Resonances In Heavy-ion Reactions Research Articles

On the excitation of double giant resonances in heavy ion reactions

The interplay of nuclear and Coulomb processes in the inelastic excitation of single- and double-phonon giant resonances in heavy ion collisions is studied within a simple reaction model. Predominance of the Coulomb excitation mechanism on the population of the single-phonon and, on the contrary, predominance of the nuclear excitation for the double-phonon is evidenced. The effect of the spreading of the strength distribution of the giant resonances on the excitation process is analyzed, showing sizeable modifications in the case of Coulomb dominated processes.

Excitation of triple giant resonances in heavy-ion reactions

We calculate the cross-section for the excitation and subsequent decay of triple giant resonances (TGR's) in several nuclei excited with heavy ions. The recently developed coherent plus incoherent theory for the excitation in conjunction with the hybrid decay model of Dias, Hussein, and Adhikari are used for the purpose. It is emphasized that the direct decay of the TGR is expected to deviate appreciably from the harmonic limit especially at low bombarding energies, owing to the incoherent contribution.

Nuclear spectroscopy, nuclear clustering and exotic shapes

Nuclear clustering has been a subject of intense study since the advent of heavy ion accelerators. Looking back more than 30 years, we are able today to see the connection between resonances in heavy ion reactions and extreme states in nuclei. In particular, excited states close to the decay thresholds into substructures show pronounced cluster structures. The ever repeated question about the possibility to describe such cluster phenomena in an extended (to a very large basis) and deformed shell model, has recently been revived in view of improved computational facilities. The new experimental facilities and the powerful new detector arrays for γ-spectroscopy and for charged particles have increased the sensitivity to study clustering phenomena by orders of magnitude. Today we are able to study nuclear structure at the limits of the mean field concept. With the advent of radioactive beams and the study of nuclei, which are weakly bound in their ground states, the question of the limits of mean field concepts has reached the low excitation energy region of nuclei.

RESONANCES IN HEAVY-ION REACTIONS: AN OVERVIEW OF CURRENT MODELS

Models of resonances in heavy-ion reactions are reviewed on the basis of recent experimental and theoretical results. Qualitative and quantitative agreement between experimental data and calculated quantities is examined. For nuclear systems where a sufficient quantity of data is available, a unified quasi-molecular description is presented. Future perspectives are discussed.

Excitation of giant resonances in heavy-ion reactions at intermediate energies: Results from the 40Ar + 90Zr and 208Pb experiments at 41 [formula omitted

Giant resonances in 90Zr and 208Pb have been studied by inelastic scattering of 40Ar at 41 MeV/u. Strength distributions and exhausted sum-rule values of different multipolarities are presented. The peak-to-background ratios and differential cross sections from inelastic scattering of heavy ions are compared to those obtained with light projectiles. The influence of Coulomb interaction on the excitation of giant resonances and the possibility to study high multipole resonances by intermediate-energy heavy ions are discussed.

Collective excitations of closed shell nuclei in heavy ion grazing collisions

Abstract The single and multiple excitations of giant resonances in heavy ion reactions is investigated in the framework of a microscopic model. The scattering process is treated semi-classically as in the Copenhagen model but the target response is constructed from a microscopic RPA calculation using Skyrme forces. The importance of an accurate description of excitation operators and transition form factors is stressed. The connection with other approaches (time-dependent Hartree-Fock approximation, boson expansion method, second RPA) is discussed. The model is applied to reactions involving 208 Pb and 40 Ca nuclei. We conclude that, under near-grazing conditions, with medium or heavy projectiles and for incident energies around 30 MeV/nucleon, there is a substantial probability of observing multiphonon states built on 2 7z.xl;hω giant resonances.

Resonances and nuclear molecular configurations in heavy-ion reactions

This paper presents a review of the phenomenon of resonances in heavy-ion reactions from the molecular-configuration standpoint. It gives an up-to-date list of recent experimental data (Sect. 2), reviews some of the basic models of resonances (Sect. 3) and describes some recent advances in heavy-ion resonance studies (Sect. 4). Finally (Sect. 5) it outlines some new lines of research.

Extension of the orbiting-cluster concept to fp shell systems

The orbiting-cluster model (OCM) of resonances in heavy-ion reactions is reviewed in the light of recent experimental results. Model predictions given earlier are compared with known data on resonances; good agreement is found. Slight modifications are introduced in the model making possible its application to a wide ensemble of heavy-ion systems in the composite mass range A = 22 to 72. Predictions of resonant behaviour are given for a number of systems. Limitations of the model are discussed.

