Orbiting features in the strongly damped binary decay of the Si28+ O16 system (original) (raw)
Related papers
Orbiting features in the strongly damped binary decay of the 28Si + 16O systems
The binary decay into strongly damped fragments and the quasielastic reactions of the 28 Siϩ 16 O system were measured at E lab ϭ107.5 and 139.0 MeV in the angular range of 30°р c.m. р150°using kinematic coincidence. The loss in the binary decay cross section due to light particle evaporation by the highly excited fragments was evaluated. The Q-value-integrated angular distributions of the primary decay exhibit the 1/sin c.m. behavior at backward angles, indicating a long lifetime. Mass distributions and the 16 O/ 12 C ratio suggest a noncompound process for the reaction mechanism. Coupled-channels calculations, including a great number of channels populated in the reactions, yield good agreement with the experimental angular distributions. ͓S0556-2813͑96͒03605-9͔
Physical Review C, 2021
The investigation of fusion reactions involving light neutron-rich exotic nuclei is of paramount significance to understand nucleosynthesis in astrophysical scenarios. It is also estimated as a possible heat source to ignite 12 C + 12 C reaction and production of x-ray superbursts from accreting neutron star. Recently, the fusion of neutron-rich 20 O with 12 C target has been studied with measurement of fusion cross-section (σ fus). Bass model under predicts the σ fus and time-dependent Hartree-Fock model also fails to explain the experimental data. To explicate the same, the investigation of 20 O + 12 C reaction at near barrier energies has been made within quantum mechanical fragmentation-based dynamical cluster-decay model (DCM). Within DCM, the fragmentation potential comprises temperature-dependent Coulomb, nuclear and centrifugal potentials, along with temperature-dependent binding energies (T.B.E.) calculated within the macroscopic approach of Davidson mass formula. Recently, we have explored the temperature-dependence of different nuclear properties and nuclear symmetry energy within microscopic relativistic mean-field (RMF) theory [M. Kaur et al., Nucl. Phys. A 1000, 121871 (2020)]. In the present work, we inculcate the microscopic T.B.E. from RMF theory within DCM and investigate the structure of fragmentation potential for 32 Si * formed in 20 O + 12 C reaction, comparatively for macroscopic (mac) and microscopic (mic) T.B.E. obtained from Davidson mass formula and RMF theory, respectively. The structure and magnitude of fragmentation potential are found to change drastically/notably along with a change in energetically favored/minimized fragments for both choices of T.B.E. The α particles (4 He, 5 He) are favored at lower angular momenta in fragmentation profile for mic T.B.E. case only, which is in the agreement with predictions of statistical model results. This change in the nuclear structure embodied via fragmentation potential energy carries its imprints in the preformation probability P 0 of different fragments and affects the contribution of individual light-charged particle (LCP) channel in the σ fus. A comparison of the relative cross-section of different LCP channels toward σ fus is quite different for both cases of T.B.E. The cross-section of 2 H and 4 He LCP channels is relatively enhanced for mic T.B.E. compared to mac T.B.E. Among different LCP channels, the 5 He channel is the major contributor in σ fus , which is in line with the results of the statistical EVAPOR model. The DCM-calculated σ fus is in agreement with the experimental data.
Dissipative Orbiting in 136^{136}136Xe+$^{209}$Bi Reactions at 28 and 62 AAAMeV
Acta Physica Polonica B, 2015
Correlations between the energy, charge and the deflection angle of the projectile-like fragments were studied for the 136 Xe + 209 Bi reaction at E/A = 28 and 62 MeV. These correlations are seen to exhibit features characteristic of dissipative orbiting, commonly found at bombarding energies of a few MeV/nucleon above the interaction barrier, but also reported in the Fermi-energy domain. It was found, that in the studied bombarding energy range, the reaction cross section is still dominated by the dissipative binary reactions of well defined projectile-and target-like fragments.
