1. It’s better to have a half-life than no life!
Radioactive Decay

2. What does it mean to be radioactive?
Atoms that are radioactive have nuclei that spontaneously decompose to form a different nuclei and produce one or more particles
These particles can be any of the following
Alpha particle (42He)
Beta particle (0-1e)
Gamma particle (00γ)
Positron (01e)
Cosmic rays

3. Radioactive (cont’d)
Atoms that are radioactive have a neutron/proton ratio much greater than 1
Radioactivity can be detected by a Geiger counter

4. How do we measure decay?
The term “half-life” is used to time radioactive decay
Half-life means the time it takes for half of a sample to decay.
After one half-life ½ of the nuclei have decayed to different nuclei
After two half-lives ¾ of the nuclei have decayed to different nuclei
14C = 5.73x103yr U = 4.46x109yr

5. Nuclear Reactions?
A nuclear reaction details how nuclei are changed through the emission (radioactive decay) or absorption (nuclear transformation) of alpha, beta, and gamma particles
Equations are balanced by making sure the sums of the atomic numbers and mass numbers on both sides of the equation are equal

6. Radioactive Decay
Alpha, beta, and gamma particles are emitted from radioactive nuclei
Alpha particle production
EX: Ra  42He Rn
Beta particle production
EX: Th  23491Pa + 0-1e
Gamma ray emission (usually accompanies alpha and betaparticles)
EX: U  42He Th + 00γ

7. Nuclear Transformation
Heavier elements are made from lighter ones by absorption of alpha particles, beta particles, or smaller nuclei
EX: 147N + 42He  178O + 11H
EX: 2713Al + 42He  3015P + 10n

8. Try These! Find the missing particle:
? + 10n  24997Bk + 0-1e
2010Ne + ?  2412Mg + 00γ
Write the balanced nuclear equation for the following radioactive decays: (a) beta decay of nickel-63; (b) alpha decay of gold-185.

9. What use is radioactivity?
Medicine – radioactive materials are used as tracers in the body
Energy sources – energy can be obtained through two nuclear processes
Fission: a nucleus divides into smaller fragments
Fusion: nuclei combine to form a larger nucleus

10. Fission Splitting nuclei releases large quantities of energy
Harnessed in nuclear power plants
Reaction is controlled by 2 methods
Neutron moderation: reduces speed of neutrons
Neutron absorption: decreases number of neutrons

12. What happens in a reactor?

13. So what is Fusion? Fusion is much better than fission
Fuels are cheaper
Products are not radioactive
Unfortunately it takes a high temperature for fusion to occur
Fusion is what produces the energy for the sun.