NUCLEAR CHEMISTRY

Rates of Decay & Half Life Radionuclides have different stabilities and decay at different rates.

Integrated Rate Equation where…  A = the amt. of decaying sample remaining at some time, t  A o = the amt. of sample present at the beginning  k = rate constant; different for each radionuclide  t = time

Integrated Rate Equation OR… where…  N = # of disintegrations per unit of time; relative activity  N o = original activity

HALF-LIFE = the amount of time required for half of the original sample to decay

Parent Daughter

HALF-LIFE Half-life = the amount of time required for half of the original sample to decay

Example: Cobalt-60 decays with the emission of beta particles and gamma rays, with a half-life of 5.27 years. How much of a 3.42  g of cobalt-60 remains after 30.0 years? How do you solve for A???

Take the ANTILOG (10 x ) of both sides.

Example: Cobalt-60 decays with the emission of beta particles and gamma rays, with a half-life of 5.27 years. How much of a 3.42  g of cobalt-60 remains after 30.0 years?

Uses of Radionuclides Radiocarbon dating: the ages of specimens of organic origin can be estimated by measuring the amount of cabon-14 in a sample.

Carbon Cycle How does C-14 get into living things???

Example: A piece of wood taken from a cave dwelling in New Mexico is found to have a carbon-14 activity (per gram of carbon) only times that of wood today. Estimate the age of the wood. (The half-life of carbon-14 is 5730 years.)

t=3744 yrs = 3740 yrs

Uses of Radionuclides ***NOTE: Objects older than 50,000 years have too little activity to be dated accurately using carbon dating; instead the following methods are used: – Potassium-40 decays to argon-40: half-life = 1.3 x 10 9 years – Uranium-238 decays to lead-206: half-life = 4.51 x 10 9 years

Example: A sample of uranium ore is found to contain 4.64 mg of uranium-238 and 1.22 mg of lead-206. Estimate the age of the ore.