So a math question says "An unspecified quantity of a radioactive element is stored in a safe vault in the year 2000. Six years later, we find there is only half the amount there was originally." one of the subquestions is to find the "TIME CONSTANT..."
I know how to do these types of questions (radioactive decay and all that jazz) so I don't need the actual answer or any explanations... rather I just need to know what exactly time constant IS. Is it the original quantity when time is zero? Or is it the half-life? Or what? How is it defined?