Question

40. If 3.0 g of Sr-90 in a rock sample remained in 1999,

how many grams of Sr-90 were
approximately
present in the original rock sample in 1943? (1) 9.0 g
(2) 6.0 g) 3.0 g (4) 12 g

Answer 1

The half-life of Sr-90 is 29 years. So in 1972 half of it remained, and then again in 2001 half of that half remained. But in 1999, the amount had only halved once, so if the amount was 3.0 g, then in 1943 it was double that, so 6.0 g.