120551696
alpha-particle emission as a probe of dynamical deformations
We have measured alpha-particle spectra at different laboratory angles from the fusion reaction Si-28+V-51 at 140 MeV. These spectra deviate at higher energies from the statistical model calculations using rotating liquid drop model values of the moment of inertia. In order to explain the experimental spectra, changes were required in the moments of inertia corresponding to deformation, which suggests dynamical effects on the deexcitation process for charged-particle emission. The comparison of decay times with formation times implies that light charged particles are preferentially emitted prior to the full relaxation of the compound nucleus. Statistical models and dynamical calculations have been employed in an attempt to interpret the experimental data. The results were compared with the Si-28+Al-27 system studied earlier in order to understand the symmetric and asymmetric entrance channel effects in the formation of the compound system.
124715654
Search for an effect of shell closure on nuclear dissipation via a neutron-multiplicity measurement
120052850
Search for entrance channel effects in heavy ion induced fusion reactions through the compound system79Rb
122194176
Search for entrance channel effects in heavy ion induced fusion reactions via neutron evaporation
120167461
Anomalous behavior of the level density parameter in neutron and charged particle evaporation
The compound nucleus $^{76}\mathrm{Kr}*$ was populated at the excitation energy of $75\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$ and angular momentum of $39\ensuremath{\hbar}$ in fusion reactions with two complementary, mass-symmetric $(^{31}\mathrm{P}+^{45}\mathrm{Sc})$ and mass-asymmetric $(^{12}\mathrm{C}+^{64}\mathrm{Zn})$ entrance channels. The neutron evaporation spectra were measured and compared with the predictions of statistical model calculations using the transmission coefficients for the spherical nuclei in the inverse absorption channel, the rotating liquid drop model moment of inertia, and the normal systematic value of $A∕8$ for the level density parameter $a$. The results for the mass-asymmetric reaction are found to be consistent with the predictions of the statistical model calculations. However, for the mass-symmetric reaction $(^{31}\mathrm{P}+^{45}\mathrm{Sc})$, the experimental spectra are found to be harder than the theoretical neutron spectra and the statistical model calculations require a lower value of $A∕10$ for the parameter $a$ to reproduce the shape of the experimental spectra, indicating the neutron to be evaporated at higher temperature for the same excitation energy and angular momentum in symmetric system. According to the dynamical model, the formation time $(37\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}22}\phantom{\rule{0.3em}{0ex}}\mathrm{sec})$ of the compound nucleus for the symmetric $^{31}\mathrm{P}+^{45}\mathrm{Sc}$ system is significantly higher than that $(29\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}22}\phantom{\rule{0.3em}{0ex}}\mathrm{sec})$ for the asymmetric $^{12}\mathrm{C}+^{64}\mathrm{Zn}$ system. This may probably lead to the formation of a temperature-equilibrated dinuclear complex that may be responsible for neutron emission at higher temperature in the case of the symmetric system.
123993434
Theoretical interpretation of the systematics of effective single-particle level densities from (n,p) reactions at 14.8 MeV energy
The universal experimental data for the energy-integrated angular distribution and the angle-integrated energy spectra for protons emitted from the (n,p) reactions at 14.8 MeV incident energy were analyzed earlier using the computer code PRECO-D2, developed on the basis of Kalbach’s semiempirical model for the preequilibrium reactions. The results of the analysis provided the semiempirical systematics of the single-particle level densities gR(exp) (effective in the residual nuclei) and gc(exp) (effective in the composite system). In order to interpret these results, we have carried out the theoretical calculations with Shlomo’s theory developed on the basis of the Green’s function approach. The theoretical values based on Shlomo’s theory for g Th (eRn )a ndg Th Rp (eRp) for the residual nucleus and g Th cn (ecn )a ndg Th cp (ecp ) for the composite systems, respectively, were calculated at various excitation energies by using a reasonable single-particle nuclear potential strength V0 ,a vailable from systematics in literature. Here, eRn and eRp are the single-particle excitation energies for single-particle level densities for the residual nucleus, and ecn and ecp are the single-particle excitation energies of effective single-particle level densities for the composite system for neutrons and protons, respectively. The Coulomb interaction potential Vc was included for protons over and above the nuclear potential V0. The total theoretical values were taken as g TTh (eR) = g Th Rn(eRn) + g Th Rp (eRp) for residual nuclei and g TTh c (ec) = g Th cn (ecn) + g TTh cp (ecp ) for the composite system. eR is the Fermi energy of the total effective single-particle level density for residual nuclei, and ec is the excitation energy of the effective single-particle level density of the composite system. Careful comparison of theoretical and experimental results shows that gR(exp) matches with g TTh R (ef )f orV i 0 = 45 MeV where (ef ) is the Fermi energy. The theoretical values g TTh (ef ) also nearly agree with the previously reported values by various groups, obtained through different approaches for a large number of cases. The values of gc(exp) always are found to be greater than gR(exp) and match with g TTh c (ec) at effective excitation energies ec, which are found to be invariably much higher than the respective ef and are positive and follow the nuclear shell model structure when plotted against A. This supports the concept that the values of effective gc(exp) are decided mainly by dominant transition, which occurs during initial stages of the multistep statistical direct preequilibrium process that involves unbound states. The values of gR(exp), on the other hand, are found to correspond to the effective eR around the Fermi energies of the bound states of residual nuclei involved in the decay processes. The ratios of gc(exp)/gR(exp) are found to follow the ( � e c� � ef � ) 1/2 f description and to match Shlomo’s theory.
