Hormonal contraceptives (the pill, the patch, and the vaginal ring) all contain a small amount of man-made estrogen and progestin hormones. These hormones work to inhibit the body's natural cyclical hormones to prevent pregnancy. Pregnancy is prevented by a combination of factors.
Definition of STRONTIUM 90. : a heavy radioactive isotope of strontium of mass number 90 that has a half-life of 29 years, that is present in nuclear waste and fallout, and that is hazardous because like calcium it can be assimilated in biological processes and deposited in the bones of human beings and animals.See strontium 90 defined for kids. a heavy radioactive isotope of strontium having the mass number 90 that is present in the fallout from nuclear explosions and is hazardous because like calcium it can be assimilated in biological processes and deposited in the bones of human beings and animalsâcalled also radiostrontium.
Strontium is the chemical element with symbol Sr and atomic number 38. An alkaline earth metal, strontium is a soft silver-white yellowish metallic element that is highly reactive chemically. The metal forms a dark oxide layer when it is exposed to air. Strontium has physical and chemical properties similar to those of its two vertical neighbors in the periodic table, calcium and barium. It occurs naturally mainly in the minerals celestine, strontianite and is mined mostly from the first two of