Tensor features and dynamical deformation of the 24Mg(2+) nucleus in the reaction 24Mg(d,dγ)24Mg at E d = 15.3 MeV

The results obtained by reconstructing of the experimental angular dependences of polarization tensors, the tensors of orientation of multipole moments, and the dynamical deformation of ²⁴Mg nuclei produced in the 2⁺ state at 1.369 MeV in inelastic deuteron scattering on ²⁴Mg nuclei at E _d = 15.3 MeV for deuteron scattering angles between 25° and 165° in the laboratory frame are presented. The experimental results are compared with the results of calculations based on various versions of the coupled-channel method. The role of spin-orbit and tensor d ²⁴Mg interactions is discussed along with the influence of the reorientation effect. The correlation features of the 2⁺ state of the ²⁴Mg nucleus at 1.369 MeV that were determined in inelastic deuteron and alpha-particle scattering on ²⁴Mg are compared.     

Calculation of the static and dynamic triaxial shapes of 24Mg

The Skyrme interaction is used in a Hartree-Fock calculation of ²⁴Mg with triaxial symmetry. A transition between axial and triaxial shapes is studied as a function of the spin-orbit strength. The effect of the other components of the interaction on the shape of ²⁴Mg is examined. Constrained Hartree-Fock calculations of the energy surface and the cranking mass parameter are used for the calculation of the intrinsic γ-vibration. The main result of the dynamical calculation is that despite the different equilibrium shapes obtained with the two forces SIII and SV, the triaxiality obtained by considering the zero-point γ-oscillation is essentially the same for both forces.     

αγ angular correlations in the inelastic scattering of α particles on 24Mg at Eα = 30.3 MeV

The results from measuring the angular dependence of differential α-scattering cross sections on ²⁴Mg with final nucleus formation in the ground and three lower excited states are presented, along with the double differential ²⁴Mg(α, αγ)²⁴Mg(2⁺, 1.369 MeV) reaction cross sections at E _α = 30.3 MeV. The spin-tensor components of the density matrix of the ²⁴Mg nucleus in the 2⁺(1.369 MeV) state are reconstructed and its orientation characteristics are determined. The experimental results are compared to theoretical results under the assumption of collective excitation and mechanisms for compound nucleus formation.     

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.     

Evidence for nonequilibrium particle emission before symmetric disintegration of a composite system formed in the 16O+40Ca reaction at 230 MeV

Measurement of fragment-fragment correlations in the reactions of 230 MeV ¹⁶O with ⁴⁰Ca and 280 MeV³²S with ²⁴Mg have been used to isolate processes in which symmetric decay follows nonequilibrium emission of one or two alpha particles. At the higher energy per nucleon. in contrast to previous observations for lower velocity projectiles, nonequilibrium emission followed by symmetric decay has approximately the same probability as the symmetric fission following complete fusion.     

The first excited state in 23Al and its influence on 22Mg(p,γ)23Al

The excitation energy of the first excited state in ²³Al was determined by the ²⁴Mg(⁷Li, ⁸He) reaction. The state is observed to be at 460 ± 60 keV and belongs to the first excited A = 23 isospin quartet. The results are used to compute the coefficients of the isobaric multiplet mass equation. The influence of this state, a resonance in the ²²Mg(p,γ) channel, on the reaction flow in rp-process nucleosynthesis is discussed in detail.     

A comparative study of the electric giant dipole resonance of 24−26Mg

The electric giant dipole resonance of ^24?26Mg has been explored up to 30 MeV excitation energy with bremsstrahlung. ΔE, E spectra of charged photo-particles and spectra of prompt deexcitation γ-rays from excited residual nuclear states were obtained at various bremsstrahlung endpoint energies. The ²⁵Mg(γ, p₀), (γ, d), ^24,25Mg(γ, α) differential cross sections as well as ^24?26Mg(γ, xγ′) integrated cross sections are presented. The results are discussed in terms of one-particle, one-hole excitations and isospin composition of giant resonance states. A comparison with calculations for ²⁴Mg gives poor agreement. Excitations from deeper shells were found in the giant dipole resonance of ²⁴Mg, but do not seem to be concentrated at higher energies. In ²⁵Mg, only weak excitations of this kind were found, and they are completely absent in ²⁶Mg.     

Configurational analysis of rotational states in the SD shell

It is shown that the shell-model states belonging to a given rotational band in ²³Na and ²⁴Mg have very similar subshell occupancies, different bands being characterised by different occupancies. On the one hand this establishes a connection, somewhat different from that provided by the SU (3) scheme, between the spherical shell model and the idea of an intrinsic state, and on the other hand helps discriminate between possible candidates for membership of a band and imposes limits on the lengths of the bands.     

Angular correlations in the inelastic-scattering process 24Mg(d, dγ)24Mg at E d = 15.3 MeV

The double-differential cross sections for the reaction ²⁴Mg(d, dγ _1.369)²⁴Mg at the projectiledeuteron energy of E _d = 15.3 MeV weremeasured for deuteron emission angles in the forward hemisphere. All even spin-tensor components of the density matrix for the 2⁺ state of the ²⁴Mg nucleus at 1.369 MeV were reconstructed, and its orientation properties were determined. These experimental results were compared with the results of calculations based on various versions of the coupled-channel method.     

