Problem: Strontium 90Sr38 has a half-life of 28.5 yr. It is chemically similar to calcium, enters the body through the food chain, and collects in the bones. Consequently, 90Sr38 is a particularly serious health hazard.
1- How long (in years) will it take for 90.9900% of the 90Sr38 released in a nuclear reactor accident to disappear?
Show me the detailed calculation of the above question.