Nuclear Chemistry

1. Nuclear Chemistry

2. Nuclear Reactions • Unstable isotopes gain stability by making changes in the nucleus • These changes are followed by large amounts of radiation • All elements with atomic number of 83 and higher are radioactive

3. 3 Types of Radiationalpha Symbol  (Greek) ‘alpha’ 42He • composed of 2 protons and 2 neutrons (helium nucleus) • more massive than beta particle • produces new particle with lower atomic # and mass # example of alpha decay 22688Ra   42He   +   22286Rn

4. 3 Types of Radiationbeta Symbol β (Greek) ‘beta’ 0-1e      and     0-1β • fast moving electrons • smaller than an alpha particle • produces new particle with higher atomic # and same mass # example of beta decay 146C   0-1e   +   147N

5. 3 Types of Radiationgamma Symbol  (Greek) ‘gamma’ • electromagnetic radiation • high energy photons (energy, not a particle) • represents energy lost when the remaining nucleons reorganize into more stable arrangements • no change in particle (mass or charge) that undergoes gamma decay

7. Half-life • Time required for one-half of the atoms of a radioisotope to give off radiation and decay into another isotope • After one ½ life, one half of the original substance remains…and so on… • Half-life graph looks like a 1st order graph of ln [ ] vs time

8. Example: half-life • N-13 has a half-life of 10 min. Assume a starting mass of 200 grams. How many grams of N-13 remain after 30 min? • ½ life = 10 min • Mass = 200 grams • Time = 30 min • Formula: time passed ÷ ½ life • Then: Divide the sample (mass) in half that many times • Answer: 30 ÷ 2 = 3 ( substance divides in ½ 3 times) • 200 ÷ 2 = 100 • 100 ÷ 2 = 50 • 50 ÷ 2 = 25 So: 25 grams remain

9. History of Radiation • Henri Becquerel discovered uranium in 1896 • Marie Curie discovered radioactivity in 1903 • Poe discovered radon in 1911

10. Detecting Radiation • Geiger counter – detects radiation, a gas-filled tube connected to a wire electrode. Used for beta radiation • Film badge – several layers of photographic film encased in plastic or metal. Used to protect people who work around radiation

11. Uses of Radiation • Agricultural research – test effects of herbicides, pesticides, and fertilizers • Medicine – used to diagnose and treat some diseases. I-131 used to detect thyroid problems • Radiation treatment – kill cancer cells • Pharmaceuticals – used for radiation therapy • Gamma knife – an alternative to surgery for removing tumors • Nuclear energy (fusion and fission)

12. Nuclear Energy: Fission 1.  Splitting of one atom into two smaller atoms 2.  advantage- can do it now 3.  disadvantage-fuel hard to get and produces waste products that are radioactive 4.  Chain reaction       a.  reaction continues because an ejected particle form the original reaction can split more nuclei       b.  critical mass-minimum volume of fissional material necessary to keep a chain reaction going 5.  Nuclear power plants       a.  produce electricity  (nearly 20% of U.S. needs; 110 plants)       b.  produce heat to boil water to make steam to turn turbines       c.  parts            1.  fuel rods-pellets of uranium dioxide            2.  control rods-absorb neutrons to control rate of reaction            3.  moderator-slows down high-speed neutrons            4.  generator-produces electricity            5.  cooling system-cools steam

13. Nuclear Energy: Fusion 1.  involves formation of a new, more massive atom by forcing two less-massive nuclei to combine 2.  powers the sun and stars 3.  advantage-produces little waste and fuel is readily available 4.  disadvantage- can’t do it on large scale yet 5.  energy released is enormous and can be calculated using Einstein’s theory of relativity   E  =   mc2