Scattering and reactions of 14C + 14C and 14C + 14C

We have studied elastic scattering, inelastic scattering and several transfer channels of the systems ¹⁴C + ¹⁴C and ¹⁴C + ¹²C over a wide range of energies up to E_c.m. = 35 eMeV and 32 MeV, respectively. The reaction channels were identified by means of kinematic coincidences between solid-state detectors, γγ coincidences were measured to determine cross sections for mutual inelastic scattering of ¹⁴C + ¹⁴C.Pronounced regular gross structures, similar to those found for ¹⁶O + ¹⁶O, are observed in the elastic excitation function of ¹⁴C + ¹⁴C at θ_c.m. = 90°, The angular distributions measured at the energies of the maxima and an optical-model analysis suggest that one or a few surface partial waves dominate the scattering behaviour. Correlated structure of narrower width is found in the inelastic channels and, to a lesser degree, in the transfer channels which appear with rather small cross sections.In ¹⁴C + ¹²C elastic scattering the gross structures are strongly fragmented, in contrast to ¹⁴C + ¹⁴C but similar to ¹²C + ¹²C. While the ¹²C(2⁺) excitation is very weak, the observed strengths of the ¹⁴C(3^?) excitation and of neutron transfer point to a substantial role of these channels as coupling partners to the elastic configuration and to their influence on the elastic scattering behaviour. A correlated intermediate structure is observed near 23.5 MeV, where a dominance of l = 18 is suggested by the elastic scattering angular distribution. This unexpectedly high l-value exceeds l_graz at this energy by at least two units of ?.     

On the decay of the photo resonance in 14N and 14C nuclei

The decay of the photo resonances in ¹⁴N and ¹⁴C nuclei is analyzed in terms of the shell model with intermediate coupling. Cross sections and branching ratios of nucleon channels are compared with experimental data. Successive decay branches are estimated.     

A study of 14N using the 13C(d,n)14N reaction

Absolute differential cross sections for the ¹³C(d, n)¹⁴N reaction were measured at deuteron bombarding energies of 4.5, 5.0 and 5.5 MeV. Spectroscopic factors and statistical compound-nucleus contributions are obtained by treating the observed cross sections as an incoherent sum of distorted-wave Born approximation and compound-nucleus contributions. Energy-averaged spectroscopic factors are derived. An anomaly is observed in the yield for the 2.313 MeV T= 1 state.     

A study of the 14C(6Li, 6He)14N reaction at 93 MeV

The reaction ¹⁴C(⁶Li, ⁶He)¹⁴N was investigated with 93 MeV ⁶Li ions in an angular interval of 7–26°. Angular distributions were analysed for the four most intense groups of ⁶He nuclei, corresponding to transitions to the ground (1₁⁺) and the excited (1₂⁺, 2₁^?, 4₁^?) states of ¹⁴N. In the theoretical analysis a mechanism of the spin-isospin excitation was suggested in the DWBA frame with the finite range of interaction and recoil in the light system (⁶Li⁶He) taken into account. In the calculations both shell-model wave functions and transition densities obtained in the theory of finite Fermi systems (FFS) were used. From the comparison between theory and experiment the Landau-Migdal force constant g′ is estimated in order to obtain some information on the degree of nuclear proximity to the threshold of pion condensation.     

194Pt(12C, 12C′) reaction and the triaxial-rotor model

Elastic and inelastic scattering differential cross sections for the ¹⁹⁴Pt(¹²C, ¹²C′) reaction at a bombarding energy of 78 MeV have been measured. Data have been obtained for 0⁺, 2⁺, 4⁺, and 2^+′, states in ¹⁹⁴Pt. The data have been analyzed using a rigid asymmetric-rotor model in coupled-channels reaction calculations. It is found that satisfactory fits to all data can be obtained but only if the hexadecapole deformation is included in the asymmetric-rotor model.     

The reaction 14C(3He,n)16O and the coexistence model of 16O

The reaction ¹⁴C(³He, n)¹⁶O has been measured at a ³He bombarding energy of 25.4 MeV. The zero-degree differential cross section for the excitation of the three low lying 0⁺T = 0 states, at energies 0.0, 6.05 and 12.05 MeV are, respectively, 1.33 ± 0.10, 0.49 ± 0.10, and 0.50 ± 0.10 mb/sr These measured cross sections are in rough agreement with single-step zero-range DWBA calculations using an empirically determined ¹⁴C ground state wave function and in which the Brown and Green coexistence-model wave functions are used to describe the ¹⁶O 0⁺ states. The angular distribution of the transition to the ground state is measured between 0° and 32°.     

