Experimental and shell-model studies of the reactions 91Zr(d,p)92Zr and 90Zr(t,p)92Zr

The results of high-resolution studies of the ⁹¹Zr(d, p) reaction at E_d = 12 MeV and the ⁹⁰Zr(t, p) reaction at E_t = 11.85 MeV are presented. Absolute cross sections have been measured for both reactions and (d, p) spectroscopic factors determined. A comparison of these results with earlier data has been made, and although many of the previous assignments have been confirmed, many new features concerning the structure of ⁹²Zr have been discovered. Shell-model calculations have been performed for ⁹¹Zr and ⁹²Zr using a neutron space which includes the $\text{2}\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$, $\text{3}\text{s}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$, $\text{2}\text{d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$, $\text{1}\text{g}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ and $\text{1}\text{h}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}$ orbits and a proton space comprising the $\text{1}\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ and $\text{2}\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ orbits. Realistic proton-neutron and neutron-neutron interactions based on the Sussex matrix elements were used in the calculations. Spectroscopic factors have been calculated for the ⁹⁰Zr(d, p) and ⁹¹Zr(d, p) reactions and cross sections calculated for the ⁹⁰Zr(t, p) reaction. In general, good agreement between the theoretical and the experimental results has been obtained.     

Atomic antiproton states in 16O, 18O, 32S, 40Ca, 44Ca and 122Sn

Atomic levels for the systems p? plus ¹⁶O, ¹⁸O, ³²S, ⁴⁰Ca, ⁴⁴Ca and ¹²²Sn are calculated in optical potentials based on the N?N interaction of Dover and Richard.     

Low-lying levels of 92Nb from the 92Zr(3He,t) and 92Zr(3He,p2nγ) reactions

The structure of ⁹²Nb has been investigated using the 33.8 MeV ⁹²Zr(³He, t) and (³He, p2nγ) reactions. Several previously unobserved levels, including several belonging to the $\text{π(}\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{)ν(}\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{)}{}^{\mathrm{?1}}$ multiplet, are reported. The results are discussed in terms of the shell model.     

Anomalous L = 0 transition observed in the reaction 40Ca(p,t)38Ca

An anomalous L = 0 transition to the 3.06 MeV state in ³⁸Ca is observed in the reaction ⁴⁰Ca(p,t) at E_p = 52 MeV. Its angular distribution and relative intensity can be explained by the cancellation of form factors.     

On the predictions of the coexistence model for the reaction 42Ca(p,t)40Ca

The coexistence model as formulated by Gerace and Green for ⁴⁰Ca has been shown to predict cross sections for the reaction ⁴²Ca(p,t)⁴⁰Ca in strong disagreement with experiment. In the present letter we demonstrate how a much improved agreement can be obtained by introducing additional kinds of basis states. Especially important are triaxially deformed components, which contain admixtures of the $\text{1}\text{s}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ states.     

12C(7Li,t)16O和20Ne(d,6Li)16O反应的研究

本文把用于处理重离子引起的单粒子转移反应的Goldfarb-Buttle方法推广到多粒子转移反应。计算了¹²C(⁷Li,t)¹⁶O和²⁰Ne(d,⁶Li)¹⁶O反应,用了¹⁶O的全相干波函数,考虑了某些反冲因素,并将结果与实验作了比较。     

Levels of 41Sc from the 40Ca(p,p)40Ca reaction

Excitation functions have been measured for ⁴⁰Ca(p, p)⁴⁰Ca, in the energy range from E_p = 2.35 to 4.85 MeV at four angles. The R-matrix formalism for multilevel cross sections was used to analyse the data; spins, parities, proton widths and reduced widths were extracted for thirty levels. Several new spin values have been deduced. A detailed comparison of the levels in the mirror system ⁴¹Ca?⁴¹Sc is given.     

