Section 3: Radioactive Decay and
Half-Life
 The
spontaneous emission of rays or
particles from certain nuclei as they
“decay,” such as Uranium.
 These
rays or particles are called nuclear
radiation.
 They come in three types:
Alpha Radiation: Helium nucleus; 2+ Charge; Low
power (0.05 mm body tissue)
 Beta Radiation: electron; 1- Charge; Moderate
power (4 mm body tissue)
 Gamma Radiation: electromagnetic wave; neutral
charge; High Power (penetrates entire body easily)

While
the process is
spontaneous, it is not
instantaneous… it takes
time!
The time required for HALF
of the atoms of a radioactive
substance to decay is called
a half-life.
Fluorine
18
9
18 ( F) has a
half-life of 110 seconds.
This material is used
extensively in medicine.
The hospital laboratory
begins the day with 10
18
grams of 9 F…
1 half-life = 110 seconds
660 seconds
= 6 half-lives
110 seconds
6
1)
2)
3)
4)
5)
6)
half-lives = 10 divided in half, 6 times
10/2 = 5 grams
5/2 = 2.5 grams
2.5/2 = 1.25 grams
1.25/2 = 0.625 grams
0.625/2 = 0.3125 grams
0.3125/2 = 0.15625 grams
After 11 minutes, only 0.16 g of
the 10 g sample remain!!!!!!