Study of the excitation functions of27Al(n, α)24Na,27Al(n,p)27Mg and28Si(n,p)28Al reactions

Cross sections for the reactions²⁷Al(n, p)²⁷Mg and²⁸Si(n,p)²⁸Al were measured by activation method between 13.40 and 14.83 MeV neutron energy. An accuracy of about 4% was achieved using the²⁷Al(n, α)²⁴Na reaction as a reference at 14.1 MeV where the relative excitation function has also been measured. Results obtained were compared to a recent compilation and that calculated by the Hauser-Feshbach model. Using the back-shifted level density formula and taking into account the contribution of the separated levels, the calculations were extended to the energy range from the threshold to 18 MeV. A structure was observed in the²⁷Al(n, α)²⁴Na reaction cross section curve around 14 MeV neutron energy.     

High resolution gamma-ray spectroscopy of the27Al(p,γ)28Si resonance reaction

High resolution gamma-ray spectra have been measured from the²⁷Al (p,γ)²⁸Si reaction for the resonances atE _p=2·482, 2·511 and 2·735 MeV at ϑ _pγ=0°, 30°, 55° and 90° using a Ge (Li) gamma spectrometer. From the spectra and the angular distributions the properties of the resonance states have been obtained. These states are the isobaric analogues of the levels at 4·69, 4·75 and 4·93MeV levels respectively in the parent nucleus A²⁸l.     

The (p,nγ) reaction on Al and Si

The reactions ²⁷Al(p, n γ) ²⁷Si and ²⁸Si(p, n γ)²⁸P have been studied at E_p = 16 and 23 MeV, respectively, with a Ge(Li) detector in coincidence with a neutron detector. In ²⁷Si, two new γ-tran- sitions were detected and accurate excitation energies were determined. In ²⁸P, the γ-decay scheme was studied for the first time and new levels were located at 879 and 1602 keV excitation energy. For both nuclei the γ-ray spectra were supplemented by neutron time-of-flight spectra. The excitation energies are compared with those of the analogue nuclei and with the predictions from Coulomb displacement calculations.     

Isobaric analogue states in28Si from (p, γ) reaction in27Al

Analogue states in²⁸Si are identified through (p, γ) reaction in²⁷Al in the energy rangeE _p =0.85–3.0 MeV. There appears hardly any indication of a mixing. Coulomb displacement energy ΔE _c for the isobaric pair²⁸Al-²⁸Si is obtained. A least squares analysis is also carried out on all the available experimental results of ΔE _c as a function of ¯Z/A ^1/3.     

The study of the width for intermediate resonances in the 27Al(d,p)28Al, 27Al(d, α)25Mg, 31P(d,p)32P and 31(d, α)29Si reactions

The protons and α-particles from the reactions ²⁷Al(d, p)²⁸Al(d, α)²⁵Mg, ³¹P(d, p)³²P and ³¹P(d, α)²⁹Si were measured and analyzed with the channel cross correlation function and auto-correlation function to determine the correlating numbers N_d and average width 〈Γ_μ〉. With these values, the theoretical intermediate widths were calculated to be 119 ± 30 keV in the ²⁹Si nucleus and 249 ± 46 keV in the ³³S nucleus, which were in good agreement, within the errors, with the present experimental results of 185 ± 37 keV in ²⁹Si and 204 ± 24 keV in ³³S.     

Destruction of26Al via the26Al(n,p)26Mg-reaction

An angular analogue to the Giant Dipole (the Giant Angle Dipole) is described. Such collective vibrational motion is specifically investigated for the case of a spin saturated large particle number system contained in a deformed harmonic oscillator well. The model predicts the ratio of the Angle Dipole to Giant Dipole excitation as equal to the deformation.     

Activation cross section for 27Al(π+,π0)27Si at 100 MeV

The activation cross section for ${}^{27}\text{Al}\text{(π}{}^{\mathrm{+}}\text{,π}{}^0\text{)}{}^{27}\text{Si at}\text{E}{}_{\mathrm{\pi }}\text{= 99 ± 9}\text{MeV}$ was determined to be 5.1 ± 2.2 mb by counting the residual β⁺ activity of ²⁷Si. This result is compared with other pion-nucleus cross sections. A value for the elementary pion-nucleon cross section inside the nucleus is derived from this result and compared with an estimate from a phenomenological expression.     

