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3: Radioactive Dating The amount of Pb-204 is constant. Uranium decays into Pb-206 & Pb-207. The ratio of 204 to 206 & 207 can therefore be used to calculate the age of the Earth. The amount of Pb-204 naturally found on the earth was difficult to determine b/c of all the �unnatural lead� produced by �leaded gasoline�. Clair Patterson calculated the age of the Earth to be 4.55 billion yrs old by using the amount of Pb-204 in meteorites. He later crusaded to get lead removed from paint and gasoline.

5: Ernest Rutherford He suspected that �pure radioactivity� was an unknown gaseous element. He left radioactive substances under a beaker that captured a gas: Radon. He discovered that one element changed into another by noticing the amount of Radon gas eventually decreased as it accumulated since it decayed into other elements. He came up with the �rules� of how one element jumps to another when decaying. He also trapped a-particles, zapped them with electricity, and proved that they were helium nuclei. He trained 11 future Nobel Prize winners.

6: Natural Fission Reactor UF6 samples from the Oklo Mine, located in Gabon, Central Africa, showed a discrepancy in the amount of the U-235 isotope. Normally the concentration is 0.720%; these samples had only 0.717% � a significant difference. This discrepancy required explanation, as all uranium handling facilities must meticulously account for all fissionable isotopes to assure that none are diverted for weapons purposes.

7: Natural Fission Reactor The % of Nd-143 and Ru-99 at the site matched that produced by the fissioning of U-235. The conclusion was that a self-sustaining nuclear chain reactions had occurred on Earth about 2 billion years ago. Later, other natural nuclear fission reactors were discovered in the region.

8: Natural Fission Reactor: How It Worked The natural nuclear reactor formed when a uranium-rich mineral deposit became inundated with groundwater that acted as a neutron moderator, and a nuclear chain reaction took place. The heat generated from the nuclear fission caused the groundwater to boil away, which slowed or stopped the reaction. After cooling of the mineral deposit, short-lived fission product poisons decayed, the water returned and the reaction started again. These fission reactions were sustained for hundreds of thousands of years, until a chain reaction could no longer be supported.

9: How big can atoms get? Because of the limit of how fast electrons can orbit the nucleus, 137 protons is the upper limit on the atom�s size.

10: Astatine & Francium Astatine has a half-life of about 400 minutes and Francium has a half-life of about 20 minutes. There�s about 1 oz. of At on the earth. There�s about 20-30 oz. of Fr on the earth. Since astatine is chemically similar to iodine, they used a Guinea pig�s thyroid gland to �prove� the existence of astatine.

11: Radium Radium glows green. Marie Curie used to wear a necklace of Radium! Mark Twain�s story, �Sold to Satan� had Satan made of pure radium. He glowed green and was hot b/c of radioactivity. Some people drank radium water thinking it would provide health benefits. Irene Joliot Curie won the Nobel Prize in 1935 and died of leukemia in 1956 just like her mom did 22 years earlier.

12: Radiotracer�s First �User� Hevesy sprinkled radioactive lead on the cafeteria meat to see if it was re-used. He brought in a Geiger counter the next day and BINGO! Click, click, click on that night�s goulash. He drank �heavy water� to find out how long it took the body to recycle a water molecule�Answer = 9 days.

13: Enrico Fermi, In 1934, Enrico Fermi bombarded uranium with slow neutrons and induced the first fission, but failed to recognize that the products were La & Ba instead of what he thought were transuranic elements. He died b/c of breathing beryllium which shredded his lungs. (He used Be to slow down the neutrons and knock them back into the uranium to cause more fission.)

14: Otto Hahn & Lise Meitner Hahn repeated Fermi�s experiment, and Meitner interpreted the results as fission instead of making heavier elements and convinced Hahn of this. In 1938, he published the results but he had to leave her name off of the paper since she had Jewish grandparents. In 1944 he won the Nobel prize for this explanation, but she got an element named after her!

15: Emilio G. Segr� He studied under Enrico Fermi in Italy. While at Berkeley, he helped discover the element astatine and the isotope plutonium-239, and found Technetium in pieces of Molybdenum from the atom smasher in the Lawrence Lab. He worked at the Los Alamos National Laboratory as a group leader for the Manhattan Project. He won the Nobel Prize in Physics 1959 with Owen Chamberlain �for their discovery of the antiproton�.

16: Radon Radon sits in the lungs because of its high density, and kills you with lung cancer.

17: Americium Used in smoke detectors. Radioactive Americium-241 releases alpha-particles that interact with smoke in the detector to change an electrical current which sound the alarm.

18: U-233 Breeder Reactor U-233 fuel assemblies can be arranged such that the thorium fuel rods are surrounded by a more-enriched seed element which contains U-235. The uranium-235 provides neutrons to the subcritical blanket. The U-233 produced there is used for fuel.

19: U-233 Breeder Reactor

20: Thorium-232 Lantern Mantles

21: The Atom Bomb Code Name: The Manhattan Project From 1942 to 1946 the project was under the command of Major General Leslie R. Groves Jr. of the US Army Corps of Engineers and the lead scientist was J. Robert Oppenheimer. The project had its roots in the Einstein�Szil�rd letter, which warned that Nazi Germany might develop nuclear weapons. The letter was written by prominent physicists, signed by Albert Einstein, and delivered to President Franklin D. Roosevelt in October 1939. The Manhattan Project, which began as a small research program that year, eventually employed more than 130,000 people at a cost of nearly $2�billion.

22: Critical Mass A critical mass is the smallest amount of �fissionable� material needed for a sustained nuclear chain reaction. Little Boy had about 2.5 critical masses. Fat Man had about 5 critical masses.

27: Hydrogen Fusion Bomb The Russian �Tsar Bomb� was the largest thermonuclear weapon ever tests. It was the equivalent of 57 Megatons of TNT.