1. Radioactivity and Nuclear Reactions
Ch , 9.4

2. Nucleus and the Strong Force
Protons and neutrons are packed tightly together
Two positives normally repel each other, so why don’t the protons in the nucleus repel?
Strong force = one of four basic forces that causes protons and neutrons to be attracted to each other
100 times stronger than electric force
Short-range force, so it weakens with distance

3. Small vs Large Nuclei
Protons and neutrons are held together less tightly in large nuclei. Why?
Small nuclei have few protons, so the repulsive force on a proton due to other protons is small
In a large nuclei, the attractive strong force is exerted only by the nearest neighbors. All the protons exert repulsive forces making the repulsive force large.

4. Radioactivity
In many nuclei, the strong force keeps the nucleus together (STABLE)
When it can’t, the nucleus can decay and give off matter and energy in a process of radioactivity
Larger nuclei tend to be unstable – all nuclei containing more than 83 protons are radioactive
All elements with more than 92 protons are synthetic and decay soon after they are created (UNSTABLE)

5. Stable and Unstable Nuclei
Smaller elements neutron to proton ratio is 1:1 to be stable isotopes
Heavier elements neutron to proton ratio is 3:2 to be stable isotopes
Nuclei of any isotopes that differ much from these ratios are unstable, whether heavy or light

6. Nuclear Radiation
When an unstable nucleus decays, particles and energy are emitted from the decaying nucleus
Alpha Particles – (2 p and 2 n lost) massive, comparatively speaking; loses energy quickly; can’t pass through paper; changes the element (transmutation); mass changes; can damage the body
Beta Particles – (n turns into p and emits e) e emitted from n; transmutation changes the element; mass doesn’t change; much faster and penetrating; damage body
Gamma Rays – electromagnetic waves that carry energy; most penetrating form; cause less damage to biological molecules

7. At a glance…

8. Radioactive Half-Life
Some radioisotopes decay in less than a second, while others take millions of years
Half-life: the amount of time it takes for half the nuclei in a sample of the isotope to decay

9. Radioactive Half-Life cont

10. Ch 21.3: Absolute-Age Dating of Rocks
Relative-age dating vs. Absolute-Age Dating
Relative-age dating: compares past geologic events based on the observed order of strata in rock record
Absolute-age dating: determines actual age of a rock, fossil, or other object

11. Radioactive Decay
Radioisotopes are found in igneous and metamorphic rocks, some fossils, and organic remains
Emission of radioactive particles and the resulting change into other elements over time is called radioactive decay
This decay stays constant regardless of the environment, pressure, temperature, or any other physical changes
So, these atomic particles become accurate indicators of the absolute age of an object

12. I love you Mrs. Sjuts! 

13. Radioactive Dating
Fossils and rocks can be dating using radioactive isotopes
Amounts of the radioisotope and its daughter nucleus are measured in a sample
Then, the number of half-lives that need to pass to give the measured amounts of the isotope are calculated
The number of half-lives is the amount of time that has passed since the isotope began to decay AND usually is the same as the age of the object.

14. Carbon Dating
The radioactive isotope C-14 is often used to find the ages of once living objects
It is naturally found in most all living things
An atom of C-14 eventually will decay into N-14 with a half-life of 5,730 years
By measuring the amount of C-14 in a sample and comparing it to the amount of C-12, scientists can determine the approx age of plants and animals that lived within the last 50,000 years

15. Uranium Dating
Some rocks contain uranium, which has two radioactive isotopes with long half-lives, both decaying into isotopes of lead
By comparing the uranium isotope and the daughter nuclei the number of half-lives since the rock was formed can be calculated
U-235  0.7 billion years
U-238  4.5 billion years

16. Ch 9.4 Nuclear Reactions
Nuclear Fission – the process of splitting a nucleus into two nuclei with smaller masses
Chain reaction – ongoing series of fission reactions
Critical mass – the amount of fissionable material required so that each fission reaction produce approximately one more fission reaction
Nuclear Fusion – two nuclei with low masses are combined to form one nucleus of larger mass

18. Nuclear Fission
Large elements need a TON of energy in order to hold their nucleus together.
When the large nucleus is split into smaller nuclei, those smaller nuclei don’t require as much energy to stay together…
So, that leftover energy is released!
Atomic bomb – used in Hiroshima and Nagasaki
Fission - Chain Reaction Nuclear Fission: Pros and Cons
Nuclear Meltdown
Cooper Nuclear Station near Brownville, NE
Fort Calhoun Nuclear Generating System between Ft. Calhoun and Blair

19. Nuclear Fusion
Need very high temperatures in order to overcome the repulsive forces. Sun's Fusion
Scientists cannot control fusion reactions for the purpose of power.
We can, however, use it to make nuclear weapons. Large ones. Hydorgen Bomb - Fusion

20. Nuclear Decay vs. Nuclear Reactions
Decay happens spontaneously
Reactions are controlled and self-sustaining and release much more energy

21. Nuclear Reaction: Plutonium
Pu-239 Used to make nuclear weapons like the one dropped on Nagasaki in 1945