Positron impact inner shell ionization

The positron impact ionization cross section for theK-shell was determined in the case of Ni, Y and Ag at 670 and 490 keV as well as for theL-shell in the case of Yb, Ta, Au and Pb at 490 keV using a beta-ray spectrometer as a source of monoenergetic electrons and anX-e ⁺ coincidence arrangement. The results for theK-shell are compared with the theoretical calculations according to Kolbenstvedt and with the earlier experimental values.     

On the nuclear interaction potential in the reactions with heavy ions

The interaction potential of heavy ions⁴He,⁶Li,¹²C and¹⁶O is constructed in the folding model. The density distribution of nuclear matter for these nuclei is calculated in the framework of the hyperspherical function method. For the calculation of the folding potentials we have employed the Skyrme nucleon-nucleon forces. The influence of several effects on the results of calculations is studied: the role of the three-body forces of the nucleon-nucleon interaction, dependence of the folding potential on the mass numbers of the colliding nuclei and the possibility of observing the monopole resonance in the ion inelastic scattering. Using our folding potential as a real part of the optical potential we have calculated the differential cross section of elastic scattering of⁶Li from¹²C at laboratory energy of lithium ionsT _L =90.0 MeV. Reasonable agreement with experiment is obtained.     

Transfer reactions with heavy ions

A simple model is derived for angular distributions in heavy ion transfer reactions which takes into account the dynamic as well as the quantal dispersion of the wave packet.     

Secondary fusion reactions in the bombardment of light-element targets with low-energy heavy ions

Neutron emission was observed experimentally at the DC-60 cyclotron at the Institute of Nuclear Physics (Astana, Kazakhstan). The neutron yields were measured in the bombardment of light-element (Be, C, Al, Al₂O₃, and LiF) targets with heavy ions (Ar, Kr, and Xe) with energies below the Coulomb barrier. The angular distributions of neutrons from the targets were also measured. It was found that the observed neutrons were produced in secondary nuclear reactions between the resting target nuclei and recoil nuclei that acquire energy in the process of elastic scattering. The experimental results were compared with calculations based on the abovementioned secondary-reaction mechanism. The calculations allow one to estimate the yields of secondary reactions to within a coefficient of 2.     

On the evaluation of SCA matrix elements for inner shell ionization by heavy charged particles

The evaluation of matrix elements for the first order semiclassical approximation (SCA) is discussed. The method of Bang and Hansteen i generalized. A simplified derivation of their straight line trajectory results is given. An alternative method of evaluating is described and formulated in the same manner as the first method. Formulae needed in the accompanying paper are derived.     

Complete fusion and quasi-fission reactions induced by Kr ions on heavy targets

Cross sections for fission (complete fusion) and quasi-fission are measured at a given angle for the systems Kr + Ho, Kr + W, Kr + Bi, Kr + U in the energy range 450–525 MeV. The cross sections for complete fusion are unexpectedly low and the cross sections for quasi-fission are high. The cross section for close collisions (sum of the complete fusion and quasi-fission cross sections) is compared to the value calculated with the critical distance concept. The possibility that complete fusion does not occur for the lowest impact parameters is discussed.     

Neutron transfer reactions with very heavy ions

We have studied neutron transfer reactions induced by ¹³²Xe on three rare-earth targets at $\text{E}\text{V}{}_{\mathrm{C}}\text{～ 1.1}$. By using particle-particle-γ coincidence techniques we were able to identify final products and states populated in the one- and two-neutron reactions.The dependence of the transfer probabilities on the distance of closest approach is discussed in terms of effective penetration factors. The results seem to indicate the importance in two-neutron transfer of intermediate states with ? 6 MeV of excitation energy. The effect of excitation energy on the enhancement of the two-neutron transfer is discussed. A qualitative interpretation of the spin dependence of the one-neutron γ-ray yields in terms of the spatial localization of the wave functions involved is given.     

Semiclassical theory of a nuclear Josephson effect in reactions between heavy ions

A semiclassical treatment of heavy ion reactions below the Coulomb barrier is given with special emphasis on a pair transfer between superconducting nuclei. The cross section is explicitly given within a schematic model. An enhhancement of the pair transfer due to superconductivity is found which, in favorable cases, may amount to a factor of 100 to 900 in the cross section.     

Transfer reactions between heavy ions

The theory of transfer reactions between heavy ions is formulated in a semi-classical approximation in terms of coupled differential equations in time which include the effects of excitation in entrance and exit channel and the non-orthogonality of the wave functions. The main effects of the exchange of energy, mass and charge are taken into account.     

Regularized quasi-classical approximation for Coulomb wave functions applied to describe nuclear reactions with heavy ions

Everywhere differentiable quasi-classical approximations in elementary functions are obtained for Coulomb wave functions. Their use for formulating boundary conditions for problems of scattering and fusion of heavy-ion nuclei is demonstrated.     

Direct two-nucleon transfer reactions and their interpretation in terms of the nuclear shell model

The distorted wave Born approximation (DWBA) treatment for direct two-nucleon transfer reactions has been derived following the formalism of Satchler, spin-orbit coupling being included in the distorted wave expansions. Methods for the evaluation of the integrals involved are described, and in particular a discussion is given of two different ‘zero-range’ approximations, one involving an assumption that the heaviest projectile has zero extent, the other assuming the interaction to have zero range. These two approaches are compared. The main emphasis, however, is directed towards extracting from experimental two-nucleon transfer reactions, reliable spectroscopic information, and to this end, shell model expressions for the spectroscopic amplitude have been derived, together with closed formulae for two-particle coefficients of fractional parentage (cfp). The JT representation is used principally throughout, but expressions are given for the LSJT representation as well as for the separate treatment of neutrons and protons. Examples illustrating (i) excitation of analogue states; (ii) comparison of (p, t) and (p, ³He) reactions to mirror states; and (iii) coherence effects between different shell model orbitals, indicate the usefulness of two-nucleon transfer reactions in determining nuclear structure information such as spins, parities, two-body matrix elements, etc. As a further aid to the analysis of experimental data, numerical tables of two-particle cfp's in the isospin formalism for j = 1/2, 3/2 and 5/2 are given for states of low seniority, and in the non-isospin formalism for j = 3/2, 5/2, 7/2 and 9/2 shells.     

