An Air Sample Is Contaminated with ¹⁵O, Which Has a Half-Life

Multiple Choice

An air sample is contaminated with ¹⁵O, which has a half-life of 2.03 min. One possible way to minimize its hazard is to pass it through a long pipe to allow it to decay inside the pipe until it can be safely released into the atmosphere. If the oxygen moves at a speed of 1.1 m/s in the pipe, how long must the pipe be for the sample to have decayed to 3.0% of its original activity just as it leaves the pipe?

A) 680 m
B) 8.0 m
C) 7.0 m
D) 2.0 m