Transcript Slide 1

V. Half life
Nuclear decay is a random event. It is impossible
to predict when a given nucleus will decay. However,
when large numbers of radioactive nuclei are present,
it is possible to predict when half of them will decay.
A. half life T = time for ½ of nuclei to decay
Half life is independent of (unaffected by changes in):
1/ pressure;
2/ temperature;
3/ concentration;
4/ when the last decay occured.
After every half life, only half of previous remains.
Each previous amount is:
divided by 2
or
multiplied by (1/2).
Original  100
amount
100%
% of
radioactive
nuclide
100/2 = 50%
50
that
50/2 = 25%
remains
25/2 = 12.5%
12.5/2 = 6.25 5
0
0
1
2
3
number of half lives
4
B. Each radioactive nuclide has its own half life T.
 A longer half life means more remains
for a longer time
100%
amount
remaining
B
50%
A
1TA
A = short
half life
1TB
B = long
half life
http://phet.colorado.edu/en/simulation/alpha-decay