Sri Lankan Journal of Physics, Volume 2, March 2001.
Terrestrial
gamma dose rates along one of the coastal highways in Sri
Lanka
C.S.Sumithrarachchi and R. Hewamanna
Department of Nuclear Science, University of
Colombo, Colombo 03, Sri Lanka
This study reports a van bone radiometric survey carried out along the A2 route to assess the annual radiation dose received by a commuter from Galle to Colombo using in-situ gamma spectrometry and a hand held environmental GM survey meter. A vehicle borne gamma spectrometric survey normally provides preliminary coverage of the radioelements in the top most part of the earth's crust. The ground concentrations of K, Th and U were also obtained along the route. The daily equivalent dose calculated was 0.50 mSv in this route. The highest dose rates were measured from Kosgoda to Ambalangoda where activity concentrations of Th was around 0.30 Bq g-1. Activity concentration of U was the least and was not detected in many places along the route. Southern Province has an average outdoors-equivalent dose of 1.54 mSv y-1. The calculated dose along the A2 route was 0.12 mSv for a commuter for 240 working days and gives the upper limit. This dose is about 10% of the average measured value for the Southern Province and is no more than a statistical variation of the natural background radiation.
Sri Lankan Journal of Physics, Volume 2, March 2001.
Observation
of defect interface states at the Cu2O/CuxS
junction using thermally stimulated I-V measurements
S.R.D.
Kalingamudali and W. Siripala
Department of Physics,
University of Kelaniya, Kelaniya, Sri Lanka
A simple method was developed to fabricate a Cu2O/CuxS p-n junction diode and I-V characteristics of the diode was measured at various temperatures. It was revealed that there are current transport mechanisms at the junction which are leading to high voltage currents. Namely, an oscillatory behaviour of the current with the temperature was observed under reverse bias conditions. This behaviour was interpreted as the thermally enhanced tunneling at the junction due to the existence of defect interface states. We believe that proper surface treatment might reduce the density if interface states and thereby improve the I-V characteristics of the diode.
Sri Lankan Journal of Physics, Volume 2, March 2001.
Study of
subcell parameters, grain size and dielectric properties of Potassium
Sodium Niobate mixed system
K. Singh, M. Uniyal, S. C.
Bhatt and B.S. Semwal
Dielectric and ultrasonic
laboratory, Department of Physics, HNB Garhwal University, Srinagar
(Garhwal)-246174, India
Pellets of K1-xNaxNbO3 mixed system of different concentration have been prepared by solid solution reaction method. The subcell parameters and grain size have been calculated using X-ray diffraction data for mixed K1-xNaxNbO3 system where x is varied from 0, 20, 40, 50, 80, 100%. The variation of unitcell parameters and grain size with composition, at room temperature have been reported. Dielectric constant and loss tangent at room temperature and at different frequencies have been reported.
Sri Lankan Journal of Physics, Volume 2, March 2001.
Activity
of cloud-to-ground lightning observed in Sri Lanka and in surrounding
area of the Indian ocean<
A.B. Weerasekara1,
D.U.J. Sonnadara1, I.M.K. Fernando1, J.P.
Liyanage2, R. Lelwala1 and T.R.
Ariyaratne1
1Department of
Physics, University of Colombo, Sri Lanka, 2Department of
Surveying Sciences, Sabaragamuwa University of Sri Lanka
Activity of cloud-to ground lightning flashes observed during the monsoon thunderstorms over Sri Lanka with a lightning locating system consisting of two direction finders (DF) is presented. The Northeast monsoon produced over 884 cloud-to-ground flashes with a peak lightning rate of 96 flashes per hour whereas Southwest monsoon produced 3,294 flashes with a peak rate of 104 flashes per hour. A relative flash density maximum of 198 flashes per 28´28 km2 was observed over Ratnapura area (6.68N, 80.40E). The percentage of positive flashes and average peak lightning current values for negative flashes are found to be 6.4% and 36 kA respectively for the Northeast monsoon period and 1.7% and 40 kA respectively for the Southwest monsoon period for the flashes that struck within 10-250 km range. No significant difference in average peak lightning current values were observed for the negative and positive flashes in both monsoons.
