Question

Question #44221

Answer 1

39.47days

Explanation:

If you start with 260mg and end with 210.6mg, then 49.4mg has decayed in 15 days.

For a half life, half of a substance needs to decay. Half of 260mg is 130mg. Therefore, when the substances mass reaches 130mg, half the original substance has decayed and the length of time it has taken to do this is the isotopes half life

If we know that 49.4mg decays in 15 days then for 130mg;

`"49.4mg"/"15days"` =3.293mg of decay per day

`"130mg"/"3.293mg per day"` = 39.47days

This is, however, a poor way of finding out a half life. Ideally, you would wait until half the substance has decayed and use that value. Radioactive decay is a completely random process and follows no exact pattern. A half life is a 'close prediction' based on what we have observed and feel is likely to occur again.