Giant core-exciton effects on Si(111) 7 × 7 surfaces

We present the first direct experimental evidence for a large surface influenced core-exciton effect on silicon. The Si(111) 7 × 7 L_2,3 absorption edge has been studied with core-level electron energy loss (ELS) and X-ray photoemission spectroscopy (XPS). An excitonic shift of ～1–2 eV have been found for transitions from Si(2p) to empty surface states.     

Analysis of the27Al(p, γ)28Si reaction at subbarrier energies in terms of the direct-semidirect model

Differential cross sections forγ-transitions to 12 states in²⁸Si following nonresonant proton capture in²⁷Al nuclei (E _p=1,625 keV) were measured and analysed in terms of the direct-semidirect model. The experimental data are reproduced only when the complex coupling constant with the GDR is enhanced for thef partial wave in the entrance channel.     

Muon level-crossing resonance in Si∶Al

A systematic investigation of five sherds from the Celtic oppidum of Manching by refiring in different atmospheres is presented. The data are part of an extended and general study of Celtic ceramics in early Europe.     

Analog giant dipole excitation in Si(n,p) at 59.6 MeV

The parent analog of the giant dipole resonance in ²⁸Si is studied by means of the (n, p) reaction. The continuum contribution to the giant dipole region was estimated by a phenomenological parameterization. The observed cross section exhausts 31% of the SJ sum rule; 88% of the GT sum rule or 67% of the Myers-Swiatecki prediction. A comparison is made to the giant resonance region observed in the ²⁸Si(p, p') reaction which was recently used, via comparison to ²⁸Si(α, α'), to infer that the GDR in ²⁸Si is not excited or at least not seen in (p, p').     

The27Al(n,d)26Mg reaction at 22 MeV

Deuteron spectra from the reaction²⁷Al(n, d)²⁶Mg has been measured at reaction angles 0°→60°, with a spectrometer comprising three multiwire proportional counters followed by a curved plastic scintillator. Spectra were obtained with an energy resolution of ～0.7 MeV and an angle resolution of ～5°. Angular distributions for transitions to the ground state and excited states at 1.81, 2.93 and 4.3 MeV in²⁶Mg were obtained. Distorted waves analysis of the angular distributions yield spectroscopic factors of 0.29(8), 0.9(3), 0.18(7) and 1.9(6) for the ground and excited states, respectively. The results are compared with previous (d,³He) and (n, d) measurements, and with theoretical predictions.     

Stellar reaction rate of26Mg(p, γ)27Al

The reaction²⁶Mg(p, γ)²⁷Al has been investigated atE _p (lab)=80–355 keV. The existence of the resonances atE _p =292 and 338 keV has been verified and new resonances were found atE _p =227 and 275 keV. Information on branching and mixing ratios,ωγ values, total widths, andJ ^π assignments for the observed resonances is given. Upper limits on theωγ strengths for expected resonances in the energy range covered are presented. The astrophysical aspects of the data are discussed in the light of the²⁶Mg(²⁶Al) isotopic anomaly.     

27Al+27Al耗散反应中间双核系统的核温度

从²⁷Al+²⁷Al耗散反应产物的激发函数中提取能量相干宽度Г,再求出双核系统的核温度T,并用相干转动的概念进行以合与解释.     

^27Al＋^27Al耗散产物反应时间的提取

用发展了的Ericson统计理论,从27Al＋27Al碰撞的耗散产物的激发函数提取了反应的相互作用时间约4．3×10-21s．     

A systematic study of (n,d), (n,n' p) and (n,pn) reactions at 14.7 MeV

Cross sections for [(n, d) + (n, n′p) + (n, pn)] reactions induced by 14.7 ± 0.3 MeV neutrons on ⁴⁴Ca, ⁴⁹Ti, ⁵⁰Cr, ^{67, 68}Zn, ⁹²Zr and ^{97, 98}Mo have been measured by the activation technique using enriched isotopes as target materials, modern radiochemical separations and high-resolution counting methods. A brief summary of the literature data and our own earlier measurements is given. Our activation data are generally in agreement with those deduced from emitted charged particle characterisation. Some systematic trends in the activation cross-section data were analysed. Similar to other (n, charged particle) reactions, the [(n, d) + (n, n′p) + (n, pn)] reaction cross section decreases as a function of (N?Z)/A; the data, however, fall on two curves, one for nuclei with neutron separation energies (S_n higher than the proton separation energies (S_p) and the other for nuclei with S_n < S_p. For nuclei with S_n ? S_p the (n, n′p) process is very important. Detailed Hauser-Feshbach calculations show that in general contributions of statistical processes to the (n, d) reaction cross section are very small.