States In Light Nuclei Research Articles

Molecular states in excited spectra of light nuclei.

The energy levels of molecular states in light nuclei are classified by irreducible representations of the group U(5). The excited spectra so classified of $^{18}\mathrm{O}$ and $^{20}\mathrm{Ne}$ compare very well with the experimental excited spectra.

Microscopic calculation of antiproton atomic-like bound states in light nuclei

The antiproton-nucleon K-matrices corresponding to the central, spin-orbit and tensor parts of the Dover-Richard interaction are parametrized by linear combinations of Yukawa functions. The antiproton-nucleus optical potential is then constructed from the two-body K-matrix or a series of light nuclei. Basically simple folding with harmonic oscillator nucleon wave functions is used. However, the angular momentum couplings are treated with special care to allow for the inclusion of the spin-orbit and tensor parts of the basic interaction. Energy level shifts in antiprotonic atoms are then calculated for 4He, 6Li, 7Li, 12C, 16O, 17O, and 18O. The numerical results show that both the spin-orbit and tensor parts contribute terms significantly larger than the present experimental uncertainties. Hyperfine and fine splitting are of the same order of magnitude and analyses of experimental data should include such splittings. Considering the crudeness of the calculations the results are in surprisingly good agreement with experimental data.

Kinematic coincidence technique to identify γ-decaying highly excited states in light nuclei

A simple kinematic coincidence technique is described for separating γ-decaying states from particle decaying states populated in two-body reactions. The method is especially suited to the discovery and further study of γ-decaying states at high excitation energies in light nuclei, but has not previously been widely exploited. Experimental applications using the reactions 12C( 16O, α) 24Mg and 12C( 6Li, d) 16O are presented and these illustrate the range of results obtainable. In particular, the method provides an excellent means of measuring the probability for γ-decay, Γ γ/Γ, of individual excited states. The general properties of reactions suitable for use with the coincidence technique are discussed.

Search for highly excited states in light nuclei with three-body reactions

Various three-body break-up reactions resulting from the bombardment of 7Li with 120 MeV 3He have been measured simultaneously in a kinematically complete experiment. Missing-mass spectra have been deduced for 4H, 4He, 4Li, 5He, 5Li, 6He, 6Li and 7Li. The ground states of 4H and 5He are well described as n-t and n-α P-wave final-state interactions, respectively. Evidence is found for relatively narrow states at very high excitation energies in several nuclei. The results are compared with those of other authors and with various theoretical predictions.

Particle-hole description of GDR states in light nuclei with closed shells±2 nucleons

The particle-hole model is presented for nuclei with closed core±2 nucleons. This model, as applied to 6 Li, 14 N, 14 C and 18 O, gives overall agreement with experiment for the low-lying and GDR states.

Isoscalar monopole and dipole transition matrix elements from inelastic alpha scattering

Using an implicit folding procedure, isoscalar monopole and dipole transition matrix elements are expressed in terms of deformation parameters and moments of the optical potential forα-scattering. Application to monopole states in light nuclei gives good agreement with data determined electromagnetically. For isoscalar dipole states, the method gives information on 〈r 3〉 matrix elements which cannot be obtained otherwise.

Quenched magnetic transitions from high spin states in light nuclei

Recent investigations of stretchedM 6 transitions in thes-d shell have uncovered the unexpected systematic trend that isoscalarM 6 transitions are two to three times more retarded than the isovector ones. We present the result of a microscopic calculation analyzing the different mechanisms usually invoked in the formation of the quenching and suggest that an additional argument based on the difference in structure between isoscalar and isovector transition densities may be playing a predominant role in explaining the data.

The measurement of entry states in light nuclei

Gamma-ray and charged-particle emission have been studied following the bombardment of 28Si and 32S with 40 MeV 16O ions and of 58Ni with 55 MeV 16O ions. The locus of states populated by particle evaporation and depopulated by gamma emission (entry line) has been studied in the 2p channel for each of these reactions by measuring the mean gamma -ray multiplicity and total proton kinetic energy. The moments of inertia for 46Ti and 72Se are deduced from the slope of the entry line. The data are compared with statistical-model calculations and show good agreement.

Quasimolecular and cluster states of light nuclei as examples of intermediate structure

4+, 6+ and 8+ resonances of the 12C+12C system, 5/2+ and 7/2+ cluster states of 19F and 0+ resonances from alpha scattering on 24Mg and 26Mg are analysed as intermediate structure data. Parameters of the underlying simple states and the couplings are deduced.

