1. Radiation
Dr. Walker

2. Objectives
Describe isotopes as a function of number of subatomic particles in an atom.
Describe and calculate half-life of a radioactive isotope.
Describe alpha, beta, and gamma radiation with respect to penetrating power, shielding, and composition.

3. Isotopes Same atom, different number of neutrons
All atoms of an element must have the same number of protons
All hydrogens have 1 proton
All heliums have 2 protons, etc., etc.
The neutrons can be different
11H, 21H, 31H
These are called isotopes

4. Atomic Symbols Review 11H, 21H, 31H
How many protons and neutrons do each of these isotopes contain?

5. Atomic Symbols Review 11H, 21H, 31H 11H = 1 proton, 0 neutrons
How many protons and neutrons do each of these isotopes contain?
11H = 1 proton, 0 neutrons
21H = 1 proton, 1 neutron
31H = 1 proton, 2 neutrons

6. Isotopes Most isotopes are stable – they do not break down
Some isotopes are unstable and break down – known as radioactive
There are rules that govern which ones are unstable that you don’t need to know
Nothing with an atomic number greater than 83 is stable

7. Radioactivity Radioactivity
Process where an unstable nucleus gives off one or more particles in the form of electromagnetic radiation
Radioactive decay is a nuclear (not chemical) processes.

8. Particles Alpha (a) Particle 23892U 23490Th + 42He 42He nucleus
Some radioactive elements give off a helium when they decay
Stopped by a sheet of paper
Example
23892U Th He

9. Particles Beta (b) Particle 23490Th 23491Pa + 0-1e + g
A beta particle is an electron (0-1e) that results from the breakdown of a neutron
10n p e
Multiple sheets of aluminum foil will stop a beta particle
23490Th Pa + 0-1e + g
Note: since the mass of an
Electron is much smaller than a neutron
Or proton, the mass number of an electron
Is zero

10. Particles Gamma (g) Ray
High energy photon given off during fission and radioactive decay
Contains no mass or electrical charge
Requires several centimeters of lead or concrete for shielding

11. Fission
The splitting of a nucleus of an atom into two or more fragments
The previous examples of decay are examples of fission
Nuclear power is generated by the fission of either Uranium or Plutonium (Dominion uses 23592U)

12. Fusion Combination of small nuclei to form larger nuclei
21H + 31H He + 10n + energy
Generates more energy than fission, but harder to start and maintain
Need REALLY high temperatures (40,000,000 C)
Manner in which stars form and generate energy

13. Transmutation
Conversion of one atom of one element to an atom of another element
Fission, fusion are BOTH examples
Transuranium elements
All elements above atomic number 92
Also known as the actinides (from actinium)
Made by neutron bombardment in a nuclear accelerator (like Jefferson Lab)

14. Transmutation Formation of transuranium elements
23892U U n (neutron capture)
23992U Np e (beta decay)
23993Np Pu + 0-1e (beta decay)

15. Half-Life
Half-life is the length of time required for half of a given sample of a radioactive isotope to decay
Iodine-131 has a half-life of about 8 days. Every 8 days, it loses half its mass

16. Half-Life Examples of half-life Isotope Half-life 3H 12.3 years 14C
14.3 days
235U
7.1 x 108 years
238U
4.51 x 109 years
239Pu
24,400 years

18. Half-Life
Iodine-131 has a half-life of 8 days. How much iodine-131 will remain from a 64 g sample in 32 days?
Each 8 days, divide by 2
Day 8, 64/2 = 32 g remaining
Day 16, 32/2 = 16 g remaining
Day 24, 16/2 = 8 g remaining
Day 32, 8/2 = 4 g remaining (Answer!)

19. How to Calculate Formula for calculating half-lives
Fraction Remaining = (0.5)n
n = number of half-lives
Previous problem
Determine number of half-lives
32 days / 8 days (half-life) = 4
Determine fraction remaining
(0.5)4 =
Multiply fraction by original mass
x 64 = 4 days (answer!)

20. Second Example
What percentage of carbon-14 remains in a sample that is 2000 years old? (Half-life of carbon = 5730 years)

21. Second Example
What percentage of carbon-14 remains in a sample that is 2000 years old? (Half-life of carbon = 5730 years)
Determine number of half-lives
2000 years / 5730 days (half-life) = 0.349
Doesn’t have to be a whole number!
Determine fraction remaining
(0.5)0.349 = 0.785
Convert decimal to fraction
0.785 x 100 = 78.5%

22. Everyday Applications
Nuclear Power (235U decay)
Smoke detectors
241Am decay ionizes air between electrodes. When smoke enters the space, the alarm is triggered
Cancer treatments
Rapidly dividing cells (like cancer cells) are more sensitive to radiation than normal cells

23. Exercises What radioactive particle requires the most shielding?
What radioactive particle has the largest mass?
The half-life of polonium 218 is 3.0 min. If you start with 20 grams of 218Po, how much will you have left after 12 min?

24. Exercises What radioactive particle requires the most shielding? gamma
What radioactive particle has the largest mass? alpha
The half-life of polonium 218 is 3.0 min. If you start with 20 grams of 218Po, how much will you have left after 12 min?
0 min – 20 g
3 min – 10 g
6 min – 5 g
9 min – 2.5 g
12 min – 1.25 g (Answer!!)

25. Terms to Remember Terms to Know Skills To Master Isotope
Alpha (a) particle
Beta (b) particle
Gamma (g) particle
Fission
Fusion
Half-Life
Perform calculations involving the half-life of a radioactive substance.

26. In Your Textbook Particle Types, pp. 877-879 Half-Life, pp. 882-884
Fission/Fusion, pp