Question

A scientist digs up sample of arctic ice that is 458,000 years old. He takes it to his lab and finds that it contains 1.675 grams of krypton-81. If the half-life of krypton-81 is 229,000 years, how much krypton-81 was present when the ice first formed? Use the formula N = N0 . The ice originally contained grams of krypton 81.

Answer 1

The correct answer is

6.70

:)

Answer 2

6.70 g

Explanation:

A common formula for determining the amount of sample remaining in terms of its half-life is

`N =N_(0)(( 1)/(2 ))^(n)`

where

`n = \frac{t }{t_{(1 )/(2 )} }`

t = 458 000 yr

`t_{(1)/(2) = \text{229 000 yr}` Calculate n

n = 458 000/229 000

n = 2.000

===============

N = 1.675 g Calculate N₀

`1.675 = N_(0)(( 1)/(2 ))^(2.000)`

1.675 = N₀ × 0.2500 Divide by 0.2500 and transpose

N₀ = 1.675/0.2500

N₀ = 6.70 g