1.

._(92)^(238)U by successive radioactive decay changes to ._(82)^(206)Pb. A sample of uranium ore was analysed and found to contain 1.0g of .^(238)U and 0.1g of .^(206)Pb. Assuming that all .^(206)Pb hasaccumulated due to decay of .^(238)U, find the age of the ore (half life of .^(238)U=4.5xx10^(9) yrs).

Answer»

SOLUTION :Number of MOLES of `.^(238)U = (1)/(238)`
Number of moles of `.^(206)Pb = (0.1)/(206)`
Applying the relationship,
`t = (2.303/(lambda) log [1 + (.^(206)Pb)/(.^(238)U)]`
`= (2.303)/(0.693) xx 4.5 xx 10^(9) log [1 + ((0.1)/(206))/((1)/(238))] = 7.098 xx 10^(8)` YEARS


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