Sri Lankan Journal of Physics, Volume 2, March 2001.
Leader
fields due to a lightning channel with an inclined upper section
C.
Gomes1 and V. Cooray2
1Department
of Physics, University of Colombo, Sri Lanka 2Institute of
High Voltage Research, Uppsala University, Sweden
It is shown theoretically the dependence of the leader field on the angle of orientation with respect to a perfectly conducting horizontal plane of the uppermost part of the lightning leader. The results were able to discern significantly large differences in the static field variation of leader channels with the same length but a certain channel segment is oriented at different angles. The outcome of our calculations consistently explains the scatter of the total leader field observed in previous studies. Otherwise, one has to assume unrealistic charge source heights or unreasonable charge densities to calculate matching values for some of the total leader fields and total leader field to return stroke field ratios, labeled as anomalous observations in the literature. In some cases, irrespective of the charge source height and the charge density, one cannot find a suitable fit with the straight channel model.
Sri Lankan Journal of Physics, Volume 2, March 2001.
Group
theoretical analysis of a system of monopoles
S.C. Joshi,
V.P. Pandey and B.S. Rajput
High Energy Physics, Department
of Physics, Kumaun University, Nainital – 263 002, India
nvestigating the behaviour of a monopole moving in the field of another monopole we have obtained energy eigenvalue and eigenfunctions of the system. It has been demonstrated that isotropic harmonic oscillator is (n+1)(n+2)/2 fold degenerate and SU(3) is the algebra to describe this system. The energy eigenvalue of monopolonium is modified from the usual energy eigenvalue of hydrogen atom due to the magnetic charge and Bohr radius of the system is very small in comparison to atomic Bohr radius. It has also been demonstrated that Hamiltonian of the monopolonium is invariant under O(4) and degree of degeneracy is n2 fold.
Sri Lankan Journal of Physics, Volume 2, March 2001.
Scattering
of monopoles and decay of anti-monopolium
P. P.
Purohit, V. P. Pandey and B. S. Rajput
Department of
Physics, Kumaun University, Nainital 263002, India
Undertaking the study of behaviour of a spin-1/2 non-Abelian magnetic monopole moving in the field of another non-Abelian monopole by solving Dirac's equation for energy eigen values and the Hamiltonian of this system has been shown to involve spin contribution. Spin momentum of a non-Abelian monopole has been shown to behave as extra energy source for non-Abelian monopole interacting with the field of another non-Abelian monopole. Interaction of spin and orbital moments of a non-Abelian monopole moving in the electromagnetic field has been analysed. S-matrix expansion, scattering amplitude and total Hamiltonian for monopole-anti-monopole scattering in non-Abelian guage theory have also been undertaken. Study of bound state of a monopole and an anti-monopole in non-Abelian gauge theory has been carried out and it has been shown that this state is very short lived and decays in to two or three photons depending on the spin-statistics of the non-Abelian monopoles involved.
Sri Lankan Journal of Physics, Volume 2, March 2001.
Pauli
equation for BPS monopoles in moduli space
P. P.
Purohit, V. P. Pandey and B. S. Rajput
Department of Physics, Kumaun University, Nainital 263002, India
Undertaking the study of behaviour of a BPS monopole moving in the field of another BPS monopole, in moduli space, Dirac's equation has been solved for energy eigen values and it has been shown that spin momentum of an interacting BPS monopole behaves as extra energy source. Introducing suitable spinors, the Pauli equation for a BPS monopole moving in the field of another BPS monopole has been solved in moduli space and it has been shown that adhoc introduction of spin in the system of two BPS monopoles perceptibly modifies the energy eigen values and eigen functions of bound states of the system.