Structure of the Hoyle state in 12C

The first excited 0(+) state in 12C (Hoyle state) has been predicted to be a dilute self-bound gas of bosonic alpha particles, similar to a Bose-Einstein condensate. To clarify this conjecture, precise electron scattering data on form factors of the ground state and the transition to the Hoyle state are compared with results of the fermionic molecular dynamics model, a microscopic alpha-cluster model, and an alpha-cluster model with reduced degrees of freedom (in the spirit of a Bose-Einstein condensed state). The data indicate clearly a dilute density with a large spatial extension of the Hoyle state. A closer inspection of the model calculations, which reproduce the experimental findings, reveals that the term Bose-Einstein condensation of three alpha particles must not be taken too literally.     

Them-state population of12C2+ in inelastic scattering

The spin alignment of the¹²C₂ ⁺ state in inelastic scattering of¹²c on⁶⁴zn at E_L=65 MeV has been measured using the γ-recoil-in-flight method. Good agreement with coupled channel calculations are obtained. The sensitivity of the spin alignment to reaction models is discussed.     

Spin precession of the12C(2 1 + ) state on recoil in polarized iron

A PAC measurement on the 4.43 MeV¹²C(2⁺) state on recoil in magnetized iron has yielded an integral precession angle of ?=+0.85(14) mrad, which exceeds the Lindhard-Winther prediction by about two orders of magnitude. Evidently, large magnetic fields act at nuclei traversing solids at high velocities (v _rec/c = 0.03 in the present case), thereby holding out the prospect ofg-factor measurements for nuclear states in this lifetime range (τ ₂ ⁺ = 6.5 × 10^?14 s).     

Angular distribution measurement for ~(12)C fragmentation via ~(12)C + ~(12)C scattering at 100 MeV/u

The angular distributions and energy spectra of~(11)B,~(10)B,and~9Be fragments of~(12)C in the angular range from 1.0°~to 7.5°~at 100 Me V/u were obtained via~(12)C+~(12)C scattering.Detailed comparisons are presented between the experimental data and the modified antisymmetrized molecular dynamics(AMD-FM),binary intranuclear cascade model(BIC)and Liege intranuclear cascade model(INCL++).The experimental angular distributions and energy spectra are well reproduced by the AMD-FM calculations but fail to be reproduced by the physical models installed in the Geant4 program,including the BIC and INCL++models.     

Elasticp+12C scattering between 0.3 and 2 MeV

Absolute differential cross-sections ofp+¹²C elastic scattering have been measured atθ _cm=89.1°, 118.7°, 146.9° for bombarding energies between 0.3 and 2.0 MeV. Revised level parameters of the first three excited states in¹³N have been extracted with aR-matrix analysis. It is shown that the influence of the bound ground-state of¹³N has an appreciable effect on low-energy scattering. Recent predictions concerning Mott-Schwinger polarization are also discussed.     

Energy dependence of heavy ion collisions 4He + 12C and 12C + 12C elastic scattering

We have studied the transparency of heavy ion collisions at high energies by using Glauber's multiple scattering theory. The good agreement between our calculation and the existing data available strongly emphasizes the dominance of the nucleon-nucleon interaction in nucleus-nucleus collisions at high energies.     

90° excitation functions for elastic scattering of 28Si+16O and 28Si+12C

The gross structures in the excitation functions for elastic scattering of ²⁸Si+¹⁶O and ²⁸Si+ ¹²C, measured at 90°, where only even partial waves contribute, are found to be anti-correlated with those at 180°. Excitation functions at both angles, including the enhanced gross structure at 180°, can be reproduced by calculations using a potential which attracts odd partial waves more than even partial waves.     

Simulation of beam optics for ~(12)C+~(12)C scattering of RCNP by using Monte Carlo method

The Monte Carlo method is used to simulate the beam optics of the WS beam line of RCNP, Osaka University in order to know the effect of collimators on the beam line to control the beam spot. According to the simulation, we do not need to use the collimator to cut the beam and the beam angular resolution can be better than 0.05° in achromatic mode. In the present paper, the actual beam condition during the beam adjustment is listed. The accelerator can provide a 12 C beam in achromatic mode and the angular resolution σ=0.7775 mrad ±0.0030 mrad.     

Relations between measured and calculated spin observables in inelastic scattering of polarized protons for excitation of the 1+, T = 0 state in 12C

We analyze the most important spin observables representing the difference functions (P-A _y ) and (P-A _y )σ, along with the spin-transfer coefficients D _NN , D _SS , and D _LL in the inelastic scattering of polarized protons. We examine the excitation of the state 1⁺, T = 0 (12.71 MeV) in the ¹²C nucleus at the energies of projectile protons E _p = 200 MeV and E _p ～ 400 MeV. These spin observables are treated in the context of the exchange features of the effective interaction.     

