(n,t) and (n, α) reactions on 9Be

A metallic ⁹Be target was bombarded with 13.99 MeV neutrons; α-particles, tritons and ⁶He recoil nuclei were detected and identified with a telescope consisting of two proportional counters and a solid state detector. Absolute differential cross sections were measured for the (n, t) reactions leading to the ground state and first excited state of ⁷Li and for the (n, α) reactions leading to the ground state and first excited state of ⁶He. No evidence for higher excited states in ⁶He has been found. An attempt has been made to interpret the observed (n, α) angular distributions in terms of the direct reaction model.     

Proton-hole states in 115In observed in the 116Sn(d, 3He) reaction

The ¹¹⁶Sn(d, ³He)¹¹⁵In reaction has been investigated at E_d = 50 MeV. Thirteen transitions to states up to 3 MeV excitation energy were studied. The measured angular distributions were compared with DWBA calculations and transferred angular momenta and spectroscopic factors were deduced. Levels at 1.04, 2.23 and 2.52 MeV were found to be excited most likely by l = 3 angular momentum transfer in contrast to previous investigations at lower incident energies in which no l = 3 transitions have been observed.     

Soft dipole mode in 8He

The low-lying spectrum of ⁸He was studied in the ³H(⁶He, p)⁸He transfer reaction for small center of mass angles. The 0⁺ ground state (g.s.) of ⁸He and excited states, 2⁺ at 3.6–3.9 MeV and (1⁺) at 5.3–5.5 MeV, were populated with cross sections of 200, 100–250, and 90–125 μb/sr. Some evidence for the excited state at about 7.5 MeV can be found in the data. The possible nature of the near-threshold anomaly above 2.14 MeV in ⁸He is related to the population of a 1⁻ continuum (soft dipole excitation) with a peak energy value at about 3 MeV. This assumption can probably resolve the problem of a large uncertainty existing in the experimental data on the ⁸He 2⁺ state energy. The article is published in the original.     

Highly excited 8Be core in the configuration of the 12C and 11B ground states

Angular distributions of the ¹²C(d, ⁶Li)⁸Be reaction at E_lab = 78.0 MeV and the ¹¹B(³He, ⁶Li)⁸Be reaction at E_lab = 71.8 MeV were measured. Transitions leading to ⁸Be in the ground state and the 3.04, 16.63, 16.92, 17.64 and 18.15 MeV excited states were observed. A DWBA analysis was performed regarding the (d, ⁶Li) and (³He, ⁶Li) reactions as direct α particle or triton transfers, respectively.     

Properties of very n -rich He isotopes

Low-energy spectra of the ^{8, 10}He nuclei were investigated in the (t, p) -type reactions at small centre-of-mass angles using ～ 25 AMeV beams of ⁶He and ⁸He nuclei. The 0⁺ ground state (g.s.) of ⁸He and excited states, 2⁺ at 3.6-3.9MeV and (1⁺) at 5.3-5.5MeV, were populated with cross-sections of 200, 100-250, and 90-125μb/sr, respectively. To account for a near-threshold anomaly observed in the ⁸He spectrum the population of a 1^- continuum (soft dipole excitation) was considered. The lowest-energy group of events in the ¹⁰He spectrum was observed at ～ 3 MeV with a cross-section of ～ 140 μb/sr. This result is consistent with the previously reported observation of ¹⁰He providing a new g.s. position for ¹⁰He at about 3MeV.     

Spectroscopy of9He with the (13C,13O)-reaction on9Be

First results of the double-charge-exchange reaction⁹Be(¹³C,¹³O)⁹He, E_Lab=380 MeV, are presented. The ground state and an excited state at 3.8 MeV are clearly seen. A preliminary value of the⁹He mass excess is obtained: 41.5±0.6 MeV. Spectra of of the⁹Be(¹³C,¹⁴O) He-reaction have been measured with high resolution. The ground state transition appears as a pronounced sharp peak, but no other narrow peaks are observed.     

