1. 14.4: Radioactivity and Nuclear Reactions

2. CHEMICAL REACTIONS: - take place in the outer valence shell of electrons
NUCLEAR REACTIONS:
- take place in the nucleus
- involve huge amount of energy as described by the equation E = mc2

3. Nuclear Reactions
Changes the nucleus of the atom.
Changes an isotope of one element into an isotope of a different element
Involve much more energy than a chemical reaction.

4. 2 types of Nuclear Reactions:
FUSION: joining together two nuclei. Occurs in stars, where hydrogen atoms are fused together to produce helium
FISSION: splitting apart two nuclei. Occurs in nuclear power plants and nuclear bombs, where uranium is a reactant. Radioactive decay occurs when fission process repeats many times as the original radioactive nucleus gets smaller and smaller.

5. Radioactive Half life - the time required for 1/2 the nuclei in a radioactive sample to decay.
This quantity can be predicted with great accuracy.

6. Each radioactive element has its own unique half life.
Half lives vary from less than 1 second to billions of years.
Radon seconds
Iodine hours
Carbon-14 5,730 years
Uranium billion years
Thorium billion years

7. FRACTIONAL AMOUNT REMAINING
Carbon-14 has a half life of 5730 yrs. If a radioactive sample has 500 grams of carbon-14, about 250 grams will decay during the first half-life. That leaves 250 grams which have not decayed. During the next half-life, half of the remaining carbon-14 (about 125 grams) will decay. Below is a chart for this sample.
Half life TIME (years)
SAMPLE (grams)
FRACTIONAL AMOUNT REMAINING
500 g 1
5,730
250 g
1/2
11,460
125 g
1/4
17,190
62.5 g
1/8
22,920
31.25 g
1/16

8. 5730 yrs
10,460 yrs