You may need a backup method of birth control if you have vaginal intercourse during the seven days after a missed pill. Some backup methods are the condom, female condom, diaphragm, or sponge. You can also use emergency contraception (morning after pill) up to five days after unprotected intercourse.
Strontium-90, a radioactive isotope, is a by-product of nuclear reactors and present in nuclear fallout. It has a half-life of 28 years. It is absorbed by bone tissue instead of calcium and can destroy bone marrow and cause cancer. However, it is also useful as it is one of the best high-energy beta-emitters known. It can be used to generate electricity for space vehicles, remote weather stations and navigation buoys.
Strontium metal was first isolated in 1808 by Sir Humphry Davy working in London using electrolysis. Davy had built a very large 600-plate battery, which he used to pass electricity through salts, breaking them down in order to isolate new elements. He mixed magnesium oxide to a paste with (probably) strontium sulfate.