How long will it take for the activity of a sample of F to d

How long will it take for the activity of a sample of F to decrease to 84 % of its initial value? Repeat part B. but instead determine the time to decrease to an additional 16 % to 68 % of its initial value.

Solution

Assuming Half life ¹⁷F is t = 66 sec
Q / q = e ^ ( - c * t )
( 1 / 2 ) = e ^ ( - c * 66 )
Ln (0.5) = - c * 66 Ln (e)
- 0.6931 = - c * 66 * 1
c = 0.010502

B) Q / q = 0.84
t = 66 sec
T = [ - t / 0.6931 ] * Ln ( Q / q )
T = [ - 66 / 0.6931 ] * Ln ( 0.84 )
T = 16.6027 sec

C) Q / q = 0.68
t = 66 sec
T = [ - t / 0.6931 ] * Ln ( Q / q )
T = [ - 66 / 0.6931 ] * Ln ( 0.68 )
T = 36.72446 sec