Recoil study of multinucleon transfer reactions: Capture of six charges by Nd targets in Ar induced reactions

doi:10.1016/0375-9474(74)90447-3

Nuclear Physics A

Volume 228, Issue 1, 5 August 1974, Pages 85-111

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Abstract

Multinucleon transfer reactions induced with Ar ions and involving the capture of six charges by the target have been studied. The targets were all the separated isotopes of Nd, and the observed nuclei were ^149gTb, ¹⁵⁰Dy, ¹⁵¹Dy. The experimental technique involved the measurement of the cross sections, angular distributions, and recoil range at each recoil angle, of the heavy residual nuclei. After transformation of the data into the c.m. system, the angular distributions appear to be peaked backwards, close to 180°. This observation suggests that the present reactions are of the same type as the multinucleon transfer reactions studied by other authors for which the angular distribution of the light fragment was peaked forward in the c.m. system. The energy distributions in the c.m. system were used to check the feasibility of various mechanisms which could lead to the production of the observed isotopes. Each mechanism was supposed to be a two-step process: the first step was the exchange, from the projectile to the target, of a number n of nucléons, leading to an excited intermediate nucleus, and the second step the deexcitation of the intermediate nucleus by nuclear evaporation. This analysis indicates that the most probable mechanisms correspond to n close to 12 (6 protons and 6 neutrons), and to an excitation energy of about 60 MeV for the intermediate nucleus. The distribution of cross sections versus the number of nucléons gained by the target is also in accord with this reaction model.

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Cross sections and recoil range measurements of the rare-earth isotones (N = 84–85) formed in ⁴⁰Ar induced reactions at E_lab = 1.76 GeV have been performed. An electrostatic collection method associated to a gas flow transport was used. The various experimental results plead in favor of an origin of these residues in the decay of highly excited precursors. Such excited precursors can be explained by an incomplete fusion mechanism. Comparisons with existing theoretical models (an extended abrasion-ablation model and intranuclear cascade calculations) have been performed.
Influence of the potential energy surface on the cross sections for deeply inelastic transfer reactions induced by heavy ions
1984, Nuclear Physics, Section A
Large differences are observed in the cross sections for deeply inelastic reactions involving the transfer of several charges from ⁴⁰Ca and ⁴⁰Ar projectiles to the same rare-earth targets. The cross sections for four and six charge transfers from projectile to target are enhanced for ⁴⁰Ca incident ions. These differences are qualitatively explained by considering that the drift paths in the (Z, A) plane are governed by a static potential energy surface which describes the composite system. Shell corrections have been included in the calculation of this potential energy surface.
Cross sections for deeply inelastic transfer reactions induced by heavy ions in rare-earth targets
1982, Nuclear Physics, Section A
Cross sections have been measured for deeply inelastic transfer reactions leading to the production of several radio-nuclides. Rare-earth targets were used and the projectiles were Ar, Cr, Fe and Cu ions. The reactions studied corresponded to transfers of two to nine protons and variable numbers of neutrons. The results obtained were used to study the evolution of some characteristics of these reactions, such as integrated cross sections and widths of the isotopic distributions, versus incident mass and transferred mass. These results confirm that mass transfer is driven by the potential energy of the composite system. The decrease of cross sections for increasing charge transfer may be quantitatively explained by assuming thermodynamical equilibrium of the mass asymmetry degree of freedom.
Complete fusion and transfer reactions induced by 273 MeV 40Ar on 159Tb
1979, Nuclear Physics, Section A
The nuclear reactions induced by 273 MeV⁴⁰Ar ions on a¹⁵⁹Tb target have been studied using recoil techniques and off-line X-ray spectrometry. The heavy products from fusionevaporation, fusion-fission, and transfer reactions can easily be separated on the basis of charge identification by X-ray spectrometry. The corresponding angular and range distributions are typical of each process. For each value of the atomic number, the average mass of the evaporation residues was determined with an uncertainty of ± 2 mass units (i.e.±1 %). The data were consistent with the assumption that 9±2 particles (nucleon and possibly some α-particles) were evaporated by the compound nucleus. The range measurements give results which agree with calculated values based on the total momentum transfer hypothesis within ± 8 %. The c.m. angular and energy distributions of transfer reaction products are typical of deep inelastic transfer reactions, with a contribution from partially damped events. The comparison of experimental data with the results of a calculation based on the model of Ngoˆand Hofmann in which statistical fluctuations are explicitly taken into account, indicates that the model reproduces correctly the position of the angular distribution maxima, for one- and two-charge transfer reactions, but underestimates the width of the angular distributions. Moreover, no transfer of more than two charges from the projectile to the target is predicted by this model while significant cross sections are observed experimentally.
Deep inelastic transfer reactions - The new type of reactions between complex nuclei
1978, Physics Reports
The review deals with a new type of nuclear reaction, deep inelastic transfe, which occurs in collisions of two complex nuclei. The following experimental features of the new reaction are discussed: (1) intense dissipation of collision kinetic energy, (2) anisotropic angular distributions of the reaction products, (3) broad charge and mass distributions of the products, (4) regularities of the cross sections of reaction exit channels, (5) the neutron-to-proton ratio of the products, and (6) the two-body character of the reaction mechanism. Special emphasis is laid on the impossibility of interpreting these features in terms of direct reactions and compound-nucleus decay. The concept of a double nuclear system formed in deep inelastic collisions of complex nuclei is introduced and grounded. The experimental features of deep inelastic transfers are interpreted in terms of this concept. The experimental techniques used to study deep inelastic transfers and the main approaches to their theoretical analysis are briefly summarized. The possible uses of the new type of reaction to investigate the processes of compound nucleus formation, production of the isotopes of light elements far from the region of β-stability, production of heavy isotopes of transfermium elements and fast-rotating nuclei with fixed spin orientation in space are considered.
Evolution from deep inelastic transfer to quasi-fission
1977, Nuclear Physics, Section A
Recoil techniques have been used to study the evolution of the features of four-charge transfer reactions in ¹⁴⁸Sm targets when the mass and energy of the projectile are varied. Beams of ⁶³Cu and ⁵⁶Fe were used, and their energies were chosen in order to be equal to 1.2B and 1.5B for both projectiles, B being the interaction barrier. The residual nuclei ^149gTb, ¹⁵⁰Dy and ¹⁵¹Dy were identified by their radioactive properties. This study has shown a continuous evolution of the characteristics of the c.m. angular distributions, especially the position of the maxima, from typical deep inelastic transfer to quasi-fission features, when the value of $E B$ decreases. For equal values of this ratio, no difference was observed between Fe and Cu induced reactions. The c.m, energies corresponding to the maximum cross section increases when the incident energy is increased, for a given projectile. At low incident energies (igE = 1.2B), the relative motion appears to be completely damped, and the distance of the two nuclei after separation is equal to about 5 fm. At higher incident energies, the c.m. energy is significantly higher. This may mean that the relative motion is not completely damped. Part of the effect may be explained by the differences in the angular momenta involved in the reaction.

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^†: Permanent address: Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA.

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Nuclear Physics A

Abstract

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Cited by (16)

Target residue cross sections and recoil energies from the reaction of 1760 MeV <sup>40</sup>Ar with medium and heavy targets

Influence of the potential energy surface on the cross sections for deeply inelastic transfer reactions induced by heavy ions

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Complete fusion and transfer reactions induced by 273 MeV <sup>40</sup>Ar on <sup>159</sup>Tb

Deep inelastic transfer reactions - The new type of reactions between complex nuclei

Evolution from deep inelastic transfer to quasi-fission