What fraction of a Sr-90 sample remains unchanged after 97.3 years

### Answers

The answer is 1/8.

Half-life is the time required for the amount of a sample to half its value.

To calculate this, we will use the following formulas:

1. ,

where:

n - a number of half-lives

x - a remained fraction of a sample

2.

where:

- half-life

t - total time elapsed

n - a number of half-lives

The half-life of Sr-90 is 28.8 years.

So, we know:

t = 87.3 years

= 28.8 years

We need:

n = ?

x = ?

We could first use the second equation, to calculate n:

If:

,

Then:

⇒

⇒

⇒ n ≈ 3

Now we can use the first equation to calculate the remained amount of the sample.

⇒

⇒