9Be(3He,n)11C and 11B(3He,n)13N Reactions at Energies below Coulomb Barrier

Angular distributions have been measured for ⁹Be(³He, n)¹¹C and ¹¹B(³He, n)¹³N reactions for the neutron group leading to the ground state at E_3He = 0.90, 1.00, 1.20, 1.40 MeV and 1.70, 1.90 MeV respectively. To fit the experimental data, the theory of two nucleon stripping reactions below the Coulomb barrier has been considered. Taking Coulomb distorted wave functions for the interacting particles in the initial channel, a closed analytical form for the differential cross-section has been obtained. The other two cases using the plane wave Born approximation and the distorted wave Born approximation are also applied to the experimental data. The agreement between the Coulomb distorted wave calculations and the experimental data is better than with the PWBA and DWBA. The spectroscopic factors are extracted by fitting the experimental data with the theoretical calculations.     

A local versus non-local t-matrix in the N(p, 2p)C reaction at 46 MeV

The angular distributions for the ¹⁴N(p, 2p)¹³C reactions at 46 MeV incident proton energy are calculated in the distorted wave t-matrix approximation (DWTA) where approximate optical-model waves are used. A comparison is made between the calculation using a local t-matrix to that of a non-local t-matrix. The (p, 2p) angular distribution is smaller in magnitude where a non-local t-matrix is employed compared to the calculation using a local t-matrix which implies that there is an overall enhancement of absorption associated with the non-local t-matrix. This also implies that differences between the local and non-local off-energy-shell effects can be significant. Parameter studies were undertaken for the distorted waves and bound state wave function and the effects on the angular distributions were similar in the local and non-local cases. The distortion effect due to the final-state focus phase dramatically changes the shape of the angular distribution. The calculations are considered to be a test of the off-energy-shell effects due to non-local interaction. This calculation is also a test of the approximate distorted waves at 46 MeV and the comparison to the ¹⁴N(p, 2p)¹³C data indicates that the distortion is reasonably well described.     

C12(d,p)C13和Ca40(d,p)Ca41基态反应质子的角分布

本实验测量了C¹²(d,p)C¹³及Ca⁴⁰(d,p)Ca⁴¹基态反应质子群的角分布和微分截面。氘核能量为13.3MeV,对C¹²和Ca⁴⁰的反应,其测量角度范围分别为3°—167°和10°—164°,每隔2.5°或5°测量一点,其主要结果如下:(1)对于这两群质子,在主削裂峯附近的实验点和用简单Butler理论算得的理论角分布曲线都符合得相当好;理论计算数据对实验数据在主峯处归一;由此而定得的核能级参数与前人所得到的是一致的。(2)大角度区的实验截面数值没有减小到象Butler理论所要求的那样小,并有非常明显的次极大出现,其位置与Butler理论所预言的不一致;这些特点可以用扭曲波理论来解释,非氘核削裂机制也可能有部分贡献。(3)在C¹²(d,p)C¹³反应中,前角度区的截面有很大下降,而后角区则有明显的增加,这些现象都和Butler理论不一致;然而,这也可以用扭曲波来解释。(4)用主峯处的截面和Butler理论算得的基态的约化宽度,对C¹²(d,p)C¹³和Ca⁴⁰(d,p)Ca⁴¹反应分别为r²=0.17和0.041;用扭曲波理论计算时,则得到较大的r²值,后者更接近于单粒子模型所预言的数值,基于上面这些事实,对本实验的数据使用扭曲波理论来进行分析似乎是值得的。     

Generalizations of distorted wave impulse approximation for nuclear (π+, π0) reactions

It is shown that corrections to the ordinary distorted wave impulse approximation are uniquely important for (π⁺, π⁰) reactions in the 3,3 region and have a significant effect towards improving agreement with the existing experiments.     

Elastic and inelastic scattering of 270 MeV3He particles from58Ni,90Zr,116Sn and208Pb

Differential cross-section angular distributions for the elastic scattering of 270 MeV³He particles from⁵⁸Ni,⁹⁰Zr,¹¹⁶Sn and²⁰⁸Pb have been measured. Optical model analysis of the cross-sections has yielded the optical model parameters for³He particles at 270 MeV. Angular distributions have also been measured for the inelastic excitation of the low-lying levels in the above mentioned nuclei. A collective model analysis using the distorted wave Born approximation (DWBA) of these cross-sections with the distorted waves generated by the optical model parameters determined from the elastic scattering analysis, has yielded the reduced transition probability (B(EL)) values consistent with those reported in the literature.     

