States In 24Mg Research Articles

An Analysis of the 12C(16O, a)24Mg Reaction

The angular distribution of a particles from the reaction 12C(160, a)24Mg was calculated, with the help of an a particle model, for the ground state of 24Mg at bombarding energies with 160 of 15�25,16�48,17�10,17�85,19�30,20�70 and 21�80 MeV. Calculated results were compared with experimental data and satisfactory agreement was obtained.

Symmetric fission of 24Mg following inelastic scattering

Symmetric fission into two 12C nuclei has been observed from states at high excitation energy in 24Mg excited in inelastic scattering. Fission to the 10B+ 4N channel has also been observed and indirect evidence for the 16O+ 8Be channel noted. The same experiment also reveals fission into 16O+ 12C from states in 28Si populated by alpha-particle pickup onto the 24Mg projectile. The correlation of the states in 24Mg observed in this experiment with those previously observed in 12C+ 12C scattering is discussed.

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.

On the Charge-Dependent Matrix Element Between the 9.516 MeV 4+ T = 1 Level and the 8.439 MeV 4+ T = 0 Level of 24Mg

A recent measurement of the ß - y circular polarization asymmetry parameter A on the isospinforbidden ß + decay of the ground state of 24Al to the 8.438 MeV 4+ T= 0 state of 24Mg yields a charge-dependent matrix element ⟨ VCD⟩Mg between the 9.516 MeV 4+ T = 1 state and the 8.439 MeV 4+ T = 0 state of 24Mg of (106 ± 40) keV, which is the largest measured value obtained so far in ß decay. Our calculation using Nilsson’s wavefunctions and a spherical Coulomb potential results in a value of 87 keV for ⟨ VCD⟩Mg . Variation of the value of ⟨ VCD⟩Mg against the deformation parameter ß shows that theory agree very well with the measured ⟨ VCD⟩Mg for ß around 0.5.

Cluster Structure in the Highly-Excited States of 24Mg

Abstract We propose a μ-truncation method for the multi-cluster orthogonality condition model (OCM) to reduce the large number of basis states. The cluster structures in the highly-excited states of 24Mg are discussed on the basis of solutions obtained by the 16O+2α OCM.

Compound versus direct processes in the 12C( 14N, d) 24Mg ∗ reaction

Angular correlations of deuterons and α-particles have been measured for the 12 C( 14 N, d) 24 Mg ∗(α) 20 Ne ( g.s.) reaction. No evidence is found for the direct transfer of a 12C nucleus populating the 13.45 MeV (6 +) state of 24Mg. Angular correlations for this state and several others are relatively featureless. This result is in disagreement with a recently published measurement.

Rotational band of 12C + 12C gross-structure resonances and its representation by a double-minimum optical potential

A detailed phase shift analysis of 12C + 12C elastic data from E cm = 5.5 to 33 MeV has revealed a pronounced sequence of gross structure resonances. They appear to form a rotational band from l = 0 to at least 16ħ, and are the dominant structural feature of the 12C + 12C reaction. The resonances are parametrized by a Breit-Wigner analysis and are simulated by shape-resonances in an optical potential with a secondary minimum at large radius. They are discussed in terms of shape-isometric doorway states in 24Mg.

Nuclear shape transitions in the finite-temperature hartree-fock approximation

The temperature dependence of five of the lowest lying deformed states in 24Mg has been investigated in the finite-temperature Hartree-Fock approximation. When we take the electric quadrupole moment as the order parameter the results display first order deformed phase transitions and second order deformed to spherical phase transitions.

Alpha decays in24Mg

It is shown that the configuration-mixed shell model predicts alpha branching ratios from high-spin 24Mg states that are in good agreement with the average experimental results whereas the statistical model gives poor agreement. It is concluded that the configuration-mixed shell model is appropriate for considering 24Mg states above 15 MeV.

The fine structure at 11.52MeV level in 24Mg obtained by γ resonant absorption method

The γ resonant absorption method has been used to determine the parameters of the 11.5MeV level in 24Mg. Two dips were observed beyond our expectations. They are identified as the resonant absorptions caused by the splitting energy levels at 11.52MeV. The energies of the corresponding states are 11519.8±0.4keV and 11520.7±0.4keV with 22.6±3.4eV and 10.0±2.9eV total level widths respectively. The fine structure and the relevant parameters of 11.52MeV state in 24Mg are given for the first time. The potential of the high resolution in the resonant absorption method is clearly demonstrated in present paper.

High-spin states in24Mg

The 12C(16O, alpha )24Mg reaction has been used to study states in 24Mg at excitation energies up to 27 MeV. Total widths have been measured for 34 states. Alpha-branching ratios and alpha - alpha angular correlations have been measured for 12 states above 19.5 MeV. Candidates for 10+ and 12+ states in 24Mg are deduced from a comparison with shell-model predictions.

G-factor of the second 4+ state in24Mg

The transient field technique has been used to determine theg-factor of the 4 2 + state at 6.010MeV excitation in24Mg. The deduced value ofg=+0.5(4) is consistent with collective model expectations. Further, the equality within experimental accuracies, of the g-factors of the 2 1 + , 2 2 + , 4 1 + and 4 2 + states agrees with theoretical predictions for thisT=0 self-conjugate nucleus, in contrast to the results for20Ne.

