Semiclassical theory of molecular collisions: Real and complex-valued classical trajectories for collinear atom Morse oscillator collisions

Real and complex-valued classical trajectories have been calculated for the collinear collision of an atom with a Morse oscillator. They are used in three semiclassical approximations for the transition probability: a Bessel uniform approximation, an Airy uniform approximation and a primitive semiclassical approximation. Comparison with exact quantum results shows that the Bessel uniform approximation is accurate even for near elastic collisions where the Airy and primitive approximations break down. The Airy and Bessel approximations agree quite closely for inelastic collisions however. The primitive semiclassical approximation is less accurate than either the Airy or Bessel approximation.     

Correlation between the fragmentation modes and light charged particles emission in heavy ion collisions

The correlation between the shape of rapidity distribution of the yield of light charged particles and the fragmentation modes in semi-peripheral collisions for70Zn+70Zn,64Zn+64Zn and64Ni+64Ni at the beam energy of 35 Me V/nucleon is investigated based on Im QMD05 code. Our studies show there is an interplay between the binary, ternary and multi-fragmentation break-up modes.The binary and ternary break-up modes more prefer to emit light charged particles at middle rapidity and give larger values of Rmid yieldcompared with the multi-fragmentation break-up mode does. The reduced rapidity distribution for the normalized yields of p, d, t,3He,4He and6 He and the corresponding values of Rmid yieldcan be used to estimate the probability of multi-fragmentation break-up modes. By comparing to experimental data, our results illustrate that 40% of the collisions events belong to the multifragmentation break-up mode for the reactions we studied.     

Semiclassical theory of atom/solid surface collisions; Solution of steele's model

Steele's model of elastic gas/surface scattering is solved semiclassically. The model is reasonably successful in reproducing the diffractive data of Smith, O'Keefe, Saltsburg and Palmer.     

Dynamics of capture and fusion in heavy ion collisions

The effect of entrance channel on decrease of the complete fusion cross sections and on the yield of reaction products are associated with the quasifission which depends on the mass asymmetry and shell structure of colliding nuclei. In reactions of massive projectile and target nuclei, the competition between complete fusion and quasifission appears at the stage of compound nucleus formation, in addition to the increase of the fission probability. It is shown that the yield of quasifission products may be symmetric or asymmetric in dependence on peculiarities of shell structure of reaction fragments. Marima of mass or charge distributions are connected with the peculiarities of shell structure of reaction fragments.     

Electron-positron pair production by collisions of non-relativistic charged particles

The cross-section for (e ⁺,e ^?)-pair production in collisions of non-relativistic charged particles has been calculated to lowest order in the fine structure constant and leading power of the relative velocity of the colliding particles. Thus the deflection of colliding particles is included in one-photon-exchange approximation, while the Coulomb distortion of the (e ⁺,e ^?)-pair is omitted. We have laid particular emphasis on current conservation. The previously neglected contribution of the spatial part of the current turns out to be dominant.     

Inelastic scattering of charged particles by a statistical atom

The angular and energy distribution of secondary electrons ejected in collisions of heavy charged particles has been calculated in the binary encounter approximation using the statistical Thomas-Fermi method. Comparisons are made with reported experimental results.     

Mechanisms and kinetics of exotic atom formation in hydrogen and helium

The current status of the theory of exotic atom formation in hydrogen and helium is briefly reviewed. The problems of the two-step mechanism of mu-atom formation in molecular hydrogen and of primary populations of hadronic metastable states in helium are discussed.     

Comprehensive decay law for emission of charged particles and exotic cluster radioactivity

A general decay formula for the emission of charged particles from metastable nuclei is developed based on the basic phenomenon of resonances occurring in quantum scattering process under Coulomb-nuclear potential. It relates the half-lives of radioactive decays with the Q values of the outgoing elements with masses and charges of the nuclei involved in the decay. The relation is found to be a generalization of the Geiger–Nuttall law in α radioactivity and explains well all the known emissions of charged particles including clusters, alpha and proton.     

