On the possibility of detecting superheavy quasimolecules

The formation of superheavy electronic quasimolecules leads to measurable deviations from the Rutherford cross section in heavy ion collisions. For the system ²³⁸₉₂U-²³⁵₉₂U with E_c.m. = 800 MeV we find an average correction of 1.5% for the scattering cross section in forward directions. Additional background contributions like electronic shielding of the nucleus, vacuum polarization, nuclear Coulomb excitation and static deformations of the nuclei are taken into account.     

Polarization forces in elastic nuclear coulomb scattering

The polarization potential is determined for the adiabatic sub-Coulomb scattering of two nuclei. No collective coordinates are used. The relevant nuclear polarizabilities are evaluated by means of sum rules. The departure from the pure Rutherford scattering law is calculated for various nuclei. For adiabatic heavy-ion collision the differential cross section is found to be reduced below the Coulomb scattering by one percent at backward angles.     

Effects of vacuum polarization and of proton polarizability in the Lamb shift of muonic hydrogen

The contributions to the Lamb shift in muonic hydrogen from hadronic vacuum polarization and from the correction associated with electron vacuum polarization and with the proton polarizability are calculated by using present-day experimental data on the cross section for e ⁺ e ⁻ annihilation into hadrons and on structure functions for deep-inelastic ep scattering. The numerical value of the total contribution to the (2P-2S) shift in muonic hydrogen is found to be 10.95 μeV. __________ Translated from Yadernaya Fizika, Vol. 64, No. 7, 2001, pp. 1358–1363. Original Russian Text Copyright ? 2001 by Martynenko, Faustov.     

Estimation of nuclear effects in heavy-ion elastic scattering

The elastic scattering of heavy ions interacting by a central complex nuclear potential is calculated in first-order perturbation theory. The differential cross section can be expressed by simple analytical formulas for a Yukawa-type potential as well as for a Woods-Saxon potential. This leads to a very easy estimate of the nuclear effects, if the energy of the projectile is in the neighbourhood of the Coulomb barrier. It is shown that the derived expressions are quite accurate compared to a full numerical solution of the Schrödinger equation, as long as the elastic cross section deviates less than about 50 % from the pure Rutherford cross section.     

Hydrogen analysis in diamond like carbon by elastic recoil detection

Among the available surface analytic instruments, elastic recoil detection (ERD) is known as a reliable method for hydrogen analysis. Since conventional fluence determination i.e. beam current integration is incredible at a large tilt angle, ion fluence is determined by the scattering spectrum that is simultaneously measured with recoil spectrum. However scattering cross sections deviate Rutherford values in the ERD energy of 1–3 MeV. Carbon scattering cross section is different from Rutherford value for higher beam energies over 1.8 MeV. As a result hydrogen content is exaggerated when fluence is determined by carbon matrix because of fluence underestimation due to lower value of scattering cross section than Rutherford’s. Therefore in order to quantify hydrogen in diamond like carbon (DLC) incident beam energy lower than 1.6 MeV should be used where carbon scattering cross sections are well agreed with Rutherford’s.     

On the Molière theory of multiple scattering of charged particles (1947–1948) and its critique in subsequent years

Several “misconceptions” regarding the theory of multiple scattering of fast charged particles in matter developed by Molière in 1947–1948 and its application in the analysis of experimental results are discussed. It is shown that the critics of this theory misinterpreted the Molière method for determining the cross section of particle scattering by atoms with the screening of their nuclear fields by electron shells described by the Thomas-Fermi statistical model. If the original Molière method is applied consistently, the obtained scattering cross section generally agrees with the results of later classical calculations carried out by Lindhard and his collaborators and other authors.     

