1. Introduction to Radiation

2. The classical atom
All radiation is a byproduct of the decay of the atom … specifically the nucleus of the atom

3. Terminology Radiation : energy in transit
High energy results in ionization
Low energy results in non-ionization
Radioactivity : the characteristic to emit energy capable of ionization
Ionization : the removal of electrons from an atom (changing the overall charge on the atom) by high energy radiation

4. 3 types of radiation
Alpha radiation
Beta radiation
Gamma radiation

5. Alpha Radiation
Occurs when a particle consisting of 2 neutrons and 2 protons is ejected from a nucleus
The ejected particle is essentially the nucleus of a helium atom

6. Alpha decay occurs only in heavy, neutron rich atoms such as Uranium, Thorium and Radium
Neutron rich means that there are many more neutrons than protons in the nucleus
235U Th a2

7. Properties of alpha radiation
Positively charged
Very heavy
Most energetic of all of the radiation
Can cause many ionizations in a short distance
Travels a few centimeters in air
Stopped by a sheet of paper
Only dangerous if ingested

8. Applications of alpha radiation
Smoke detectors
Alpha source ionizes the air to allow for the passage of small currents through an air gap. Smoke obstructs this flow … setting the alarm off
Power source
Used in space probes and pace makers
Ion engines

9. Beta Radiation Ejection of an electron from the nucleus of an atom
How can a nucleus eject an electron?

10. The electron is created out of the nucleus for beta decay
The nuclear weak force causes a neutron to decay into an electron, a proton and an anti-neutrino
1n p1 + 0e-1 + v-

11. Beta decay occurs in neutron rich atoms
A common radiation type in all nuclear reactors
Decay of rhenium into osmium
187Rh Os76 + 0e-1 + v-

12. Properties of Beta radiation
Negatively charged
Nearly massless
React less readily compared to alpha radiation
Can travel several meters in air
Stopped by thin sheets of plastic or metal
Travels faster than light in certain materials (water) resulting in Cherenkov radiation

14. Applications of Beta radiation
Radiation therapy used to destroy cancer cells
Radioactive tracers
Used to check thickness of materials such as paper

15. Gamma Radiation Present in most of the other forms of decay processes
After a radioactive decay the daughter nuclei is fairly energetic and will release some of this excess energy as a gamma ray pulse / burst

16. Properties of gamma radiation
Similar in nature to light or microwaves
Only higher in energy
No mass
No charge
Travels at / near the speed of light
Interact through collisions with electrons
Lose energy slowly
Can travel hundreds of meters in air

17. Application of Gamma Radiation
Used in cancer surgery
Gamma ray knife
Sterilization of food products
Irradiation
Scanning
CT scans
Container scans at airports
Molecular changes in materials
Turns white topaz into blue topaz

18. summary Charge Mass Alpha = positive Beta = negative Gamma = neutral
Alpha = heavy
Beta = nearly massless
Gamma = massless

19. Half life
Describes the time required for nuclear material to be reduced by half
Each radioactive isotope has different half lives
Carbon-11 = 20 minutes
Uranium-238 = 4.5 x 109 years

20. Half life game Everyone tosses one coin Heads leave the game
Tails continue to toss until no one is left in the game
Questions
What does your graph resemble?
Why is this?

21. Predicting the quantity remaining
Number of elapsed half-lives
Fraction remaining
Percentage remaining
1/1
100% 1
50% 2
25% 3
1/8
12.5% 4
1/16
6.25% n
1/2n
100% / 2n

22. Applications of half life
Dating
Carbon-14 decays to carbon-12. The ratio can be used to date archeological artifacts
Toxicology
Predict the effects of certain toxins in the human body over time