Nuclear Chemistry Lesson 2

F ission splitting a nucleus into two or more smaller nuclei 1 g of 235U = 3 tons of coal

F ission chain reaction - self-propagating reaction critical mass - mass required to sustain a chain reaction

Fission and the Atomic Bomb Two masses are kept apart until detonation. When combined they create a critical mass and the chain reaction begins Little Boy & Fat Man

Fission Nuclear Reactors Shearon Harris

Fission Reactors Shearon Harris, like all reactors that supply us with electricity, is a fission reactor. Shearon Harris operates using uranium rods enriched to 3% U-235, but controls the rods from reacting too quickly by using neutron absorbing cadmium and boron

Nuclear Waste Spent rods can be reused in some cases Some products, though, are extremely radioactive and must be safely stored for approximately 20 half lives (thousands of years)

Fusion combining of two nuclei to form one nucleus of larger mass thermonuclear reaction – requires temp of 40,000,000 K to sustain 1 g of fusion fuel = 20 tons of coal occurs naturally in stars

Fusion in the Sun Supplies the Earth with nearly limitless energy today Sun will eventually run out of fusible matter and will die.

Fusion Nuclear Reactors Bikini Island Nuclear Test Like “mini” suns Need tons of energy to get the reaction started and keep it going Currently not sustainable but potentially could give “clean” energy

Fission vs. Fusion FISSION FUSION 235U is limited fuel is abundant danger of meltdown toxic waste thermal pollution fuel is abundant no danger of meltdown no toxic waste not yet sustainable

Uses of Radiation Food Irradiation  radiation is used to kill bacteria and increase shelf-life of food Irradiated milk has a shelf life of 3 months without refrigeration. USDA has approved irradiation of meats and eggs. Radioactive Tracers explore chemical pathways trace water flow study plant growth, photosynthesis

Uses of Radiation Radiation Treatment Iodine-131 is used to measure thyroid activity. The gas xenon-133 is used to diagnose respiratory problems. Iron-59 is used to diagnose anemia. larger doses are used to kill cancerous cells in targeted organs internal or external radiation source

Dangers of Radiation Radiation fragments and ionizes molecules found in biological tissue. This causes mutations that can disrupt mitosis and normal cell function. Can cause various types of cancer in the exposed individual If mutations occur in the gametes (sperm or egg cells) they may be passed on to the offpsring

Effects of Radiation

Half-Life The time required for one half of the nuclei of a radioisotope sample to decay to stable products. Every half-life, the mass of a sample is cut in half. Formula: m = mo(0.5)t/h m = mass after decay t = time mo = original mass h = half-life Thus, # half-lives = t/h

Practice Problem Carbon-14 emits beta radiation and decays with a half-life of 5730 years. Assume you start with a mass of 2.00 x 10-12 g of carbon-14. How many grams of the isotope remain after 17,190 years? m = mo(0.5)t/h m = (2.00 x 10-12g)(0.5)17190/5730 m = 2.50 x 10-13 g

Practice Problem What is the half life (h) of a radioisotope if a 12 gram sample decays into a 3 gram sample over a period of t = 25.0 years? # Half-lives: 12 g (0 half-life)  6 g (1 half-life)  3 g (2 half-lives) # half-lives = t/h 2 = 25 yrs/h h = 12.5 years