Trinucleon cluster states in 18F and 18O
Abstract
We propose that a number of low-lying negative-parity states in 18F and 18O can be understood as (A = 15) + (A = 3) cluster states. We introduce a cluster-core interaction consisting of a local central part which gives rise to the usual L(L + 1) rotational spacing, and three spin-dependent terms: spin-spin, tensor-spin and spin-orbit. These interactions will stagger the levels obtained by coupling the total intrinsic spin S = 0 or 1 to the orbital angular momentum L and we show that the strengths of these interactions can be chosen to yield good fits to the low-lying energy spectra. We note that a relation exists between the 18F and 18O spectra, and we point out that this can be understood if an isospin-exchange factor is introduced in the spin-spin interaction. In fact, both the 18F and 18O energy spectra can be generated from essentially the same cluster-core interaction, the rotational and spin-orbit components of which are closely related to those of the “parent” nucleus 19F. A number of high-spin states in both nuclei are predicted to lie quite close to where strongly populated states have been observed in heavy-ion three-nucleon transfer reactions. Electromagnetic transition strengths between cluster states are also calculated and are in good agreement with the available experimental data.
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Alpha cluster states in <sup>16</sup>O
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Detailed study of the cluster structure of light nuclei in a three-body model. (I). Ground state of <sup>6</sup>Li
1984, Nuclear Physics, Section AA model for three composite particles is used to study the ground state of the 6Li nucleus making allowance for the Pauli principle. The relevant wave functions are found by solving a set of two-dimensional Hill-Wheeler integral equations on the quadrature Chebyshev grid. A nonorthogonal many-dimensional gaussian basis was taken to be the expansion basis, so that the wave functions obtained could be presented in the form of a superposition of gaussian functions convenient for applications. Six models (potentials) of the interaction in the NN and Nα subsystems including the central, spin-orbit, and tensor forces are studied. The Coulomb interaction is treated exactly (i.e. not in a perturbative manner). The wave functions obtained are used to analyze a broad spectrum of experimental data, including the 6Li ground state. The applied model, which contains not a single free parameter, has been shown to permit a simultaneous description of the following principal parameters of the 6Li ground state: the binding energy, the rms charge radius, the αd spectroscopic factor, the asymptotic constant of the αd channel, the charge form factor Fch(q2), the magnetic elastic form factor FM1(q2) (up to q2 ≲ 2.5 fm−2), the form factors of the quasielastic scattering reactions (x, xα) and (x, xd), and the cross section for the diffractive scattering of protons from the 6Li nucleus with Ep = 600 MeV and Ep = 1 GeV in a large range of scattering angles.
Potential model treatment of <sup>3</sup>He cluster states in <sup>17</sup>O
1983, Physics Letters BA potential cluster model is used to calculate the energies of states in 17O having a 14C + 3He structure. Excellent agreement with recently reported experimental data on two low-lying positive parity bands of states having isospins and is found, and some additional states are predicted.
A study of <sup>3</sup>He capture in light nuclei
1983, Nuclear Physics, Section AExcitation functions at θ = 90° have been measured for , , and , in the range E3He = 3–19 MeV. The first reaction has also been studied at θ = 40°. Excitation functions at 90° have also been measured for and for E3He = 19–26 MeV. Angular distributions have been measured for the first four reactions.
For the most excitation functions, a broad peak is observed, several MeV wide, centred at about Ex≈ 20 MeV. Superimposed on this, in some cases, are narrower peaks, with width ≈ 1 MeV. Energies and widths have been extracted for all resonances.
Cluster-model calculations have been carried out, using methods similar to those which have proved successful for low-lying states in A= 18–19 nuclei. No satisfactory correspondence with the present results was found. The shell model has been used to calculate Γ3He and Γγ for 1ħω excitations in the final nuclei. These generally show good agreement with the trends of the experimental data. The results are consistent with the excitation of the giant dipole resonance in 3He capture, but much more weakly than in proton capture.
Microscopic nucleus-nucleus potentials
1981, Physics ReportsThis report attempts to establish a link between microscopic theories of the nucleus-nucleus interaction, such as the Generator Coordinate Method (GCM), and phenomenological potential models of appealing simplicity. A characteristic feature of the GCM is the reference to a non-orthogonal basis of many-nucleon model wave functions. Successively eliminating the long range and the short range non-orthogonality of the GCM representation leads to a two-step folding relation which connects the collective Hamiltonian of relative motion of the two nuclei with microscopic matrix elements of the model wave functions. This procedure elucidates the relation between nucleus-nucleus potentials and energy surfaces of the Born-Oppenheimer type. The two-step folding relation may be used to derive simple (local) nucleus-nucleus potentials from microscopically calculated many-body matrix elements. Microscopically founded nucleus-nucleus potentials derived in this way are discussed for the αα, 16O16O, α40Ca and 3Hα systems. In most cases, the results of a full microscopic descriptio n of elastic nucleus-nucleus scattering are well approximated by the simple potential, provided the orthogonality of the wave function of relative motion to the “redundant states” in the interior of the interaction region is ensured.
Effects of core distortion on α-cluster states in <sup>18</sup>F
1980, Physics Letters BThe α-cluster spectrum of 18F is qualitatively improved by including mixing with excited states of the 14N core. Additional positive parity levels which should be observable in α-transfer experiments are predicted.