放射性束弹性散射实验中的一种位置校准方法

在弹性散射实验中,探测器的位置校准是非常重要的。结合兰州放射性束流线(RIBLL)的实际情况,以低能轻炮弹在重靶上的弹性散射截面在前角区为卢瑟福散射的事实为依据,发展了一种简单而有效的位置校准方法。通过蒙特卡洛模拟来检测弹性散射角分布与不同方向上位置未校准时的依赖关系。该方法成功地应用在~7Be与重靶的弹性散射实验中,得到了正确的微分截面角分布。     

On polarized neutron scattering from magnetized samples and the spin echo effect

The scattering of polarized neutrons from magnetized samples is considered in the general case of arbitrary orientation between the incident polarization, the magnetic field of the sample and the polarization of the scattered neutrons. Including both nuclear and magnetic scattering the general expressions for the cross section and the polarization of the scattered beam are derived in the case of small-angle scattering. It is shown that under certain experimental conditions an effect analogous to the Neutron Spin Echo should be observed, which could be used to measure small energy transfers. The contribution arising from the scattering by spin waves is examined in detail.     

Influence of vacuum energy on scattering

We deal with photon-electron scattering which occurs between two uncharged conducting parallel plates moving away from each other at a constant velocity. The electromagnetic vacuum field between two plates is defined by the configuration of space and also interacts with the electrons. We show the relevant operators for both the electron and photon fields and the computation of the corresponding Feynman propagator,S-matrix, and scattering cross section, taking into account the influence of the changeable vacuum field. Correction terms in the computedS-matrix and scattering cross section manifest the influence of the changeable vacuum field. We analyze an example for low-energy scattering of the influence of the changeable vacuum field upon the scattering cross section.     

Role of a fullerene shell upon stuffed atom polarization potential

We have demonstrated that the polarization of the fullerene shell considerably alters the polarization potential of an atom, stuffed inside a fullerene. This essentially affects the electron elastic scattering phases as well as corresponding cross sections. We illustrate the general trend by particular examples of electron scattering upon endohedrals Ne@C₆₀ and Ar@C₆₀. To obtain the presented results, we have suggested a simplified approach that permits to incorporate the effect of fullerenes polarizability into the Ne@C₆₀ and Ar@C₆₀ polarization potential. By applying this approach, we obtained numeric results that show strong variations in shape and magnitudes of scattering phases and cross sections due to effect of fullerene polarization upon the endohedral polarization potential.     

Corrections to the Thomson cross section caused by relativistic effects and by the presence of the drift velocity of a classical charged particle in the field of a monochromatic plane wave

An approach to the solution of the relativistic problem of the motion of a classical charged particle in the field of a monochromatic plane wave with an arbitrary polarization (linear, circular, or elliptic) is proposed. It is based on the analysis of the 4-vector equation of motion of the charged particle together with the 4-vector and tensor equations for the components of the electromagnetic field tensor of a monochromatic plane wave. This approach provides analytical expressions for the time-averaged square of the 4-acceleration of the charge, as well as for the averaged values of any quantities periodic in the time of the reference frame. Expressions for the integral power of scattered radiation, which is proportional to the time-averaged square of the 4-acceleration of the charge, and for the integral scattering cross section, which is the ratio of the power of scattered radiation to the intensity of incident radiation, are obtained for an arbitrary inertial reference frame. An expression for the scattering cross section, which coincides with the known results at the circular and linear polarizations of the incident waves and describes the case of elliptic polarization of the incident wave, is obtained for the reference frame where the charged particle is on average at rest. An expression for the scattering cross section including relativistic effects and the nonzero drift velocity of a particle in this system is obtained for the laboratory reference frame, where the initial velocity of the charged particle is zero. In the case of the circular polarization of the incident wave, the scattering cross section in the laboratory frame is equal to the Thompson cross section.     