Formation of covalent nuclear molecules in the 13C + 12C system

Angular distribution's of the elastic scattering of ¹³C on ¹²C and the inelastic scattering leading to the lowest-lying $\text{1}\text{2}{}^{\mathrm{+}}$ and $\text{5}\text{2}{}^{\mathrm{+}}$ states in ¹³C have been measured at energies close to the Coulomb barrier. Analyses carried out in the framework of a complete coupled-reaction-channel theory show that extremely polarized single-particle molecular orbits (hybridization) are formed during the scattering process which give rise to a multiple-step interaction of the valence nucleon, i.e. the formation of a covalent nuclear molecule.     

Alpha-heavy-ion angular correlations from 28Si + 12C

Alpha particles have been measured in coincidence with heavy recoil nuclei from the ²⁸Si + ¹²C reaction. At E_lab = 87 MeV angular correlations for alphas between 15° and 55° and heavy ions at angles ?9°, ?12° and ?15° have been taken. An excitation function of coincidence events with θ_α = 30° and θ_HI = ?12° has been measured for 84 MeV < E_lab < 91.5 MeV. The results are well described by a statistical-model calculation for compound nucleus decay. No evidence is found for additional processes.     

A microscopic description of nuclear molecules: Application to the 12C + 12C system

The interaction energy between two oblate ¹²C ions is calculated by means of the constrained Hartree-Fock method. The influence of the mutual orientation of the ions is investigated by considering two extreme configurations: an axial symmetric one where the two ions approach each with their symmetry axes aligned with the collision axis and a triaxial one where the axes of the fragments are perpendicular to the collision line. The corresponding potentials V₁ and V₂ display very distinct features. In particular the minima of the potentials occur for quite different interdistances. A method is devised for constructing from V₁ and V₂ the potentials and coupling factors between two ions rotating with definite angular momentum. Using these quantities in a coupled channel calculation, we explain the gross features of the elastic, single 2⁺ inelastic and double inelastic cross sections. The same calculation yields good agreement with the fusion data.     

Coupled-channel fusion and inelastic scattering calculations for 18O + 44Ca and 12C + 48Ti

Fusion and inelastic scattering coupled-channel calculations are carried out for the systems ¹⁸O + ⁴⁴Ca and ¹²C + ⁴⁸Ti. Comparison between ¹²C + ⁴⁸Ti and ³²S + ²⁴Mg sub-barrier fusion cross-section enhancement is made using simple analytical expressions. The distribution of the angular momentum absorbed by the compound nucleus is discussed in a quantum-mechanical coupled-channel model.     

Energy dependence of the 24Mg(16O, 12C)28Si reaction

Excitation functions for the reaction ²⁴Mg(¹⁶O, ¹²C)²⁸Si(g.s., 2⁺₁) were measured at 5°(lab) in the energy range 32 < E_c.m. < 49 MeV. Although the resonant structure, previously observed at lower energies, becomes progressively weaker, three new correlated maxima have been observed near E_c.m. = 37.5, 40.2 and 43.5 MeV. Angular distribution measurements at these energies yield spin assignments, from P²_j(cos θ) comparisons, of 27, 29 and 31, respectively. Attempts to find a consistent optical-model fit to the elastic scattering in the entrance channel and an exact finite-range DWBA fit to the four-nucleon transfer reaction in this energy range were unsuccessful. Such a failure is to be expected if strong couplings between the elastic channel and inelastic channels of either the initial or final system are important. The features of the resonance phenomena in the transfer reaction are discussed within a band crossing model framework.     

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.     

The 14C(p, γ0)15N cross section below Ep = 12 MeV

The cross section for the ¹⁴C(p.γ₀)¹⁵N reaction has been measured up to E_p = 12 MeV. These measurements cover the region of the main component of the giant dipole resonance in ¹⁵N previously observed in the inverse ¹⁵N(γ, p₀)¹⁴C reaction. The structures seen are compared to recent measurements of the ¹⁴N(p, γ₀)¹⁵O cross section at corresponding energies in ¹⁵O, allowing clear identification of $\text{T =}\text{1}\text{2}\text{and}\text{3}\text{2}$ states. A comparison of the present experimental results is also made to recent bound and continuum shell model calculations for this region of ¹⁵N.     

