RGM Calculations Research Articles

12C+12C fusion in a multichannel folding model

The 12C+12C fusion reaction is investigated using a folding potential in a multichannel approach involving the 12C(0+1, 2+, 0+2, 3-) states. The 12C densities (including transition densities) are taken from the RGM calculation of Kamimura. For the nucleon-nucleon interaction, we use the DDM3Y density-dependent interaction. Owing to the explicit presence of inelastic channels, the imaginary part of the optical potential only contains a short-range fusion contribution. The S-factor is then virtually insensitive to the precise value, and the model is free of any fitting parameter. From the coupled-channel system, we determine the elastic and fusion cross sections simultaneously. As elastic data are available around the Coulomb barrier, this simultaneous treatment offers a good test for the reliability of the model. In the fusion cross section, the role of the inelastic channels and, in particular of the 12C(0+1)+12C(0+2) channel involving the Hoyle state, is discussed.

12C+12C and 16O+16O fusion reactions at low energies

The 12C+12C and 16O+16O fusion reactions are investigated in a folding model. We use a multichannel approach involving the 12C(0+1, 2+, 0+2, 3-) states. The 12C densities (including transition densities) are taken from the RGM calculation of Kamimura. For the nucleon-nucleon interaction, we use the DDM3Y density-dependent interaction. Owing to the explicit presence of inelastic channels, the imaginary part of the optical potential only contains a short-range fusion contribution. The S-factor is then virtually insensitive to the precise value, and the model is free of any fitting parameter. From the coupled-channel system, we determine the elastic and fusion cross sections simultaneously. For the 16O+16O fusion cross section, we show preliminary results obtained in a single-channel approximation, where the 16O densities is obtained from an α+12C cluster calculation.

High-Lying 6Li Levels at Excitation Energy of around 21 MeV

The $^3$H+$^3$He cluster structure in $^6$Li was investigated by the $^3$H($\alpha$,$^3$H $^3$He)n kinematically complete experiment at the incident energy $E_\alpha$ = 67.2 MeV. We have observed two resonances at $E_x^*$ = 21.30 and 21.90 MeV which are consistent with the $^3$He($^3$H, $\gamma$)$^6$Li analysis in the Ajzenberg-Selove compilation. Our data are compared with the previous experimental data and the RGM and CSRGM calculations.

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

Angular distributions for the 6He(p, γ0 + 1)7Li process at the energy Eγ = 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 Eγ = 22–30 MeV are calculated.

Coupled-Channel RGM Calculations with a New Cluster Wave Function for a Five-Nucleon System

A new type of cluster internal wave function has been proposed. This wave function can produce improved result, especially for the cluster binding energy. As a second application, we have considered the d+He and p+He elastic scatterings and the He(d, p)He reaction based on the coupled-channel RGM with this type of wave function. The agreement between the calculated results and the experimental data is quite satisfactory.

The p+ 6He interaction from Ec.m.=0.5 to 25 MeV

The p– 6He potential has been determined by inverting the S-matrix, calculated from single-channel RGM without absorption, over the energy range E c.m.=0.5,1.0,…,25 MeV. Energy-dependent IP inversion was used, but with energy-independent spin–orbit terms. A potential with odd- and even-parity components reproduces S lj ( E) from l=0 to l=4 over the whole energy range. The central components of the potential have a smooth, predominantly linear, energy dependence that is consistent with global phenomenology. We compare the similar neutron– 6Li (IAS) interaction. Various features in the potentials deserve explanation. The procedure employed here could extract dynamic polarization potentials for the p– 6He interaction from S lj ( E) from multichannel RGM calculations, should these become available.

A study of six quark cluster states in chiral SU(3) quark model

The energies of the (0 S) 6 six quark cluster states are calculated in the chiral SU(3) quark model. The results show that some states with high strangeness have more attraction from the chiral SU(3) coupling, and this feature is interesting in discussing if there exists some new narrow width six quark states. Further, we did a RGM calculation to study some multi-strangeness dibaryon states. We found that ΩΩ dibaryon is a deeply bound state and ΞΩ dibaryon is slightly bound.

Antisymmetry and channel coupling contributions to the absorption for [formula omitted

To understand recently established empirical p+ α potentials, RGM calculations followed by inversion are made to study contributions of the d+ 3He reaction channels and deuteron distortion effects to the p+ α potential. An equivalent study of the d+ 3He potential is also presented. The contributions of exchange non-locality to the absorption are simulated by including an phenomenological imaginary potential in the RGM. These effects alone strongly influence the shape of the imaginary potentials for both p+ α and d+ 3He. The potentials local-equivalent to the fully antisymmetrised-coupled channels calculations have a significant parity-dependence in both real and imaginary components, which for p+ α is qualitatively similar to that found empirically. The effects on the potentials of the further inclusion of deuteron distortion are also presented. The inclusion of a spin-orbit term in the RGM, adds additional terms to the phase-equivalent potential, most notably the comparatively large imaginary spin-orbit term found empirically.

Extended RGM calculations of meson - meson scattering

Meson - meson scattering is investigated in the framework of the non-relativistic resonating group method using an interquark potential composed of a central and a spin - spin part. The individual meson wavefunctions are expanded in extended harmonic oscillator bases or represented by a superposition of Gaussian-shaped functions. The interaction kernels are calculated using usual shell model techniques. These kernels and the corresponding phase shifts are presented for various channels. Their sensitivity to the accuracy of the meson wavefunctions is discussed.

