Non-equilibrium emission of complex fragments from p+Au collisions at 2.5 GeV proton beam energy

Energy and angular dependence of double differential cross sections d$^2\sigma$/d$\Omega$dE was measured for reactions induced by 2.5 GeV protons on Au target with isotopic identification of light products (H, He, Li, Be, and B) and with elemental identification of heavier intermediate mass fragments (C, N, O, F, Ne, Na, Mg, and Al). It was found that two different reaction mechanisms give comparable contributions to the cross sections. The intranuclear cascade of nucleon-nucleon collisions followed by evaporation from an equilibrated residuum describes low energy part of the energy distributions whereas another reaction mechanism is responsible for high energy part of the spectra of composite particles. Phenomenological model description of the differential cross sections by isotropic emission from two moving sources led to a very good description of all measured data. Values of the extracted parameters of the emitting sources are compatible with the hypothesis claiming that the high energy particles emerge from pre-equilibrium processes consisting in a breakup of the target into three groups of nucleons; small, fast and hot fireball of $\sim$ 8 nucleons, and two larger, excited prefragments, which emits the light charged particles and intermediate mass fragments. The smaller of them contains $\sim$ 20 nucleons and moves with velocity larger than the CM velocity of the proton projectile and the target. The heavier prefragment behaves similarly as the heavy residuum of the intranuclear cascade of nucleon-nucleon collisions. %The mass and charge dependence of the total production cross %sections was extracted from the above analysis for all observed %reaction products. This dependence follows the power low behavior %(A$^{-\tau}$ or Z$^{-\tau}$)

Variation of nonequilibrium processes in p+Ni system with beam energy

The energy and angular dependence of double differential cross sections dsigma/dOmega dE were measured for p, d, t, 3,4He, 6,7Li, 7,9Be, and 10,11B produced in collisions of 0.175 GeV protons with Ni target. The analysis of measured dfferential cross sections allowed to extract total production cross sections for ejectiles listed above. The shape of the spectra and angular distributions indicate the presence of other nonequilibrium processes besides the emission of nucleons from the intranuclear cascade, and besides the evaporation of various particles from remnants of intranuclear cascade. These nonequilibrium processes consist of coalescence of nucleons into light charged particles during the intranuclear cascade, of the fireball emission which contributes to the cross sections of protons and deuterons, and of the break-up of the target nucleus which leads to the emission of intermediate mass fragments. All such processes were found earlier at beam energies 1.2, 1.9, and 2.5 GeV for Ni as well as for Au targets, however, significant differences in properties of these processes at high and low beam energy are observed in the present study.Comment: 10 pages, 9 figure

Comparison of nonequilibrium processes in p+Ni and p+Au collisions at GeV energies

The energy and angular dependence of double differential cross sections d2sigma/dOmega dE were measured for p, d, t, 3,4,6He, 6,7,8Li, 7,9,10Be, 10,11B, and C produced in collisions of 1.2, 1.9, and 2.5 GeV protons with a Ni target. The shape of the spectra and angular distributions does almost not change whereas the absolute value of the cross sections increases by a factor about 1.7 for all ejectiles in this beam energy range. It was found that energy and angular dependencies of the cross sections cannot be reproduced by the microscopic model of intranuclear cascade with coalescence of nucleons and the statistical model for evaporation of particles from excited, equilibrated residual nuclei. The inclusion of nonequilibrium processes, described by a phenomenological model of the emission from fast and hot moving sources, resulting from break-up of the target nucleus by impinging proton, leads to very good reproduction of data. Cross sections of these processes are quite large, exhausting approximately half of the total production cross sections. Due to good reproduction of energy and angular dependencies of d2sigma/dOmega dE by model calculation it was possible to determine total production cross sections for all studied ejectiles. Results obtained in this work point to the analogous reaction mechanism for proton induced reactions on Ni target as that observed previously for Au target in the same beam energy range.Comment: 11 pages, 10 figures

