A study of the reaction 12C(α, α′)12C exciting the 1+T = 0 level at 12.71 MeV

The differential cross section for the excitation in the inelastic scattering of 36 MeV α-particles of the 1⁺T = 0 level in ¹²C has been measured. Calculated angular distributions suggest that the transition proceeds primarily by two-step reactions rather than by the one-step reaction involving the two-body alpha-nucleon spin-orbit potential.     

The15N(p,α 0)12C reaction at stellar energies

The¹⁵N(ρ, α₀)¹²C reaction has been investigated in the energy range ofE _p (lab)=78-810keV. The measurement of the excitation functions and α-particle angular distributions involved solid targets as well as a quasi-point supersonic jet gas target. The determination of absolute cross sections has been carried out with the gas target. The observed energy dependence of the total cross sections can be described in terms of two-level Breit-Wigner shapes including the resonances atE _p (J ^π)=335(1^?) and 1,028(1^?)keV. The data lead to a zero-energy intercept of the astrophysicalS(E) factor ofS(0)= 65±4MeV-b. The angular distributions are asymmetric around 90° and require an additional amplitude in the reaction mechanism, which interferes predominantly with the 335 keV resonance. The origin of this background amplitude is discussed.     

Tensor polarization of 12C[2+ 1] in the 16O(13C,12C)17O reaction at 50 MeV

The ¹⁶O(¹³C,¹²C)¹⁷O reaction at 50 MeV has been investigated using the kinematical coincidence method. Polarization tensors t ₂₀ and t ₄₀ of ¹²C[2⁺ ₁] for the quantization axis taken along the direction of propagation have been measured by analyzing the energy spectrum of ¹²C[2⁺ ₁], modulated by the effect of γ ray emission. The deduced t ₄₀ values significantly deviate from zero, contrary to the prediction of the distorted-wave Born approximation theory based on one-step p shell neutron stripping without spin-dependent interactions. The phenomenological spin–orbit interaction necessary to reproduce the magnitude of measured t ₄₀ is found to be much larger than the folding model prediction. It is shown that the experimental polarization tensors as well as the cross sections can be reproduced by introducing multi-step processes involving excitations in ¹²C and ¹³C without introducing spin-dependent interactions. Received: 2 August 1999 / Revised version: 3 February 2000     

Fusion-fission in the35Cl +12C reaction at Elab=180 MeV

The properties of the two-body channels populated in the³⁵Cl +¹²C reaction, at a bombarding energy of 180 KeV, have been studied by means of a kinematical coincidence technique. Binary reaction products show full energy equilibration and isotropic angular distributions in the center-of-mass frame. The asymmetrical elemental distribution of the fully-damped yields, similar to that observed previously in the³²S +²⁴Mg reaction, suggests the occurence of fusion-fission rather than orbiting.     

Analyzing powers in the 12C( \vec d ,p)13C reaction at the energy T d = 270 MeV

The preliminary results on the tensor T₂₀ analyzing power for the ¹²C(,p)¹³C* reaction with the excitation of ¹³C levels and the d(,p)X reaction at the energies T _d = 140, 200 and 270 MeV at the emission angle Θ _cm = 0° are presented. The data on the tensor A _yy and vector A _y analyzing powers for the ¹²C(,p)¹³C* reaction at the energy T _d = 270 MeV in the angular range from 4° to 18° in the laboratory are also obtained.     

Polarisation effects in the 12C(3He,pp) reaction at 33MeV

Differential cross sections and analysing powers were measured for the ¹²C(³He, pp)¹³C reaction induced by a 33 MeV polarised ³He beam at many combinations of detection angles of the coincident protons in both coplanar and out-of-plane configurations. Data characterised by low relative proton energies were successfully described by the sequential breakup model while at higher relative energies other reaction mechanisms become important.     

Analysis of 14C(π+, π-) 14O Reaction at 50 MeV

The ground states of ¹⁴C and ¹⁴O are described by a cluster wavefunction and the ¹⁴C_gs(π⁺, π^-) ¹⁴O_gs DIAS transition at 50 MeV is calculated in the Glauber theory. The results are in agreement with experimental data qualitatively and indicate that the effect of the l2 C core on the reaction is important.     

The24Mg(p,t) reaction at 50 MeV

Angular distributions are given for tritons from the ground and first two excited states of the²⁴Mg(p, t)²²Mg reaction. Excitation energies, spins and parities of these levels are given, and a new level also reported.     

Sequential processes in the14N(τ,pα)12C* reaction

α-particle and proton spectra in coincidence with the 4.44 MeVγ-ray from the¹²C first excited state have been taken atE _τ MeV. Several states in¹³N and¹⁶O are seen to contribute to the decay sequenceα?p andp?α respectively. Estimates are given for the branching of these two decay modes and for a possible simultaneous break-up.     

Isospin mixing observed in the reaction 12C(6Li, α)14N

The reaction ¹²C(¹²Li, α)¹⁴N was studied to investigate the isospin mixing of high-lying levels in ¹⁸F. Excitation functions and angular distributions of the α-transitions to the ground, first and second excited states in ¹⁴N were measured for bombarding energies from 3.2 to 8.0 MeV. The isospin-forbidden cross section for the excitation of the lowest T = 1 state in ¹⁴N at 2.31 MeV was found to lie between 1–2 % of that of the allowed transitions. A partial wave analysis of the α₁ angular distribution data revealed a strong resonance with J^π = 2⁺ at E_x = 15.99 MeV. Arguments are presented which tentatively identify this resonance as being due to two close-lying 2⁺ levels with different isospin.     

Two-proton transfer reaction48Ca(18O,16C)50Ti at 102 MeV

Differential cross sections for¹⁸O elastic scattering and the (¹⁸O,¹⁶C) and (¹⁸O,¹⁷N) reactions on⁴⁸Ca were measured at 102 MeV using a Q3D magnetic spectrograph. The transitions to the 7/2^? ground state (g.s.) of⁴⁹Sc and the 0⁺ (g.s.), 2⁺ (1.554 MeV), 4⁺ (2.675 MeV), and 6⁺ (3.198 MeV) states of⁵⁰Ti were analyzed by DWBA calculations which include finite-range and recoil effects. Simple cluster-transfer calculations were done for all two-proton transfer transitions. For the 0⁺ (g.s.) transition a two-nucleon transfer code employing microscopic wave functions was also used. It was found that absolute cross sections for this kinematically well-matched transition were underrated by a factor of about 7 for a reasonable amount of configuration mixing in the nuclear states involved in this transition. This factor is very close to the value 5 derived for the similarly well-matched⁴⁸Ca(¹⁸O,¹⁶O)⁵⁰Ca reaction.     

Five-nucleon transfer in the12C(d,7Li)7be reaction atE lab=78.0 MeV

Angular distributions of the¹²C(d,⁷Li)⁷Be reaction to the ground and to the unresolved first excited states of⁷Li or⁷Be nuclei were measured in the entire angular region in the centre of mass system atE _lab=78.0 MeV. Both the one-step five-nucleon cluster transfer as well as two-step sequential transfers were considered in the theoretical analysis. The former mechanism was found to dominate, but the latter is also not negligible.     

Three-body final state breakup in the27Al(14N,X) reaction at 116 MeV bombarding energy

The energy spectra and angular distributions of products in the reaction²⁷Al(¹⁴N,X) have been measured at 116 MeV bombarding energy. It is shown that the energy spectra of the products lighter than the projectile, are well described by a three-body breakup calculation. The experimental total breakup cross-section estimated in the present work, together with Glas-Mosel calculation of the fusion cross-section, are in a reasonable agreement with the optical model total reaction cross-section.