Populations of sublevels 24Mg(2+) nucleus formed in the reaction 24Mg(d,d1γ)24Mg at E d = 15.3 MeV

Angular dependences of density matrix spin tensors and sublevel populations are experimentally reconstructed for the ²⁴Mg(2⁺, 1.369 MeV) nucleus formed in the inelastic scattering of deuterons by ²⁴Mg at E _d = 15.3 MeV and deuteron emission angles from 25° to 165° (lab). The experimental results are compared to those from calculations using different versions of the coupled-channel method.     

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.     

Polarization Features of the 24Mg(2+) Nucleus Produced in the Reaction 27Al(p, α)24Mg(2+)

At the proton energy of E_p = 7.4 MeV, the double-differential cross sections for the reaction ²⁷Al(p, α₁γ)²⁴Mg were measured for 11 values of the alpha-particle emission angle in the range of θ_α = 30°–160°(lab). All even components of the density-matrix spin-tensors were reconstructed for the oriented ²⁴Mg nucleus in the 2⁺ state at 1.369 MeV, and the polarization features of this nucleus, including the populations of magnetic sublevels of the nucleus for all spin projections, multipole-moment orientation tensors, and the quadrupole and hexadecapole tensor polarizations, were determined. Relevant experimental results were compared with their counterparts calculated for the triton-pickup mechanism within the coupled-channel method and in the statistical limit of the compound-nucleus model.

     

~(16)O ~(24)Mg和~(20)Ne (24)Mg弹性散射的机制

本文考虑了两碰撞核间核子结团的转移机制,解释了象~(16)O ~(24)Mg和~(20)Ne ~(24)Mg这样一些4N核间的弹性散射微分截面后角振荡上升的反常现象.在原子核分子轨道模型的理论框架下,将交换势的强度作为唯一的可调参数,数值计算较自然地拟合实验结果.     

Reaction rate of 24Mg(p,γ)25Al

The proton-capture reaction on ²⁴Mg has been investigated in the bombarding energy range of E_p=0.2–1.7 MeV. Resonance properties (strengths, branching ratios and lifetimes) of low-energy resonances have been measured. From the experimental results, accurate proton partial widths, γ-ray partial widths and total widths (Γ_p, Γ_γ, and Γ) have been deduced. The present experimental information establishes the ²⁴Mg+p reaction rates over the temperature range T=0.02–2.0 GK with statistical uncertainties of 5% to 21%. Our recommended reaction rates deviate from previous estimates by 18% to 45%. Based on our results, we can rule out the recent suggestion that the total width of the E_R=223 keV resonance has a significant influence on the reaction rates. We also discuss several effects that might give rise to systematic uncertainties in the reaction rates. The astrophysical implications for hydrogen burning of ²⁴Mg at low stellar temperatures are presented.     

Study of the 24Mg(α, 12C)16O reaction in the energy range Elab = 24.9–27.76 MeV

The ²⁴Mg(α,¹²C)¹⁶O and ²⁴Mg(α, α')²⁴Mg reactions have been used to search for resonances in the ²⁸Si compound nucleus. The excitation functions were measured in the energy range between 24.9 and 27.76 MeV. Angular distributions of ¹²C nuclei and elastic and inelastic scattering of α-particles have been measured at energies corresponding to extrema of excitation functions. Significant anomalies have been found at E_ex = 31.5 and 33,1 MeV. The spins and parities of these structures are assigned as 9⁻ and 11⁻, respectively.     

Search for low-energy resonances in 27Al(p, α)24Mg

The known low-energy resonances in ²⁷Al(p, γ)²⁸Si at e_R = 203, 223, 293 and 327 keV have been searched for in the ²⁷Al(p, α)²⁴Mg reaction. The observed upper limits for the resonance strength together with the results from previous work show that the MgAl cycle is not closed at all stellar temperatures of interest and that in the important temperature range near T₉ = 0.1 the (p, γ) reaction proceeds at least 100 times faster than the (p, α) reaction. The results might be of importance for the explanation of extinct ²⁶Al in meteoritic samples as well as of the 4 solar masses of ²⁶Al found in the interstellar medium via γ-astronomy.     

Re-evaluation of the ^23Mg（p,γ） ^24Al reaction rate

Based on a new screening Coulomb model, this paper discusses the effect of electron screening on proton capture reaction of 23Mg. The derived result shows that, in some considerable range of stellar temperatures, the effect of electron screening on resonant reaction is prominent; on the non-resonant reaction the effect is obvious only in the low stellar temperatures. The reaction rates of ^23Mg（p,γ） ^24Al would increase 15%-25% due to the fact that the electron screening are considered in typical temperature range of massive mass white dwarfs, and the results undoubtedly affect the nucleosynthesis of some heavier nuclei in massive mass white dwarfs.     