Implications of angular momentum conservation for fluctuations in heavy ion reactions

A method is presented for calculating synthetic excitation functions and angular distributions which includes angular momentum conservation. The results of the calculations are used to study the effect of GAMMA/sub J//D/sub J/, the average coherence width divided by the average level density for each value of J, on fluctuations, angular distributions, and changes in the angular distributions near maxima in the excitation functions. The relation between GAMMA/sub J//D/sub J/ and the observation of resonances in heavy ion reactions is discussed. The implications of these studies on fluctuation analysis are also discussed.

Book review

Book review

On resonance phenomena in nuclear reaction cross sections

The conclusions obtained using the continuum shell model for resonance phenomena are compared with experimental data from the 52Cr+p reaction obtained at energies with and without isobaric analogue resonances. The influence of channel coupling on the result of an autocorrelation analysis is investigated for the 15N+n nuclear reaction cross section calculated theoretically. Some conclusions are drawn on resonances in heavy-ion reactions.

Application of a band-crossing model for resonances inO16+O16scattering

A band-crossing model that has been proposed as a possible mechanism for resonances in heavy ion reactions is applied to energy dependent structure in the $^{16}\mathrm{O}$ + $^{16}\mathrm{O}$ system. The recently observed intermediate-width structure in the 6.13 MeV gamma-radiation yield can be well understood in terms of the band-crossing model, assuming the crossing of the elastic potential resonance band and an aligned rotational band in which the intrinsic spin ($3\ensuremath{\hbar}$) and the relative angular momenta are coupled to their maximum value. Numerical calculations based on this model reproduce all of the observed energy dependent structure of the cross section in the $^{16}\mathrm{O}$ + $^{16}\mathrm{O}$ interaction, i.e., the gamma-radiation yield from the ${3}_{1}^{\ensuremath{-}}$ state of $^{16}\mathrm{O}$, as well as the total fusion and elastic scattering data. Each oscillation in the fusion excitation function is interpreted as reflecting a shape resonance of each new grazing partial wave in the entrance channel as it becomes active with increasing energy. The observed anticorrelation of the total fusion and the 90\ifmmode^\circ\else\textdegree\fi{} excitation function of elastic scattering data is reproduced naturally by the model. It is concluded that these data support the existence of nuclear molecular resonances in the $^{16}\mathrm{O}$ + $^{16}\mathrm{O}$ system.NUCLEAR REACTIONS $^{16}\mathrm{O}$ + $^{16}\mathrm{O}$ scattering, $10<~{E}_{\mathrm{c}.\mathrm{m}.}<~41$ MeV; calculated elastic scattering excitation functions, fusion cross sections, and ${3}_{1}^{\ensuremath{-}}$ inelastic cross sections. Resonance mechanism for heavy ion reactions.

On the nature of heavy-ion resonances in the40Ca composite system

The recent data on resonances in heavy-ion reactions proceeding through the composite 40Ca system via different entrance and exit channels are shown to be well understood within the predictions of an orbiting-cluster model based on the molecular-resonance window concept. A similar set of experiments to further explore the idea is suggested.

Resonances: Population of low-level density regions?

A simple explanation based primarily on the binding energies of nuclei in the entrance channel and level densities calculated with the shell model is proposed to explain the occurence of resonances in heavy-ion reactions for sd-shell nuclei.

Resonances in heavy-ion reactions as orbiting-cluster phenomena

The existing experimental evidence for resonances in heavy-ion reactions is interpreted in a unified way, based on the molecular resonance-window concept. Predictions are given for nuclear systems most likely to exhibit resonances.

A semiempirical prediction of resonances in heavy-ion reactions for s-d shell nuclei

A semiempirical prediction of the occurrence of resonances in heavy-ion reactions, based on an estimate of the spreading width of the resonances via level-density calculations, is attempted. The calculations are applied to heavy-ion reactions leading to composite nuclei in the s-d-shell region (24<or=A<or=32). The results agree well with existing experimental data and yield predictions on hitherto unobserved regions of resonances.

A Band Crossing Model of Resonances in Heavy Ion Reactions. I: Resonances in 12C-16O Scattering

A Band Crossing Model of Resonances in Heavy Ion Reactions. I: Resonances in 12C-16O Scattering

Schematic Model for Continuum Resonances in Heavy-Ion Reactions

The small widths of high-lying resonances can be explained by a fragmentation of a quasimolecular shape resonance through coupling to at least two exit doorway states.Received 9 May 1977DOI:https://doi.org/10.1103/PhysRevLett.39.3©1977 American Physical Society