Pion single charge-exchange reaction on nuclei near the (3, 3) resonance

Angle integrated cross-sections for the pion single charge-exchange reaction on¹³C and⁷Li have been calculated at several energies in the distorted wave impulse approximation employing the off-shell nature of the pion-nucleon scattering amplitude and using the Breit-Wigner formula for its energy dependence. Effect of the two nucleon correlations in the nucleus on the cross-section is also studied. Our results are in rough accord with the experimental data. The major part of this work was done while the author was at the University of Manitoba, Canada.     

Interpretation of the experimental evidence concerning the quadrupole moment of Bi209 — A test of the shell model

Attempts are made to construct a model of the quadrupole moment of Bi²⁰⁹ which will be consistent with the hfs interaction constant and the Bi²⁰⁹-Pb²⁰⁸ isotone shift observed in muonic x-rays. We achieve good agreement by postulating that the Bi²⁰⁹ quadrupole moment is due to a single proton in anh _9/2 state and to a distorted Pb²⁰⁸ core which has a deformation of about 1%. The inferred quadrupole moment is found to be 0.37 barns of which 0.12 barns is due to the distorted core.     

Electron impact excitation of the resonance transitions of highly ionized atoms of the Be-, Mg-, and Zn-isoelectronic sequences

Electron impact excitation collision strengths for the ns²¹S - nsnp¹P resonance transitions of highly ionized Be, Mg, and Zn-like ions have been computed in the distorted wave approximation, including the effects of exchange and target state correlation. Good agreement is observed between these data and collision strengths computed in the Coulomb-Born and Born approximations at high incident energies. Analytic fits to the distorted wave data are presented.     

An SU(4) invariant compactification of d = 11 supergravity on a stretched seven-sphere

We construct on S⁷ an SU(4) invariant solution of d = 11 supergravity in which the metric on the seven-sphere, regarded as a U(1) bundle overCP³, is distorted by stretching the U(1) fibers, and the four-index field strength F_MNPQ is non-zero in the S⁷ directions. This solution presumably corresponds to the SU(4) invariant extremum of the de Wit-Nicolai potential.     

Ligand field splitting of d orbitals in nine-coordinated sites of capped antiprism structure: Application to monazite

The splitting of the energy levels of d¹ ions in a field of nine ligands arranged in a capped antiprism is calculated for both the regular and distorted structure. In the regular capped antiprism, the ground state is found to be the degenerate state dxy, dx²-y²; in the distorted structure, the ground state is dx²-y². The results are consistent with experimental ESR data on the V⁴⁺: CePO₄ system.     

Effect of crystal field on the spin density at the copper nucleus in copper complexes

The role of lower symmetry component of the crystal field in causing a mixing of excited 3d ^x−1 4s with the ground 3d ^x configuration and leading to spin density at the nucleus for iron group ions was suggested by Griffith and Orgel. This mechanism has been examined in detail for the two low-symmetry copper complexes, one square planar (D_4h symmetry) and the other distorted tetrahedron (D_2d symmetry) and the calculation has been performed using the powerful Racah method and tensor operator technique. It is found that for the two types of copper complexes, copper pthalocyanin (square planar, D_4h symmetry) and cesium copper chloride (distorted tetrahedron, D_2d symmetry) the contribution from this mechanism to the spin density at the nucleus vanishes identically.     

EPR investigations of Cu(II) complexes with 5′-CMP and 5′-GMP

Electron paramagnetic resonance investigation of the Cu(II) complexes with guanosine-5′-monophosphate (5′-GMP) and cytidine-5′-monophosphate (5′-CMP) shows the affinity of the Cu(II) ion to interact with the base and the phosphate group. The different modes of the coordination of the metal ion at the nucleotide and the water molecules lead to octahedral species, distorted by dynamical Jahn-Teller effect (g₀ = 2.106) for the Cu(II)-5′-CMP complex and rhombically distorted (g₁ = 2.358, g₂ = 2.126, g₃ = 2.068) or tetragonally distorted (g_∥^′ = 2.299, g_⊥^′ = 2.126) for the Cu(II)-5′ -GMP complex. The compound with 5′-CMP presents also a more stable in time square-planar species (g_∥ = 2.265, A_∥ = 162 G, g_⊥ = 2.076). The local symmetry changes in aqueous solution by coordination of water molecules.     

Defects and impurities in nanodiamonds: EPR, NMR and TEM study

EPR, ¹³C NMR and TEM study of ultradisperse diamond (UDD) samples is reported. The compounds show a high concentration of paramagnetic centers (up to 10²⁰ spin/g), which are due to structural defects (dangling C-C bonds) on the diamond cluster surface. The anomalous reduction in the spin-lattice relaxation time of ¹³C (from several hours in natural diamond to ∼150 ms in UDD clusters) is attributed to the interaction between the unpaired electrons of the paramagnetic centers and nuclear spins. ¹³C NMR line-width reflects the fact that the structure of the UDD surface is distorted in comparison to the ‘bulk’ diamond structure.     