Spectroscopy of 42Ca from 41Ca(d,p)

Energy levels in ⁴²Ca up to 7.8 MeV have been studied in the neutron capture reaction ⁴¹Ca(d, p)⁴²Ca with 12 MeV bombarding energy. Ninety-four excited states have been identified and angular distributions have been measured in the interval from 5° to 110° by means of a broad-range magnetic spectrograph. The angular distributions together with DW calculations have been used to determine I_n values and spectroscopic factors. The $\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ strength sum agrees with shell-model expectations if the f_{$\text{7}\text{2}$} spectroscopic factors are renormalized by $\text{1}\text{0.75}$, in line with other $\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$. transfer experiments on ⁴⁰Ca and ⁴¹Ca. A similar renormalization of the l_n = 1 spectroscopic factors brings this strength sum in accordance with the shell-model calculations. The effective ($\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}{}^2$) matrix elements for ⁴²Ca are compared with the corresponding matrix elements of ⁴²Sc and ⁴⁸Sc. The differences between the three sets of matrix elements are of the order of a few hundred keV or less. The monopole centroid energy of the ($\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{)}{}^2$ multiplet is shifted downwards in the mass-42 nuclei compared to ⁴⁸Sc, possibly indicating the importance of the monopole pairing force near ⁴⁰Ca.     

15N excitation contribution to 48Ca(16O, 15N)49Sc reaction

The effect of ¹⁵N excitation process is studied in the reaction ⁴⁸Ca(¹⁶O, ¹⁵N)⁴⁹Sc. The excitation process is included into a generalized non-local optical potential for a scattersing ¹⁵N-⁴⁹Sc and is found to be responsible for a shift of a grazing peak in the exact finite-range DWBA calculation.     

Mesures des vies moyennes des niveaux de 1K alimentes par les réactions 39K(t,p) et 27Al(16O, 2p)

Twenty-four levels in ⁴¹K at excitation energies below 5 MeV have been identified in the reactions ³⁹K(t, p)⁴¹K and ²⁷Al(¹⁶O, 2p)⁴¹K, at incident beam energies of 3.0 and 34 MeV respectively. Using the recoil-distance technique and the Doppler-shift attenuation method, mean lifetimes (in ps) were obtained for the following levels: 980 keV, 0.42^0.30_0.15; 1294 keV, > 5; 1560 keV, 0.58 ± 0.22; 1582 keV,> 1.5; 1677 keV, 6⁺³_?1; 1698 keV, 1.3 ± 0.4; 2528 keV, 230 ± 15; 2762 keV, < 2; 2775 keV, 68 ± 4; 4274 keV, < 2; 4983 keV, 95 ± 15. The positive parity states are suggested to have predominantly 2p-1h configurations. As a by-product, mean lifetimes for five levels in ⁴¹Ca, populated via the ²⁷Al(¹⁶O, pn)⁴¹Ca reaction, were also obtained.     

On the mechanism of the (3He,t) reaction

The (³He, t) reactions are investigated by means of the second-order perturbation method with the (³He-α-t) process and the ordinary DWBA term. The analyses are performed on the data of ⁴⁸Ca(³He, t)⁴⁸Sc(0⁰⁺, 2⁺, 4⁺, 6⁺), ⁹⁰Zr(³He, t)⁹⁰Nb(2⁺, 4⁺, 6⁺, 8⁺) and ^{46, 48, 50}Ti(³He, t)^{46, 48, 50}V(0⁺. The results show that the (⁺He-α-t) process is an important process in these reactions and a very good agreement between observed and calculated cross sections is obtained. The energy dependence of the cross section of the ⁹⁰Zr(³He, t)⁹⁰Nb(O⁺) reaction is also discussed.     

Value of the absolute cross section for the reaction 40Ca(16O, 12C)44Ti

The reaction ⁴⁰Ca(¹⁶O, ¹²C)⁴⁴Ti(g.s.) is calculated making use of a microscopic finite-range form factor and full recoil. The states connected by the reaction are described in terms of shellmodel wave functions. They were obtained making use of Kuo-Brown matrix elements in the (p, sd) and (f, p) subspaces for the case of ¹⁶O and ⁴⁴Ti, respectively. The predicted value of the cross section is a factor of the order of 100 smaller than the experimental value.     

Low-energy scattering parameters and atomic level shifts in the p̄16O,p̄32S and p̄40Ca systems

A relationship between the low-energy scattering parameters and atomic level shifts is analyzed in the cases of the p?¹⁶O, p?³²S and p?⁴⁰Ca systems. The corresponding scattering lengths are calculated on the basis of energy level shifts evaluated earlier by means of an optical potential.     

