Results 1 - 10 of 58
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[en] Male pupae of the domesticated silkmoth, P. ricini were irradiated with 600 - 6000 R of 60Co gamma ray and studied for the nature and frequency of visible chiasmata in the meiotic spermatocytes. Significant increase in lower doses (600, 1200 R) and decrease in higher dose (6000 R) were observed. More interstitial chiasmata were induced in the medium bivalents; and low frequency of terminals restricted to the smaller bivalents. The minimum chiasma per bivalent was one and never zero. Nature of monocentric versus holocentric chromosomes with regard to the gamma induced chiasmata were, however, discussed. (author)
[en] In this work, we study the evolution of primordial black holes within the context of Brans-Dicke theory by considering the presence of a dark energy component with a super-negative equation of state, called phantom energy, as a background. Besides Hawking evaporation, here we consider two types of accretion - radiation accretion and phantom energy accretion. We found that radiation accretion increases the lifetime of primordial black holes whereas phantom accretion decreases the lifespan of primordial black holes. Investigating the competition between the radiation accretion and phantom accretion, we found that there is an instant during the matter-dominated era beyond which phantom accretion dominates radiation accretion. So the primordial black holes which are formed in the later part of radiation-dominated era and in matter-dominated era are evaporated at a quicker rate than by Hawking evaporation. But for presently evaporating primordial black holes, radiation accretion and Hawking evaporation terms are dominant over the phantom accretion term and hence presently evaporating primordial black holes are not much affected by phantom accretion. (orig.)
[en] We will present a brief review of various surrogate methods employed for compound nuclear cross-section measurements along with our recent results using the hybrid surrogate ratio approach for determination of neutron induced fission cross sections of 233Pa and 234Pa isotopes
[en] We investigate the evolution of primordial black hole mass spectrum by including both accretion of radiation and Hawking evaporation within Brans-Dicke cosmology. We also consider the effect of evaporation of primordial black holes on the expansion dynamics of the universe. The analytic solutions describing the energy density of the black holes in equilibrium with radiation are presented. We demonstrate that these solutions act as attractors for the system ensuring stability for both linear and nonlinear situations. We show, however, that inclusion of accretion of radiation delays the onset of this equilibrium in both radiation and matter-dominated eras. (author)
[en] This paper presents the analytical calculation and simulation for the beam optics study of a 30° sector magnet. This sector magnet will be used to measure the energy of a 1.5 MeV electron beam being injected from an RF linac. From initial beam parameters, arc length of the magnet and number of ampere-turns have been optimised. To find out beam size, Transfer matrix method is used for different initial beam conditions. A program is written in MATHEMATICA to solve the envelope equation in both dispersive and non-dispersive plane . To validate this program, simulation is carried out in the software CST PARTICLE STUDIO. (author)
[en] Beam trials have been carried out in an indigenously developed DC electron accelerator at Electron Beam Centre, Kharghar in the voltage range from 1-1.8 MeV and current range 0-10 mA. Current in the Beam Optics elements like focussing solenoid, steering coil and magnetic field in the scanning magnet were adjusted to realize optimum beam transmission. A second scanning magnet made from ferrite cores operating at about 2.35 kHz and scanning across the foil was incorporated in the beam line to ensure longevity of the exit window. Simulation work has also been done to understand the beam dynamics in the 3 meter long accelerating column and the 4 meter long beam-line. The paper gives a brief description of the accelerator, the results of beam simulation and measurement of beam transmission. (author)
[en] We consider rotating primordial black holes (PBHs) and study the effect of accretion of radiation in the radiation-dominated era. The central part of our analysis deals with the role of the angular momentum parameter on the evolution of PBHs. We find that both the accretion and evaporation rates decrease with an increase in the angular momentum parameter, but the rate of evaporation decreases more rapidly than the rate of accretion. This shows that the evaporation time of PBHs is prolonged with an increase in the angular momentum parameter. We also note that the lifetime of rotating PBHs increases with an increase in the accretion efficiency of radiation as in the case of nonrotating PBHs.
[en] Currently a DC accelerator designed and developed by Accelerator and Pulse Power Division is undergoing operational trials. It is necessary to tailor the beam optics elements like Steering coils, Focusing coils and magnetic field in the scanning system to obtain optimum transmission of beam power to the job. These elements have been used to operate the accelerator at 1 MeV, 8 kW with a transmission efficiency of 80% . In this paper, we will discuss some of the problems which are still encountered and dwell on some measures for further improvements. (author)
[en] Beam dynamics study of a 30 MeV,7 kW, 2856 MHz standing wave biperiodic on-axis coupled cavity RF electron Linac as a neutron source is carried out in the code ASTRA to find the optimum operating parameters of the accelerator. Simulation of neutron production is performed in FLUKA code.