Evidence for inelastic processes in the 24Mg(13C, 12C)25Mg reaction at elab = 30 MeV

The ²⁴Mg(¹³C, ¹²C)²⁵Mg reaction has been studied at 30 MeV using a magnetic spectrometer. Differential cross sections for transitions to several final states in ²⁵Mg have been measured and analysed using an exact finite range DWBA code. The DWBA predictions have fitted the bell-shaped distributions satisfactorily, yielding spectroscopic factors which are in reasonable agreement with those obtained using (d, p) reactions. The exceptions are the $\text{3}\text{2}$⁺ state at 0.97 MeV which displays a marked departure from the bell-shaped angular distribution obtained for the other $\text{3}\text{2}$⁺ state at 2.80 MeV, and the $\text{7}\text{2}$⁺ state at 1.61 MeV whose angular distribution has an unusual shape, displaying a deep minimum located at the grazing angle. A semiquantitative model has been used to suggest that the angular distribution for the 0.97 MeV state is evidence for the coupling of inelastic processes in this transition. In the case of the 1.61 MeV state it is suggested that the angular distribution shows the influence of indirect Coulomb excitation on the transfer cross sections.     

Electrofission of 24Mg

The electron induced fission of ²⁴Mg leading to the ground states of two carbon nuclei has been studied using 25 to 45 MeV electrons. The observed sin²2θ angular distribution of the carbon nuclei indicates the dominance of E2 virtual photon absorption. The yield of ground state carbon nuclei is observed to decrease with increasing excitation energy in ²⁴Mg above 24 MeV.     

Analysis of elastic and inelastic α + <Superscript>24</Superscript>Mg scattering within the <Emphasis Type="Italic">S</Emphasis> matrix model involving regge poles

A generalization of the phenomenological S-matrix model taking into account isolated Regge poles is proposed for simultaneously describing refractive effects in the cross sections for the elastic and inelastic scattering of light nuclei. The cross sections for elastic α + ²⁴Mg scattering are analyzed at energies of 50, 54, 65.7, 81, and 119 MeV. The analysis of the cross sections for elastic scattering is supplemented with an analysis of the inelastic scattering of alpha particles that is accompanied by the excitation of the first excited state (2⁺) of ²⁴Mg nuclei. It is shown that the proposed model makes it possible to describe satisfactorily all of the aforementioned cases of elastic and inelastic scattering, correctly reproducing the refraction Airy structures and anomalous large-angle scattering that are observed at large scattering angles.     

The structure of 24Mg using the cranked cluster model

The structure of the positive parity states in ²⁴Mg has been investigated using the cranked alpha-cluster model. A comparison of our results with Nilsson-Strutinsky calculations for ²⁴Mg indicates that shell nonuniformities in the single-particle energy spectrum play an important role in determining the stability of alpha-cluster configurations with large deformations. Comparison of our calculations with experimental data suggests that the resonances observed in ¹²C+¹²C reactions near the Coulomb barrier and those seen in ¹²C+¹²C elastic and inelastic scattering at higher energies are associated with different shape isomers in ²⁴Mg.     

Transient field measurements of g-factors for 24Mg AND 26Mg

The g-factors of the first-excited J^π = 2⁺ states of ²⁴Mg and ²⁶Mg have been measured with the ion-implantation perturbed angular correlation technique (IMPAC). The precession of the spins of nuclei recoiling into a magnetized iron backing is predominantly caused by the transient magnetic field for these very light and short-lived (τ_m ≈ 1 ps) nuclei. The transient field, which attains a value of 200 T for the Mg isotopes, is present only during the slowing-down of the recoiling nucleus and results in average precession angles of about 1.5 mrad. The experimental results are treated in the framework of the transient field theory of Lindhard and Winther. This yields g-factors of g = +0.42b ± 0.09 and g = +1.3 ± 0.3 for ²⁴Mg and ²⁶Mg, respectively. The results are compared with theoretical predictions and for ²⁴Mg also with a recent time-differential deorientation experiment.     

The 24Mg(α, α')24Mg reaction; statistical analysis

The ²⁴Mg(α, α')²⁴Mg reaction to the 1.37 MeV state has been studied over an α-energy range of 9.625–13.825 MeV, in ≈40 keV steps, and over a 25°–160° angular interval. These cross sections have been analysed in terms of statistical theory and a number of deviations from its predictions are found. These deviations point to the importance of non-statistical processes, such as intermediate structure, to the α-scattering. The average compound nuclear width o₁ 62±7 keV is found for ²⁸Si over the 18–22 MeV excitation.     

(6Li,d) reactions on 24Mg and 26Mg at 73 MeV

The ^{24, 26}Mg(⁶Li, d)^{28, 30}Si reactions have been studied at 73 MeV bombarding energy. The angular distributions were analyzed with exact finite-range distorted wave Born approximation calculations assuming a direct α-cluster transfer. Extracted spectroscopic strengths leading to low-lying levels of ²⁸Si and relative spectroscopic strengths between transitions to ²⁸Si and ³⁰Si ground states are consistent with those previously obtained by several α-transfer reactions. Many strongly populated levels have been observed at E_x ? 10 MeV for ²⁸Si. A marked similarity was found between the deuteron spectrum and the ²⁴Mg(α, α)²⁴Mg excitation function in this excitation energy region. A brief comparison of the present α-transfer results with previous two-nucleon transfer data leading to ^28,30Si is also presented.     

Unelastische Elektronenstreuung im Bereich der Riesenresonanz von24Mg,26Mg und40Ca mit Primärenergien kleiner als 60 MeV

Inelastic electron scattering at low primary energies and scattering angles smaller than 180° represents a successful method for the investigation of giant resonances, even though the elastic radiation tail is not known exactly. Energy resolution and statistical accuracy are superior to other methods. It is shown, that the giant resonances in²⁴Mg,²⁶Mg and⁴⁰Ca are excited mainly via E1-absorption. Integrated cross-sections agree with results of photon-experiments. A splitting of the²⁶Mg-giant resonance into two broad bumps is interpreted as isospin-splitting.