Chapter 11 Nuclear Chemistry Background Radiation Three-fourths of all exposure to radiation comes from background radiation. Most of the remaining one-fourth comes from medical irradiation such as X-rays. X ray machine Production of X rays 11/2 1
Radiation Damage to Cells Radiation is capable of removing electrons from cells forming ions, hence the term ionizing radiation. Molecules can also splinter into neutral fragments called free radicals. Free radicals can disrupt cellular processes. 11/3 Radiation Damage to Cells Radiation often affects the fastest growing cells and tissues such as white blood cells and bone marrow. 11/4 2
Radiation Damage to Cells Ionizing radiation can also disrupt DNA causing mutations. 11/5 Sources of radiations Cosmic rays: 90% proton, 9% α particles, 1%βparticles. 11/6 3
Nuclear Equations In nuclear equations, we balance nucleons (protons and neutrons). The atomic number (number of protons) and the mass number (number of nucleons) are conserved during the reaction. # of nucleon(s) charge p n γ He 1 1 0 4 0 1 0 0 2 1 e 4 2α 0 1β 0 1 e 11/7 Nuclear Equations Alpha Decay 11/8 4
Beta Decay Nuclear Equations neutron > proton + electron 11/9 Nuclear Equations Double Beta Decay 2 neutrons > 2 protons + 2 electrons Ge As + 76 76 0 32 33 1 e Ge Se + 76 76 0 32 34 2 1 e lower binding energy than Ge-76. Single beta decay cannot occur. higher binding energy than Ge-76. Double beta decay occurs. It is the rarest known kind of radioactive decay; it was observed for only 10 isotopes: 48 Ca, 76 Ge, 82 Se, 96 Zr, 100 Mo, 116 Cd, 128 Te, 130 Te, 150 Nd, and 238 U. 11/10 5
Nuclear Equations radiation describes any process in which energy travels through a medium or through space, ultimately to be absorbed by another body. 11/11 Nuclear Equations Positron emission: A positron is a particle equal in mass to an electron, but with opposite charge. proton > neutron + positron positron + electron = gama ray 11/12 6
Nuclear Equations Electron capture: A nucleus absorbs an electron from the inner shell. proton + electron > neutron Electron capture is followed by emission of X rays or Auger electrons 11/13 7
Nuclear Equations 11/15 Nuclear Equations 11/16 8
Nuclear Equations 11/17 Half-Life Half-life of a radioactive sample is the time required for ½ of the material to undergo radioactive decay. Fraction remaining = 1/2 n 11/18 9
Radioisotopic Dating 11/19 Radioisotopic Dating Carbon-14 dating: The half-life of carbon-14 is 5730 years. Carbon-14 is formed in the upper atmosphere by the bombardment of ordinary nitrogen atoms by neutrons from cosmic rays. 1 14 14 0 n + 7 N 6 C + 1 1 H 14 6 C 14 7 N + 0 1 e ( + ν ) e 11/20 10
Radioisotopic Dating Tritium dating: Tritium is a radioactive isotope of hydrogen. It has a half-life of 12.26 years and can be used for dating objects up to 100 years old. 1 6 4 0 n + 3 Li 2He + 3 1 H 1 10 4 0 n + 5 B 2 2He + 3 1 H 1 14 12 0 n + 7 N 6 C + 3 1 H 11/21 Artificial Transmutation Bombardment of stable nuclei with alpha particles, neutrons, or other subatomic particles cause new elements to form. This process is known as artificial transmutation. 11/22 11
Uses of Radioisotopes Tracers Radioisotopes can be easily detected through their decay products. Therefore, they can be used to trace their movement. Some uses of tracers include: Detect leaks in underground pipes. Determine frictional wear in piston rings. Determine uptake of phosphorus and its distribution in plants. Labeling in organic synthesis 11/23 Uses of Radioisotopes Irradiation of Food Radioisotopes can destroy microorganisms that cause food spoilage. 11/24 12
