A Thallium Source with a Half-Life Of $3.7$ Years Was Certified At

Multiple Choice

A thallium source with a half-life of $3.7$ years was certified at $10 \mathrm { kBq }$ ten years ago. What is its activity now?

A) $1.5 \mathrm { kBq }$
B) $3.3 \mathrm { kBq }$
C) $1.0 \mathrm { kBq }$
D) $4.7 \mathrm { kBq }$