuclear force is investigated.

States in 8Be studied through the reaction 11B(p, α)8Be with 40 MeV protons

Spectroscopy of the α- and τ-particles from 40 MeV proton bombardment of 11 B reveals transitions to 8 Be states up to 19 MeV. The ratio of excitation of the 16.6 MeV state to the 16.9 MeV state is 2.3 ± 0.4. The 8 Be(4 + ) state is found at 12.5 MeV with a width of 4.0 ± 0.5 MeV. States in 9 Be excited most strongly are the g.s. and 2.43 MeV level; a state at 3.1 MeV is excited with about 1 % of the strength of the g.s. transition. Angular distributions show forward-peaking for all states.

The role of the form of the hypernucleus wave function in the 9ΛBe → ααp π− decay

The energy and angular distributions of the 9 Λ → ααp π − decay products are calculated with the use of 9 Λ Be wave function in the form g αα ( r αα ) g α Λ ( r α1 Λ) g α Λ ( r α 2 Λ). Two maxima corresponding to the 0 + and 2 + states of 8Be are obtained in the αα relative energy distribution in agreement with the experimental data.

Final-state interactions in the [formula omitted] reaction

The 9Be + p → d + 2α reaction has been studied at a proton bombarding energy of 9.0 MeV, by the coincident detection of pairs of reaction products. Mass identification of one detected particle has been accomplished using a time-of-flight technique. The reaction yield has been shown to be dominated by final-state interactions through states in 8Be and 6Li, with little or no yield from direct three-body disintegration. Theoretical fits to the data using the generalized density of states functions reproduce quite accurately the shapes of the spectra. Efforts to fit the angular dependence of the yield have met with limited success.

The width of the 2.9 MeV state in 8Be from the 7Li(d,n)8Be reaction

Experimental results on the 7Li(d,n)8Be reaction at 3.72 and 4.76 MeV bombarding energy reported here, and previous results at lower energies are successfully interpreted in terms of a two-body final-state interaction in a three-body system, resolving an existing discrepancy between two-body phase shifts (or parameters) and the width of the neutron peak.

Properties of the low-lying positive-parity states in 9Be and 13C

Excitation energies and electromagnetic form factors of the low-lying positive-parity states have been calculated in 9Be and 13C on the basis of a particle-core coupling model. The results are compared with recent electron scattering experiments and photon data. The first excited levels in the two nuclei show a large contribution from the spin term of the electromagnetic interaction at low-momentum transfer q 2 < 0.6 fm −2.

Cross-section measurements for the reaction 10B(p, 3He)8Be

Abstract Cross sections have been measured for the transitions to the ground state and first excited state of 8Be and to the two 2+ levels at 16.63 MeV and 16.93 MeV excitation in the reaction 10B(p, 3He) at Ep = 49.5 MeV. The angular distributions of the cross section were compared with DWBA predictions.

A study of the second excited state of8Be by the10B(d, ?2)8Be-reaction

A study of the second excited state of8Be by the10B(d, ?2)8Be-reaction

The 18O( 3He, n) 20Ne and 7Li( 3He, n) 9B reactions

Information on the level structure of 20Ne and 9B has been obtained from the 18O( 3He, n) 20Ne and 7Li( 3He, n) 9B reactions at E( 3 He) = 3.1 MeV . The time-of-flight technique was used to obtain neutron spectra and angular distributions were measured from 0° to 140°. The angular distributions were analysed using DWBA two-particle stripping theory and two new states in 20Ne at 12.41 and 13.10 MeV were strongly excited and tentatively identified as 0 +. A group corresponding in position to a state in 9B at 1.5 MeV, in a 90° measurement at an incident energy of 3.1 MeV, was attributed to the decay of the 11.82 MeV state in 9Be. Groups in the neutron spectrum leading to the ground state of 9Be, an unresolved doublet at about 2.5 MeV and a level at 4.8 MeV were also observed.

