Showing papers by "Alok Chakrabarti published in 2007"
TL;DR: In this paper, it has been shown that defects govern the room temperature magnetic property of nanocrystalline ZnO, which exhibits a paramagnetic behavior at room temperature but becomes ferromagnetic once oxygen defects are introduced in it.
62 citations
TL;DR: In this paper, the room temperature M?ssbauer spectra for all the samples indicate the paramagnetic nature of the prepared samples, and the changes of these parameters with concentration, x, confirm that the Cd2+ ions prefer to go to the tetrahedral 'A' site compared to the octahedral 'B' site in this Zn(1?x)CdxFe2O4 cubic spinel ferrite system.
Abstract: Single phase Zn(1?x)CdxFe2O4 (x = 0.0, 0.1, 0.3, 0.5, 0.7 and 1.0) ferrite samples have been prepared by the solid state reaction method. The room temperature M?ssbauer spectra for all the samples indicate the paramagnetic nature of the prepared samples. M?ssbauer spectra have been deconvoluted separately for the tetrahedral 'A' site and the octahedral 'B' site to identify the variations of the M?ssbauer parameters, i.e.?isomer shift, quadrupole splitting and linewidth, with the concentration of Cd doping, x, for the tetrahedral 'A' site and octahedral 'B' site. Changes of these parameters with concentration, x, confirm that the Cd2+ ions prefer to go to the tetrahedral 'A' site compared to the octahedral 'B' site in this Zn(1?x)CdxFe2O4 cubic spinel ferrite system. To study the changes in the electron momentum distributions, coincidence Doppler broadening of the electron positron annihilation ?-radiation measurement technique has been employed. The results indicate that positrons are annihilating less with the oxygen 2p electrons and other core electrons in the case of mixed (Zn(1?x)CdxFe2O4) ferrites than ZnFe2O4 or CdFe2O4 ferrites.
35 citations
01 Aug 2007-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: A project to build an ISOL type radioactive ion beam facility has been undertaken at Variable Energy Cyclotron Centre, Kolkata as discussed by the authors, and the status of RIB facility being built at VECC is presented.
Abstract: A project to build an ISOL type radioactive ion beam facility has been undertaken at Variable Energy Cyclotron Centre, Kolkata. The status of RIB facility being built at VECC is presented. Stable ion beams of 30 keV/u have already been accelerated with very high efficiency through the RFQ. The completion of the accelerator system to 400 keV/u is expected in 2007. A second phase for production of neutron-rich RIB through photo-fission route and further acceleration of RI beams using Linacs up to about 6–7 MeV/u is under consideration.
34 citations
TL;DR: The system design and measurements along with results of beam acceleration test will be presented and transmission efficiencies will be measured.
Abstract: A 33.7MHz heavy-ion radio frequency quadrupole (RFQ) linear accelerator has been designed, built, and tested. It is a four-rod-type RFQ designed for acceleration of 1.38keV∕u, q∕A⩾1∕16 ions to about 29keV∕u. Transmission efficiencies of about 85% and 80% have been measured for the unanalyzed and analyzed beams, respectively, of oxygen (O2+16, O3+16, O4+16), nitrogen (N3+14, N4+14), and argon (Ar4+40). The system design and measurements along with results of beam acceleration test will be presented.
10 citations
TL;DR: In this article, a lumped element approach for the design and implementation of line phase shifters, 3-dB hybrid coupler and power divider/combiner was proposed to generate triangular and saw tooth wave forms at 25 MHz.
Abstract: Triangular and Sawtooth wave generation at RF frequency is one of the important tasks for the design of buncher circuit in particle accelerators to increase the bunching efficiency. On the basis of Fourier series method different non-sinusoidal signals like triangular, sawtooth etc. are generated with combination of harmonics of sinusoidal signal with different amplitude and phase. These multi harmonic non-sinusoidal waves can be generated using passive RF components like phase-shifter, hybrid-coupler, power combiner/divider etc. This paper deals with lumped element approach for design and implementation of line phase shifters, 3-dB hybrid coupler and power divider/combiner, which have been used for the generation of triangular and saw tooth wave forms at 25 MHz. The ABCD (transfer) matrix formulation is used for the analytical prediction of the performance of these components. Experiments have been carried out to validate the analytical results.
1 citations
01 Dec 2007
TL;DR: In this article, the design of loop coupler for RF power feeding and also of a tuner for fine frequency tuning of this RFQ cavity is presented, and a 33.7 MHz, 1.7 meter long heavy-ion radio frequency quadrupole (RFQ) linear accelerator has recently been commissioned.
Abstract: Variable energy cyclotron centre (VECC) is presently developing an isotope separator on-line (ISOL) postaccelerator type of radioactive ion beam (RIB) facility. A 33.7 MHz, 1.7 meter long heavy-ion radio frequency quadrupole (RFQ) linear accelerator has recently been commissioned. The design of loop coupler for RF power feeding and also of a tuner for fine frequency tuning of this RFQ cavity are presented.