Measurement of total M shell photoionization cross sections for Au,Pb, Th and U in the energy region 6–12 keV

The total M shell relative photoionization cross-sections for Au, Pb, Th and U have been measured in the energy region 6–12 keV. External conversion K X-rays of suitable elements has been employed as incident photons to photo ionize the total M shell of elements under investigation. The method provides relative cross-sections therefore does not make use of theoretically calculated average M shell fluorescence yields which involve uncertainties of the order of 20%. No evidence of deviation from calculated values of cross-sections have been observed within experimental errors for all incident photon energies.     

Hadronic Interactions in the Energy Region of Future Hadron Colliders,Dual Topological Unitarization of Hard and Soft Hadronic Cross Sections

The dual topological unitarization of hard and soft hadronic collisions is formulated as a Monte Carlo event generator for events containing both the soft (low p ?) and hard (jets, minijets) component of hadron production. The parameters of the model are determined from fits to the energy dependence of the total and inelastic hadron cross-sections and from the predictions of the QCD-parton model for the perturbative hard constituent scattering cross sections. The predictions of the model for TeV colliders are presented. Interesting changes of the produced multiparticle system are found when selecting classes of events with and without hard jets or minijets.     

Measurement and interpretation of fermion-pair production at LEP energies from 130 to 172 GeV

The data collected with the DELPHI detector at centre-of-mass energies between 130 and 172 GeV, during LEP operation in 1995 and 1996, have been used to determine the hadronic and leptonic cross-sections and leptonic forward–backward asymmetries. In addition, the cross-section ratios and forward–backward asymmetries for flavour-tagged samples of light (uds), c and b quarks have been measured. No significant deviations from the Standard Model expectations are found. The results are interpreted by performing S-matrix fits to these data and to the data collected previously at the energies near the resonance peak (88-93 GeV). The results are also interpreted in terms of physics beyond the Standard Model: contact interactions, R-parity violating SUSY particle exchange and of possible Z bosons. Received: 9 February 1999 / Published online: 14 October 1999     

Photo-protons from beryllium irradiated with intermediate energy bremsstrahlung

Data on the differential cross-sections for the emission of photo-protons from beryllium irradiated with bremsstrahlung of various end-point energies up to a maximum of 600 MeV are presented and discussed. Particular attention has been paid to the photon energy-region around 150 MeV, where a dip in the total cross-sections for photon absorption has been reported. No evidence of anomalous structure is observed. The data are compared with the predictions of the intra-nuclear cascade model PICA. Good fits can be obtained with a value of 7.2±1.0 for the quasi-deuteron constant.     

Response of bubbles to diagnostic ultrasound: a unifying theoretical approach

The scattering of ultrasound from bubbles of m radius, such as used in contrast enhancers for ultrasound diagnostics, is studied. We show that sound scattering and “active” emission of sound from oscillating bubbles are not contradictory, but are just two different aspects derived from the same physics. Treating the bubble as a nonlinear oscillator, we arrive at general formulas for scattering and absorption cross-sections. We show that several well-known formulas are recovered in the linear limit of this ansatz. In the case of strongly nonlinear oscillations, however, the cross-sections can be larger than those for linear response by several orders of magnitude. The major part of the incident sound energy is then converted into emitted sound, unlike what happens in the linear case, where the absorption cross-sections exceed the scattering cross-sections. Received: 26 February 1998 / Revised: 13 March 1998 / Accepted: 15 March 1998     

On the extensions of mass-zero representations of the poincaré group

It is shown that the extension of two representations of the Poincaré group with mass zero and definite helicities which occur in theoretical physics (two component neutrino) do not fall in to the framework of Hilbert extension theory. To get extensions useful in physics, the representation spaces are restricted according to a criterion of simplicity. Then it is proved that there exists a non-trivial extension only if the difference of the helicities is one in modulus, or if the helicities are both equal to zero. As desired, the two component neutrino fits well into this scheme.     