A study of the second excited state of8Be by the10B(d,α2)8Be-reaction

The second excited state of8Be has been studied by analysis of the coincidence spectra of the reaction10B(d, α)2α forE d =1.0-2.0 MeV. The excitation energy was found to be 12.0±0.4 MeV, and the reduced width 0.85±0.12 MeV. Differential crosssections of the (d, α2)-reaction were deduced.

Decay modes of 9Li and states of 9Be

The β-decay of the 9Li nucleus and the subsequent particle decays of the unbound states of the 9Be nucleus have been investigated with two complementary techniques, a recoil-particle method and a beta-neutron coincidence method. 9Li nuclei were produced by the 18O( 7Li, 9Li) 16O reaction at a bombarding energy of 20 MeV and by the 3H( 7Li, 9Li)p reaction with a 14 MeV bombarding energy. The energy spectrum of the delayed alphas and the time-of-flight spectrum of the delayed neutrons were obtained. The half-life was measured to be 177±3 ms. Besides the known decay branches to the ground state and to the 2.43 MeV state in 9Be, a new decay branch to an unbound state in 9Be at an excitation energy of 2.78±0.12 MeV was observed. The branching ratios and the log ft values were found to be (65.0 −2.4 +2.7) %, (32.0 −3.7 +2.7)%, (3.0 −0.3 +2.7)% and 5.12 −0.02 +0.01, 5.00 −0.05 +0.04, 5.97 −0.28 +0.05 to the ground state, the 2.43 MeV state and the 2.78 MeV state, respectively. The observed properties of the 2.78 MeV state favor an assignment of 1 2 − . This state decays mainly by neutron emission to the ground state of 8Be and has a c.m. width of 1.10±0.12 MeV. The fraction of the decays of the 2.43 MeV state in 9Be involving emission of a neutron to the ground state of 8Be was found to be (6.4±1.2)%.

Search for the lowest T = 2 state of 8Be : Theory

Shell model calculations suggest that 6Li + d reactions should be used to search for the lowest T = 2 state of 8Be.

Search for the lowest T = 2 state of 8Be: Experimental

An anomaly with width Γ = 10 ± 3 keV has been observed in the excitation functions for 6Li + d reactions at an excitation energy in 8Be of 27.483 ± 0.010 MeV. It is interpreted as being due to the isospin forbidden excitation of the lowest T = 2 state f 8Be.

The ??Decay of 8B, and 2+ States Of 8Be

The {l-decay of 8B has been investigated by measuring the energy distribution of the &lt;x-particles from subsequent breakup of 8Be. The data have been analysed, in conjunction with data from &lt;X-o&lt; elastic scattering, in a three-level R-matrix formalism. Consistent fits are obtained for a channel radius of 6�0�0�5 fm, and the existence of a broad 2+ state of 8Be near 12�0 MeV, of width 14 MeV, is confirmed.

States in 9Be from 10B(t, α) 9Be

At E t = 12.9 MeV, α-groups from the 10B(t, α) 9Be reation have been observed to the ground state of 9Be and to excited states at E t = 1.7, 2.43, 3.02±0.05 ( Γ = 320±60 keV), 11.26±0.04 ( Γ = 530±70 keV) and, possibly, at 14.5 MeV ( Γ ≈ 800 keV). The T = 3 2 state at E x = 14.39 MeV was seen, but the intensities of the α-groups are very low, typically 5% of the intensity of the group to the 2.43 MeV state. The angular distributions of the α-particles to the 2.43 MeV state are sharply peaked forward and backward. The ground state α-particles are not peaked in the backward direction. Angular distributions of α-particles from the 9Be(t, α) 8Li reaction to 8Li (0, 0.98, 2.26, 6.53) are also reported.

Even and odd parity states in 9Be

Results of a projected Hartre-Fock calculation are presented both for the even and odd parity states of 9Be. It is found that the even parity states come down very low in the energy spectrum and explain the occurrence of non-normal parity states at low energies.