• Rajesh Kumar

Articles written in Pramana – Journal of Physics

• Investigation of the boundary value problem corresponding to a generalized Skyrme lagrangian

A detailed numerical analysis of the boundary value problem resulting from the most general Skyrme type lagrangian containing up to quartic terms in field gradients is presented. The additional parameters in the lagrangian can be related to pion-pion scattering lengths. It is found that solutions to the boundary value problem does not exist for all values of the parameters and in particular, for the values predicted from pion-pion scattering data. Physical quantities of the nucleon are calculated for the highest possible values of the parameters admitting a solution and are compared with the corresponding values for the Skyrme model and experimental values.

• Thick-target X-ray bremsstrahlung spectra produced in 6.5 keV and 7.5 keVe--Hf collisions

The absolute doubly differential cross-sections (DDCS) for production of the thick-target X-ray bremsstrahlung spectra in collisions of 6.5 keV and 7.5 keV electrons with thick Hf target are measured. The X-ray photons are counted by a Si(Li) detector placed at 90° to the electron beam direction. The bremsstrahlung spectra are corrected for various ‘solid-state effects’ namely, electron energy-loss, electron back-scattering, and photon-attenuation in the target, in addition to the correction for detector’s efficiency. The DDCS values after correction, are compared with the predictions of a most accurate thin-target bremsstrahlung theory [H K Tseng and R H Pratt,Phys. Rev.A3, 100 (1971); Kisselet al, Atomic Data Nucl. Data Tables28, 381 (1983)]. Also, a dependence of the absolute DDCS on atomic numberZ of the targets (47Ag,79Au and72Hf) at 7.0 keV and 7.5 keV electron energies has been studied. The agreement between experiment and theory is found to be satisfactory within 27% systematic error of measurements. However, an apparent systematic difference between experiment and theory in the region of low-energy photons has been explained qualitatively by considering the fact that the hexagonal atomic structure of Hf offers possibly a greater magnitude of ‘solid-state effects’ in respect of blocking the low-energy bremsstrahlung photons from coming out of the target surface than does the cubic-face centered structure of Ag and Au target in similar conditions of the experiment.

• Operation of a capacitor bank for plasma metal forming

Previously metal forming has been done using electromagnet in pulsed power mode, better known as magneform [1]. Here we will be presenting a different technique for metal forming. We are using water as a medium for this process. By discharging the stored electrical energy of the capacitor bank in water, we are getting the desired result i.e. to form (expand or compress) a wide range of workpiece to the desired shapes. The advantage of this method over conventional method is that it uses low power (negligible running cost). It does not require any post assembly cleaning degreasing and is hence environmentally ‘friendly’.

• The automatic liquid nitrogen filling system for GDA detectors

An indigenously developed automatic liquid nitrogen (LN2) filling system has been installed in gamma detector array (GDA) facility at Nuclear Science Centre. Electro-pneumatic valves are used for filling the liquid nitrogen into the high purity germanium detector cryostat. The temperature of the out-flowing gas/liquid from the cryostat is monitored using platinum resistor thermometer. The program allows for automatic filling at regular intervals with temperature monitoring from a remote terminal.

• Status report on the folded tandem ion accelerator at BARC

The folded tandem ion accelerator (FOTIA) facility set up at BARC has become operational. At present, it is used for elemental analysis studies using the Rutherford backscattering technique. The beams of1H, 7Li, 12C, 16O and 19F have been accelerated up to terminal voltages of about 3 MV and are available for experiments. The terminal voltage is stable within ±2 kV. In this paper, present status of the FOTIA and future plans are discussed.

• Superconducting linear accelerator system for NSC

This paper reports the construction of a superconducting linear accelerator as a booster to the 15 UD Pelletron accelerator at Nuclear Science Centre, New Delhi. The LINAC will use superconducting niobium quarter wave resonators as the accelerating element. Construction of the linear accelerator has progressed sufficiently. Details of the entire accelerator system including the cryogenics facility, RF electronics development, facilities for fabricating niobium resonators indigenously, and present status of the project are presented.

• Covalent immobilization of myosin forin-vitro motility of actin

The present study reports the covalent immobilization of myosin on glass surface andin-vitro motility of actin-myosin biomolecular motor. Myosin was immobilized on poly-L-lysine coated glass using heterobifunctional cross linker EDC and characterized by AFM. Thein-vitro motility of actin was carried out on the immobilized myosin. It was observed that velocity of actin over myosin increases with increasing actin concentration (0.4–1.0 mg/ml) and was found in the range of 0.40–3.25 μm/s. The motility of actinmyosin motor on artificial surfaces is of immense importance for developing nanodevices for healthcare and engineering applications

• Accelerator development in India for ADS programme

At BARC, development of a Low Energy High Intensity Proton Accelerator (LEHIPA), as front-end injector of the 1 GeV accelerator for the ADS programme, has been initiated. The major components of LEHIPA (20 MeV, 30 mA) are a 50 keV ECR ion source, a 3 MeV Radio Frequency Quadrupole (RFQ) and a 20 MeV drift tube linac (DTL). The Low Energy Beam Transport (LEBT) and Medium Energy Beam Transport (MEBT) lines match the beam from the ion source to RFQ and from RFQ to DTL respectively. Design of these systems has been completed and fabrication of their prototypes has started. Physics studies of the 20{1000 MeV part of the Linac are also in progress. In this paper, the present status of this project is presented.

