A study of the reactions γp→ωp and γp→ωp and γp→ωΔ+

The differential and total corss sections and the decay density matrix elements have been measured for the reactions, γp→ωp and γp→ωΔ⁺ (1232) in the photon energy range 2.8 to 4.8 GeV. The total cross sections for ωΔ⁺ (1232) photo-production are found to be slightly larger than those for elastic ω photo-production in this energy range. The data are compared to the predictions of a theoretical model and the contributing exchange mechanics are discussed.     

Real parts of scattering amplitudes and Regge phenomenology

High energy scattering amplitudes are computed using the Harari model for the imaginary parts and fixed t dispersion relations for the real parts. This procedure induces a corrective term to the real part of the Regge amplitudes whose effects are investigated in π-nucleon and K-nucleon charge exchange reactions.     

On the phenomenological rate equation in a model exchange reaction

The limits of validity of the phenomenological rate equation, and the phenomenological rate constant k_f and k_b are found for the exchange reaction $\text{A + BC}\textcolor{red}{}\text{AB + C}$ within the framework of simple multistate models. The possibility of macroscopically long transient times is discussed. The rate constants are shown to depend on the total densities n_A, n_B and n_C of the chemical species present in the mixture, when nonequilibrium effects are important. The distinction between a rate constant and a flux coefficient is illustrated. Differences among exchange, dissociation-recombination, and isomerization reactions in that regard are discussed.     

Transfer reactions induced by 16O on 29, 30Si

Angular distributions for one- and two-nucleon transfer reactions induced by ¹⁶O on ^{29, 30}Si and for the elastic scattering of ¹⁶O on ^{28, 29, 30}Si have been measured at 73.5 MeV bombarding energy. The results are analyzed with the DWBA code BRUNHILD that includes recoil effects. Spectroscopic factors extracted for all observed transitions in one-nucleon transfer reactions agree well with those derived from light panicle reactions. The effects of recoil on the Spectroscopic factors for transitions to final states with different spins are discussed. The transitions from smooth to oscillating angular distributions are examined. It is found that the shape of the angular distributions depends on both the matching conditions of the reaction and the localization of the S-matrix amplitudes in L-spacef.     

Time-dependent Hartree-Fock calculation of 12C + 12C with a realistic potential

We have used a realistic single-panicle K-matrix model to compute the head-on scattering of ¹²C + ¹²C at incident projectile lab energies of 3.2, 6.4, 12.8, 19.2, 25.6, 32, 51.2 and 64 $\text{MeV}\text{nucleon}$, above the Coulomb barrier, in the time-dependent Hartree-Fock approximation. Direct and exchange Coulomb forces as well as spin-orbit forces are included. A large deformed harmonic oscillator basis is used. Spatial density and current distributions at various times are shown. The outgoing energy is found to be E₀ = 0.8E_in?28 (MeV), in the c.m. system. Fusion and fully relaxed scattering are observed at low energy. Some compression is seen at higher energies but no shock waves can be detected. Consequences for heavy-ion reactions are discussed.     

Coulomb energies from quark exchanges between nucleons

The Coulomb exchange kernel between two-nucleon clusters of quarks is calculated by using the resonating-group method. The resulting Coulomb quark-exchange energy increases the Coulomb energy difference in the A = 3 mirror nuclei (by as much as 4% for large nucleons), but decreases it (by ?2 to ?4%) in p-shell nuclei. Other quark effects in charge-dependent (and asymmetric) interactions are briefly discussed.     

Reaction rates and energy spectra for nuclear reactions in high energy plasmas

Total reaction rates and energy spectra of the generated particles are discussed for fusion reactions in high energy plasmas. Examples, discussed in some detail, concern elliptic and monoenergetic velocity distributions of the plasma. One obtains energy spectra with very typical shapes which should be useful for diagnostic purposes. This is true in particular, of reactions between different particles such as thed-t reaction.     

Differential-Thermal and X-Ray Analysis of TlFeS<Subscript>2</Subscript> and TlFeSe<Subscript>2</Subscript> Chalcogenides

Triple compounds with the formulas TlFeS₂ and TlFeSe₂ and magnetic properties are investigated via X-ray diffraction, differential-thermal, and thermogravimetric analyses. Their crystal structures are found. It is ascertained that they are described by monoclinic space group C2/m under normal conditions. The atomic coordinates and interatomic distances are determined. From differential-thermal and thermogravimetric analyses performed at temperatures of 30–900°C, it is revealed that stronger covalent bonds are implemented in TlFeS₂ crystals than in TlFeSe₂ compounds. The effects associated with energy exchange in the compounds under study are observed. The physical nature of the observed effects is discussed.     