Emission of direct particles in heavy ions collisions

This paper presents a theoretical model for the emission of fast light particles derived from the PEP (Promptly Emitted Particles) model. This model is extended to the emission of fast alpha particles. With some restrictions, analytical formulae are derived for the production rate and the mean angular momentum associated with fast particles. Most of the qualitative features predicted by the analytical formulae are confirmed by the numerical results obtained from a more realistic calculation where the trajectories of the particles are followed during the whole collision. It is argued that PEP alpha particles emitted preferentially in low angular momentum collisions, could represent the major part of the fast alpha particles observed in incomplete fusion reactions.     

Semiclassical description of multipair transfer processes in heavy ion collisions with superfluid systems

Pair transfer processes involving a superfluid system are studied in terms of phase space distributions constructed in a product representation which blends both ordinary- and gauge-space degrees of freedom. The time evolution of these distributions is followed by solving a collection of classical equations of motion, the quantal fluctuations being accounted for by the sampling of all possible initial orientations of the (undetermined) intrinsic system in gauge space. The excitation of the pairing rotational degree of freedom — corresponding to a variation in the number of particles — is induced by a gauge-deformed ion-ion potential, as befits the superfluid character of the target. Different orientations leading to the same final mass transfer may produce (in the case of large pairing deformation) interference effects in the final population of the members of the pairing rotational band. We also discuss how this approach can be used to describe the effect of pair transfer modes on sub-barrier fusion processes.     

Multiplicity distribution of strange particles in heavy ion collisions

We study the multiplicity distribution of strange particles in a hadronic gas constrained by exact strangeness conservation. The multiplicity distribution obtained is narrower than both the Poisson and negative binomial distributions. Correlations among strange particles are also discussed. The results presented might be useful in determining the thermodynamic parameters (volume, temperature and baryon density) of a hadronic gas possibly formed in relativistic nuclear collisions.     

Pair production of charged Higgs particles through two-photon process inpp collisions

In order to obtain model-independent estimates for the production of charged Higgs particles atpp colliders, in particular at the SSC, we investigate their pair production through electromagnetic processes. It turns out that the dominant contribution comes from photon-photon annihilation. For a Higgs mass of a few hundred GeV the two-photon process is thus an appropriate candidate to look for charged Higgs particles.     

A possible mechanism for acceleration of heavy charged particles

A law of motion for a charged particle in a variable magnetic field is found. It is shown that the parametric effect of the magnetic field can be used for acceleration of heavy charged particles.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 30–33, February, 1972.     

On the formation mechanism of the exotic atom of light nuclei

Starting from the supposition that an exotic system constituted of a hadron, a nucleus, and an electron, which interact with each other by Coulomb pair forces, forms a quantum-mechanical system, the interaction potential between the hadron and the nucleus in the exotic system is analytically derived. It is shown that the structure of the additional potential depends on the three-body system charge structure, as well as on the isotopic one. It is precisely this asymmetry both in the electric charges and in the masses of the constituent particles that is responsible for the long lifetime of the exotic systems.     

Polarization bremsstrahlung of heavy charged particles in a polycrystal

Polarization bremsstrahlung (PBS) of a fast ion scattered in a polycrystalline medium is calculated and analyzed with allowance for the contributions from the coherent and incoherent channels of the process. It is shown that scattering of a projectile from the crystal lattice of the target is responsible for typical features of the PBS spectrum. For example, PBS is suppressed (as compared to radiation emitted by a single atom) in the low-frequency part of the spectrum, where coherent PBS dominates. In the intermediate spectral region, a step structure is formed as a result of “elimination” of the contribution from the reciprocal lattice vector with a preset magnitude to the coherent component of the process. Finally, incoherent PBS dominates in the high-frequency part of the spectrum and the process occurs as in the case of a single atom. These spectral peculiarities of PBS are determined by the structure of the target and depend on the velocity of the projectile and the emission angle, and can be observed in experiments dealing with radiation emitted by fast charged particles in thin polycrystalline films.     

Light particles emission and incomplete fusion in heavy ion collisions

Light particles emission in heavy-ion collisions is considered in terms of direct-reaction mechanisms. The extreme high-energy part of the inclusive spectrum of light particles is shown to arise essentially from the stripping mechanism while the usually observed maximum of the spectrum is formed by a superposition of several mechanisms. The significance is emphasized of the heavy-fragment stripping in the synthesis of the exotic superheavy nuclei.