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Title: Spectroscopy studies using two-nucleon knockout

Abstract

Two-proton removal reaction cross sections, from 208Pb at 1 GeV/nucleon, are estimated as an example of the direct population of (high-spin) seniority-2 isomeric states, here in 206Hg. Nucleon removal by both the stripping and diffractive mechanisms is considered. The cross sections in this specific (test) case are significant and can provide direct two-nucleon removal predictions of isomeric ratios.

Authors:
 [1]
  1. Department of Physics, School of Electronics and Physical Sciences, University of Surrey, Guildford GU2 7XH (United Kingdom)
Publication Date:
OSTI Identifier:
20798345
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 819; Journal Issue: 1; Conference: 12. international symposium on capture gamma-ray spectroscopy and related topics, Notre Dame, IN (United States), 4-9 Sep 2005; Other Information: DOI: 10.1063/1.2187910; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; CROSS SECTIONS; GEV RANGE; ISOMER RATIO; ISOMERIC NUCLEI; KNOCK-OUT REACTIONS; LEAD 208; MERCURY 206; PROTONS; SPECTROSCOPY; SPIN; STRIPPING

Citation Formats

Tostevin, J. A. Spectroscopy studies using two-nucleon knockout. United States: N. p., 2006. Web. doi:10.1063/1.2187910.
Tostevin, J. A. Spectroscopy studies using two-nucleon knockout. United States. doi:10.1063/1.2187910.
Tostevin, J. A. Mon . "Spectroscopy studies using two-nucleon knockout". United States. doi:10.1063/1.2187910.
@article{osti_20798345,
title = {Spectroscopy studies using two-nucleon knockout},
author = {Tostevin, J. A.},
abstractNote = {Two-proton removal reaction cross sections, from 208Pb at 1 GeV/nucleon, are estimated as an example of the direct population of (high-spin) seniority-2 isomeric states, here in 206Hg. Nucleon removal by both the stripping and diffractive mechanisms is considered. The cross sections in this specific (test) case are significant and can provide direct two-nucleon removal predictions of isomeric ratios.},
doi = {10.1063/1.2187910},
journal = {AIP Conference Proceedings},
number = 1,
volume = 819,
place = {United States},
year = {Mon Mar 13 00:00:00 EST 2006},
month = {Mon Mar 13 00:00:00 EST 2006}
}
  • Sudden single-nucleon removal reactions from fast radioactive beams are now key to studies of the structure of rare isotopes. The sensitivity of the heavy residue's parallel momentum distribution to the orbital angular momentum of the removed nucleon is a crucial feature with a high spectroscopic value. Two-nucleon removal reactions provide experimental reach toward the rarest nuclear species. We show that the residue parallel momentum distributions in these reactions offer a clear spectroscopic signal of the angular momentum of the pair of nucleons removed, and thus of the residue final state spins and spectroscopy. Our formalism is applied successfully to newmore » final-state-inclusive measurements of like-nucleon pair removal reactions to states in neutron-rich {sup 36}Mg and neutron-deficient {sup 20}Mg. We also confront a new final-state-exclusive decomposition of two-proton knockout data to states in neutron-rich {sup 26}Ne.« less
  • The contributions to the cross sections of intermediate energy two-nucleon knockout reactions from events in which one nucleon is removed by the stripping (inelastic breakup) mechanism and a second by the diffraction (elastic breakup) mechanism are discussed. The small additional contributions from two-nucleon diffraction events are also estimated. The approach used combines the eikonal reaction and shell model structure theory frameworks. For reactions involving the removal of two well-bound like nucleons, at incident energies of order 100 MeV per nucleon, the additional cross sections are shown to be of approximately the same size as those from events in which bothmore » nucleons are stripped in inelastic interactions. These more complete dynamical calculations now permit a quantitative comparison of the theoretical cross sections with recent partial cross-section measurements of the two-neutron (two-proton) removal reactions from neutron-deficient (neutron-rich) nuclei. As has been observed in both nuclear- and electron-induced single-nucleon knockout reaction analyses, the theoretical two-nucleon knockout cross sections overestimate the measured values, requiring a suppression of the two nucleon shell-model transition strengths. The deduced two-nucleon suppression factors, R{sub s}(2N), are consistent with a value of 0.5 for each of the five reactions considered.« less
  • The longitudinal momentum distributions of the cross sections of heavy projectile-like residues after fast, direct two-like-nucleon knockout reactions are discussed. Both the two-nucleon inelastic breakup (stripping) and the stripping-diffraction removal events are considered. We show that, because the two mechanisms have a very similar nuclear surface localization, they generate essentially identical longitudinal momentum distributions. The approach used combines reaction dynamics, using the sudden, eikonal and spectator-core approximations, with structure wave functions from the many-body shell model. The sensitivities of the resulting longitudinal momentum distributions to the orbital angular momenta, the separation energies, and the angular momentum coupling of the twomore » removed nucleons are clarified. In particular, the widths of these distributions are shown to provide a very clear signal of the total angular momentum of the removed-nucleon pair--pairs coupled to larger total angular momentum giving broader distributions. These now complete distributions, from correlated wave functions, are significantly different from earlier uncorrelated estimates. Confirmation of these theoretical expectations is presented, based on very recent intermediate-energy, residue final-state inclusive and exclusive two-nucleon removal measurements.« less
  • Reactions that involve the direct and sudden removal of a pair of like or unlike nucleons from a fast projectile beam by a light target nucleus are considered. Specifically, we study the three two-nucleon removal channels from {sup 12}C that populate final states in the {sup 10}Be, {sup 10}B, and {sup 10}C reaction residues. The calculated two-nucleon removal cross sections and the residue momentum distributions are compared with available high-energy data at 250, 1050, and 2010 MeV per nucleon, i.e., data that are inclusive with respect to the bound final states of the residues. The measured np removal cross sectionsmore » only are significantly greater than the values calculated, suggesting that the reaction mechanism observes enhanced np spatial correlations compared to those present in the shell-model wave functions.« less