arXiv subjects
Publications and source records attributed to Rajeev K. Puri.
We study the transverse flow for systems having various N/Z ratios. We find the transverse flow is sensitive to N/Z ratio and, in fact, increases with N/Z of the system. The relative contribution of symmetry energy and isospin dependence of nucleon-nucleon cross section is also investigated. We find the greater sensitivity of symmetry energy in the lighter systems compared to heavier ones.
We performed a systematic study of the formation of fragments with different mass ranges in 197Au+197Au collisions at incident energies between 20 - 1000 MeV/nucleon and at impact para- meter between ^b = 0-0.98. The aim of present study is to understand the complex dependence of fragment production on incident energy and impact parameter. Our results clearly indicate that the QMD simulations of 197Au+197Au predict different behavior for different mass ranges than for IMF's with a change in incident energy and impact parameter. All charge yields can be parameterized by a power law and no signal of liquid-gas phase transition is seen as no unique dependence of tau on impact parameter is seen.
We study the formation of fragments by extending the minimum spanning tree method (MST) for clusterization. In this extension, each fragment is subjected to a binding-energy check calculated using the modified Bethe-Weizsacker formula. Earlier, a constant binding-energy cut of 4 MeV/nucleon was imposed. Our results for 197Au +197 Au collisions are compared with ALADiN data and also with the calculations based on the simulated annealing technique. We shall show that the present modified version improves the agreement compared to the MST method.
We demonstrate the role of the mass asymmetry in the energy of vanishing flow by studying asymmetric reactions throughout the periodic table and over entire colliding geometry. Our results, which are almost independent of the system size and as well as of the colliding geometries indicate a sizable effect of the asymmetry of the reaction on the energy of vanishing flow.
We study the effect of isospin degree of freedom on the balance energy (E$_{bal}$) as well as its mass dependence throughout the mass range 48-270 for two sets of isobaric systems with N/Z = 1 and 1.4 at different colliding geometries ranging from central to peripheral ones. Our findings reveal the dominance of Coulomb repulsion in isospin effects on E$_{bal}$ as well as its mass dependence throughout the range of the colliding geometry.
We study the N/Z dependence of balance energy (E$_{bal}$) for isotopic series of Ca having N/Z varying from 1.0 to 2.0. We show that the N/Z dependence of E$_{bal}$ is sensitive to symmetry energy and its density dependence at densities higher than saturation density and is insensitive towards the isospin dependence of nucleon-nucleon cross section
We simulate the central reactions of nearly symmetric, and asymmetric systems, for the energies at which the maximum production of IMFs occurs (E$_{c.m.}^{peak}$).This study is carried out by using hard EOS along with cugnon cross section and employing MSTB method for clusterization. We study the various properties of fragments. The stability of fragments is checked through persistence coefficient and gain term. The information about the thermalization and stopping in heavy-ion collisions is obtained via relative momentum, anisotropy ratio, and rapidity distribution. We find that for a complete stopping of incoming nuclei very heavy systems are required.
We simulate the central reactions of nearly symmetric, and asymmetric systems, for the energies at which the maximum production of IMFs occurs (E$_{c.m.}^{peak}$).This study is carried out by using hard EOS along with cugnon cross section and employing MSTB method for clusterization. The mass dependence of various quantities (such as average and maximum central density, collision dynamics as well as the time zone for hot and dense nuclear matter) is also presented. In all cases (i.e., average and maximum central density, collision dynamics as well as the time zone for hot and dense nuclear matter) a power law dependence is obtained.
In the present study, we have simulated the central reactions of nearly symmetric and asymmetric systems over the entire periodic table for different values of energies using QMD model as event generator. These reactions are simulated for the different equations of state, nn cross-sections and different widths of Gaussians. We have observed that the multiplicity of IMFs shows a rise and fall with increase in beam energy in the center-of-mass frame as already predicted experimentally/theoretically. We have also studied the mass dependence of peak Ec.m. and peak . It has been observed that peak Ec.m. increases linearly with system mass whereas a power law dependence has been observed for peak IMFs with tau \approx 1.0. Our calculations using hard EoS along with cugnon cross-section and MSTB method are in good agreement with experimental data. Similar power law dependence is also observed for various fragments.
Collective flow and balance energy in asymmetric heavy-ion collisions
Influence of the Range of Interaction on the Stability of the Nucleus propagating with Momentum Dependent Interactions.
Our present studies has shown that the mass dependence of EVF show mass asymmetry independent behaviour. This is due the fact that with increase in asymmetry, the number of nucleon-nucleon collisions and repulsive Coulomb interactions decreases, therefore EVF increases. The increase in EVF with asymmetry is more for lighter nuclei as compared to heavier nuclei due to the further less magnitude of Coulomb repulsions in lighter nuclei as compared to heavier ones.
We study the stability of fragments using microscopic binding energy criteria in heavy-ion collisions.
In the present study we find that nuclei having double width do not emit free nucleons for a long period of time necessary to study heavy-ion collisions. Also, the ground state properties of all the nuclei are also described well. In the low mass region, the obtained nuclei are less bound but stable. Heavy mass nuclei have proper binding energy and are stable
We study the effect of isospin degree of freedom on the balance energy (E$_{bal}$) as well as its mass dependence throughout the mass range 48-270 for two sets of isobaric systems with N/Z = 1 and 1.4 at different colliding geometries ranging from central to peripheral ones. Our findings reveal the dominance of Coulomb repulsion in isospin effects on E$_{bal}$ as well as its mass dependence throughout the range of the colliding geometry. Our results also indicate that the effect of symmetry energy and nucleon-nucleon cross section on E$_{bal}$ is uniform throughout the mass range and throughout the colliding geometry. We also present the counter balancing of nucleon-nucleon collisions and mean field by reducing the Coulomb and the counter balancing of Coulomb and mean filed by removing the nucleon-nucleon collisions.
Using an isospin-dependent quantum molecular dynamics (IQMD) model, nuclear stopping is analyzed in asymmetric colliding channels by keeping the total mass fixed. The calculations have been carried by varying the asymmetry of the colliding pairs with different neutron-proton ratios in center of mass energy 250 MeV/nucleon and by switching off the effect of Coulomb interactions. We find sizable effect of asymmetry of colliding pairs on the stopping and therefore on the equilibrium reached in a reaction.
A study of elliptical flow is presented with respect to the asymmetry of colliding nuclei using the reactions of 24Cr50 +44 Ru102, 16S32 +50 Sn120 and 8O16 +54 Xe136 at incident energies between 50 and 250 MeV/nucleon within the framework of isospin-dependent quantum molecular dynamics model. For the present analysis, total mass of the colliding pairs is kept fixed and asymmetry is varied as ? = 0.2, 0.3, 0.7. The elliptical flow shows a transition from in-plane to out-of-plane in the mid rapidity region with incident energy. The transition energy is found to increase with the asymmetry for lighter fragments.
We have studied the fragment production mechanism in the set of four reactions 197Au79+12C6, 197Au79+26Al13, 197Au79+63Cu29 and 197Au79+208Pb82. The reactions are simulated at an energy 600 MeV/nucleon and collision geometry is varied from central to peripheral (= b/bmax = 0 to 1). A theoretical investigation has been carried out on the study of mass dependence of intermediate mass fragments (5\leqA\leqAtot/6) and other fragments. It is observed that multiplicity shows a good agreement for low Zbound, but it fails for high Zbound. This failure is due the method of analysis MST which we had used in our analysis, because MST method gives one heavy cluster at the time of high density. The discrepancy between theory and experiments can be removed by using reduced isospin dependent NN cross section and sophisticated clustrization algorithm SACA.