• Hybrid recoil mass analyzer at IUAC – First results using gas-filled mode and future plans

Hybrid recoil mass analyzer (HYRA) is a unique, dual-mode spectrometer designed to carry out nuclear reaction and structure studies in heavy and medium-mass nuclei using gas-filled and vacuum modes, respectively and has the potential to address newer domains in nuclear physics accessible using high energy, heavy-ion beams from superconducting LINAC accelerator (being commissioned) and ECR-based high current injector system (planned) at IUAC. The first stage of HYRA is operational and initial experiments have been carried out using gas-filled mode for the detection of heavy evaporation residues and heavy quasielastic recoils in the direction of primary beam. Excellent primary beam rejection and transmission efficiency (comparable with other gas-filled separators) have been achieved using a smaller focal plane detection system. There are plans to couple HYRA to other detector arrays such as Indian national gamma array (INGA) and $4\pi$ spin spectrometer for ER tagged spectroscopic/spin distribution studies and for focal plane decay measurements.

• Excitation energies and oscillator strengths for the $1s^2 2s^2 2p^6 3s^2 3p^6 3d {}^2 D^e \to 1s^2 2s^2 2p^6 3s^2 3p^5 3d^2 {}^2 P^o, {}^2 D^o, {}^2 F^o$ transitions in V4+

We have calculated the excitation energies ($\Delta E$) and optical oscillator strengths (OOS), of both length ($f_L$) and velocity ($f_V$) forms, for the $1s^2 2s^2 2p^6 3s^2 3p^6 3d {}^2 D^e \to 1s^2 2s^2 2p^6 3s^2 3p^5 3d^2 {}^2P^o, {}^2D^o, {}^2F^o$ transitions in V4+ ion of the potassium isoelectronic sequence by employing multiconﬁguration Hartree–Fock (MCHF) method exactly in the same way as we did in our earlier work (Tiwary et al, Pramana – J. Phys. 46, 381 (1996)). We have compared the available relevant experimental data and our earlier theoretical results obtained by employing the conﬁguration interaction (CI) method (Tiwary et al, J. Phys. B: At. Mol. Phys. 16, 2457 (1983)). Our present investigation clearly demonstrates that the MCHF method is more accurate than the CI method.

• Neutron detector array at IUAC: Design features and instrumentation developments

The characteristics and performance of the newly commissioned neutron detector array at IUAC are described. The array consists of 100 BC501 liquid scintillators mounted in a semispherical geometry and are kept at a distance of 175 cm from the reaction point. Each detector is a $5''\times 5''$ cylindrical cell coupled to $5''$ diameter photomultiplier tube (PMT). Signal processing is realized using custom-designed home-made integrated electronic modules which perform neutron–gamma discrimination using zero cross timing and time-of-flight (TOF) technique. Compact custom-built high voltage power supply developed using DC–DC converters are used to bias the detector. The neutrons are recorded in coincidence with fission fragments which are detected using multi-wire proportional counters mounted inside a 1m diameter SS target chamber. The detectors and electronics have been tested off-line using radioactive sources and the results are presented.

• A computer modelling and its partial experimental validation to study the attenuation of electromagnetic waves in plasma using CST MICROWAVE STUDIO®

There is a huge interest among the scientific fraternity to generate plasma that can selectively absorb or reflect the incident microwaves. Simulations have been carried out to study the absorption of microwaves in plasma using plane wave as a source. In real experiments, the source of microwaves is not always a plane waveand hence the exact simulated replication of the experiment cannot be done using a plane wave source. In order to generate the exact experimental conditions, a horn antenna has been designed and used as a source. A computermodel to study the attenuation of X-band (8–12) microwaves in a plasmamedium is prepared and partially validated using suitable initial experiments. The study can be extended to any target microwave frequency band. The presentwork discusses the preliminary simulations that are carried out to study the effect of plasma frequency (ω$_p$) and collisional frequency (υ$_c$) on attenuation of microwaves (MW) of 8–12GHz using CST®MWS®. The plasma istreated as a Drude dispersive material whose properties are governed by two plasma parameters, namely plasma frequency (ω$_p$) and collisional frequency (υ$_c$). The simulation is carried out on an array of plasma tubes enclosedin a housing made of teflon. This chamber is then illuminated with microwaves using a horn antenna unlike other simulations where the source of the signal is a plane wave. Using a horn antenna as the transmitter and receiverallows exact simulation of the experimental conditions in the laboratory. The amount of attenuation is measured by considering the difference in return losses with and without plasma. The attenuation of incident microwave isstudied by varying plasma frequency from 0.02GHz to 3GHz at a fixed collisional frequency of 10$^10$ S$^−1$. The simulation is also carried out by varying υc from 10$^8$ to 10$^11$ S$^−1$ at a constant ωp. An experiment to validate thesimulation is designed to validate the simulation results. For experimental purpose, fluorescent tube array (FTA), which is a series connection of commercially available tubes is excited using a high-frequency power supply ofsuitable voltage. The simulation and initial experimental results are compared and are in good agreement with each other. This model serves as a tool to study the attenuation of MW in plasma with given ω$_p$ and υ$_c$well before the experiment is carried out. This can also be used to select optimum working points for further experiments.

• Pramana – Journal of Physics

Volume 97, 2023
All articles
Continuous Article Publishing mode

• Editorial Note on Continuous Article Publication

Posted on July 25, 2019