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Experiments on 2°8Pb bombarded by 17O at 22 MeV/nucleon (ORNL) and 84 MeV nucleon (GANIL) are reviewed. Inelastically scattered projectiles were detected at forward angles in coincidence with gamma rays seen in NaI (ORNL) or in BaF2 (GANIL). The 17O were identified by 6 Si telescopes covering THETA = 11. 5/degree/--14.5/degree/ (ORNL) or by the focal-plane detector system of the energy-loss spectrometer SPEG, set to accept THETA = 1. 5/degree/--5.0/degree/ (GANIL). The .gamma.-ray data provide information on the multipole character of various parts of the giant resonance region, matrix elements between the GR region and low-lying states in 2°8Pb, and the relative contribution of direct and compound process to .gamma.0 decay. At the higher energy the 9--15 MeV GR region is excited very strongly. The isovector giant dipole is dominant over most of the angles studied. Significant contributions from the isoscalar giant quadrupole and monopole resonances are also present. Decomposition of the GR into L = 1, 2, and 0 components was based on coincidences with the overwhelmingly dipole .gamma.0 transitions. The magnitude (1.7 +- 0.2%) and energy distribution of the .gamma.0 branch can be reproduced well by a parameter-free calculation. The .gamma.0 decay of the isoscalar giant quadrupole resonance is more easily observed at the lower energy. The .gamma.0 angular correlations confirm the presence of E2 radiation from states in the 9--11 MeV region. The B(E2) implies that the ratio of neutron to proton matrix elements is consistent with the expected value of N/Z. This conclusion is confirmed by evidence form Coulomb-nuclear interference in the singles data at 84 MeV/nucleon. Photon decays to excited states indicate that 4 and/or 6/sup +/ strength is present around 9--10 MeV, and are consistent with a monopole contribution from 12.5--15.5 MeV. 20 refs., 14 figs.
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Languages : en
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Experiments on 2°8Pb bombarded by 17O at 22 MeV/nucleon (ORNL) and 84 MeV nucleon (GANIL) are reviewed. Inelastically scattered projectiles were detected at forward angles in coincidence with gamma rays seen in NaI (ORNL) or in BaF2 (GANIL). The 17O were identified by 6 Si telescopes covering THETA = 11. 5/degree/--14.5/degree/ (ORNL) or by the focal-plane detector system of the energy-loss spectrometer SPEG, set to accept THETA = 1. 5/degree/--5.0/degree/ (GANIL). The .gamma.-ray data provide information on the multipole character of various parts of the giant resonance region, matrix elements between the GR region and low-lying states in 2°8Pb, and the relative contribution of direct and compound process to .gamma.0 decay. At the higher energy the 9--15 MeV GR region is excited very strongly. The isovector giant dipole is dominant over most of the angles studied. Significant contributions from the isoscalar giant quadrupole and monopole resonances are also present. Decomposition of the GR into L = 1, 2, and 0 components was based on coincidences with the overwhelmingly dipole .gamma.0 transitions. The magnitude (1.7 +- 0.2%) and energy distribution of the .gamma.0 branch can be reproduced well by a parameter-free calculation. The .gamma.0 decay of the isoscalar giant quadrupole resonance is more easily observed at the lower energy. The .gamma.0 angular correlations confirm the presence of E2 radiation from states in the 9--11 MeV region. The B(E2) implies that the ratio of neutron to proton matrix elements is consistent with the expected value of N/Z. This conclusion is confirmed by evidence form Coulomb-nuclear interference in the singles data at 84 MeV/nucleon. Photon decays to excited states indicate that 4 and/or 6/sup +/ strength is present around 9--10 MeV, and are consistent with a monopole contribution from 12.5--15.5 MeV. 20 refs., 14 figs.
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Inelastic scattering of medium energy heavy ions provides very large cross sections and peak-to-continuum ratios for excitation of giant resonances. For energies above about 50 MeV/nucleon, giant resonances are excited primarily through Coulomb excitation, which is indifferent to isospin, thus providing a good probe for the study of isovector giant resonances. The extremely large cross sections available from heavy ion excitation permit the study of rare decay modes of the giant resonances. In particular, recent measurements have been made of the photon decay of giant resonances following excitation by 22 and 84 MeV/nucleon 17O projectiles. The singles results at 84 MeV/nucleon yield peak cross sections for the isoscalar giant quadrupole resonance and the isovector giant dipole resonance of approximately 0.8 and 3 barns/sr, respectively. Data on the ground state decay of the isoscalar giant quadrupole and isovector giant dipole resonances are presented and compared with calculations. Decays to low-lying excited states are also discussed. Preliminary results from an experiment to isolate the 2°8Pb isovector quadrupole resonance using its gamma decay are presented. 22 refs., 19 figs., 1 tab.
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Coincidence experiments designed to study the decay of giant resonances (GR) can, in principle, provide information on the microscopic structure of the giant resonance region to supplement the large body of singles inelastic electron and hadron scattering data which has been acquired over the last decade. Furthermore, such coincidence experiments can benefit from the large cross sections for excitation of the isoscalar GR by inelastic scattering of heavy ions without suffering from problems which appear to limit the usefulness of heavy ions in singles experiments. This paper is a preliminary report on the use of the ORNL Spin Spectrometer, a 4.pi., segmented NaI gamma ray spectrometer to study the neutron and gamma decay of the GR region (E* approx. 9-20 MeV) in 2°8Pb. Results are presented and discussed. (WHK).