Angular distributions of single pion charge exchange reactions to isobaric analog states in light nuclei

Measurements of the angular distributions of the single charge exchange reactions to isobaric analog states for $^{13}\mathrm{C}({\ensuremath{\pi}}^{+}, {\ensuremath{\pi}}^{0})^{13}\mathrm{N}$ and $^{15}\mathrm{N}({\ensuremath{\pi}}^{+}, {\ensuremath{\pi}}^{0})^{15}\mathrm{O}$ at 165 MeV are described. The two angular distributions are very similar. The shapes are reproduced by semiphenomeno-logical isobar-doorway calculations and by second-order coupled channels calculations. The calculated magnitudes are low by about a factor of 2. The measurements are consistent with older angle-integrated cross sections for $^{13}\mathrm{C}$.NUCLEAR REACTIONS $^{13}\mathrm{C}$, $^{15}\mathrm{N}({\ensuremath{\pi}}^{+}, {\ensuremath{\pi}}^{0})$, ${T}_{\ensuremath{\pi}}=164$ MeV; measured $\ensuremath{\sigma}(\ensuremath{\theta})$; IAS transitions; enriched targets; test of reaction models.

A variational study of the ground and excited states of light nuclei in a three-body model on the complete basis. I. General formalism

The variational method proposed recently is used to develop a formalism for calculating the structure of light nuclei in terms of the multi-cluster model. The technique is developed to calculate all the matrix elements of the Hamiltonian on a multi-dimensional gaussian basis (MGB) including the central, spin-orbit and tensor forces. The basis constructed is shown to give rise to convenient pure analytical formulae for all the matrix elements of the Hamiltonian and, moreover, for all the observables of practical interest such as the RMS radius, the quadrupole and magnetic moments, the electromagnetic form factors etc. A method to take account of the Pauli principle in the composite-particle system based on the introduction of a projecting addend in the Hamiltonian is described. Essential advantages of the projection technique described are demonstrated.

A variational study of the ground and excited states of light nuclei in a three-body model on the complete basis. II. The structure of6He-6Li-6Be nuclei in the α+2N model

For pt.I see ibid., vol.8, no.5, p.667-78 (1982). The variational approach to calculations of multicluster systems which was developed in part I, is applied to a study of low-lying states with Jpi T=1+0 and 0+1 in nuclei with A=6. The interaction Hamiltonian includes the central spin-orbit and tensor forces. The effect of the Pauli principle is included through the requirement of orthogonality of the total wavefunction to the forbidden OS state in the n- alpha and p- alpha subsystems. The Coulomb interaction is included accurately. The P-component admixtures to the total wavefunction are studied. The value of the mathematical expectation of the 6Li Hamiltonian is shown to be relatively insensitive to the P-component contribution. The character of saturation in the pseudo-potential coupling constant corresponding to the contribution of the forbidden states is studied. The calculated Coulomb differences for the 6He-6Li-6Be isobaric triplet prove to be in rather good agreement with the experimental data, as are the value of the RMS radius and the behaviour of the charge form factor of the 6Li ground state.

Correlations and structure of a 3α system with the Ali-Bodmer force

By solving the Schrödinger equation for a 3-body bound system, we investigate the correlations among three α-particles interacting pairwise with the Ali-Bodmer plus Coulomb force. From a comparison among various calculated states, we have found 2 types of excitation mode and 2 rotational bands which support the concept of intrinsic states in light nuclei.

Radiative Capture of Intermediate-Energy Protons to High-Lying States in Light Nuclei

Observations are reported from the first systematic studies of proton radiative capture at intermediate energies. In addition to captures to the ground and first few excited states, the reactions $^{11}\mathrm{B}$($p$,$\ensuremath{\gamma}$)$^{12}\mathrm{C}$ and $^{27}\mathrm{Al}$($p$,$\ensuremath{\gamma}$)$^{28}\mathrm{Si}$ reveal unexpectedly strong transitions to isolated high-lying states. These latter transitions could take place via second-harmonic giant resonances. Protons on $^{12}\mathrm{C}$ produce a rich spectrum of $\ensuremath{\gamma}$ rays which may arise from captures to high-lying single-particle states.

A computation of the optical potential in nuclear matter from a separable nucleon-nucleon interaction

The first two terms of the low-density expansion of the optical potential in nuclear matter are computed starting from the Hamman-Ho-Kim separable nucleon-nucleon interaction. A Monte Carlo method is used to calculate the second order contribution. The lifetime of 1s hole states in light nuclei is computed by means of a local density expansion. The effect of renormalization corrections and the E-dependence of the optical potential in relation to the hole state widths are discussed.

Prediction of the high-spin selectivity of compound reactions induced by heavy ions

Two procedures are described to predict the selectivity of heavy-ion (HI) compound reactions for excitation of high spins. The applicability of statistical-model calculations in respect to yrast line effects is discussed. Contour diagrams of the total cross sections σ(E ∗, I), dσ(E ∗, I)/ dE ∗ and dσ(E ∗)/ dE ∗ are derived, yielding the gradient dσ(E ∗, I)/ dI and the p to “background” ratio of high-spin states as well as the “optimum Q-value” for any given HI compound reaction. The dependence of both the optimum Q-value and the shape of dσ(E ∗)/ dE ∗ on the critical L-value at high bombarding energies can be used to determine L crit. This is demonstrated for the reaction 12 C + 14 N → 26 AI . A rougher estimate of the selectivity is given by the “grazing-collision picture” which is based on a consideration of the angular momentum balance. Using the reactions 10B( 12C, d), 12C( 12C, d), 12C( 14N, d), 11B( 14N, p), 13C( 14N, p), 10 B( 14 N, α) and 12C( 14N, 6Li) as examples, the theoretical predictions are shown to be in excellent agreement with experiment, for bombarding energies ranging between 40 and 120 MeV. The possibility to predict the high-spin selectivity is the precondition for an application of HI compound reactions for investigations of yrast lines and converts this class of reactions into an outstanding means for spectroscopy of high-spin states in light nuclei.

