Question

Nathan Thomson, one of the the first inhabitants of lord howe Island. Decided to plant some eruopean deciduous trees in his garden. Unifortunately the exact timing of planting the seeds is not known, over the years, pollen produced by the trees accumulated at the bottom of the lake near Nathan,s house. Very small quantities of radioactive `.^(210)Pb` (`t_(1//2)` = 22.3 years) were deposited at the same time. Note that european deciduous trees pollinate in their first year of growth.
In 1995, a team of researchers sampled a sediment core from the bottom of the lake. the examination of sediment core of found that:
(a) Pollen of trees first occurs at the depth of 50 cm.
The activity of `.^(210)Pb` at the top of sediment core is 356 Bq/kg and at 50 cm depth 1.40 Bq/kg.
In what year did Nathan Thomson plant the seeds?
A. `1719 +- 2`
B. `1819 +- 2`
C. `1519 +- 2`
D. `1919 +- 2`

Answer 1

Correct Answer - b
`(0.693)/(t_(1//2)) = (2.303)/(t_("age")) log ((N_(0))/(N))`
`(0.693)/(22.30) = (2.303)/(t_("age")) log ((356)/(1.40))`
`t_("age") = 176` yrs