Nuclear and Coulomb interactions in coherent fragmentation of relativistic nuclei in a photoemulsion

The role of the nuclear and Coulomb interactions in coherent fragmentation of relativistic nuclei is discussed with the cluster-model analysis of the experimental data on the fragmentation of ⁷Li (P = 3A GeV/c) via the ³H + ⁴He channel in photoemulsion used as an example. The calculated electromagnetic contribution of ～10% to the cross section is not in conflict with the photoemulsion data and the upper estimate of ～40% derived from the earlier measurements of total cross sections for fragmentation of light nuclei using the counter technique. The observed irregularities in the differential cross section for ⁷Li fragmentation with a separated Coulomb peak at a very small momentum transfer Q are ascribed to the overlap of nuclear diffraction patterns arising from light (C, N, O) and heavy (Ag, Br) photoemulsion nuclei. The predicted diffraction cross sections in the inelastic channel drastically differ from the usual shape of nuclear diffraction in an elastic channel. For pure targets, they have a shape of oscillations with a few peaks of comparable intensity and show strong dependence on the form of the surface nuclear density and radii of the intranuclear cluster and target nucleus. The probability for two-body clustering in ⁷Li is estimated at about 0.7.     

Peripheral fragmentation of relativistic nuclei 11B in nuclear track emulsion

Data obtained from a nuclear track photoemulsion exposed to a beam of ¹¹B nuclei with a momentum of 2.75 GeV/c per nucleon are reported. Peripheral interactions where the total charge of particles emitted within the forward cone of relativistic fragmentation is equal to the charge of the projectile nucleus are analyzed to study the clustering of the ¹¹T nucleus. It is found that the three-body breakup of 2 + 2 + 1 charge configuration is a leading process. Tritons are revealed to play a crucial role in the most peripheral interactions of this type. Events interpreted as charge exchange of the 11B nucleus to excited states of the ¹¹C* nucleus above the nucleon-coupling threshold were observed for the first time. Prospects for studying the ¹¹C nucleus are discussed.     

Secondary nuclear fragment beams for investigations of relativistic fragmentation of light radioactive nuclei using nuclear photoemulsion at Nuclotron

Slowly extracted relativistic beams of light nuclei and a beam transportation line net system constitute a good base for secondary nuclear beams forming at the LHE accelerator facility. A recent years activity in the field at the Laboratory is connected with a project on study light nuclei structure by means the emulsion technique [1,2]. The paper shortly summarizes results of the work.     

On a fragmentation mechanism of relativistic heavy ions

A model is proposed describing main features of a behaviour of the fragmentation cross sections for relativistic ions including their relative yields. The reaction is assumed to proceed in two stages: At the first one the ion is excited by the peripheral collision with a nucleus, at the second one it decays statistically in flight with emitting a fragment. A strong analogy is demonstrated for the process with the corresponding reactions of nonrelativistic ions.     

Yield of 8Be nuclei originating from 10B fragmentation in photoemulsion at an energy of 1 GeV per nucleon

The fraction of the channel ¹⁰B → ⁸Be → ² α is estimated at (18 ± 3)%. The constants of the distributions with respect to the alpha-particle emission angle and the angle between the alpha-particle momenta are found to be 20.5 ± 0.7 and 31.7 ± 2.0 mrad, respectively. These values agree with the results of the calculations performed prior to our experiment under the assumption of the limiting fragmentation of relativistic nuclei.     

Quasi-free electron scattering in a relativistic model of the nucleus

Longitudinal and transverse response functions of quasi-free electron scattering have been calculated in mean field approximation for a relativisticσ-ω model, including non-linearities in theσ-field. As a consequence of the completely consistent and fully relativistic treatment of wave functions and current operators, gauge invariance is perfectly satisfied throughout the calculation. The results indicate that models with the same nuclear bulk properties lead to similar response functions within 10%. Our results agree with the experimental data for¹²C and²³⁸U, but cannot describe the longitudinal response in the Ca-Fe region. Predictions for²⁰⁸Pb are given for comparison with future experiments.     

On the relativistic description of the nucleus

We present a formalism able to generalise to a relativistically covariant scheme the standard nuclear shell model. We show that, using some generalised nuclear Greens functions and their Lehmann representation we can define the relativistic equivalent of the non-relativistic single-particle wave function (not losing, however, the physical contribution of other degrees of freedom, like mesons and antinucleons). It is shown that the mass operator associated to the nuclear Greens function can be approximated with the equivalent of a shell model potential and that the corresponding single-particle wave functions can be easily derived in a specified frame of reference and then boosted to any other system, thus fully restoring the Lorentz covariance.PACS:   21.60.Cs Shell model     

Some features in the angular divergence of relativistic electron beams reflected and refracted by foil

The horizontal and vertical angular divergences of relativistic electron beams passing through a foil and reflected by a foil are experimentally measured. The effect of the angle between the electron beam and the foil plane on the intensity and angular divergence of beams is studied. The interaction of particles with a copper foil 50 μm thick and aluminum foil 200 μm thick is studied. A microtron with a particle energy of 7.4 MeV is used as an electron source.     