Simple potential model for cluster states in light nuclei

We present a simple model for three and four particle cluster states in light nuclei. These states are considered as bound states and single particle resonances of a cluster-core potential, which is obtained by folding the cluster and core mass densities. We calculate some properties of these states in $^{16}\mathrm{O}$ and $^{20}\mathrm{Ne}$, such as the rms radii, $B(E2)$ values, $\ensuremath{\alpha}$-decay widths, and energy spectra. Good agreement with available data is obtained and some predictions are made for $B(E2)$ values in the ${K}^{\ensuremath{\pi}}={0}^{\ensuremath{-}}$ bands in $^{16}\mathrm{O}$ and $^{20}\mathrm{Ne}$. This model is also used to interpret recent heavy ion three particle transfer data. Dynamical support is offered for high spin assignments in $^{15}\mathrm{N}$ and $^{15}\mathrm{O}$ previously based on kinematical considerations.NUCLEAR STRUCTURE $^{15}\mathrm{N}$, $^{16}\mathrm{O}$, $^{20}\mathrm{Ne}$; calculated energies, $J$, $\ensuremath{\pi}$, $B(E2)$ values, $\ensuremath{\alpha}$ widths, radii in cluster model with folded potential.

Realistic Effective Interaction between Nucleons in Cluster States of Light Nuclei: Starting-Energy-Dependent Interaction and Its Application to Alpha-Cluster plus 16O-Core Model of 20Ne

Realistic Effective Interaction between Nucleons in Cluster States of Light Nuclei: Starting-Energy-Dependent Interaction and Its Application to Alpha-Cluster plus 16O-Core Model of 20Ne

High-spin states inK39fromMg24(O18,p2nγγ⋯)K39

The electromagnetic decays of several high-spin states in $^{39}\mathrm{K}$ were studied via heavy-ion-induced reactions involving $^{18}\mathrm{O}$ and $^{19}\mathrm{F}$ bombardments of targets of $^{24}\mathrm{Mg}$, $^{26}\mathrm{Mg}$, and $^{27}\mathrm{Al}$. The $^{39}\mathrm{K}$ states were formed most strongly in the $^{24}\mathrm{Mg}(^{18}\mathrm{O},p2n\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\cdots})^{39}\mathrm{K}$ reaction which provided the main body of quantitative evidence we report. The identification of specific transitions in $^{39}\mathrm{K}$, and the resultant decay scheme, are based on Ge(Li) $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidence spectra and also on $\ensuremath{\gamma}$-ray yield curves measured for $20\ensuremath{\le}{E}_{B}\ensuremath{\le}61$ MeV. Lifetimes of $^{39}\mathrm{K}$ states were measured by the recoil distance method. These lifetimes together with $\ensuremath{\gamma}$-ray angular distributions restrict the allowable spin-parity assignments and multipole mixing ratios for the transitions studied. Arguments based on the proposed reaction mechanism are invoked to give a most probable decay scheme for the high-spin states involved. The resulting data provide new information on the high-spin structure of $^{39}\mathrm{K}$ and also illustrate the power of these heavy-ion-induced compound-nucleus reactions as spectroscopic tools for the investigation of high-spin states in light nuclei.[NUCLEAR REACTIONS $^{24}\mathrm{Mg}(^{18}\mathrm{O},p2n\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\cdots})$, $E=20\ensuremath{-}61.5$ MeV; $\ensuremath{\sigma}(E,{E}_{\ensuremath{\gamma}})$, $\ensuremath{\gamma}\ensuremath{\gamma}$ coin; deduced $^{39}\mathrm{K}$ levels, tabulated and identified 120 $\ensuremath{\gamma}$ rays from $^{24}\mathrm{Mg}$+$^{18}\mathrm{O}$ at 40 MeV; measured $\ensuremath{\sigma}({E}_{\ensuremath{\gamma}},\ensuremath{\theta})$, ${T}_{\frac{1}{2}}$ for $^{39}\mathrm{K}$ transitions; deduced $\ensuremath{\Lambda}$ for transitions and ${J}^{\ensuremath{\pi}}$, $\ensuremath{\delta}$ for high-spin $^{39}\mathrm{K}$ levels.]

On the rotational states in light nuclei

Some properties of the projected Hartree-Fock functions which describe the ground state bands in 8Be, 12C and 20Ne, and the excited 8p-8h band in 16O are studied in order to answer the question whether these states correspond to real rotational motion in these light nuclei.