The half-life of is 20 year

CHEMISTRY · Subjective · US High School · Chemistry · Atomic Structure & Nuclear · Atomic Structure & Nuclear

Problem

The half-life of

{}_{38}^{90}\text{Sr}

is 20 year. If a sample of this nucleide has activity of 8000 disintegration per minute, its activity after 80 year will be

5 \times 10^a

dpm. What is

a