Nuclear Medicine Radiation therapy: Nuclear radiation can be used to kill cancerous cells. Radiation is most lethal to fastest growing cells. Radiation is aimed at the cancerous tissue. Patients undergoing radiation therapy often experience nausea and vomiting, which are early signs of radiation sickness. 11/25 Nuclear Medicine Diagnostic Uses of Radiation 11/26 13
Nuclear Medicine Gamma ray imaging: Technetium-99m emits gamma radiation. It can be used to image the heart and other organs and tissues. healthy heart diseased heart 11/27 Nuclear Medicine Positron Emission Tomography (PET): A patient inhales or is injected with positron-emitting isotopes such as carbon-11 or oxygen-15. When positrons encounter electrons, they emit two gamma rays, which exit the body in opposite directions. PET scans can be used to image dynamic processes. 11/28 14
PET MRI Penetrating Power of Radiation Alpha radiation is least penetrating and can penetrate the outer layer of skin. Alpha radiation is stopped by a sheet of paper. Beta radiation can penetrate through a few cm of skin and tissue. Beta radiation is stopped by a sheet of aluminum foil. Gamma radiation will pass right through a body. Gamma radiation requires several cm of lead to stop. 11/30 15
Penetrating Power of Radiation Fire detector 11/31 Ionization fire detectors Americium (Source of α particles) 11/32 16
Penetrating Power of Radiation Two means of protecting one s self from radiation are distance and shielding. Distance: Move away from the source. The intensity of radiation decreases with increasing distance from the source. Shielding: Lead is a commonly used shield for radiation. 11/33 Energy from the Nucleus By 1905, Albert Einstein had developed his famous mass energy equation: E = mc 2 E = Energy m = Mass c = Speed of light 11/34 17
Energy from the Nucleus When protons and neutrons combine to form a nucleus, a small amount of mass is converted into energy. This is known as binding energy. 11/35 Binding Energy 11/36 18
The Building of the Bomb Nuclear fission: Fission occurs when larger nuclei split into small nuclei. U-234, U-235, and U-238, undergo radioactive decay by emission of an alpha particle accompanied by weak gamma radiation 11/37 Nuclear Chain Reaction Fission of one nucleus produces neutrons that can cause the fission of other nuclei, thus setting off a chain reaction. 11/38 19
Manhattan Project The Manhattan Project was launched by President Roosevelt in 1939. It consisted of four separate research teams attempting to: Sustain the nuclear fission reaction Enrich uranium Make fissionable plutonium-239 Construct a fission atomic bomb 1 239 239 92U + 0n 92U 93Np 238 ( 0 e) + 1 239 94 Pu ( 0 e) + 1 11/39 Atomic Bomb Manhattan Project 11/40 20
Manhattan Project Mushroom cloud over Nagasaki from the detonation of Fat Man, August 9, 1945. 11/41 Radioactive Fallout Many radioactive isotopes are produced in a nuclear bomb blast. Some are particularly harmful to humans. Among these are strontium- 90 and iodine-131. Strontium-90: Has a half-life of 28.5 years and is chemically similar to calcium. It is obtained from dairy and vegetable products and accumulates in bone. Iodine-131: Has a half-life of 8 days. It concentrates in the thyroid glands. 11/42 21
Thyroid gland 11/43 Nuclear Power Plants Civilian nuclear power plants use less enriched uranium (2.5-3.5% uranium-235 rather than 90% for weapons). The nuclear chain reaction is controlled for the slow release of heat energy. The heat is used to make steam, which turns a turbine to produce electricity. problem: production doesn t always match needs 11/44 22
Thermonuclear Reactions Nuclear fusion is a thermonuclear reaction. Smaller atomic nuclei are fused into larger nuclei in such a reaction. The principle reaction on the sun is one such reaction. Tokamak 11/45 11/46 23
The Nuclear Age 11/47 24