Evidence for the constant-matrix-element mechanism in the breakup of the3He+7Li system and highly excited states in6Li

The inclusive alpha particle spectra from the breakup of the³He+⁷Li system atE ³He=42.9 MeV are analyzed in the frame of the nuclear reaction model whose matrix element does not depend on the relative energies of the outgoing particles and is therefore constant. The comparison with a recent analysis of thep+⁹Be interaction, leading to the same composite system, has shown the correlation of the final-state configuration on the entrance-channel cluster structure.the existence of broad excited states for⁶Li excitation energies between 19 and 28 MeV is confirmed.     

Three-particle correlations from208Pb+6Li

Three-particle correlations in the reaction²⁰⁸Pb+⁶Li were studied near the Coulomb threshold between \(E_{6_{Li} } = 24\) and 30 MeV. Three reaction mechanisms contribute predominantly to the observed coincidences of the charged particles: 1. Coulomb excitation of the 2.184 MeV,J=3⁺ state of⁶Li, followed by the decay intoα+d, 2. Deuteron pick-up of the⁶Li to the ground state of⁸Be and sequential decay into twoα-particles and 3. Neutron-transfer to the ground state and the first excited states of²⁰⁹Pb:²⁰⁸Pb(⁶Li,αp). The last two reaction mechanisms explain the previously measured large contributions to theα-channel relative to thed-channel.     

(p,t) Reaction studies on some even isotopes of samarium

The (p, t) reaction on the even isotopes¹⁴⁴Sm,¹⁴⁸Sm and¹⁵⁰Sm has been investigated at an incident proton energy of 25.5 MeV. Angular distributions have been measured for transitions to the ground state and excited states up to an excitation energy of about 2.5 MeV. Especially theL=0 angular distributions are discussed.     

Microscopic multi-channel calculations for the10Li system

A microscopic multichannel calculation for the¹⁰Li system has been performed in the framework of the Refined Resonating Group Method. Elastic neutron scattering off the⁹Li ground state and transitions into four excited states were considered. The energy spectrum of¹⁰Li is deduced from a phase shift analysis. Besides theJ ^π = 1⁺ ground state, five excited states are identified.     

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.     

Spin assignment for the 1.89 MeV level in42Sc

The gamma decay mode and the spin value of the 1.89 MeV state of⁴²Sc were investigated by studying the⁴⁰Ca(³He,p γ)⁴²Sc reaction at 10.0 MeV energy of the incident³He beam. The analysis of thep-γ angular correlation of the 1.89 MeV ground state transition — using method II of Litherland and Ferguson — yields the spin assignmentJ=1 for this level.     

Search forγ-ray transitions within the5Li groundstate

A search forγ-ray transitions within the broad groundstate of⁵Li has been carried out via the⁴He(p, γp ^*)⁴He reaction atE _p (lab)=1.5?7.0 MeV. Differentially pumped gas targets of the extended and quasi-point types have been used. The results show that the set-up and detection techniques utilized are not sensitive enough to observe such intrastate transitions.     

Scattering and transfer reactions for 6, 7Li + 90, 91Zr

Elastic scattering data have been measured for the ⁷Li + ⁹⁰Zr, ⁶Li + ⁹⁰Zr, and ⁶Li + ⁹¹Zr systems at E(Li) = 34 MeV. Inelastic scattering data for the ⁷Li + ⁹⁰Zr and ⁶Li + ⁹⁰Zr systems were also measured for the 2⁺(2.18 MeV) and 3^?(2.75 MeV) states in ⁹⁰Zr and the $\text{1}\text{2}{}^{\mathrm{?}}\text{(0.48}\text{MeV}\text{)}$ state in ⁷Li. Optical model analyses of the elastic scattering data and DWBA analyses for the states in ⁹⁰Zr were performed. The deduced deformation lengths for the 2⁺ state agreed with those extracted in other studies but the deformation length for the 3^? state was smaller. The ⁹⁰Zr(⁷Li, ⁶Li)⁹¹Zr angular distributions were measured for the 1.21 and 2.03 MeV states and the 2.19 MeV doublet in ⁹¹Zr. Also, ⁹⁰Zr(⁷Li, ⁶He)⁹¹Nb angular distributions were measured for the ground states, 0.10, 3.41 and 4.82 MeV states in ⁹¹Nb. The transitions well matched in angular momentum were described by finite-range DWBA calculations, while other transitions displayed the same phase problems seen with heavier ions. The extracted spectroscopic information was consistent with the results of other reaction studies. At the present energy, it was not possible to determine whether the l = 1 phase problem that occurs for heavy-ion single-nucleon transfer reactions on 2s-1d shell nuclei occurs in ⁹¹Zr also.     