High spin collective excitations in 101Ru

The energy level structure of ¹⁰¹Ru was studied using the reactions ¹⁰⁰Mo(α, 3n)¹⁰¹Ru and ¹⁰⁰Mo(³He, 2n)¹⁰¹Ru. Excitation functions, γγ coincidences and γ-ray angular distributions were measured. Three ΔI = 2 cascades proceeding to a $\text{5}\text{2}{}^{\mathrm{+}}$, $\text{7}\text{2}{}^{\mathrm{+}}$ and $\text{11}\text{2}{}^{\mathrm{?}}$ state were observed. A decay scheme is presented showing energies up to 5849 keV and spins up to $\text{35}\text{2}$. The bands are discussed within the framework of the Nilsson model with Coriolis coupling in which the recoil effect has been properly introduced.     

Compound transfer and direct transfer reactions induced by 17O on 13C

The elastic scattering, inelastic scattering, single-neutron transfer reactions ¹³C(¹⁷O, ¹⁶O) ¹⁴C, ¹³C(¹⁷O, ¹⁸O)¹²C and ¹³C(¹⁷O, ¹⁸O_{2+, 1.98})¹²C, and seven other exit channels which involve ⁷Li, ⁹Be, ¹¹B and ¹⁵N have been measured for the system ¹⁷O+¹³C at 12.9 and 14 MeV c.m. It is shown that all reactions mentioned above have significant contributions from compound nuclear decay, following fusion of projectile and target.     

Elastic and inelastic scattering of 16O and 12C by 24Mg near the Coulomb barrier

Angular distributions for ¹⁶O + ²⁴Mg and ¹²C + ²⁴Mg elastic and inelastic (2⁺, 1.37 MeV state in ²⁴Mg) scattering have been measured at energies spanning the Coulomb barrier. Apart from the structure typical of strong destructive Coulomb-nuclear interference, the data exhibit some additional specific features. Coupled channel calculations were performed, along with DWBA calculations to analyse the data using fixed coupling strengths deduced from the results of Coulomb excitation work. The importance of higher-order effects such as reorientation, is demonstrated.     

Sequential calculations for heavy-ion induced two-nucleon transfer on 14N, 15N and 16O

¹¹B and ¹³C induced two-nucleon transfer data on ¹⁴N, ¹⁵N and ¹⁶O are compared with exact finite-range sequential transfer calculations. The data appear to be consistent with this reaction model and the assumed shell-model structure of the states populated. Single-nucleon transfer data on these targets is also analyzed using the DWBA. Modifications to the exit channel optical potential are required to obtain agreement with shell-model spectroscopic factors.     

12C(d, α2)10B and isospin violating two-step reactions

A model-independent S-matrix analysis for the isospin violating ¹²C(d, α₂)¹⁰B(E_x = 1.74 MeV) reaction was performed and the results compared to a recently published two-step coupled channels calculation. There are multiple solutions to the S-matrix fits. but it is found that none of the possible solutions are compatible with the partial-wave decomposition based upon the two-step mechanism. The data are satisfactorily fitted with a sum of Breit-Wigner resonances. When a non-resonant background is included in the calculation the result indicates that the magnitude of such a contribution is less than 2 % of the measured total cross section at E_d = 15 MeV and is consistent with zero. The reaction is therefore interpreted to proceed almost entirely through the compound nucleus.     

Measurement of the total neutron cross section of 14N and 24Mg

The total neutron cross section of ¹⁴N and ²⁴Mg has been determined for neutron energies between 1.0 and 5.2 MeV. For this purpose, the attenuation of a continuous neutron spectrum in absorbing samples of liquid natural nitrogen and enriched ²⁴Mg has been measured in open geometry with the time-of-flight technique. A time resolution of 0.07 ns/m was achieved. The obtained data improve the knowledge on the cross section of ¹⁴N above 2 MeV and of ²⁴Mg in the total energy range. In the latter, a large number of resonances is observed for the first time.