Relativistic quantum mechanic calculation of photoionization cross-section of hydrogenic and non-hydrogenic states using analytical potentials

Photoionization process is a subject of special importance in many areas of physics. Numerical methods must be used in order to obtain photoionization cross-sections for non-hydrogenic levels. The atomic data required to calculate them is huge so self-consistent calculations increase computing time considerably. Analytical potentials are a useful alternative because they avoid the iterative procedures typical in self-consistent models. In this work, we present a relativistic quantum calculation of photoionization cross-sections for isolated ions based on an analytical potential to obtain the required atomic data, which is valid both for hydrogenic and non-hydrogenic ions. Comparisons between our results and others obtained using either widely used analytical expressions for the cross-sections or more sophisticated calculations are done.     

Cross-sections and leptonic forward-backward asymmetries from the Z^0 running of LEP

During 1993 and 1995 LEP was run at 3 energies near the Z peak in order to give improved measurements of the mass and width of the resonance. During 1994, LEP operated only at the Z peak. In total DELPHI accumulated data corresponding to an integrated luminosity of approximately 116 pb. Analyses of the hadronic cross-sections and of the cross-sections and forward-backward asymmetries in the leptonic channels used the most precise evaluations of the LEP energies. In the dimuon channel, events with a photon radiated from the initial state have been used to probe the cross-sections and asymmetries down to PETRA energies. Model independent fits to all DELPHI lineshape and asymmetry data from 1990 to 1995 have been carried out giving values of the resonance parameters: These values are significantly more precise than those previously published. The results are interpreted in terms of the Standard Model. Received: 4 February 2000 / Revised version: 7 March 2000 / Published online: 8 June 2000     

Simultaneous multiphoton ionization by two radiation fields. Effects of the statistical properties of the radiation

Summary We report on calculations of differential and total ionization cross-sections of hydrogen atoms irradiated by two radiation fields with different properties. One of the fields is of low intensity and relatively high frequency, the other is of low frequency and high intensity. In particular, we show that the inclusion of the multimode structure of the low-frequency laser field modifies considerably the shape of the angular distribution of the photoelectrons and the rates of ionization into the different channels characterized by the number of low-frequency photons exchanged. Further, we find that the average energy exchanged between the photoelectrons and the low-frequency radiation field is independent of the statistical properties of the low-frequency laser field.     

Free electron-positron pair production in collisions of Au (10.8 GeV/u) with Cu , Ag and Au

Total and differential cross-sections for the production of free electron-positron pairs are calculated for the reactions Au⁷⁹⁺ (10.8 GeV/u) on Cu²⁹⁺, Ag⁴⁷⁺ and Au⁷⁹⁺. The methods used are the semiclassical approach and the solution of the time-dependent Dirac equation by a coupled channel method with free wavepakets describing the created fermions. The obtained total cross-sections are in good agreement with the experimental data. The differential cross-sections give informations about the correlation between the electron and positron. Received 21 December 1999 and Received in final form 6 March 2000     

Prompt leptons in cosmic rays

Summary Energy spectra and zenith-angle distributions of cosmic-ray muons, neutrinos and antineutrinos of prompt generation for energy interval (1÷10⁶) TeV are calculated. For calculations of differential cross-sections of D^±, D⁰, ⁰ and Λ_c production inNN and πN interactions the recombination quark-parton model (RQPM) is used. Accounting of nuclear effects is done by using the additive quark model and the optical model of nucleus. Detailed comparison of results obtained in RQPM with corresponding predictions of quark-gluon string model (MQGS) is carried out. Dynamics of semi-leptonic D- and Λ_c and energy losses of muons in the atmosphere are taken into account. Calculations of hadronic cascades in the atmosphere are done with accounting of growth with energy of total inelastic hadron-nucleus cross-sections, steepening of primary cosmic-ray spectrum and processes of pion regeneration. The comparison of our calculations with experimental data and with calculations of other authors is given.     

Helium atom in the monochromatic electromagnetic field

We apply a non-perturbative procedure for the calculation of the total photoionization cross-section of two-electron atomic systems. The procedure is based on the Floquet-Fourier representation of the time-dependent Schr?dinger equation. With the use of the Hylleraas-type basis functions, the total photoionization cross-sections obtained are within the accuracy of a fraction of a percent, which, we believe, is the most accurate estimate for the cross-sections available. The total photoionization cross-sections for neutral helium deviate notably from the benchmark experimental data [J.A.R. Samson et al., J. Phys. B 27, 887 (1994)].     