Electron scattering measurements of inelastic M3 transitions

Inelastic M3 form factors for the excitation of the 5.236 MeV 3 + state in 24Mg and for the excitation of the 10.376 MeV 3 +, T = 1 state in 28Si have been measured. These form factors are compared with full 2s1d shell-model calculations in order to investigate the experimental quenching of M3 transition strength which is expected in the light of previous work. The shell-model predictions do not agree with the experimental data. In the case of the 24Mg 5.236 MeV state the data are enhanced by a factor of ∼2 with respect to the shell-model prediction, whereas in the case of the 28Si 10.376 MeV state the data are suppressed by a factor of ∼5. In the former case it is found that a small admixture of the 3 2 + state shell-model wave function into the 3 1 + state wave function gives good agreement with the data. The effects of this admixture on other observables are investigated. No similar mechanism is found to explain the 28Si M3 transition. In view of the basic disagreement between the shell-model predictions and the experimental data, no conclusions about M3 quenching can be drawn. The validity of previous analyses using this technique is seriously questioned.

Anomalous g-Factor measurements using transient fields

The transient field technique has been used to measure precessions of excited states in24Mg. The results are compared with those of20Ne for which g-factor values were obtained in strong contradiction to current theories. The backbending observed for20Ne is proposed to be responsible for this finding in analogy to observations for the rare earth nucleus158Dy.

DWIA predictions of (p,p') data using electromagnetically constrained densities

DWIA predictions and comparison with experiment are made for 650 and 800 MeV proton scattering to low lying states in 24Mg, 26Mg, 28Si, 30Si, 34S, 40Ca and 42Ca. Electromagnetic constraints on proton and neutron ground-state and transition densities are used to minimize nuclear structure uncertainties. Generally good agreement with the data is seen.

G-factor measurements of excited states in 24Mg

Precessions of the yrast 2 1 + and 4 1 +, and the second 2 2 + states in 24Mg have been measured employing the transient field technique. The deduced g-factors for the 4 1 + and the 2 2 + states of g = +0.4(3) and g = +0.6(2), respectively, agree with theoretical predictions for this T = 0 self-conjugate nucleus. In addition, the lifetime of the 4 1 + state has been measured to be τ = 48(9) fs in agreement with previous experiments. No irregular behaviour of the transient field at short interaction times was found. The results are contrasted with the controversial findings for 20Ne.

The 24Mg( 16O, 16O') reaction and triaxial structures in 24Mg

Angular distributions for the elastic and inelastic scattering of 16O from 24Mg, exciting the 2 1 + (1.37 MeV), 4 1 + (4.12 MeV) and 2 2 + (4.24 MeV) states, have been measured at E c.m. = 43.5 MeV, an energy at which resonance-like structure has been observed previously in the related 24Mg( 16O, 12C) 28Si reaction. In particular, the 4 1 +, 2 2 + doublet has been resolved for the first time for heavy-ion projectiles. The data have been well described by coupled-channels calculations within the framework of a Davydov-Filippov asymmetric rotor model for the low-lying states of 24Mg, which has been extended to include a symmetric hexadecapole shape component. The optical model potential for the 16O + 24Mg interaction was found to have a moderate real well depth and some surface transparency. The shape parameters for the nuclear potential were determined to be β (N) 2 = 0.25, γ = 22° and β 4 (N) = −0.065 and the corresponding deformation lengths are in good agreement with earlier light-ion results. The inclusion of a negative symmetric hexadecapole component leads to an improved description of the reduced transition rates. The triaxial structure of 24Mg is discussed.

Stellar reaction rate of 20Ne(α, γ) 24Mg

The reaction 20Ne(α, γ) 24Mg has been investigated at E α (lab) = 0.55–3.20 MeV. Neon gas enriched to 99.95% in 20Ne was recirculated in differentially pumped gas target systems of the extended and quasipoint jet types. New resonances were found at E α (lab) = 958, 1226, 1260, 1704 and 2277 keV, which correspond to known states in 24Mg. Excitation energies, γ-ray decay schemes, γ-ray angular distributions, resonance widths and strengths as well as J π and T-assignments are reported for all the resonances. Information on low-lying states in 24Mg is also obtained. The nuclear and astrophysical aspects of the results are discussed.

The validity of the compound nucleus mechanism in the 12C( 16O, α) reaction at high energies

Excitation functions for several discrete states in 24Mg excited in the 12C( 16O, α) reaction are studied from E( 16 O) = 40 MeV to 150 MeV . A Hauser-Feshbach analysis is performed for states with J π = 0 + through 10 + and a consistent interpretation of these data is obtained in a compound nucleus model with reasonable critical angular momenta. We show that the energy dependence of the high spin selectivity is in agreement with the absence of selectivity recently reported for the 14N( 14N, α) reaction at high energy. Contrary to recent speculations, no compelling evidence for preequilibrium or direct processes in 16O + 12C reactions is found.

A search for giant resonances by inelastic proton scattering on24Mg

A straightforward method is proposed for the observation of giant resonances based on the phase shift analysis of the inelastic transition between a 0+ ground state and a weakly excited 0+ state. The method is tested by analysing the differential cross section of inelastic proton scattering leading to the 0+ (Eex=6.43 MeV) excited state of24Mg.