Determination of the reaction-matrix elements of the D(d,n)3He and D(d,p)3H reactions forE d ≤500 keV

All available data of the mirror fusion reactions D(d, n)³He and D(d, p)³H have been subjected to a new analysis in order to extract the matrix elements of all 16 transitions necessary for inclusion of alll2 waves. Their energy dependence was assumed to be governed solely by Coulomb penetrabilities. The Levenberg-Marquardt algorithm was used to fit all experimental data. The experimental data are reproduced satisfactorily. The results compare well with anR-matrix analysis and with refined resonating group calculations. No suppression of quintet entrance-state transitions and therefore no neutron suppression in polarized fusion can be derived from this analysis.This work was funded by the German Federal Ministers for Research and Technology (BMFT) under the contract numbers 06-OK-153 and 06-OK-272     

Many-particle decays of α-chain structures in24Mg

We have searched for evidence of exotic cluster configurations in²⁴Mg resembling a linear chain of α particles in various many-particle final states of the¹²C+¹²C system, including¹²C(O ₂ ⁺ )+¹²C(O ₂ ⁺ ) and⁸Be+¹⁶O^*(4α). Such configurations are predicted to occur by a number of different theoretical models of the structure of²⁴Mg. An array of highly segmented double-sided silicon strip detectors permits detailed, high resolution reconstruction of these many-charged-particle final states.     

X-ray intensities following the fusions of dμd,dμt and pμd

Muonic X-ray spectra of μ³He and μ⁴He from dμd, pμd, and dμt fusion are analyzed for various target densities. Theoretical values of the intensity ratio μ³He(3→1)/μ³He(2→1) for dμd and pμd fusion at liquid hydrogen density are, respectively, 0.132 and 0.0553. These are in good agreement with the experimental results.     

A study of the 29,30Si(α, d)31,32P and the 29,30Si(d, α)27,28 Al reactions

The ${}^{\mathrm{29,30}}\text{Si}\text{(α,}\text{d}\text{)}{}^{\mathrm{31,32}}\text{P}$ reactions have been studied at a beam energy of 25 MeV and the ${}^{\mathrm{29,30}}\text{Si}\text{(}\text{d}\text{, α)}{}^{\mathrm{27,28}}\text{Al}$ reactions have been studied using a 12.3 MeV tensor polarised deuteron beam. The data have been analysed using the microscopic DWBA. Three representations of the nucleon-nucleon interaction have been compared by incorporating the appropriate spectroscopic amplitudes for two nucleon transfer obtained from shell model calculations, in the microscopic form factor.     

Excitation of Jπ=2+ resonances in 24Mg by the 23Na(p, 12C)12C reaction

Angular distributions of the ²³Na(p, ¹²C_g.s.)¹²C_g.s. reaction were measured at energies on top of resonance-like structures or close to them in the range E_p=8−18 MeV and were analysed using parametrized S-matrix elements. Partial cross sections proceeding through compound nuclear states of ²⁴Mg with various spin J were derived. In was found that the resulting cross sections for J=2 exhibit correlated structures with the “fissioning resonances” recently observed by the ¹²C(¹²C, λ₀) and ²⁴Mg(α, α') ¹²C_g.s + ¹²C_g.s. reactions.     

Measurements of Γγ/Γ for states of 24Mg in the excitation region 10< Ex< 12MeV

Measurements of Γ_γ/Γ have been carried out for about 40 states of ²⁴Mg in the excitation region 10 to 12 MeV using a recoil-coincidence technique. The information obtained has been combined with known values of ωγ to determine Γ_γ, and Γ_α. Widths of the order of 0.01 to 100 eV can be determined accurately using this method. Some previous data on levels in this excitation region are discussed. Excitation energies and electromagnetic transition rates are compared with theoretical predictions. Two notable conclusions are the observation of a considerable excess in E2 strength in the 10 to 12 MeV region compared with that predicted by the shell model, and the identification of the 4⁺ 11.219 MeV level as possibly being a member of a collective band based on the 0⁺, 6.432 MeV level.     

The nuclear structure of 126Te studied with (d,p), (d,3He) and (d,d′) reactions

At the Munich Tandem Accelerator the reactions ¹²⁵Te(d, p)¹²⁶Te, ¹²⁶Te(d, d′)¹²⁶Te and ¹²⁷I(d, ³He)¹²⁶Te were measured with deuteron energies between 24 and 28 MeV up to excitation energies of about 3.2 MeV. Using γ-lines from previous (n,γ), (n,n′γ) and (γ,γ′) experiments, a level scheme of ¹²⁶Te up to above 3 MeV was established. The results are compared with quasiparticle-phonon model calculations.