Observation of double-Pomeron exchange in alpha-alpha collisions at the CERN intersecting storage rings

We observed the process αα→ααX in which the α′s were emitted uncorrelated in the forward direction and the charged component of the clusterX was confined to a limited portion (|η|?2) of the central region. We identified such reactions as being due to double-Pomeron exchange, for which we found a cross-section of (720±140)μb. The raw mean charged multiplicity of the clusterX was found to be 6.76±0.07 with a dispersionD=4.8. The measurements were performed at the CERN ISR at a centre-of-mass energy of \(\sqrt s = 126\) GeV. Similarities are drawn between double-Pomeron exchange in αα and inpp collisions.     

Erratum to: Dilepton production in proton-induced reactions at SIS energies with the GiBUU transport model

We present dilepton spectra from p + p , d + p and p + Nb reactions at SIS energies, which were simulated with the GiBUU transport model in a resonance model approach. These spectra are compared to the data published by the HADES and DLS Collaborations. It is shown that the ?? spectral function includes non-trivial effects already in elementary reactions, due to production via baryon resonances, which can yield large contributions to the dilepton spectrum. Dilepton spectra from nuclear reactions in the energy range of the HADES experiment are thus found to be sensitive also to properties of nucleon resonances in the nuclear medium.     

Gaussian approximations for the nuclear Coulomb interaction

The kernel 1/¦r-r′¦=1/y in the direct term of the average Coulomb potential of the nuclear Hartree-Fock model is approximated by a sum of gaussians iny. For 0.5≦y≦30 Fm, a sixteen term expression is found such the direct Coulomb energy is obtained to one part in 10³. The exchange Coulomb potential is estimated in the statistical model. Applications of these accurate and practical approximations to fission calculations are discussed.     

The short-range nucleon-nucleon repulsion

The short-range repulsion (0.2–0.4 fm) between nucleons is investigated. The opposing effects of ω-meson exchange and ε-meson (J^p = 0⁺) exchange are investigated, and the relation to Regge behaviour is demonstrated using fixed-s dispersion relations. The energy dependence of the short-range interaction is emphasized, and experimental data on polarization in elastic NN scattering at high energy are used to give the necessary coupling constant.     

The effect of the δ(1236) in nuclear matter

The three main corrections to the binding energy of nuclear matter that involve the Δ (1236) are calculated with exchange effects and realistic correlation functions. It is found that their net effect at K_F = 1.36 fm^?1 is small, but that their K_F dependence has a considerable effect on the saturation density.     

Some tests for the helicity structure of the Pomeron in ep collisions

We discuss the reaction ep→epp?X in the onephoton exchange approximation, where it is in essence the reaction γ*p→p?X. A large rapidity gap is required between the particle or particles of the proton remnant pJ and those of X. We define a suitable azimuthal angle between a leptonic and a hadronic plane. The dependence of the cross section on is given explicitly and can be used to extract cross sections and interference terms for the reactionγ*p→p?X corresponding to the various helicities of the virtual photon γ*. The interference terms can be used to test models for the large rapidity gap events in a sensitive way. We discuss in detail models with factorizing Pomeron exchange and in particular the Donnachie- Landshoff Pomeron model. We make some remarks on soft colour exchange models and on possible effects of QCD background vacuum fields. We conclude with a suggestion to look for Odderon exchange in exclusive deep inelastic high energy reactions like γ*p→,p?π⁰and ?p→p?η.     

Ignition thresholds for deuterium-tritium mixtures contaminated by high-<Emphasis Type="Italic">Z</Emphasis> material in cone-focused fast ignition

Evaluations of the energy for thermonuclear ignition of a compressed deuterium-tritium mixture contaminated by a high-Z material are presented. Mixing at the atomic level is considered and the results are given as a function of the contaminant fraction. The reference situation is that of cone-focused fast ignition (CFFI). The numerical 2D simulations for this study were performed by a Lagrangian 2D hydrocode that includes real matter EoS, real matter opacity coefficients, and packages for finite-range energy deposition by reaction products and the relative in-flight reactions. A simple estimate is presented for the effects of high-Z material blobs on the ignition energy (macroscopic mixing). Possible sources for fuel contamination in CFFI are discussed.     

Exchange splitting of acceptor states in semimagnetic-semiconductors: Magnetoresistance studies of Cd1-xMnxTe

Measurements of resistivity as a function of temperature and magnetic field in p-Cd_1-xMn_xTe are reported. A negatove magnetoresistance has been found and shown to originate from the magnetic field induced lowering of the acceptor binding energy. It is demonstrated that the experimental results can be quantitatively described if two effects are taken into account: (i) orbital quenching of the p-d exchange splitting of the four-fold degenerate acceptor level, (ii) destructive effect of a magnetic field on a contribution to the binding energy given by thermodynamical fluctuation of magnetization.     

The nuclear force and a magnetic monopole model of hadrons

The two-pion exchange potential of the nuclear force is constructed from the phase shifts of the low energy πN and ππ scattering. The large difference between the potentials thus constructed from the phenomenological potentials of Hamada-Johnston and of Bryan is pointed out. It is found that this difference has the form of the attractive Van der Waals potential plus an inner repulsive core. The existence of the Van der Waals force is discussed in connection with the magnetic monopole model of hadrons.