Question

2) The isotope90_Sr has a half-life of 28.8 years. What is the activity, measured in atoms/second of a 50 mg sample of Sr? (10 pts.)

Answer 1

The activity of Sr isotope is
`2.6217* 10^(11)atom/s`.

Step-by-step explanation:

Mass of the Sr isotope = 50 mg =0.050 g

Moles of Sr isotope :

=
`(0.050 g)/(87.62 g/mol)=5.7064* 10^(-4) mol`

Number atoms of of Sr isotope:

`=5.7064* 10^(-4) mol* 6.022* 10^(23) atoms=3.4364* 10^(20) atoms`

Half life of the Sr isotope =
`t_(1/2)=28.8 years= 9.08352* 10^(8) s`

`1 year =3.154* 10^(7) seconds`

Activity of the Sr isotope = k

`\lambda =(0.693)/(t_(1/2))=(0.693)/(9.08352* 10^(8) s)=7.629* 10^(-10) s^(-1)`

Activity in atom/second:

= Number of atoms ×
`\lambda`

`=3.4364* 10^(20) atoms* 7.629* 10^(-10) s^(-1)`

`=2.6217* 10^(11) atom/s`