1. The Atomic Nucleus

2. Remember…
Rutherford discovered the nucleus using the gold foil experiments
J.J. Thomson discovered the electron using cathode ray experiments
The cathode ray led to the discovery of radioactivity

3. Discovery of Radioactivity
Wilhelm Roentgen – 1896:
German physicist
discovered a “new kind of ray”
“New rays” are NOT deflected and can pass through opaque materials
Called these X-rays
Opaque: not able to be seen thru

4. Strong Nuclear Force
Attractive force that acts between protons and neutrons; very strong but only at extremely short distances
Atoms with large nuclei are not as stable as an atom with a very small nucleus
Large atoms are more likely to fall apart or emit particles/energy
All nuclei with more than 83 protons are radioactive
Nucleons are protons or neutrons
Strong nuclear force between two protons if they are very close to one another, but if the protons spread out, the strong nuclear force is very weak
So generally, if we look at the periodic table, the elements with more than 83 protons are not found naturally and we only see them create in the science laboratory. With so many protons, they have a very large atomic nucleus compared to small elements, so they decay very rapidly, and even in the lab, they may only exist for seconds

5. Radioactivity
Radioactive Decay: when the nucleus of an unstable isotope emits particles, (releases energy) in order to become stable
After decay, the element changes into a different isotope of the same element, or a completely different element
Nuclear Radiation: The matter, or energy, that is emitted, during radioactive decay
Nuclear radiation causes changes in the nucleus of an atom

6. Radioactive Rays
Three types of nuclear radiation – Alpha, Beta, and Gamma
Rutherford discovered Alpha Rays and Beta Rays

7. Alpha Particles
Alpha Rays: positively charged particles he called alpha particles
Consist of two protons and two neutrons that are ejected from the atom
Do not easily penetrate solid material
Relatively large in size
High kinetic energy which can cause damage to the surface of a material

8. Beta Particles
Beta Rays: identical to cathode rays; simply another name for an electron being ejected from a nucleus
Faster than alpha particles
Able to penetrate light materials such as paper and clothing
Can penetrate deeply into the skin

9. Gamma Rays
Gamma Rays: discovered by other scientists; carry no electric charge and no mass—they are an extremely energetic form of nonvisible light
Pure energy
Greater energy in a gamma ray than there is in visible light
More harmful to us than either alpha or beta particles because they can cause structural damage to our cells

10. Transmutation The changing of one element to another
When a radioactive nucleus emits an alpha or beta particle, the identity of the nucleus changes because the atomic number has changed

11. Transmutation
If an element ejects an alpha particle  result is a new atom with a mass number decreased by 4 and an atomic number decreased by 2
2 spaces back on periodic table because 2 fewer protons
If an element ejects a beta particle  result is a new atom with no change in mass number but atomic number increased by 1
1 space forward on periodic table because 1 more proton

12. Beta Decay
On board, do decay of Ra (radium)  ? e answer: At (astatine)
Po (polonium)  Pb (lead) + ? Answer: alpha particle

13. Radioactivity is Natural
You are exposed to radiation every day, but small amounts are not really harmful.
We have adapted to survive natural and man made sources of radiation
sun, rocks, soil, computers, smoke detectors, x-rays
Exposure varies from one location to another
Places higher in elevation and lots of rocks get more radiation

14. Units of Radiation
Radiation is measured in rems, lethal doses begin at 500 rems
The radiation we receive from the environment is only a fraction of 1 rem
Typically exposed to 360 millirems per year
Radon is the leading source of natural radiation (seeps through cracks in the ground—why we check our basements!)

15. Medical Applications
Radioisotopes and radiation have many applications in the field of medicine
Radioactive tracers are used to diagnose diseases
X-Rays, mammograms, CAT scans (all methods of seeing inside the body).
Radiotherapy (radiation for chemo)
During radiation therapy, a patient may receive doses of 200 rems each day for a period of weeks

16. Half-Life
Time it takes for half the atoms in a sample of radioactive material to break down by radioactive decay
Every time a half-life passes, half of what you started with has decayed
Example: radium-226 has a half-life of 1,620 years; half of a sample of radium will decay to other elements after 1,620 years!
The shorter the half-life, the more radioactive the substance

17. Half-Life
Half-life is exponential – as the number of parent isotope atoms decreases, the number of daughter isotopes increases

18. Isotopic Dating
Carbon-14 is the most common isotope of carbon (6 protons and 8 neutrons)
Carbon-14 is radioactive and can form carbon dioxide, which is used by plants for photosynthesis
all plants have a small amount of radioactive carbon-14, and all plants are consumed in some way, therefore all living things contain a small amount of radioactive carbon-14

19. Carbon-14 Dating Carbon-14’s half-life is 5,730 years
If a plant has 20 atoms of carbon-14, it will have 10 atoms of carbon-14 in 5,730 years!
We can calculate the age of carbon-containing things by measuring their amount of radioactive carbon-14
We can predict the age with about 15 percent uncertainty
If we say something is 500 years old, it could be between 425 (low) and 575 (high) years old

20. Nuclear Fission
Strong nuclear force between neutrons and protons dominates the repulsive force between the protons
When very large atoms are bombarded with a neutron, the nucleus splits into many fragments
Nuclear Fission: the splitting of the nucleus
Discovered by German scientists Otto Hahn and Fritz Strassmann

21. Uranium-235
Uranium has a mass number 235 and is one of the most common atoms to undergo fission
When it is hit with a neutron, three neutrons are released
Those three neutrons can cause the fission of more uranium atoms, releasing more neutrons, which causes more fission
Known as a chain reaction—a self-sustaining reaction in which the products of one reaction cause more reaction events.

23. Uses of Nuclear Fission
Energy released by the fission of one uranium-235 nucleus is about 7 million times the energy released by the explosion of one TNT molecules
Energy produced by fission was introduced to us in the form of nuclear bombs
About 20% of electrical energy in the U.S. is generated by nuclear fission reactors

24. Nuclear Fusion Nuclear Fusion: small nuclei fuse (or combine) together
Nuclei must be travelling at extremely high speeds in order to combine
High speeds correspond to high temperatures found within the sun—thermonuclear fusion
~657 million tons of hydrogen is fused to 653 million tons of helium each second

25. Use of Nuclear Fusion
Thermonuclear bomb, or the hydrogen bomb—first detonated in 1952
Typical thermonuclear bomb made by the U.S. today could be about 1000 times more destructive than the atomic bomb that was detonated over Hiroshima at the end of WWII
Potential positive uses of fusion could be the controlled releases of vast amounts of clean energy