Distorted surface oxygen structure on UO2(100)

Low-energy electron diffraction (LEED) has been combined with ion-scattering spectroscopy (ISS) measurements of He⁺ at 500 eV to characterize experimentally the surface structure formed by oxygen atoms on UO₂(100). Insight into the surface geometry required to generate the LEED features was gained via laser transform simulation and kinematical diffraction analysis of two-dimensional arrays. Integrating the above approaches leads to a UO₂(100) surface model consisting of a monolayer of oxygen atoms arranged in distorted bridge-bond, zig-zag chains along 〈100〉 directions. Configurational energies were calculated which support the distorted UO₂(100) zig-zag structure.     

Final state interactions in nuclear pion photoproduction over the (3, 3) resonance

An impulse approximation calculation is made on the reaction ⁵¹V(γ, π⁺)⁵¹Ti from the region just above photopion threshold to the tail of the (3, 3) resonance. Pion final state distortions are taken into account through realistic optical potentials. Results are compared to those for plane-wave and surface-produced pions and to recent experiment. Comparison is made between surface-produced pions and pions distorted by the s-wave component of the optical potential.     

共面不对称条件下He和Ar原子（e, 2e）反应过程中的极化效应和后碰撞相互作用

采用修正后的扭曲波玻恩近似(DWBA)理论,计算了共面不对称几何条件及大能量转移和小动量转移条件下的He(1s²),Ar(3p⁶)和Ar(2p⁶)(e, 2e)反应三重微分截面.将理论计算结果与实验结果及由Brauner,Briggs和Klar提出的BBK方法、标准的DWBA理论计算结果进行了比较,发现在共面不对称几何条件及大能量转移和小动量转移条件下,极化效应和后碰撞相互作用在He(1s²),Ar(3p^{6< 关键词： (e;2e)反应 极化效应 后碰撞相互作用 共面不对称几何条件}     

Cluster knockout reactions

Cluster knockout reactions are expected to reveal the amount of clustering (such as that of α, d and even of heavier clusters such as¹²C, ¹⁶O etc.) in the target nucleus. In simple terms, incident medium high-energy nuclear projectile interacts strongly with the cluster (present in the target nucleus) as if it were existing as a free entity. Theoretically, the relatively softer interactions of the two outgoing particles with the residual nucleus lead to optical distortions and are treated in terms of distorted wave (DW) formalism. The long-range projectile–cluster interaction is accounted for, in terms of the finite range (FR) direct reaction formalism, as against the more commonly adopted zero-range (ZR) distorted wave impulse approximation (DWIA) formalism. Comparison of the DWIA calculations with the observed data provide information about the momentum distribution and the clustering spectroscopic factor of the target nucleus. Interesting results and some recent advancements in the area of (α, 2 α) reactions and heavy cluster knockout reactions are discussed. Importance of the finite-range vertex and the final-state interactions are brought out.     

119Sn Mössbauer, NMR (1H, 13C and 119Sn) and infrared study of tetracoordinated tin(IV) complexes with 4-[((E)-1-{2-hydroxy-5-[(E)-2-(aryl)-1-diazenyl]phenyl}methylidene)amino]benzoates

A series of organotin(IV) complexes of composition R₃Sn[O₂CC₆H₄{N= C(H)C₆H₃-2-OH(N=NC₆H₄R)}-p] (R = Ph or Bz; R = H, 2-CH₃, 3-CH₃, 4-CH₃) have been investigated by ¹¹⁹Sn Mössbauer, ¹H, ¹³C, ¹¹⁹Sn NMR and IR spectroscopic techniques. ¹¹⁹Sn Mössbauer data indicated a distorted tetrahedral geometry for the triphenyltin(IV) complexes while the tribenzyltin complexes exhibit a distorted trigonal bipyramidal coordination geometry with equatorial benzyl groups and the axial positions occupied by an O atom from the carboxylate ligand and the O atom from the water ligand. The ¹¹⁹Sn-NMR chemical shifts confirm that the Sn atom in triorganotin complexes is four-coordinate in CDCl₃ solution.     

The DWIA analysis of the pion photoproduction on carbon

The inclusive pion spectra in the¹²C(γ,π) reaction are calculated in the distorted wave impulse approximation (DWIA). The final state pion-nucleus interaction was constructed within the framework of the multiple scattering theory. The sensitivity of the cross section to the choice of different optical potential variants is investigated.