An approximate phase shift formula applied to elastic scattering of electrons by mercury atoms

A recently published, approximate formula for the scattering phase shifts of electrons in a screened Coulomb field of the Hulthén type is investigated in more detail and shown to be applicable to the fast computation of the elastic differential scattering cross section and the Mott polarization and other functions describing polarization phenomena. Although these phase shifts show a much less pathological behaviour than the pure Coulomb phases, the partial wave expansion of the scattering amplitudes still has a weak divergence in the forward direction corresponding to a singularity which is, however, much less severe than the singularity of the Rutherford scattering amplitude. The examples chosen for demonstration in tabular form are concerned with 46 keV or 204 keV electrons elastically scattered by mercury atoms, a case which has received attention in other publications. The tables include exact values for a three-term Yukawa potential which is to represent, in analytical form, the realistic potential, exact values for a suitable Hulthén potential, and values computed by means of the approximate phase shift formula. As to the choice of the screening exponent of the Hulthén potential which enters the approximate phase shift formula, it is found that this exponent should be adjusted so as to approximate the realistic potential uniformly. The value so obtained is smaller, in the case of the mercury atoms here considered by about 11%, than the value which would be needed for fitting the realistic potential shift, due to screening, at the origin.     

Sub-barrier interaction between deuterons and 58, 62Ni nuclei

The interaction between deuterons and ^{58, 62}Ni nuclei at energies of E _d = 3.5, 4.5 and 5.16 MeV is investigated. The discrepancy between measured scattering elastic cross section and the Rutherford ones is higher than the value calculated theoretically by considering deuterons polarization and Coulomb breakup. Analysis of measured cross section of ^{58, 62}Ni(d, p) reaction and the results of calculation of Coulomb breakup cross section integrated over neutron emission angles shows that that the dominant mechanism of proton formation is the reaction of neutron transfer to the target nucleus.     

Heavy-flavor contribution to Bhabha scattering

We evaluate the last missing piece of the two-loop QED corrections to the high-energy electron-positron scattering cross section originating from the vacuum polarization by heavy fermions. The calculation is performed within a new approach applicable to a wide class of perturbative problems with mass hierarchy. The result is crucial for the high-precision physics program at existing and future e(+) e(-) colliders.     

On the detection of nuclear spin waves by inelastic neutron scattering

The possibility of measuring nuclear spin waves (NSW) by inelastic neutron scattering is discussed. The differential cross section and scattered state polarization for the scattering of thermal neutrons from systems described by the Suhl-Nakamura Hamiltonian are developed in the Van Hove correlation function formalism; the relevant correlation functions for the Suhl-Nakamura system are computed. The implications of these calculations for the feasibility of detecting nuclear spin wave modes in neutron scattering experiments are discussed.     

Breakdown of normal threshold dispersion relation for the vacuum polarization

Stating a concrete example, it is shown that the vacuum polarization develops anomalous singularities. The analytic structure of the vacuum polarization in these circumstances is discussed in some detail. It appears that its large q² behaviour is not linked anymore to the asymptotic form of the e⁺e^? total cross section. Since it is the large q² behaviour of the vacuum polarization which solely can be calculated in asymptotically free gauge theories (giving in leading order the naive quark model result), this is a warning to using the naive quark model result for the e⁺e^? total cross section as well in fitting the data.     

Positrons from supercritical fields of giant nuclear systems

During collisions of heavy nuclei with a combined chargeZ?160 the electronic 1s-state is deeply bound due to the strong Coulomb field, forZ≧173 it even enters as a resonance the lower continuum of the Dirac-Hamiltonian. In pure Rutherford scattering no qualitative indication for the filling of a dynamically createdK-hole by the spontaneous positron creation process is predicted, but the study of heavy-ion collisions with nuclear time delay due to the attractive nuclear force promises clear signatures for the decay of the vacuum. Emphasis is laid also on the quantitative influence of the electron-electron interaction and ofE0-transitions in the giant nuclear system on positron emission, the latter treated in a classical approximation. We compare our results with recent experimental data of two different groups at GSI, Darmstadt.     

Relativistic corrections to small-angle scattering of spin-1 nuclei

The differential cross section for the elastic small-angle scattering of nonidentical spin-1 nuclei at intermediate and low energies is obtained in a general form on the basis of the QED formalism. Deviations from Rutherford scattering and a complicated dependence of this cross section on the energies and masses of such nuclei in this energy region are revealed.