1. Nuclear Chemistry

2. Antoine Henri Becquerel (1852-1908) February 1896. Antoine Henri Becquerel, a French scientist, was conducting an experiment which started with the exposure of a uranium-bearing crystal to sunlight. Once the crystal had sat in the sunshine for a while, he placed it on a photographic plate. As he had anticipated, the crystal produced its image on the plate. Becquerel theorized that the absorbed energy of the sun was being released by the uranium in the form of x-rays. Further testing of this theory had to be put off for a few days because the sky had clouded up and the sun had disappeared. For the next couple of days he left his sample of uranium in a closed drawer along with the photographic plate.

3. When the weather had cleared, he returned to the drawer to retrieve his gear. He was surprised to find that the crystal had left a clear, strong image on the photographic plate. How could this be? There was no source of energy to produce the image! What Becquerel had discovered was that a piece of mineral which contained uranium could produce it's image on a photographic plate in the absence of light. What he had discovered was radioactivity! He attributed this phenomenon to spontaneous emission by the uranium.

4. Pierre Curie (1859-1906) Marie Curie (1867-1934) The husband and wife team of Pierre and Marie Curie became interested in Becquereal's discovery. While experimenting with their own uranium-containing ore, they came up with the term "radioactivity" to describe the spontaneous emissions that they studied. This word is still used today to describe this special characteristic of some elements.(radioisotopes). While comparing the activity of pure uranium to a uranium ore sample, they found that the ore was significantly more radioactive than the pure material. They concluded that the ore contained additional radioactive components besides the uranium. This observation led to the discovery of two new radioactive elements which they named polonium and radium.

5. Did you know this?? In 1903, Becquerel and the Curies together received the Nobel Prize in physics. This award was for their discovery of radioactivity and their other contributions in this area. Marie Curie received a second Nobel Prize in 1911 for the discovery of polonium and radium. She was the first person to win two Nobel Prizes. Did you know that the Curie's had a word named after them? The curie is a basic unit of measurement for describing radioactivity.

6. Types of Radiation Alpha particles: α Positively charged …essentially the nucleus of a helium atom 2 neutrons and 2 protons They travel short distances, have large mass Beta particles: β- Negatively charged….electrons emitted when a neutron decays to form a proton and emits the beta particle Gamma radiation: γ High energy radiation…more energy than x-rays! Released by nucleus along with beta and alpha decay

7. Penetrating Power Alpha radiation can be stopped by a sheet of paper; beta can be stopped by a sheet of plastic; gamma is stopped by several inches of lead or several feet of concrete!

8. Natural Transmutation  Transmutation = change of nucleus of an atom of an element to another element (must involve a change in the number of protons!) Natural transmutation = the change of naturally radioactive elements by emission of a radioactive particle  Isotopes of elements with atomic numbers less than 20 whose neutron: proton ratio is NOT 1:1 are likely to undergo spontaneous nuclear “decay” (i.e. loss of a radioactive particle) (for example…. carbon-12 is stable, carbon-14 is radioactive)  All isotopes of elements with atomic numbers > 82 are radioactive (“unstable”)

9. Beta Decay Converts a neutron to a proton and an electron 19 protons 23 neutrons 20 protons 22neutrons

10. Positron Decay Converts a proton to a neutron and a positron (anti-matter of electrons)

11. Balancing Nuclear Equations In order to balance nuclear transmutation reactions, the number of protons and total mass must remain the same on both sides of a nuclear equation.

12. Artificial Transmutation Artificial transmutation = isotopes that are NOT naturally radioactive can be transmutated by “bombardment” with nuclear particles.

13. Half-Life amount of time required for one-half of the isotope to undergo radioactive decay The half-life of a radioisotope CANNOT be changed!! # of half-lives amount remaining 0101 11/2 21/4 31/8

14. Half-Lives can vary…. How many half-lives will Sr-90 undergo in 112 years? How many days must elapse for I-131 to undergo 3 half-lives ?

