CHAPTER 10
Investigating the Nucleus
Isotopes
NATURAL TRANSMUTATIONS
Alpha Decay
BETA DECAY
GAMMA RADIATION
DECAY RATE AND HALF LIFE
e.g. Thorium-234 has a half life of 24 d
If we start with 1 kg, then in 24 days, there is 0.5 kg left. There
will be 0.25 kg left in 48 days, and 0.125 kg in 72 days.
e.g. The half-life of Strontium-90 is 28 a. If 60 g are currently in a
sample of soil, estimate the amount 90 a later.
n = 3.214
No = 60 g
N = ?
N = 60 g(1/2)3.214
N = 6.5 g
e.g. A 1 kg sample of thorium has 2 times the radioactivity as 0.5 kg.
Radioactive Dating
T = (T1/2)n
T = (5730 a)(2)
T = 11460 a
E.g. A sample of uranium ore is 3/4 uranium and 1/4 lead. How old is the
sample?
At T= 0, the ratios were all uranium (i.e. 4/4) and no lead. Therefore
No = 1
N = 3/4
n = ?
0.75 = 1(1/2)n
n = 0.415
T = (T1/2)n
T = (4.6 X 109)(0.415)
T = 1.91 X 109 a
January 22, 2014