Potential cluster approach to the description of the 7Li + γ ai p6He reactions

Angular distributions for the ⁶He(p, γ_{0 + 1})⁷Li process at the energy E _γ = 40 MeV are calculated within the potential cluster approach. It is shown that the observed cross section is well reproduced when E1 and E2 transitions are taken into account; in this case, unlike the case in the RGM calculations, the dominating mechanism is direct capture to the ground state of the ⁷Li nucleus. Total cross sections for direct photodisintegration ⁷Li (γ, p₀)⁶He in the energy interval E _γ = 22–30 MeV are calculated.     

Intrastate γ-transitions: A spectroscopic tool?

In the framework of a potential model we have calculated the various bremsstrahlung cross sections into the⁵Li ground state, includingM 1 andE 2 γ-transitions leading from the high energy wing of the⁵Li ground state resonance into states belonging to the same resonance at lower energy (intrastate transition). Our calculation supports the hypothesis of Schmalbrock et al. [1] that intrastate transitions ofM 1 andE 2 multipolarity exist. While we find a maximum cross section of roughly 1.4 nb for theE 2 transition, we predict the cross sections forM 1 intrastate transition to be less than 3·10^?5nb. An experimental observation of the intrastate γ-ray emission appears to be very difficult due to the dominance of competing resonant (M 1) and direct (E 1) capture processes. Schmalbrock et al. have suggested to deduce magnetic dipole and electric quadrupole moments of resonant states from the measurements of the respectiveM 1 andE 2 intrastate transitions. We will show that theM 1 intrastate cross sections do not yield the appropriate information to determine the magnetic dipole moment. We will also discuss thatE 2 intrastate transitions do not seem to be a suited tool to find the quadrupole moment of an unstable state.     

Evidence of non-statistical structures in the elastic and inelastic scattering of58Ni+58Ni and58Ni+62Ni and intermediate dinuclear states

Excitation functions and angular distributions of⁵⁸Ni+⁵⁸Ni and⁵⁸Ni+⁶²Ni scattering at energies just above the Coulomb barrier have been measured aroundθ _cm=90° in energy stepsΔE _cm=0.25 MeV fromE _cm ? 110 MeV toE _cm ? 120 MeV for⁵⁸Ni+⁵⁸Ni and fromE _cm ? 110 MeV toE _cm ? 118 MeV for⁵⁸Ni+⁶²Ni. Evidence for structure of non-statistical character has been found in the angle-summed excitation functions; this evidence is corroborated by the analysis of the angular distributions. This is the first time that non-statistical structure in elastic and inelastic scattering is reported with high confidence level for this mass and excitation energy ranges. Attempts are presented to understand the nature of this structure, including the presence of intermediate dinuclear states and virtual states in a potential well.     

Investigation of large angle structure in α-scattering from calcium isotopes betweenE α=36–61 MeV

Elasticα-scattering angular distributions have been measured atE _α=36.2 MeV, 39.6 MeV, 42.6 MeV, 49.5 MeV, 61.0 MeV for⁴⁰Ca and atE _α=36.2 MeV, 42.6 MeV, 49.5 MeV and 61.0 MeV for⁴⁴Ca, respectively. At backward angles the data display an oscillatory structure forE _α<50 MeV and more smoothly decreasing slopes atE _α =61.0 MeV resembling the data obtained at higher energies. The⁴⁰Ca data belowE _α =50 MeV show the well known backward enhancement, which at 42.6 MeV and 49.5 MeV can be fitted by aP ₁₄ ² and aP ₁₆ ² respectively. Together with previous data,P _L ²-structures have now been observed for allL-values betweenL=8 andL=16. The slope of the curveL(L+1) versus excitation energy is slightly smaller forL>12 than forL<12. Optical model analyses (within a Woods-Saxon-folding model) lead to large differences between the⁴⁴Ca and⁴⁰Ca parameters. Furthermore, in our parametrization, the⁴⁰Ca real potential depth shows dramatic changes with energy. This feature seems outside the domain of the optical model and requires consideration of additional effects (e.g. antisymmetrization) not included in the standard optical model. Present microscopic calculations on the basis of the Resonating Group Method are discussed in connection with the characteristic features ofα-scattering from⁴⁰Ca.     

