Potassium (40K) decays to Argon (40Ar) with a half-life value of 1.3 billion years. 40K is the parent isotope and 40Ar is the daughter isotope. Laboratory analysis of a rock sample showed that there are 0.13ppm of 40K and an equal amount of 40Ar in the rock. (ppm: parts per million)

Carbon is one of the fundamental elements in everything that's alive on Earth. The three naturally occuring isotopes of carbon are 12C (mass fraction = 0.99), 1³C (mass fraction = 0.01) and radioactive 14C. The relative abundance or mass fraction of 14C is about 10-12 (or 1 in 1012 atoms). This radiocarbon originates from cosmic rays interacting with nitrogen atoms in the atmosphere and has a half-life time of 5730 years. Since it's half-life time is a lot higher than the time the atoms need to go through the carbon cycle, all living biomass at the Earth's surface has the same abundance of 14C as in the atmosphere. After a plant or animal has deceased the amount of 14C atoms will decay exponentially according to the following formula: = mo · 2-t/tı/2 with mo as the mass fraction at t = 0 and t1/2 as the half-life time. Since we know the abundance of 14C in the atmosphere, we can use this equation to estimate the time of death of an organism. This method is known as carbon dating.…

The radioactive gas krypton-85, produced by nuclear power plants as well as volcanoes, is present in trace amounts in earth’s atmosphere. Its half-life is 10.8 years. Suppose a volcano released 250 g of krypton-85 in an eruption. How much would remain after (a) 10.8 years, (b) 15 years, and (c) 50 years? Round to the nearest tenth of a gram.

Radioactive decay can be described by the following equationln A = ln A0 - ktwhere A0 is the original amount of the substance, A is the amount of the substance remaining after time t, and k is a constant that is characteristic of the substance.For the radioactive isotope strontium-90, k is 2.47 x 10-2 years -1.If the original amount of strontium-90 in a sample is 38.9 mg, how much strontium-90 remains after 28.4 years have passed?_____ mg.