Experimental investigation of highly excited states of the 5,6He and 5,6Li nuclei in the (6Li, 7Be) and (6Li, 7Li) one-nucleon pickup reactions

The (⁶Li, ⁷Be) and (⁶Li, ⁷Li) reactions on ⁶Li and ⁷Li nuclei were investigated in the angular interval 0°–20° in the laboratory system at a ⁶Li energy of 93 MeV. In addition to low-lying states of the ^5,6He and ^5,6Li nuclei, broad structures were observed near the t(³He)+d and t(³He)+t thresholds at the excitation energies of 16.75 (3/2⁺) and ～20 MeV (for ⁵He), 16.66 (3/2⁺) and ～20 MeV (⁵Li), 14.0 and 25 MeV (⁶He), and ～20 MeV (⁶Li). The angular distributions measured in the ⁷Li(⁶Li, ⁷Be)⁶He reaction for transitions to the ground state (0⁺) and excited states at E _x=1.8 MeV (2⁺) and 14.0 MeV of the ⁶He nucleus were analyzed by the finite-range distorted-wave method assuming the 1p-and 1s-proton pickup mechanism. The (⁶Li, ⁷Be) and (⁶Li, ⁷Li) reactions were shown to proceed predominantly through the one-step pickup mechanism, and the broad structures observed at high excitation energies are considered as quasimolecular states of the t(³He)+d and t(³He)+t types.     

Correlation investigations of the low-energy 10He spectrum

The spectrum of low-lying states in the ¹⁰He nucleus is investigated for the two-neutron transfer reaction ³H(⁸He, p)¹⁰He. The secondary beam of ⁸He nuclei with the energy 21.5 MeV/nucleon and a cryogenic tritium target are used in the experiment. The ¹⁰He ground state is observed in the missing mass spectrum at the energy of 2.1 MeV (Γ ～ 2 MeV) above the decay threshold. Analysis of the angular correlations of the ¹⁰He decay products yields the spin and parity of two excited ¹⁰He states, J ^π = 1^? in the energy range from 4 to 6 MeV and J ^π = 2⁺ at energies above 6 MeV.     

Charge exchange reaction 14C(6Li, 6He)14N

Angular distributions of the charge exchange reaction ¹⁴C(⁶Li, ⁶He)¹⁴N leading to the 1⁺ ground state and 3.95 MeV 1⁺, and 5.20 MeV 2^? excited states at the 34 MeV incident beam energy were analyzed and measured. The 62 MeV data of Goodman et al. were also reanalyzed. The direct one-step charge exchange caused by the spin-isospin dependent term in the two-body interaction can account well for the observed data. The strength of spin-isospin dependent effective interaction (gaussian form with a range parameter of 1.8 fm) was extracted to be 18.5 MeV.     

Spin-dependence and coherent summations in two-nucleon transfer reactions

The differential cross sections of the ¹⁹F(p, ³He)¹⁷O and ¹⁹F(p, t)¹⁷F reactions leading to the ground and first three excited states have been measured at an incident energy of 42.4 MeV. The polarization analysing powers of two of the (p, ³He) reactions have been measured at a higher energy of 49.5 MeV with a polarized incident beam. The experimental results have been analysed in terms of conventional DWBA theory, and the importance of interference terms arising from the proper coherent summations contained in the definition of the differential cross section and analysing power, have been investigated. It is found that the interference term arising from the coherent summation over the transferred spin S is significant and should not normally be neglected.     

Spectroscopy of excited states of 8He

The ¹⁰Be(¹²C,¹⁴O)⁸He-reaction has been used to study the levels of ⁸He. In addition to the known excited state of ⁸He at E_x = 3.6 MeV, with J^π = 2⁺, three additional states were found at excitation energies of 4.54(25) MeV, 6.03(10) MeV and 7.16(4) MeV.     

Study of low-lying Rb levels in the Rb(τ, α)Rb reaction

The low-lying levels in ⁸⁶Rb were investigated via the ⁸⁷Rb(τ, α)⁸⁶Rb reaction with a 16 MeV ³He beam. Nine excited levels at 0.49, 0.56, 0.87, 0.98, 1.02, 1.09, 1.42, 1.66 and 2.12 MeV excitation were identified. A distorted-wave analysis was performed yielding spectroscopic information about these levels.     

Proton-hole states in 57Co studied with the 58Ni(d, 3He) 57Co reaction at 78 MeV

The ⁵⁸Ni(d, ³He)⁵⁷Co reaction was measured at a bombarding energy of 78 MeV. Energy levels up to 7.0 MeV excitation energy in ⁵⁷Co were studied. Angular distributions of the ³He particles, corresponding to transitions to the ground state and to 42 excited states in ⁵⁷Co, were analyzed in the range of θ_lab = 2.7° to 25°. Exact finite-range DWBA calculations were employed to extract l-values and spectroscopic factors. Shell-model calculations were carried out in an fp-shell model space. In addition, calculations of the energy levels in ⁵⁷Co were performed in the SU(6) particle-vibration model (PTQM). Satisfactory agreement is observed between the experimental results and both theoretical predictions.     