Empirical relation and establishment of shell effects in (<Emphasis Type="Italic">n</Emphasis>, 2<Emphasis Type="Italic">n</Emphasis>) reaction cross-sections at 14 MeV

The experimental data for (n, 2n) reaction cross-sections around 14 MeV neutron energy have been collected from the literature and analysed for the isotopes having 1 ≤ Z ≤ 82. The empirical relations for the reaction cross-sections have been obtained, which show fairly good fits with the experimental values. The shell effects have been established at magic nucleon numbers for (n, 2n) reaction cross-sections around 14 MeV neutron energy. The odd-even effects have also been observed as the cross-sections for odd-mass nuclei are higher than their neighbouring even-even nuclei.      

Direkte Messung des (n, 2n)-Wirkungsquerschnitts von Niob 93

Using the watertank-method for natural niobium σ _n ,2 _n =1.35±0.25 barn was found. This value agrees with statistical model calculations and fits the systematics of the (n, 2n) cross-sections.     

Development of thermal reactor lattice physics methods

This paper describes the reactor physics methods developed for thermal reactor lattices in India. The formulation of the models introduced is based on energy-dependent integral neutron transport theory. More emphasis was put on the development of lattice cell calculational methods which indeed form the basis of physics design of nuclear reactors. The physical formulation and the cross-sections used were subjected to comprehensive validation tests through analyses of experimental information. The comparison of computed and measured parameters have amply brought out the soundness of the physical formalism and the cross-sections used in our calculational procedures.     

Double electron capture cross-sections by protons in collisions with He

Double electron capture (DEC) by protons from He was studied in collisions at energies in the keV regime, theoretically and experimentally. Theoretical cross-sections were calculated using the electron nuclear dynamic approach and a binomial distribution method in the energy range 1–100 keV. Experimental cross-sections were measured by means of the grow-rate method in the energy range of 4–10 keV. The cross-sections measured are consistent with those of the previous data at the high energies of the measured interval and show a different trend for the low energy. This behavior is consistent with those of other DEC cross-sections measured by protons from He-like targets. With the two collision models, it is proven that the reference data for this system are consistent only with the assumption of uncorrelated electrons and with independent target-projectile nuclei dynamics.     

Fixed poles, t-channel unitarity,and rising cross-sections

If the Pomeron is a fixed pole, it must be “shielded” from t-channel unitarity by a special type of cut. We show how to obtain such a cut. There are no arbitrary parameters between the cut and the pole, and definite predictions of rising cross-sections, shrinkage and (ReF)/(ImF) result. These are found to be in good agreements with high energy data. Previously we obtained a very similar cut (with similar fits), but we no longer require use of an exotic trajectory.     

Effect of Polarization Potential on Proton–Sodium Inelastic Scattering

Inelastic collisions of protons with sodium atoms are treated for the first time within the framework of the coupled static and frozen core approximations. The method is used for calculating partial and total cross-sections with the assumption that only two channels (elastic and hydrogen formation in 2s-state) are open. The calculations are carried out, in each case, for seven values of the total angular momentum ?(0?≤???≤?6). In the second channel, the effect of “switching on” the polarization potential of hydrogen (in 2s-state) on the coupled static cross-sections is investigated. Although the resulting hydrogen (in 2s-state) formation cross-sections are smaller than the elastic ones, their large values should draw the attention of experimental and theoretical physicists to the field of proton–alkali atom collisions. Our results for the total hydrogen (2s-state) formation cross-sections and those determined by previous authors are in reasonable agreement.     

New results for the production of Λ and Σhyperons in antineutrino scattering from protons

We obtain total and differential cross-sections for the strangeness changing charged current reactions ˉ + p → Λ + L ⁺ and ˉ + p → Σ⁰ + L ⁺ , where L is a charged lepton, either an electron, muon or tau. We do this by making use of the standard dipole form factors normally used and of the new form factors recently obtained from recoil proton measurements in electron-proton electromagnetic scattering. We also obtain the contributions of the individual form factors to the total and differential cross-sections for both sets of form factors. We find that the differential and total cross-sections for Λ production change only slightly between the two sets of form factors but that the differential and total cross-sections change substantially for Σ⁰ production. We discuss the possibility of distinguishing between the two cases for the experiments planned by the MINERν A Collaboration.