Coupled-channel fusion and inelastic scattering calculations for 18O + 44Ca and 12C + 48Ti

Fusion and inelastic scattering coupled-channel calculations are carried out for the systems ¹⁸O + ⁴⁴Ca and ¹²C + ⁴⁸Ti. Comparison between ¹²C + ⁴⁸Ti and ³²S + ²⁴Mg sub-barrier fusion cross-section enhancement is made using simple analytical expressions. The distribution of the angular momentum absorbed by the compound nucleus is discussed in a quantum-mechanical coupled-channel model.     

Analogue states in 47Ca

The ⁴⁸Ca(³He, ⁴He)⁴⁷Ca and ⁴⁸Ca(p, d)⁴⁷Ca reactions were used to observe six levels in ⁴⁷Ca above 12 MeV excitation. Analysis of the data has yielded precise excitation energies for the lowest $\text{T =}\text{9}\text{2}$ levels in ⁴⁷Ca; which are analogs of low-lying levels in ⁴⁷K. Comparison of experimental and calculated Coulomb displacement energies for the K-Ca isotopes is made.     

The (3He,n) reaction on 16O and 18O

The (³He, n) reaction on ¹⁶O and ¹⁸O has been used to study low-spin states in ¹⁸Ne and ²⁰Ne up to E_x ≈ 8 and 20 MeV, respectively. The measured neutron angular distributions have been analysed using DWBA. By a comparison with shell-model calculations in the (s, d) shell it is found that most of the two-proton transfer strength can be explained within that shell. Important contributions, however, from the (f, p) shell in low-lying negative parity states are also present.     

Microscopic study of heavy-particle transfer reactions: The (16O, α) reactions on 16O and 28Si

The transfer reactions ²⁸Si(¹⁶O, α)⁴⁰Ca and ¹⁶O(¹⁶O, α)²⁸Si have been studied within the framework of the two-channel generator coordinate method. The geometry of the reactions has been discussed in terms of the cross-channel overlap kernels of the generating functions. A clear connection between maxima in the reaction rate and entrance channel resonances has been established. A two-step reaction mechanism involving quasimolecular resonances of inelastic ¹⁶O-¹⁶O channels is discussed as a possible explanation for narrow structures seen in the ¹⁶O(¹⁶O, α)²⁸Si reaction cross section.     

在独立α集团模型下对敲出反应16O(p,pα)12C和16 O(α,2α)12C的研究

在独立α集团模型下，利用扭曲波冲量近似(DWIA)，计算了实验室系下入射能量为101.5MeV 的敲出反应¹⁶O(p，pα)¹²C和实验室系下入射能量分别为90Me V和140MeV 的敲出反应¹⁶O(α,2α)¹²C.得到的反应截面和谱因子与实 验数据基本符 合，比用壳模型的结果有了一定的改进，表明独立α集团模型能较好地描述α集团敲出反应 的机理. 关键词： α集团模型 敲出反应 反应截面 谱因子     

Spectroscopic studies of 37,39K using the 40,42Ca(p, α) reactions

The ⁴⁰Ca(p, α) ³⁷K reaction has been studied at 42.5 MeV bombarding energy with an overall energy resolution of 45 keV. Excitation in ³⁷K was observed for the 0.00 MeV, $\text{3}\text{2}{}^{\mathrm{+}}\text{; 1.37}\text{MeV}\text{,}\text{1}\text{2}{}^{\mathrm{+}}\text{; 2.28}\text{MeV}\text{; 2.75}\text{MeV}\text{,}\text{5}\text{2}{}^{\mathrm{+}}\text{; 3.25, 4.69, 5.69, 6.05, 7.00, 7.32}\text{and}\text{7.84}\text{MeV}$ states. No known negative parity states are populated in ³⁷K via the (p, α) reaction, closely resembling the features observed in the ³⁹K(p, t)³⁷K reaction. Results of this reaction and the previously investigated ⁴²Ca(p, α)³⁹K reaction are used in a combined analysis, with emphasis on a comparison of the relative strengths of states populated in these two reactions. Core excitation, which is known to be important in the Ca nuclei, plays an important part in understanding the strengths of the observed transitions. Microscopic three-nucleon form factors were calculated for all transitions of interest, and the normalizations of these form factors used in extracting the relative strengths from zero range DWBA calculations. Simple configurations for the transferred nucleons are assumed in this comparison, in an attempt to explain the main features of the (p, α) reaction.