Structures and reactions of biomolecular ions produced with electrospray ionization

Photo-induced reaction of [Fe(III)-protoporphyrin]⁺ (hemin⁺) ions solvated with dimethylsulfoxide (DMSO) is investigated by using a tandem mass spectrometer with electrospray ionization. We measure the photodissociation yields of mass-selected hemin⁺(DMSO)_n clusters for n = 0-3. The mass spectra of the fragment ions show the -cleavage of carboxymethyl groups in addition to the evaporation of solvent molecules. Yield of the -cleavage reaction is found to depend strongly on the excitation energy and the number of solvent molecules. We also examine photo-induced reactions of multiply-charged cytochrome c ions, (M + nH)^{n +} ( n = 9-17). Photoionization is found to be the dominant process for the lower charged states ( n = 9-12) and its yield decreases rapidly with increasing the charge. The photoionization is ascribed to the emission of electron by multiphoton excitation of heme under the influence of Coulomb attractive potential arising from the charges in the polypeptide chain. Model calculations of the Coulomb potential suggest that the structure of the polypeptide chain is completely elongated.     

Two-nucleon transfer reactions between heavy ions

DWBA formulation of the two-nucleon transfer reactions between heavy ions is presented, neglecting the recoil effect. The perturbation is assumed to act between the core and each of the transferred pair. When we approximate the interaction so as to act between the core and the c. m. of the pair, we can extend the method commonly used in analysing (t, p) and (p, t) reactions. Integrals appearing in the DWBA form factor are evaluated exactly. Calculations are compared with the experimental data in the case of the²⁶Mg(¹⁸O,¹⁶O)²⁸Mg reaction.     

Momentum distributions in fragmentation reactions with relativistic heavy ions

The momentum distribution (or angular distribution) in inelastic heavy ion reactions is calculated by using a two-step model (“abrasion” and “ablation”). First, all nucleons in the volume element where projectile and target overlap spatially during the collision are sheared away. The remaining prefragment (the projectile minus the sheared off nucleons) has a recoil momentum proportional to the Fermi momentum. The prefragment is left in an excited state and emits nucleons, the recoil momentum given to the final fragment is proportional to the nuclear temperature. This two-step model reproduces the overall trend and the isotopic dependence for the widths of the experimental momentum distributions. Contrary to previous theoretical studies we find that surface and friction phenomena lead to an anisotropy: The momentum distributions in transverse direction are always broader than in the longitudinal direction by about 5 to 10%.     

Momentum distributions in fragmentation reactions with relativistic heavy ions

The momentum distribution (or angular distribution) in inelastic heavy ion reactions is calculated by using a two-step model (abrasion and ablation). First, all nucleons in the volume element where projectile and target overlap spatially during the collision are sheared away. The remaining prefragment (the projectile minus the sheared off nucleons) has a recoil momentum proportional to the Fermi momentum. The prefragment is left in an excited state and emits nucleons, the recoil momentum given to the final fragment is proportional to the nuclear temperature. This two-step model reproduces the overall trend and the isotopic dependence for the widths of the experimental momentum distributions. Contrary to previous theoretical studies we find that surface and friction phenomena lead to an anisotropy: The momentum distributions in transverse direction are always broader than in the longitudinal direction by about 5 to 10%.     

Production cross sections for the heaviest nuclei in complete fusion reactions induced by heavy ions

Production of the heaviest nuclei in complete fusion reactions induced by heavy ions has been considered in a systematic way in the framework of the conventional barrier passing model coupled with the statistical model. Available data on excitation functions for fission and production of evaporation residues (ER) in very asymmetric combinations induced by ions lighter than Ne on actinide target nuclei are described rather well in the framework of these models. The data allow one to adjust model parameters and to reveal the quasi-fission effect caused by the interaction with deformed target nuclei, which is manifested in the suppression of the ER production at sub-barrier energies. For reactions induced by Mg and heavier projectiles, quasi-fission is starting to suppress fusion (ER production) at energies above the Coulomb barrier. One has to introduce empirically the quantity of the fusion probability P_fus to reproduce the ER excitation functions in the framework of the conventional approach. The exponential dependence of P_fus on the combined fissility parameter (a similar parameter that was introduced for the extra-push energy scaling) was found in search for scaling for the P_fus values resulting from the data analysis.     

Effect of shell structure in the fusion reactions

The fusion reactions are studied in the central collisions ⁸²Se+ + ¹³⁴Ba and ⁸²Se+ + ¹³⁸Ba by the improved isospin-dependent quantum molecular-dynamics model, where the nucleus ¹³⁸Ba has a closed neutron shell N = 82 . Comparing the shell correction energies and fusion probabilities of these two reactions with the ones of other asymmetric or more symmetric reaction systems that form the same compound nuclei, we find the dependence of the fusion reaction on the nuclear shell structure of the colliding nuclei. The experimental data of the fusion probabilities are described well by the present model. The result suggests that the neutron shell closure N = 82 promotes fusion.