1. Radioactivity Polonium and radium X-Rays
Marie Curie
Wilhelm Roentgen
Radioactivity
Spontaneous emission of radiation from the nucleus of an unstable isotope.
Antoine Henri Becquerel

2. Radioactive Decay Unstable nucleus emits particle and energy
Most common decays involve the emission of
 - particle ( Decay)
 - particle ( Decay)
 - particle ( Decay)

3. Alpha Decay
Alpha decay occurs when there are too many protons in the nucleus which cause excessive electrostatic repulsion.
An alpha particle is ejected from the nucleus.
An alpha particle is 2 protons and 2 neutrons.
An alpha particle is also a helium nucleus.
Alpha particle symbol:

4. The Numbers Atomic mass number: number of nucleons
Atomic number: number of protons
Neutrons = number of nucleons – number of protons

5. Beta Decay Beta decay occurs when neutron to proton ratio is too big
A neutron is turned into a proton and electron and an antineutrino
The electron and the antineutrino are emitted

6. Gamma Decay
Gamma decay occurs when the nucleus is at too high an energy
Nucleus falls down to a lower energy level
High energy photon – gamma ray - is emitted

7. Sources of Radiation

8. Penetrating Power

9. Shielding

10. Radioactive Decay 4.5 x 109 yr half-life 24 day half-life
1.17 min half-life
250,000 yr half-life

11. U 238 Decay
Decay Series

12. Half-Life
Half-life is the time required for half of the element to decay to another element.
For Thorium-234, the half-life is 24 days.
That means that every 24 days half of the thorium-234 in a sample has decayed.
If you begin with a 1 kg chunk of Thorium-234, after 24 days, you will have ½ kg of Thorium-234.
After 48 days?
¼ kg
After 72 days?
1/8 kg
After 96 days?
1/16 kg
After 120 days?
1/32 kg

13. Carbon Dating Cosmic rays cause transmutation of Nitrogen to Carbon-14
C-14 is radioactive with a half-life of 5730 years
It decays back to Nitrogen by beta decay
The ratio of C-12 (stable) atoms to C-14 atoms in our atmosphere is fairly constant – about 1012/1
This ratio is the same in living things that obtain their carbon from the atmosphere

14. Carbon Dating
The radioactive carbon isotopes in the skeleton diminish by one-half every 5730 years.