One Material Used in Nuclear Bombs Is $239 \mathrm { Pu }$

Multiple Choice

One material used in nuclear bombs is $239 \mathrm { Pu }$ , with a half-life of 24,000 years. How long must we wait for a buried stockpile of this substance to decay to $1 / 1000$ of its original activity?

A) 1,500 years
B) 240,000 years
C) 150,000 years
D) 82,000 years
E) $1,200,000$ years