Answer:
63 years
Eighth
The number of half lives
Step-by-step explanation:
It will take 63 years for half of the sample to decay
In 189 years, eighth of the sample will be left
Scientists can figure out how old a sample is by multiplying the number of half lives by the length of the half life.
Half life is the time taken by a radioactive sample to decay to half of the original amount.
Therefore, for a radioactive element with a half-life of 63 years, it will take 63 years for the sample to decay to half of the original amount.
After 189 years, only an eighth of the sample will be left.
That is, 189 years is equivalent to 3 half-lives
Therefore, if the original amount is 1, then;
1 → 0.5 → 0.25 → 0.125
Thus, scientists can figure out how old a sample is by multiplying the number of half lives by the length of the half life.