Exchange contributions to nucleus-nucleus potentials deduced from RGM phase shifts using inversion

Abstract We have determined, for certain representative cases, the representation in terms of local potentials of the contribution to the nucleus-nucleus interaction of one-nucleon exchange, core exchange and intermediate exchange terms. We do this by applying S l -to- V ( r ) inversion, using the IP method, to phase shifts from RGM calculations of Fujiwara and Tang, and LeMere et al. For tα at 18 MeV we find a shape parity dependence which is identical in nature to that found in other cases recently. For 3 He+ α at 60 MeV, a strong parity shape dependence still occurs, but of slightly different form. For α + 16 O, the 4N exchange generates a small parity dependence of the same nature, but this seems to disappear in the full RGM calculation. In the last two cases, we show the characteristic forms of potentials due to the different exchange terms. These calculations indicate the scope of inversion as a means of extracting information from microscopic calculations concerning the nucleus-nucleus interaction.

Energy dependence of a local equivalent potential for RGM phase shifts for 16O + 16O

We have found, using the IP inversion method, the local representation of a potential that is S( l) equivalent to the RGM nonlocal potential of Wada and Horiuchi. Phase shifts corresponding to RGM calculations at laboratory energies 30, 41, 49, 59, 150, 350 and 500 MeV were inverted and the resulting local potentials compared with the local (but l-dependent) potentials obtained previously in the WKB-RGM scheme. The present l-independent potentials exhibit a smooth radial variation and show marked differences from previous results. The energy dependence arises from that of the exchange term and from the conversion of the l-dependence into an additional energy dependence. In particular, we show that the energy dependence of the volume integrals in this energy region is different from earlier WKB-RGM predictions.

Self-consistent calculation of the interactions of lightest nuclei with 6Li

The multicluster dynamic model of light nuclei, studied and verified earlier as applied to 6Li nucleus is used together with the folding model to find the interaction potentials in the X+6Li systems (X=n, p, 3He, 3He, 4He). The calculations of the real parts of the potentials are self-consistent and, in contrast to the previous RGM calculations of the same systems, do not include any free parameters. A good agreement between theoretical predictions and the respective experimental data on elastic scattering of the A<4 lightest nuclei from 6Li has been demonstrated. The potentials found are parametrized in the standard Woods-Saxon form.

K−N exoticS channelI=1,0 phase shifts: a test of the non annihilating quark quark potential

In this paper we present a method which avoids—in RGM calculations—ex0licit evaluations of overlap kernels in configuration space. Phase shifts are directly calculated by the use ofT-matrix formalism, without resorting to numerical evaluations of non-local Schrodinger equations. Different two body potentials can be directly compared within the very same RGM calculation. As an example, we evaluateS waveI=1,0K−N phase shifts for three different sorts of quark-quark potentials: The ones used by Bhaduri et al. [3], Bender et al. [4], and finally by Campbell and Robson [8]. These phase shifts are shown to depend sharply on the details of the adopted interquark force, therefore distinguishing among potentials which otherwise fare equally well for spectroscopic calculations. None of the above mentioned potentials suffice to explain the experimentally observedS waveK−N phase shifts.

Alpha-cluster states in16O based on a12C(O2+) core

A 12C- alpha model for rotational bands in 16O based on the 12C core in its ground and first excited states has been extended to include the 12C(O2+) level at 7.65 MeV. A double folding prescription has been used to determine the potential matrix with transition densities taken from a 3 alpha RGM calculation of 12C. The coupled-channels problem including the 01+, 21+ and 02+ levels of 12C has been solved and positive- and negative-parity bands based on the 12C(02+) state have been identified with known 16O excited states. The calculation also confirms earlier assignments of 16O levels based on 12C(01+ and 21+).

Comparison of various approximations for resonating group method basis states

Various approximations have been used in RGM calculations for the basis states: (i) oscillator model, (ii) equal oscillator frequencies and (iii) admission of spurious centre-of-mass motion. For example α- 208Pb the validity of these approximations is tested.

The oscillator frequency in resonating-group-method calculations

For the example α- 16O we present simple RGM calculations with equal ( ω = ω′) and different ( ω ≠ ω′) oscillator frequencies for the two nuclei. In the case ω ≠ ω′ and ω → ω′ the one-channel RGM space for angular momentum zero contains all 20Ne states with four particles in the s-d shell and total spatial symmetry ( [⨍] = [4]). These states form a basis for low-lying excited 0 + states of 20Ne. The ω ≠ ω′ calculation (as well for ω → ω′ as for realistic ω, ω') exhibits, therefore, resonances corresponding to these states. We present also the calculation for ω = ω′ where these physically important resonances are missing.

A parity dependent orthogonality condition model derived from parity projected energy surfaces

Using a relation connecting the effective nucleus-nucleus potentials of the orthogonality condition model with matrix elements of a two-centre harmonic oscillator shell-model, parity dependent but otherwise local nucleus-nucleus potentials are derived from parity projected energy surfaces of the two-centre shell model. The potentials are derived without explicit reference to the nucleus-nucleus potentials of the resonating group method and without adjusting parameters to the results of RGM calculations. Potentials obtained for the n-α and 3H-α systems show the odd-even dependence expected from microscopic and phenomenological investigations. With the corresponding parity dependent potential the OCM is able to reproduce the results of a full RGM calculation very well in the case of elastic 3H-α scattering.

Application of the resonating group method to the scattering of light and medium heavy nuclei

A method is proposed for applying the resonating group method to the scattering of medium heavy nuclei. The RGM potentials are determined by directly unfolding the associated integral kernels of the generator coordinate method. A one channel RGM calculation is performed for the elastic scattering of two 16O nuclei. The results show a series of resonances constituting an almost perfect rotational band, which seems to be responsible for the gross structure found experimentally in the excitation functions.