Elastic alpha-12C scattering and the 12C(alpha,gamma)16O E2 S factor

Angular distributions of 12C(alpha,alpha)12C have been measured for E(alpha) = 2.6-8.2 MeV, at angles from 24 to 166, yielding 12 864 data points. R-matrix analysis of the ratios of elastic scattering yields a reduced width amplitude of gamma12 = 0.47 +/- 0.06 MeV(1/2) for the Ex = 6.917 MeV (2+) state in 16O(a = 5.5 fm). The dependence of the chi2 surface on the interaction radius a has been investigated and a deep minimum is found at a = 5.42(+0.16)(-0.27) fm. Using this value of gamma12, radiative alpha capture and 16N beta-delayed alpha-decay data, the S factor is calculated at E(c.m.) = 300 keV to be S(E2)(300) = 53(+13)(-18) keV b for destructive interference between the subthreshold resonance tail and the ground state E2 direct capture.     

Dominant angular momentum of gross structure in inelastic C+C(2) scattering

The gross structures observed at the CM energies of 24, 30 and 36 MeV in the angle-integrated ¹²C+¹²C(2⁺) cross section are attributed to contributions of the dominant angular momenta of 16, 18 and 20, respectively, based on analyses of the angular distributions. These assignments are shown to be favorable also for predictions of other available data such as particle-γ correlations, alignments of the spin substates and the elastic excitation functions.     

The12C(2 1 + ) state as probe for transient magnetic fields in polarized iron

PAC measurements on the 4.43 MeV¹²C(2⁺) state on recoil in magnetized iron at velocitiesv _ion=2.1v ₀, 6.0v ₀, 7.4v ₀ yield integral precession angles of =+0.72(18), +0.94(16) and +0.71(18) mrad, respectively. The results supplementary to existing precession data are interpreted by a distribution of C⁵⁺ ions implying a K-shell polarization of 28% and an effective charge larger than measured after emergence from the solid. The low-velocity precession tends to disagree with the empirical law of linear relationship between transient field and ion velocity. The presence of molecular orbital effects is discussed.     

Comparison of predictions for alignment in inelastic scattering of 12C + 12C

The predictions for the spin alignment in the single 2⁺ excitation in ${}^{12}\text{C +}{}^{12}\text{C}$ scattering in four typical models, i.e., the Austern-Blair diffraction model, the Band Crossing Model, the DWBA model and the strong-coupling model, are compared among themselves and with experiment.     

Emission of unbound 8Be and 12C * (0+ 2) clusters in compound nucleus reactions

We have studied the emission of light unbound clusters, ⁸Be and ¹²C ^* (0⁺₂), in the reactions ¹⁸O + ¹³C ^{31} Si ^{23} Ne + ⁸Be and ²⁸Si + ²⁴Mg ^{52} Fe ^{40} Ca + ¹²C ^* (0⁺₂). The -ray spectra obtained in coincidence with ⁸Be and ¹²C ^* (0⁺₂) emission have been studied relative to the statistical emission of two or three -particles. The angular-momentum-to-energy balance of the cluster emission is compared with that of multiple- emission. The properties of the energy spectra of the binary process and the population of the residual nuclei by cluster emission are discussed. It is observed that cluster emission carries away less excitation energy on average than the sequential emission of the individual components.     

Screening effects on ~(12)C+~(12)C fusion reaction

One of the important reactions for nucleosynthesis in the carbon burning phase in high-mass stars is the ~(12)C+~(12)C fusion reaction. In this study, we investigate the influences of the nuclear potentials and screening effect on astrophysically interesting ~(12)C+~(12)C fusion reaction observables at sub-barrier energies by using the microscopic α-αdouble folding cluster(DFC) potential and the proximity potential. In order to model the screening effects on the experimental data, a more general exponential cosine screened Coulomb(MGECSC) potential including Debye and quantum plasma cases has been considered in the calculations for the ~(12)C+~(12)C fusion reaction. In the calculations of the reaction observables, the semi-classical Wentzel-Kramers-Brillouin(WKB) approach and coupled channel(CC)formalism have been used. Moreover, in order to investigate how the potentials between ~(12)C nuclei produce molecular cluster states of ~(24)Mg, the normalized resonant energy states of ~(24)Mg cluster bands have been calculated for the DFC potential. By analyzing the results produced from the fusion of ~(12)C+~(12)C, it is found that taking into account the screening effects in terms of MGECSC is important for explaining the ~(12)C+~(12)C fusion data, and the microscopic DFC potential is better than the proximity potential in explaining the experimental data, also considering that clustering is dominant for the structure of the ~(24)Mg nucleus.