Angular Distributions Of Nucleons Research Articles

Physics with low energy radioactive beams

This is a review of the basic mechanisms leading to high energy breakup reactions, of the formalisms used to describe them and of some of the methods to obtain the optical potentials necessary in calculations involving exotic nuclei. Semiclassical reductions of the DWBA approximation for inclusive and exclusive breakup will be presented. The observables that can be calculated are projectile’s core parallel momentum distributions, angular distributions of nucleons from the breakup, total breakup cross sections. Methods to study resonances at threshold in unbound nuclei are also introduced. In this case the exclusive observable calculated is the neutron-core relative energy spectrum. Finally, we study the two neutron transfer to the continuum reaction between two “normal” nuclei. The observable is the continuum excitation energy spectrum of the “exotic” residual nucleus created.

Investigation of the reaction mechanism for the four-particle photodisintegration of a carbon nucleus

The four-particle photodisintegration of a carbon nucleus in the reactions 12C(γ, p)3H2α and 12C(γ, n)3H2α is investigated by a method that employs a diffusion chamber in a magnetic field. It is shown that these reactions proceed according a sequential-type scheme: excited states of 11B and 11C nuclei decay to weakly excited states of 8Be, 7Li, and 7Be nuclei. It is concluded that nucleons are knocked out from the s shell. In the excitation curve for the 2α system in the reaction 12C(γ, p)3H2α, a resonance is found between the maxima corresponding to the ground and the first excited state of the 8Be nucleus, and this resonance is identified as a ghost anomaly. The branching fractions of the decay modes are determined. The angular distributions of nucleons in the reaction c.m. frame are measured. The energy dependence of the asymmetry coefficient for the angular distributions is obtained. A fast increase in this coefficient is observed in the energy range 38–40 MeV. It is concluded that the asymmetry coefficient depends on the excitation energy of the final nucleus in the region of intermediate photon energies.

Centaurus A as the source of ultrahigh-energy cosmic rays?

We present numerical simulations for energy spectra and angular distributions of nucleons above ${10}^{19} \mathrm{eV}$ injected by the radio-galaxy Centaurus A at a distance 3.4 Mpc and propagating in extra-galactic magnetic fields in the submicro Gauss range. We show that field strengths $B\ensuremath{\simeq}0.3 \ensuremath{\mu}\mathrm{G}$, as proposed by Farrar and Piran, cannot provide sufficient angular deflection to explain the observational data. A magnetic field of intensity $B\ensuremath{\simeq}1 \ensuremath{\mu}\mathrm{G}$ could reproduce the observed large-scale isotropy and could marginally explain the observed energy spectrum. However, it would not readily account for the $E=320\ifmmode\pm\else\textpm\fi{}93 \mathrm{EeV}$ Fly's Eye event that was detected at an angle $136\ifmmode^\circ\else\textdegree\fi{}$ away from Cen-A, and it saturates observational upper bounds on the strength of extra-galactic magnetic fields. High energy cosmic ray experiments now under construction will be able to detect the level of anisotropy predicted by this scenario. We conclude that for magnetic fields $B\ensuremath{\simeq}0.1--0.5 \ensuremath{\mu}\mathrm{G}$, considered as more reasonable for the local supercluster environment, in all likelihood at least a few sources within $\ensuremath{\simeq}10 \mathrm{Mpc}$ from the Earth should contribute to the observed ultrahigh-energy cosmic ray flux.

The angular distribution of the 12C(γ,pn) reaction for Eγ=120−150 MeV

The angular distribution of nucleons emitted in the 12C(γ,pn) reaction has been measured using tagged photons at the Mainz microtron MAMI. The variation of the reaction strength with the polar angles of the two emitted nucleons is reported for Eγ=120−150 MeV. The proton angular distribution peaks at more backward angles than the 2H(γ,p) differential cross section indicating a departure from the simple quasi-deuteron model of 2N photo-emission. The distribution shape is in reasonable agreement with microscopic theoretical models which include both π- and ρ-exchange.

Angular distributions following three-nucleon pion absorption.