Some special features in the filling of the Fermi sphere with quark quasiparticles

The filling of the Fermi sphere with quarks treated as quasiparticles of the model Hamiltonian for four-fermion interaction is studied.     

Measurement of the elliptic flux of Z ⩾ 2 charged particles in collisions of relativistic nuclei with photoemulsion nuclei

The azimuthal asymmetry is measured for the emission of Z ≥ 2 particles from the interaction of ²²Ne, ²⁴Mg, ³²S, ⁵⁶Fe, ¹⁹⁷Au, and ²⁰⁷Pb nuclei with photoemulsion nuclei that is induced by semicentral collisions characterized by projectile energies in the range E _pr = 1.88–200 GeV per nucleon and by impact-parameter (b) values in the range 0.12 ≤ b/b _max ≤ 0.70. The results of these measurements are compared with the results of similar measurements for protons. It is found that, at a low energy of E _pr ≈ 2 GeV per nucleon, the ratio of the azimuthal-anisotropy coefficients v ₂ for Z ≥ 2 particles and protons is 6 ± 2, but that, for energies in the region E _pr ≥ 4 GeV per nucleon, the coefficients in question agree with each other. This may suggest that, at low energies, Z ≥ 2 particles are predominantly formed at an early stage of the development of a collective flow. For E _pr ≥ 4 GeV per nucleon, these particles are presumably formed at the stage of nuclear-matter expansion. Other possible explanations for the results of the observation of an elliptic flux of Z ≥ 2 particles are discussed.     

Observation of truly cold fragmentation of a heavy nucleus

The results of a careful investigation of the mass-energy-charge correlations of the fragments produced by fission of thorium-232 by 5 MeV neutrons are presented. The phenomenon of truly cold fragmentation of a thorium nucleus into tellurium-134 and strontium-99 in the quantum ground states is observed. It is shown that the reaction energy is completely exhausted by the kinetic energy of the fragments in their mutual field. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 10, 752–754 (25 May 1998)     

The nonlinearity of the scalar field in a relativistic mean-field theory of the nucleus

The form of the nonlinear self-coupling of the scalar meson field in a nuclear relativistic mean-field theory is investigated. The conventional ansatz is shown to produce instabilities in critical applications. A modified self-coupling is proposed which guarantees stability under all conditions.     

Parton models and fragmentation of relativistic heavy ions

Parton models of particle fragmentation in high-energy particle collisions are extended to fragmentation of heavy ions into baryons and mesons in high-energy nuclear collisions. Good agreement between experiment and theory is demonstrated.     

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%.     

Multiparticle production of doubly charged fragments in the fragmentation of relativistic nuclei

Features of angular distributions of events involving two or more doubly charged fragments of relativistic nuclei ²²Ne, ²⁴Mg, ¹⁴N, ¹¹B, and ¹⁰B in photoemulsions are studied. It is found that, in all cases, with the exception of the case of the intermediate-state decay ⁸Be → 2α, the fragments in these events are independent of one another. The inclusive angular distributions of fragments of relativistic nuclei ²²Ne for events in which the number of particles ranges between one and five are identical. Thus, the emission angle of each fragment of a relativistic nucleus does not depend either on other fragments or on the presence or absence of product particles and target-nucleus fragments in an event.     

Some problems in relativistic thermodynamics

The relativistic equations of state for ideal and real gases, as well as for various interface regions, have been derived. These dependences help to eliminate some controversies in the relativistic thermodynamics based on the special theory of relativity. It is shown, in particular, that the temperature of system whose velocity tends to the velocity of light in vacuum varies in accordance with the Ott law T = T ₀/√1 ? v ²/c ². Relativistic dependences for heat and mass transfer, for Ohm’s law, and for a viscous flow of a liquid have also been derived.     

Some special features of the transition to chaos in the self-modulation of surface spin waves

The results of experimental investigations of the transition from regular to stochastic self-modulation of intense surface spin waves are presented. It is found that the transition to chaos follows the scenario of a sequence of period-doubling bifurcations. The fractal dimensions and the Kolmogorov entropy are determined for different regimes. The experiments are performed on an apparatus consisting of a microwave oscillator with a spin-wave delay line in the feedback circuit. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 4, 243–246 (25 August 1997)     

Searching for exotic cluster structure in the absorption of pions by the 11B nucleus

Correlation measurements of the reaction of stopped pion absorption ¹¹B(π^?, tt)X are made with a semiconductor double-arm charged particle spectrometer on a low-energy pion beam at the LAMPF meson factory. Analysis of a two-dimensional Dalitz plot and the momentum distribution of the residual nucleus allows us to identify the absorption of pions in a 6Li intranuclear cluster and demonstrate the configuration ⁶Li + ⁵He_g.s is present in the ¹¹B nucleus.