73714687
Charged Hadron Multiplicity Distribution at Relativistic Heavy-Ion Colliders
The present paper reviews facts and problems concerning charge hadron production in high energy collisions. Main emphasis is laid on the qualitative and quantitative description of general characteristics and properties observed for charged hadrons produced in such high energy collisions. Various features of available experimental data, for example, the variations of charged hadron multiplicity and pseudorapidity density with the mass number of colliding nuclei, center-of-mass energies, and the collision centrality obtained from heavy-ion collider experiments, are interpreted in the context of various theoretical concepts and their implications. Finally, several important scaling features observed in the measurements mainly at RHIC and LHC experiments are highlighted in the view of these models to draw some insight regarding the particle production mechanism in heavy-ion collisions.
118721274
Wounded quarks and multiplicity at relativistic ion colliders
In this paper, we propose a parameterization which is based on a phenomenological model involving the wounded quarks interactions for explaining the average charged particle multiplicity 〈nch〉, the central pseudo-rapidity density 〈(dn/dη)η=0〉 and the complete rapidity dependence of dn/dη in relativistic heavy-ion collider experiments. The model also interrelates nucleus-nucleus (A-A collisions with p-A and p-p interactions. Our parameterization rests on simple assumptions regarding the mean number of participating quarks and their average number of collisions. The results for 〈nch〉 and their variations with the mass number of colliding nuclei, center-of-mass energy (√sNN) and collision centrality are well supported by the available experimental data. Finally we give the predictions from our model for A-A collisions at the Large Hadron Collider (LHC) and Compressed Baryonic Matter (CBM) experiments. Our results indicate the existence of a possible universal production mechanism for p-p, p -A and A-A collisions.
119414440
Cometary panspermia explains the red rain of Kerala
Red coloured rain occurred in many places of Kerala in India during July to September 2001 due to the mixing of huge quantity of microscopic red cells in the rainwater. Considering its correlation with a meteor airbust event, this phenomenon raised an extraordinary question whether the cells are extraterrestrial. Here we show how the observed features of the red rain phenomenon can be explained by considering the fragmentation and atmospheric disintegration of a fragile cometary body that presumably contains a dense collection of red cells. Slow settling of cells in the stratosphere explains the continuation of the phenomenon for two months. The red cells under study appear to be the resting spores of an extremophilic microorganism. Possible presence of these cells in the interstellar clouds is speculated from its similarity in UV absorption with the 217.5 nm UV extinction feature of interstellar clouds.
83809193
New biology of red rain extremophiles prove cometary panspermia
This paper reports the extraordinary biology of the microorganisms from the mysterious red rain of Kerala, India. These chemosynthetic organisms grow optimally at an extreme high temperature of 300 degrees C in hydrothermal conditions and can metabolize inorganic and organic compounds including hydrocarbons. Stages found in their life cycle show reproduction by a special multiple fission process and the red cells found in the red rain are identified as the resting spores of these microbes. While these extreme hyperthermophiles contain proteins, our study shows the absence of DNA in these organisms, indicating a new primitive domain of life with alternate thermostable genetics. This new biology proves our earlier hypothesis that these microbes are of extraterrestrial origin and also supports our earlier argument that the mysterious red rain of Kerala is due to the cometary delivery of the red spores into the stratosphere above Kerala.
119347677
On the Shallow Decay of Some GRB Afterglows
Half of the radio afterglows for which there is a good temporal coverage exhibit, after 10 days from the burst, a decay which is shallower than at optical frequencies, contrary to what is expected within the simplest form of the standard model of relativistic fireballs or jets. We investigate possible ways to decouple the radio and optical decays. First, the radio and optical emissions are assumed to arise from the same electron population, and we allow for either a time‐varying slope of the power‐law distribution of electron energy or for time‐varying microphysical parameters. Then we consider two scenarios where the radio and optical emissions arise in distinct parts of the GRB outflow, either because the outflow has an angular structure or because there is a long‐lived reverse shock. We find that only the last scenario is compatible with the observations.