• AJAY KUMAR

Articles written in Pramana – Journal of Physics

• Radon exhalation studies in building materials using solid-state nuclear track detectors

Indoor radon has been recognized as one of the health hazards for mankind. Building materials constitute the second most important source of radon in dwellings. The common building materials used in the construction of dwellings are studied for radon exhalation rate. The ‘Can’ technique using LR-115 type-II solid-state nuclear track detector has been used for these measurements. The radon exhalation rate in these samples varies from 4.75 m Bq m−2 h−1 (0.14 m Bq kg−1 h−1) for limestone to 506.76 m Bq m−2 h−1 (15.24 m Bq kg−1 h−1) for soil.

• Lattice vibrational properties of transition metal carbides (TiC, ZrC and HfC)

Lattice vibrational properties of transition metal carbides (TiC, ZrC and HfC) have been presented by including the effects of free-carrier doping and three-body interactions in the rigid shell model. The short-range overlap repulsion is operative up to the second neighbour ions. An excellent agreement has been obtained between theory and experiment for their phonon dispersion curves and Debye temperature variations. It is concluded that the contributions of free-carrier doping and three-body interactions are essential for the description of the lattice dynamics of these carbides.

• Properties ofBc meson

The mass spectrum ofcb meson is investigated with an effective quark-antiquark potential of the form -αc/r +Arνwith ν varying from 0.5 to 2.0. TheS andP-wave masses, pseudoscalar decay constant, weak decay partial widths in spectator model and the lifetime ofBcmeson are computed. The properties calculated here are found to be in good agreement with other theoretical and experimental values at potential index,ν = 1

• A high resolution X-ray crystal spectrometer to study electron and heavy-ion impact atomic collisions

We have studied fast ion–atom and electron–atom collision processes using a reconditioned high resolution X-ray spectrometer. The X-rays, generated by the collisions, are dispersed by a curved ADP crystal (Johansson geometry) and detected by a gas proportional counter. A self-written LabVIEW based program has been used to give precise and controlled movement to the crystal and for data acquisition. The performance was tested by detecting the K𝛼 diagram and satellite lines of several elements. The K𝛼 satellite lines of Al have been studied in collision with 3–12 keV electrons and 40 MeV C4+ ions. In ion collisions as large as four L-vacancies are created simultaneously with the K-vacancy, compared to two satellites in case of the e-impact. In addition, we have measured the X-rays from H-, He- and Li-like Si ions which arise due to the electron loss/capture process in highly charged 80 MeV Si7+ ions in collision with thin carbon foil. Approximate charge state distribution has been obtained using this new technique.

• Heavy flavor baryons in hypercentral model

Heavy flavor baryons containing single and double charm (beauty) quarks with light flavor combinations are studied using the hypercentral description of the three-body problem. The confinement potential is assumed as hypercentral Coulomb plus power potential with power index 𝜈. The ground state masses of the heavy flavor, $J^{P} = \dfrac{1}{2}^{+}$ and $\dfrac{3}{2}^{+}$ baryons are computed for different power indices, 𝜈 starting from 0.5 to 2.0. The predicted masses are found to attain a saturated value in each case of quark combinations beyond the power index $\nu = 1.0$.

• Spectral distribution of the $2S \to 1S$ two-photon transition in atoms and few-electron ions

The two-photon decay of the $2S$ state to the ground state in dressed atoms and oneor two-electron ions has been studied for several decades. Relativistic calculations have shown an 𝑍-dependence of the spectral shape of this two-photon transition in one- or two-electron ions. We have measured the spectral distribution of the $1s2s {}^1 S_0 \to 1_s {}^2 {}^1 S_0$ two-photon transition in He-like tin at the ESR storage ring using a new approach for such experiments. In this method, relativistic collisions of initially Li-like projectiles with a gaseous target were used to populate exclusively the ﬁrst excited state, $1_s2_s$, of He-like tin, which provided a clean two-photon spectrum. The measured two-photon spectral distribution was compared with fully relativistic calculations. The obtained results show very good agreement with the calculations for He-like tin

• Viscous Ricci dark energy model with matter creation: Exact solution and observational tests

In this paper, the dissipative mechanism (bulk viscosity and matter creation) is introduced to describe the effects of cosmic non-perfect fluid on the Ricci dark energy (RDE) model. We consider matter creation and bulk viscosity as two independent irreversible processes. Assuming suitable forms of the bulk viscous coefficient and matter creation rate, we find the exact solution of the field equations. We carry out fitting analysis on the cosmological parameters in the model by using Type Ia supernovae data, observational Hubble data and baryon acoustic oscillation (BAO) data with cosmic microwave background. We plot the trajectory of cosmological parameters with the best-fit values of model parameters and discuss all possible (deceleration, acceleration and their transitions) evolutions of the model. The current values of deceleration parameter and equation of state parameter are found to be $q_0=-0.362$ and $\omega_{\mathrm{eff}} = -0.575$, respectively. The age of the Universe is found to be $t_0 \simeq 13.397$ Gyr, which is very close to the $\Lambda$CDM model. We further discuss the geometrical diagnostic parameters such as statefinder and $Om$ to distinguish the model with $\Lambda$CDM model. Finally, we discuss the behaviour of energy conditions for our model and find that the model satisfies the null energy condition (NEC), weak energy condition (WEC) and dominant energy condition (DEC) while it violates strong energy condition (SEC).

• # Pramana – Journal of Physics

Volume 95, 2021
All articles
Continuous Article Publishing mode

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019