1.

A sample of pitchblende is found to contain 50% minimum and 2.425% of lead. Of this lead only 93% was Pb^(26) isotope. If the disintegration constant is 1.52 xx 10^(-10) yr^(-1), how old could be the pitchblende deposidts?

Answer»

SOLUTION :Mole of `U^(238) = (50)/(100 xx 238) = 2.1 xx 10(-3)`
Mole of `Pb^(26) = (2.425)/(100) xx (93)/(100 xx 206) = 0.109 xx 10^(-3)`
`N_(0) = (x + y) = 2.1 xx 10^-3) + 0.109 xx 10^(-3) = 2.209 x 10^(-3)`
`N = x = 2.1 xx 10^(-3)`
`LAMBDA = (2.303)/(t) log ((N_(0))/(N))`
`1.52 xx 10^(-10) = (2.303)/(t) log (2.209 xx 10^(-3))/(2.1 x 10^(-3))`
`t = 3.3 xx 10^(8)` YEARS


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