A sample of tritium is decayed to 89.3% of its original amount after 2 years. What is the half life?

half-life-tritium

#1

A sample of tritium is decayed to 89.3% of its original amount after 2 years. What is the half life? How long would it take the sample to decay to 20% of the original amount?

Answer:

t1/2 = t * ln(2)/ln(N0/Nt)
where,
t1/2 = half time
t=time gone by = 2 years
N0= initial count = 100
Nt = final count = 89.3
ln is natural log (base e)
putting the values we get…

t1/2 = 2 x ln(2)/ ln(100/89.3)
=2 x 0.693 / 0.113
=12.26 years (Half life)

now to calculate t20 or the time taken to decay to 20% of original
t20= 2 x ln(100/20) / ln (100/89.3)
= 2 x 1.609/0.113
=28.47 years