Fusion and binary-decay mechanisms in the 35Cl+24Mg system at E/A≈8 MeV
Physical Review C, 1998
Compound-nucleus fusion and binary-reaction mechanisms have been investigated for the 35 Clϩ 24 Mg system at an incident beam energy of E lab ϭ 282 MeV. Charge distributions, inclusive energy spectra, and angular distributions have been obtained for the evaporation residues and the binary fragments. Angle-integrated cross sections have been determined for evaporation residues from both the complete and incomplete fusion mechanisms. Energy spectra for binary fragment channels near the entrance-channel mass partition are characterized by an inelastic contribution that is in addition to a fully energy damped component. The fully damped component which is observed in all the binary mass channels can be associated with decay times that are comparable to, or longer than, the rotation period. The observed mass-dependent cross sections for the fully damped component are well reproduced by the fission transition-state model, suggesting a fusion followed by fission origin. The present data cannot, however, rule out the possibility that a long-lived orbiting mechanism accounts for part or all of this yield. ͓S0556-2813͑98͒02302-4͔
Molecular resonance and highly deformed fission fragments in 28Si+28Si
Physical Review C, 2000
A high-resolution measurement of fragment-fragment-␥ triple coincidence events in the symmetric and near-symmetric mass exit channels from the 28 Siϩ 28 Si reaction has been undertaken using the EUROGAM Phase II ␥-ray spectrometer. The bombarding energy of E lab ( 28 Si)ϭ111.6 MeV has been selected to populate the conjectured J ϭ38 ϩ quasimolecular resonance in the 56 Ni dinuclear system. In the 28 Siϩ 28 Si symmetric mass exit channel, the resonance behavior is clearly verified at the chosen energy. The population of highly excited states in the 24 Mg, 28 Si, and 32 S nuclei is discussed within a statistical fusion-fission model. Evidence is presented for selective population of states in the 28 Si fragments arising from the symmetric fission of the 56 Ni compound nucleus. The enhanced population of the K ϭ3 1
Binary decay of Ni56 formed in the 32S+24Mg reaction
Physical Review C, 1989
Fully energy-damped yields from the S+ Mg reaction have been measured at center-of-mass energies of E, =51.6 and 60.5 MeV with the use of an experimental arrangement where both of the resulting heavy fragments could be detected in coincidence. Energy, velocity, and angular distributions 'of the reaction fragments have been determined. The cross sections prior to secondary light-particle emission have been deduced for the breakup of the compound system into different mass channels. These data are discussed in terms of two possible reaction mechanisms: fusion followed by fission and deep-inelastic orbiting.
Physical Review C, 2005
The dynamical cluster-decay model (DCM) is developed further for the decay of hot and rotating compound nuclei (CN) formed in light heavy-ion reactions. The model is worked out in terms of only one parameter, namely the neck-length parameter, which is related to the total kinetic energy TKE(T) or effective Q-value Q ef f (T) at temperature T of the hot CN, defined in terms of the CN binding energy and ground-state binding energies of the emitted fragments. The emission of both the light-particles (LP), with A≤4, Z≤2, as well as the complex intermediate mass fragments (IMF), with 4<A<20, Z>2, is considered as the dynamical collective mass motion of preformed clusters through the barrier. Within the same dynamical model treatment, the LPs are shown to have different characteristics as compared to the IMFs. The systematic variation of the LP emission cross section σLP , and IMF emission cross section σIMF , calculated on the present DCM match exactly the statistical fission model predictions. It is for the first time that a non-statistical dynamical description is developed for the emission of light-particles from the hot and rotating CN. The model is applied to the decay of 56 N i * formed in the 32 S+ 24 Mg reaction at two incident energies Ec.m.=51.6 and 60.5 MeV. Both the IMFs and average T KE spectra are found to compare resonably nicely with the experimental data, favoring asymmetric mass distributions. The LPs emission cross section is shown to depend strongly on the type of emitted particles and their multiplicities.
2020
A useful tool to underline possible structure effects on the competition between different reaction mechanisms, which may change the expected decay chain probability, is the exclusive study of light charged particles emission from hot light composite systems. In particular, the influence of projectile structure may be evidenced by studying the competition between fast and thermal emissions. In this framework, the four reactions 16 O+ 30 Si, 18 O+ 28 Si, 19 F+ 27 Al at 7 MeV/u and 16 O+ 30 Si at 8 MeV/u have been carried out using the GARFIELD+RCo array at Legnaro National Laboratories. Some anomalies in the α-particle emission channels have been evidenced in the measurements reported above, showing in an exclusive way the observed effects related to the entrance channels. The experimental results are compared to statistical model predictions, for which the same filtering and complete event selection have been applied.
Fission fragment spectroscopy on a 28^{28}28Si + 28^{28}28Si quasi-molecular resonance
1997
Fragment-fragment-γ triple coincident measurements of the 28 Si + 28 Si reaction at E lab. = 111.6 MeV carefully chosen to populate J = 38 + resonance have been performed at the VIVITRON tandem facility by using Eurogam Phase II γ-ray spectrometer. In the 28 Si + 28 Si exit-channel, the resonance behavior of the 28 Si + 28 Si reaction at the beam energy is clearly confirmed. An unexpected spin disalignment has been observed in the measured angular distributions in the elastic, inelastic, and mutual excitation channels. This disalignment is found to be consistent with particle-γ angular correlations and supported by the molecular model prediction of a "butterfly motion". The K π = 0 + 3 band corresponding to the large prolate deformation of the 28 Si is more intensely fed in the resonance region. The selective population of highexcited states are discussed within a statistical fusion-fission model. In the 32 S + 24 Mg exit-channel, the spectroscopic study of the 32 S, has revealed the contribution of a new γ-ray transition 0 + (8507.8 keV) → 2 + 1 (2230.2 keV).