Proton polarization and differential cross section for the (3He,p) reaction on 6Li and 9Be at 14 MeV

Angular distributions of the proton polarization and the differential cross section have been measured for the reaction (³He, p) initiated by 14 MeV incident ³He particles and proceeding to the ground and the first excited states of the final nuclei ⁸Be and ¹¹B. Large polarization values were observed, especially for the ⁹Be(³He, p)¹¹B reaction leading to both the ground and the first excited states in ¹¹B. The experimental results have been analysed in terms of a two-nucleon transfer spindependent distorted-waves theory using finite-range formalism and including corrections due to the non-locality of the optical potentials. A proper coherent summation over L and S, whenever necessary was included in the DWBA calculations of the polarization and the differential cross section as implied by the presence of the spin-orbit terms in the optical-model potentials used to generate the distorted waves.     

High-spin states in123Te

The¹⁰Be(¹²C,¹⁴O)⁸He-reaction has been used to study the levels of⁸He. In addition to the known excited state of⁸He at E _x =3.6MeV, withJ ^π=2⁺, three additional states were found at excitation energies of 4.54(25)MeV, 6.03(10)MeV and 7.16(4)MeV.     

Mass 2 and 3 cluster structure study with quasi-free reactions induced by 58 MeV protons on 9Be, 12C and 14N

Cross sections for (p, pd) and (p,p³He) reactions at 58 MeV have been measured for ⁹Be, ¹²C and ¹⁴N targets. An energy resolution of about 400 keV permitted identification of several excited states in the different residual nuclei. The experimental results are presented and analysed in the framework of the distorted-wave impulse approximation. Spectroscopic and mechanism information is discussed. Some additional quasi-free reactions involving t, ³He and α structure of ⁹Be have been observed and are also reported.     

Direct reactions involving exotic nuclei 8He and 5H

The angular distribution of 26 MeV/n ⁸He ions elastically scattered from a gaseous helium target was measured in a wide CM angular range. Results are discussed in terms of the potential scattering and neutron transfer. The angular distributions of elastic scattering as well as 1n and 2n transfer reactions of these ions on protons are presented. Finite-range DWBA calculations made for the 2n transfer reaction leading to the ground (0⁺) and excited (2⁺) states of ⁶He underestimate the cross section for 2n transfer to ⁶He(0⁺). Analysis of data for this reaction channel suggests the importance of a direct ⁵H-cluster exchange process. A resonance state of ⁵H with an energy of 2 MeV above the decay threshold n+n+ ³H was obtained for the first time by making use of the reaction p(⁶He,²He)⁵H.     

An experimental study of He elastic,inelastic and charge-exchange scattering from Li

A target of ⁶Li was bombarded with the ³He beam from the University of Illinois cyclotron. Differential cross sections for the elastic scattering, the inelastic scattering to the first two excited states of ⁶Li, and the (³He, t) charge-exchange reaction to the ground state of ⁶Be were determined over angular ranges of approximately 20° to 115° (c.m.) at ³He energies of 24.6 MeV and 27.0 MeV. (The weak inelastic transition to the 3.56 MeV state of ⁶Li, ordinarily obscured by a background of three-body break-up, was observed by requiring a coincidence at most angles between the scattered ³He and the ⁶Li recoil.) The ratio of the integrated charge-exchange cross section between 55° and 115° to the integrated inelastic cross section for this transition (both with ΔT = 1) is somewhat less than expected from isospin considerations (i.e., about 1.6 instead of 2.0).     

Quest for the 10He nucleus

The spectrum of ¹⁰He was studied by means of the ³H(⁸He, p)¹⁰He reaction at a laboratory energy of 25 MeV/A and small center-of-mass angles. Missing mass spectrum of ¹⁰He was derived from the obtained p-⁸He coincidence. A resolution of 0.7 MeV was achieved in this spectrum for the measured ¹⁰He energy. Most likely, a well isolated group of 10 events detected between 2 and 5 MeV and showing a maximum at about 3 MeV in the spectrum of the present work exhibits the ¹⁰He g.s. resonance.