![Heavy Ion Coulomb Excitation and Gamma Decay Studies of the One and Two Phonon Giant Dipole Resonances in [sup 208]Pb and [sup 209]Bi PDF](https://books.google.com/books/content/images/frontcover/s2G8DAEACAAJ?fife=w80-h100)
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Projectile -- photon coincidences were measured for the scattering of an 80 MeV/nucleon [sup 64]Zn beam from [sup 208]Pb and [sup 209]Bi targets at the GANIL heavy ion accelerator facility. Projectile-like particles between 0.5[degrees] and 4.5[degrees] relative to the incident beam direction were detected in the SPEG energy loss spectrometer where their momentum, charge, and mass were determined. Photons were detected in the BaF[sub 2] scintillation detector array TAPS. Light charged particles produced in the reaction were detected in the KVI Forward Wall. The analysis of the data acquired in this experiment is focused on three different phenomena: (1) the two phonon giant dipole resonance, (2) time dependence of the decay of the one phonon giant dipole resonance, and (3) giant resonance strength in projectile nuclei.
Author: P.F. Bortigan
Publisher: Taylor & Francis
ISBN: 1000940667
Category : Science
Languages : en
Pages : 290
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The series of volumes, Contemporary Concepts in Physics, is addressed to the professional physicist and to the serious graduate student of physics. The subject of many-body systems constitutes a central chapter in the study of quantum mechanics, with applications ranging from elementary particle and condensed matter physics to the behaviour of compact stellar objects. Quantal size effects is one of the most fascinating facets of many-body physics; this is testified to by the developments taking place in the study of metallic clusters, fullerenes, nanophase materials, and atomic nuclei. This book is divided into two main parts: the study of giant resonances based on the atomic nucleus ground state (zero temperature), and the study of the y-decay of giant resonances from compound (finite temperature) nuclei.
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Results from studies of gamma decay of giant resonances in 2°8Pb and 9°Zr following inelastic excitation by 22 and 84 MeV/nucleon 17O ions are presented. Data on ground state decay of isoscalar giant quadrupole and isovector giant dipole resonances are presented and compared with calculations. Decays from resonances to low lying excited states are also discussed. Preliminary results from an attempt to isolate the isovector quadrupole resonance in 2°8Pb using its gamma decay are presented.
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Inelastic scattering of medium energy heavy ions provides very large cross sections and peak-to-continuum ratios for excitation of giant resonances. For energies above about 50 MeV/nucleon, giant resonances are excited primarily through Coulomb excitation, which is indifferent to isospin, thus providing a good probe for the study of isovector giant resonances. The extremely large cross sections available from heavy ion excitation permit the study of rare decay modes of the photon decay of giant resonances following excitation by 22 and 84 MeV/nucleon 17O projectiles. The singles results at 84 MeV/nucleon yield peak cross sections for the isoscalar giant quadrupole resonance and the isovector giant dipole resonance of approximately 0.8 and 3 barns/sr, respectively. Data on the ground state decay of the isoscalar giant quadrupole and isovector giant dipole resonances are presented and compared with calculations. Decays to low-lying excited states are also discussed. Preliminary results from an experiment to isolate the 2°8Pb isovector quadrupole resonance using its gamma decay are presented.
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Results are presented for excitation of giant multipole resonances by inelastic scattering of 350 and 500 MeV 16O projectiles from 9°Zr and 2°8Pb. The giant quadrupole resonance is excited with large cross sections and a very large resonance peak to continuum ratio is obtained. Extracted cross sections agree with DWBA calculations which use standard collective model form factors. Using 380 MeV 170 to excite the giant resonances, the .gamma.-ray decay has been measured for the giant quadrupole resonance region of 2°8Pb. 10 references.
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The role of intermediate energy heavy ions in the study of giant multipole resonances is explored, with emphasis on gamma decay coincidence experiments. Experiments on 2°8Pb bombarded by 84 MeV/nucleon 17O are discussed and compared with earlier work at 22 MeV/nucleon. The role of Coulomb excitation in the 84 MeV/nucleon data is emphasized and some consequences for study of isovector resonance strength are explored. A comparison of the excitation and decay of the isovector giant dipole resonance in 2°8Pb and 2°9Bi excited with 84 MeV/nucleon 17O scattering is presented. 35 refs., 16 figs., 1 tab.
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Languages : en
Pages : 11
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We briefly explore how large cross sections for excitation of both isoscalar and isovector giant multipole resonances which can be obtained using intermediate energy heavy-ion reactions can be utilized in photon-decay coincidence experiments to provide new information on subjects ranging from basic nuclear structure properties to resonance damping and pre-compound decay. We also discuss experiments in which photon-decay techniques are used as a tag to isolate and identify very weakly excited modes, enabling us to explore such diverse subjects as hadronic excitation of the giant dipole resonance, the distribution of isovector quadrupole strength in 2°8Pb, and the excitation of two-phonon giant resonance strength. 25 refs., 12 figs.