Solution of the10Li-Puzzle

The mass of¹⁰Li has been measured with two different reactions:⁹Be(¹³C,¹²N)¹⁰Li,E _Lab=336 MeV, and¹³C(¹⁴C,¹⁷F)¹⁰Li,E _Lab=337 MeV. The mass excess of 33.445(50) MeV is deduced from theQ-value measurement.¹⁰Li is found to be particle-unstable with respect to one-neutron emission by 0.42(5) MeV. In the analysis of the first reaction a low lying excited state is found at 0.38(8) MeV. This state and the ground state can be most probably identified as the 1⁺/2⁺-doublet coupled from the [π 1p3/2 ?ν 1p 1/2] configuration, the 1⁺-state being the ground state. The (¹³C,¹²N)-reaction populates the 1⁺-state strongly due to a spin-isospin-flip character of the dominant part of the transition amplitude. The 2⁺-member corresponds to the mass given by Wilcox et al. A second excited state is observed at 4.05(10) MeV with a width of 0.7(2) MeV, it can be associated with theν 1d 5/2-strength. The second reaction is fully supporting the interpretation of the ground state doublet. The excited state at 4.05 MeV is not observed in this reaction and indeed it should not, because the reaction does not populate in first order excited neutron configurations. The levels are well described by mean field calculations including pairing correlations. The lowest resonance in the calculations is theν 1/2^?-configuration, whereas theν 1/2⁺-configuration shows at the neutron threshold a strong non-resonant contribution.     

Exact finite-range DWBA description of the60Ni(160,12C)64Zn reaction at 60 MeV incident energy

Cross section angular distributions of⁶⁰Ni(¹⁶O,¹²C)⁶⁴Zn reactions leading to three strongly excited states at 60 MeV incident energy and the¹⁶O+⁶⁰Ni and¹²C+⁶⁴Zn elastic scattering at 60 MeV respectively 45 MeV and 54 MeV have been measured using aQ3D magnetic spectrograph. EFR-DWBA calculations assuming the transfer of anα-cluster in its 0s ground state are able to describe the general features of the strongly oscillating experimental angular distributions using a surface transparent optical model potential. The optical model parameters used in the DWBA calculations are obtained from fits of the elastic scattering data of incident and exit channels. The importance of “correct” optical model parameters in the exit channels for relative spectroscopic factors will be discussed and the extracted relative spectroscopic factors will be compared to previous (⁶Li,d) results.     

Seniority-three yrast states in theN=82 nucleus147Tb

Firm spin-parity assignments for the high-spin states up to 3.5 MeV in the one-proton nucleus¹⁴⁷Tb were obtained from¹⁴⁴Sm(⁶Li, 3n) in-beamγ-ray and conversion electron measurements. The energies of these two-particle one-hole excitations were calculated from the shell model with empirical nucleon-nucleon interaction energies. The calculated energy splittings agree well with experiment, whereas the theoretical excitation energies disagree by ?1 MeV if recently measured ground state masses are used.     

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.     

Polarisation und differentieller Wirkungsquerschnitt der Neutronen aus der Reaktion9Be(α,n)12C

The differential cross section and the angular distribution of the polarization of neutrons from the reaction⁹Be(α, n) leading to the ground state of¹²C have been determined at 1.75 and 1.96 MeV energy of theα-particles. The polarization was measured by left-right asymmetry induced by elastic scattering from⁴He. From Blatt, Biedenharn and Simon, Welton theory analysis a set of spectroscopic data has been obtained for five states of the compound nucleus¹³C.     

High-lying excited states in <Superscript>10</Superscript>Be from the <Superscript>9</Superscript>Be(<Superscript>9</Superscript>Be,<Superscript>10</Superscript>Be)<Superscript>8</Superscript>Be reaction

A transfer-reaction experiment of ⁹Be(⁹Be, ¹⁰Be)⁸Be was performed at a beam energy of 45 MeV. Excited states in ¹⁰Be up to 18.80 MeV are produced using missing mass and invariant mass methods. Most of the observed high-lying resonant states, reconstructed from the α + ⁶He and t + ⁷Li decay channels, agree with the previously reported results. In addition, two new resonances at 15.6 and 18.8 MeV are identified from the present measurement. The 18.55 MeV state is found to decay into both the t + ⁷Li_g.s. and t + ⁷Li* (0.478 MeV) channels, with a relative branching ratio of 0.93 ± 0.33. Further theoretical investigations are encouraged to interpret this new information on cluster structure in neutron-rich light nuclei.     

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.     

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.