Competition of coalescence and "fireball" processes in nonequilibrium emission of light charged particles from p+Au collisions

The energy and angular dependence of double differential cross sections was measured for p,d,t,He,Li,Be, and B isotopes produced in collisions of 1.2 and 1.9 GeV protons with Au target. The shape of the spectra and angular distributions almost does not change in the beam energy range from 1.2 to 2.5 GeV, however, the absolute value of the cross sections increases for all ejectiles. A phenomenological model of two emitting, moving sources reproduces very well spectra and angular distributions of intermediate mass fragments. Double differential cross sections for light charged particles (LCP) were analyzed in the frame of the microscopic model of intranuclear cascade (INC) with coalescence of nucleons and statistical model for evaporation of particles from excited residual nuclei. Energy and angular dependencies of data agree satisfactorily neither with predictions of microscopic intranuclear cascade calculations for protons, nor with coalescence calculations for other LCP. Phenomenological inclusion of another reaction mechanism - emission of LCP from a "fireball", i.e., fast and hot moving source - combined with the microscopic model calculations of INC, coalescence and evaporation of particles leads to very good description of the data. It was found that nonequilibrium processes are very important for production of LCP. They exhaust 40-80% of the total cross sections - depending on the emitted particles. Coalescence and "fireball" emission give comparable contributions to the cross sections with exception of 3He data where coalescence clearly dominates. The ratio of sum of all nonequilibrium processes to those proceeding through stage of statistical equilibrium does almost not change in the beam energy range from 1.2 GeV to 2.5 GeV for all light charged particles.Comment: 14 pages, 12 figures, IV tables, \pacs{25.40.-h,25.40.Sc,25.40.Ve

Investigation of the Three-Nucleon System Dynamics in the Deuteron-Proton Breakup Reaction

Precise and large sets of cross section, vector A x , A y and tensor A xx , A xy , A yy analyzing power data for the 1 H(d, pp)n breakup reactions were measured at 100 and 130 MeV deuteron beam energies with the SALAD and BINA detectors at KVI and the Germanium Wall setup at FZ-Jülich. Results are compared with various theoretical approaches which model the three-nucleon system dynamics. The cross section data reveal a sizable three-nucleon force (3NF) and Coulomb force influence. In case of the analyzing powers very low sensitivity to these effects was found and the data are well describe by 2N models only. For A xy at 130 MeV, serious disagreements were observed when 3NF models are included in the calculations

Gregor Lang-Wojtasik (2008): Schule in der Weltgesellschaft – Herausforderungen und Perspektiven einer Schultheorie jenseits der Moderne. Weinheim, München: Juventa 2008, 240 S. [Rezension]

Rezension zu: Gregor Lang-Wojtasik (2008): Schule in der Weltgesellschaft – Herausforderungen und Perspektiven einer Schultheorie jenseits der Moderne. Weinheim, München: Juventa 2008, 240 S., ISBN 978-3-7799-1267-

Studies of the three-nucleon system dynamics in the deuteron-proton breakup reaction

One of the most important goals of modern nuclear physics is to contruct nuclear force model which properly describes the experimental data. To develop and test predictions of current models the breakup $^{1}H\left ( \vec{d}, pp \right )n$ reaction was investigated experimentally at 100 and 130 MeV deuteron beam energies. Rich set of data for cross section, vector and tensor analyzing powers was obtained with the use of the SALAD and BINA detectors at KVI and Germanium Wall setup at FZ-Jülich. Results are compared with various theoretical approaches which describe the three-nucleon (3N) system dynamics. For correct description of the cross section data both, three-nucleon force (3NF) and Coulomb force, have to be included into calculations and influence of those ingredients is seizable at specific parts of the phase space. In case of the vector analyzing powers very low sensitivity to any effects beyond nucleon-nucleon interaction was found. At 130 MeV, the $A_{xy}$ data are not correctly described when 3NF models are included into calculations