• S Bhattacharya

Articles written in Pramana – Journal of Physics

• Fusion of light exotic nuclei at near-barrier energies: Effect of inelastic excitation

The effect of inelastic excitation of exotic light projectiles (proton-as well as neutron-rich)17F and11Be on fusion with heavy target has been studied at near-barrier energies. The calculations have been performed in the coupled channels approach where, in addition to the normal coupling of the ground state of the projectile to the continuum, inelastic excitation of the projectile to the bound excited state and its coupling to the continuum have also been taken into consideration. The inclusion of these additional couplings has been found to have significant effect on the fusion excitation function of neutron-rich11Be on208Pb whereas the effect has been observed to be nominal for the case of proton-rich17F on the same target. The pronounced effect of the channel coupling on the fusion process in the case of11Be is attributed to its well-developed halo structure.

• Small-angle neutron scattering study of aggregate structures of multi-headed pyridinium surfactants in aqueous solution

The aggregate structures of a set of novel single-chain surfactants bearing one, two and three pyridinium headgroups have been studied using small-angle neutron scattering (SANS). It is found that the nature of aggregate structures of these cationic surfactants depend on the number of headgroups present in the surfactants. The single-headed pyridinium surfactant forms the lamellar structure, whereas surfactants with double and triple headgroups form micelles in water. The aggregates shrink in size with increase in the number of headgroups in the surfactants. The aggregation number (N) continually decreases and the fractional charge (α) increases with more number of headgroups on the surfactants. The semimajor axis (a) and semiminor axis (b = c) of the micelle also decrease with the increase in the number of headgroups in the surfactants. This indicates that hydrocarbon chains in such micelles prepared from multiheaded surfactants adopt bent conformation and no longer stay in extended conformation.

• Experimental study of the $\pi h_{11/2}$ band in 113Sb

In the present work, the excited states of 113Sb were populated in the 100Mo(20Ne, $p6n$) reaction at a beam energy of 136 MeV. States only up to $59/2^−$ were observed in the $\Delta J = 2$ band. Mean lifetimes for the ﬁve states (from 4460 to 7998 keV) were measured for the ﬁrst time using Doppler shift attenuation method. An upper limit of the lifetime (0.14 ps) was estimated for the 9061 keV, $47/2^−$ state. The $B(E2)$ values, derived from the present lifetime results, correspond to a large quadrupole deformation of $\beta_2 = 0.32$. The observed reduction in the experimental $B(E2)$ values for the 918.4 keV (spin $39/2^− \to 35/2^−$) and 985 keV (spin $43/2^− \to 39/2^−$) transitions may be interpreted as due to the proton alignement in the $g_{7/2}$ orbital. The dynamic moment of inertia was observed to be about half of the rigid body value at the highest observed frequency.

• Decay of Hoyle state

The prediction of Hoyle state was necessitated to explain the abundance of carbon, which is crucial for the existence of life on Earth and is the stepping stone for understanding the abundance of other heavier elements. After the experimental confirmation of its existence, soon it was realized that the Hoyle state was `different’ from other excited states of carbon, which led to intense theoretical and experimental activities over the past few decades to understand its structure. In recent times, precision, high statistics experiments on the decay of Hoyle state have been performed at the Variable Energy Cyclotron Centre, to determine the quantitative contributions of various direct $3\alpha$ decay mechanisms of the Hoyle state. The present results have been critically compared with those obtained in other recent experiments and their implications have been discussed.

• Fusion–fission dynamics studies using mass distribution as a probe

Study of quasifission reaction mechanism and shell effects in compound nuclei has important implications on the synthesis of superheavy elements (SHE). Using the major accelerator facilities available in India, quasifission reaction mechanism and shell effects in compound nuclei were studied extensively. Fission fragment mass distribution was used as a probe. Two factors, viz., nuclear orientation and direction of mass flow of the initial dinuclear system after capture were seen to determine the extent of quasifission. From the measurement of fragment mass distribution in 𝛼-induced reaction on actinide targets, it was possible to constrain the excitation energy at which nuclear shell effect washed out.

• # Pramana – Journal of Physics

Volume 94, 2020
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Posted on July 25, 2019

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