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).     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

46.8MeV的(-p)+12C非弹性散射

在Glauber多重散射理论框架下,使用跃迁密度方法和三种NN湮没势,计算了46.8MeV的反质子在12C上的非弹性散射微分截面.理论曲线与实验数据符合得较好.     

The12C+12C reaction at subcoulomb energies (II)

The reaction¹²C+¹²C has been studied in the energy range E_c.m.=2.8–6.3 MeV by charged-particle spectroscopy. Angular distributions of the proton and α-particle exit channels were obtained. The excitation functions do not reveal evidence for the phenomenon of absorption under the barrier. The data have been extrapolated to the energy region of astrophysical interest. The existence of reported and new intermediate resonance structures is discussed.     

The12C+12C reaction at subcoulomb energies (I)

The reaction¹²C+¹²C has been studied in the energy rangeE _cm=2.45–6.15 MeV byγ-ray spectroscopy. Gamma-ray transitions from a large number of excited states in²⁰Ne,²³Na and²³Mg were observed, which show strong and rapid yield variations. When the influence of the Coulomb barrier is removed, these structures appear superimposed on a flat reaction yield, which does not show a strong increase at low energies, in contrast to previous work. These results obviate the need for the hypothesis of absorption under the barrier at least down toE _cm=2.45 MeV. The nuclear and astrophysical aspects of the data are discussed.     

Observation of the nuclear rainbow scattering for12C+12C atE Lab =300 MeV

The elastic and inelastic scattering of¹²C on¹²C has been measured in the angular range between 2.8° and 70.4° in the c.m. system atE _Lab =300 MeV. Optical model calculations have been performed with Woods-Saxon and folded potentials, the ground state and the first 2⁺-state were coupled in the calculations. The large cross sections of the elastic scattering at large angles is related to the nuclear rainbow scattering, which is centered at about 56°. This requires a potential depth of 100 MeV at a distance of 3 fm, the fit to the data is sensitive down to this region. The calculations with the folded potential show a better agreement with the data than those with the Woods-Saxon shape. The total reaction cross section of 1,420 mb, obtained from the optical model analysis, corresponds to the geometrical value; no transparency is observed.