We present an analysis of the energy and angular distributions of nucleons following three-nucleon pion absorption. Three-nucleon absorption is treated as a one-step process whose transition matrix element is constant with respect to the energy of the final state nucleons. The inclusion of partial wave amplitudes for incident pions of angular momentum less than two shows good agreement with the experimental data in the Delta-resonance region.

Particle correlation and energy boost of emitted nucleons in heavy-ion reactions

This work investigates the particle correlation effect on the energy boost of emitted nucleons in HI reactions. Specifically, the authors study the following model process: in the first phase of the nucleus-nucleus collision, a part of the projectile nucleons undergoes two successive collisions. First, they impact on correlated particles (clusters) inside the target. Second, the reflected nucleons collide with the projectile-like remanent. By means of both analytical calculations and BUU simulation methods, the energy spectra and angular distributions of nucleons after such two-step collisions were evaluated. The results show that the particle correlation could lead to a prominent energy boost and a forward-peaked distribution of scattered nucleons.

Pion absorption in tritium at intermediate energies.

The angular distribution of nucleons from a kinematically complete measurement of pions absorbed in $^{3}\mathrm{H}$ on nucleon pairs with isospin T=0 and T=1 at incident pion energies of 119, 206, and 300 MeV are presented. The T=0 data are quite similar to pion absorption data in deuterium. The integrated absorption cross sections scale within errors with the number of isoscaler neutron-proton pairs. The T=1 cross sections, which correspond to absorption on dineutrons, are an order of magnitude smaller. The angular distributions for isovector absorption show a significant asymmetry, indicating interference effects between amplitudes with or without \ensuremath{\Delta} isobars in the intermediate states. The existence of a significant three-nucleon absorption component is established. The integrated absorption cross sections for processes involving two and three nucleons were determined. The neutron and proton momentum probability densities in $^{3}\mathrm{H}$ were determined from the spectator recoil resulting from quasifree two-nucleon pion absorption.

Two-nucleon absorption of π+ and π− on 3He across the Δ-resonance region

Abstract The angular distributions of nucleons from a kinematically complete measurement of pions absorbed in 3He on nucleon pairs with isospin T = 0 and T = 1 at incident pion energies of 64, 119, 162 and 206 MeV are presented. The T = 0 data are quite similar to pion absorption data in deuterium but scale with the number of nucleon pairs. The T = 1 cross sections are an order of magnitude smaller and the angular distributions show a significant asymmetry. This asymmetry together with the measured energy dependence indicates interference effects between amplitudes with and without Δ isobars in the intermediate states.

Nucleon-nucleon scattering in excited nuclei

The kinematics of two-body nucleon-nucleon scattering inside an excited nucleus are calculated. Closed-form expressions are deduced for energy and angular distributions of nucleons following single two-body scattering. The Pauli principle is taken into account in deducing these expressions. The kinematical effects of creation and annihilation of particle-hole pairs are shown explicitly. The results for single scattering are extended to multiple two-body interactions through appropriate recursive relations. The expressions derived can be used to calculate the energy spectra and angular distributions of nucleons emitted in nucleon-induced and heavy-ion fusion reactions.

Effect of the structure of He3 and H3 on their cross sections for total electrodisintegration

Angular distributions of nucleons produced in the total electrodisintegration of three-nucleon nuclei are calculated. Both K-harmonic and model Gaussian functions are used as nuclear wave functions in the calculation. It is shown that it is possible to obtain agreement between the calculated and experimental distributions by using the K-harmonic wave functions if states of mixed symmetry and final-state interactions are taken into account.

Angular distribution of nucleons in nucleon-induced preequilibrium reactions

We present a model, leading to a generalised master equation, from which both angular distributions and spectra of preequilibrium nucleons can be successfully calculated. Implications and limitations of this model are discussed.

High Energy Elastic Scattering of Nucleon from Nuclei

The angular distributions of nucleons elastically scattered from nuclei are analyzed at energies ranging from 95 to 340 Mev. Predictions on the angular distribution are examined. All the predictions seem to be satisfied.

Deuteron stripping with polarized deuterons

In order to estimate the effect of using polarized deuterons on the left- right assymetry in the angular distribution of nucleons from deuteron stripping reactions, the distorted-wave Born approximation has been used. Spin-orbit coupling has been neglected. (W.D.M.)