15. Nuclear Energy All nuclear energy is derived from the conversion of small amounts of mass to energy. Einstein’s relativity equation E = mc 2 explains the relationship between matter and energy (c = 3.00 x 10 8 m/s …it is the speed of light) When the mass of nuclear reactants (before) is compared to the products (after), a small amount of mass is unaccounted…this is called the mass defect and is the mass that is converted to energy

16. Nuclear Fission All existing nuclear power plants use nuclear fission as the source of energy Fission involves the splitting apart of large nuclei into smaller nuclei with the release of large amounts of energy A commonly used reaction involves the capture of a neutron by a U-235 nucleus and its splitting apart into Ba- 141 and Kr-92 plus 3 neutrons

17. Fission Pros Releases more energy than conventional fuels No greenhouse gases Viable source of energy (we can do it!) Cons U-235 accounts for only 3% of the world’s uranium Non-renewable resource Highly radioactive waste products (difficult to dispose)

18. Nuclear Fusion Fusion involves the joining of small nuclei to release large amounts of energy One of the most common reactions involves the joining of H-2 (deuterium) and H-3 (tritium)atoms to form He-4 and a neutron Fusion powers our sun!!

19. Fusion pros Much more energy than fission Abundant fuel (H-2 and H-3) in sea water Safe, non-toxic, stable waste products cons Requires extremely high pressures and temperatures to overcome repulsion by nuclei

20. Nuclear Accidents March 1979 Three Mile Island, Pa Partial meltdown released radiation No immediate deaths April 1986 Chernobyl, Ukraine Worst nuclear disaster in history, released more radiation, 31 deaths

21. Risks of Exposure to Radiation

23. How does radiation cause health effects? alpha, beta and gamma radiation are forms of ionizing radiation, which has enough energy to strip away electrons from atoms (creating ions) or to break some chemical bondsionizing radiationions living tissue in the human body can be damaged by ionizing radiation …the body attempts to repair the damage, but sometimes the damage cannot be repaired or it is too severe or widespread mistakes made in the natural repair process can lead to cancerous cells because children are growing more rapidly (and their cells are dividing more rapidly), they are more sensitive to radiation effects radiation can also cause damage to DNA, leading to mutation in offspring

24. How much radiation is needed to cause health effects? Exposure (rem) Health Effect Time to Onset (without treatment) 5-10 changes in blood chemistry 50nauseahours 55fatigue 70vomiting 75hair loss2-3 weeks 90diarrhea 100hemorrhage 400possible deathwithin 2 months 1,000 destruction of intestinal lining internal bleeding and death1-2 weeks 2,000 damage to central nervous system loss of consciousness;minutes and deathhours to days

25. Some radioactive elements are more dangerous than others organs in the body use an element cannot distinguish between radioactive and non-radioactive isotopes radioactive iodine concentrates in the thyroid, because the thyroid needs iodine to function normallyiodine calcium, strontium-90 and radium-226 have similar chemical properties. …so strontium and radium in the body tend to collect in calcium-rich areas, such as bones and teeth. They contribute to bone cancerstrontium-90radium-226 radioisotopes with long half-lives emit radiation slowly, while those with short half-lives emit radiation more quickly

26. Calculate your exposure… http://www.ans.org/pi/resources/dosechart/

27. Benefits of Radioisotopes Medical Uses: Iodine-131 because the thyroid uses iodine, radioactive iodine can be used to detect and treat thyroid disorders Tc-99 most commonly used radioactive tracer used to track blood flow in heart and brain (tumor detection)

28. Co-60 used as a source of gamma radiation targeted to cancer cells. proper dosage can destroy cancer cells and preserve healthy cells

29. Benefits of Radioisotopes Tracers used to follow pathways of chemical reactions Phosphorus-32 traces fertilizer uptake in plants Carbon-14 traces carbon in organic reactions Hydrogen-3 (tritium) traces hydrogen in chemical reactions

30. Benefits of Radioisotopes Dating determines the age of objects Carbon-14: percent of carbon 14 present in all living things is constant when an organism dies, carbon- 14 is no longer replenished using ratio of carbon-14 to carbon 12, the age of a fossil can be determined Uranium -238 used to determine the age of rocks (“geologic formations”)

31. Miscellaneous Benefits Americium-241 used in smoke detectors! ionizes air, smoke disrupts the ionization, causing alarm to sound Radiation is used to kill bacteria in fresh fruits, vegetables and meats!