Leukocytes or white blood cells typically make up 4000-10,000 WBCs for every microliter of blood. If your white blood cell count drops below 3500 WBCs for every microliter of blood it causes a condition called leukopenia that causes cramps, fever, sore gums, diarrhea, sneezing, headaches, sore throat, etc.
Magnesium (Mg) naturally occurs in three stable isotopes, 24 Mg, 25 Mg, and 26 Mg. There are 19 radioisotopes that have been discovered, ranging from 19 Mg to 40 Mg. The longest-lived radioisotope is 28 Mg with a half-life of 20.915 hours. The lighter isotopes mostly decay to isotopes of sodium while the heavier isotopes decay to isotopes of aluminium. The shortest-lived is 39 Mg with a half-life shorter than 180 nanoseconds, or possibly 40 Mg, with a half-life longer than 170 nanoseconds (the half-life of 19 Mg is unknown). Standard atomic mass: 24.3050(6) u. A chart showing the abundances of the naturally-occurring isotopes of magnesium.
Element 61, Promethium (Pm), is also unstable. The most stable isotope of the element, promethium-145, has a half-life of 17.7 years; promethium-146 has a half-life of only 5.53 years, while that of promethium-147 is 2.62 years. There are a number of other isotopes as well, but the majority of them have half-lives that are less than 30 seconds.