Question

The half-life against beta decay of the strontium isotope Sr9038is 28 yr. (a) What does Sr9038become after beta decay? (b) What percentage of a sample of Sr9038will remain undecayed after 112 yr?

Answer 1

a)After ẞ decay ,

Sr 90 38 becomes Sr 90 37

b) t 1/2= 28 yrs

112 yrs means 4× 28=4 ×t 1/2

Let the amount of Sr isotope be n

After one half life

n-->n/2

After 2 half life,

n/2-->n/4

After 3 half life,

n/4-->n/8

after 4 th half life,

n/8-->n/16

n/16=0.0625n

% substance remaining=0.065n/n×100=6.25%

I hope this helps ( ╹▽╹ )