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2. B.Kumar and B.P. Singh. International Journal of Applied Radiation and Isotopes, Vol.30, p.493.
3. B Kumar and B.P Singh.Indian Journal of Pure and Applied Physics, Vol.19, 1981, p.49.
4. B.P Singh and Bhishm Kumar,Indian Journal of Pure and Applied Physics, Vol.26, 1988, P. 376.
5. B.P Singh and Satish Chandra,Journal of Hydrology, Vol.37, 1977, p. 189.