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Potassium-40 (40 K) is a radioactive isotope of potassium which has a long half-life of 1.25 billion years. It makes up about 0.012% (120 ppm ) of the total amount of potassium found in nature. Potassium-40 undergoes three types of radioactive decay .
Stable isotope variations of calcium (most typically 44 Ca/ 40 Ca or 44 Ca/ 42 Ca, denoted as 'δ 44 Ca' and 'δ 44/42 Ca' in delta notation) are also widely used across the natural sciences for a number of applications, ranging from early determination of osteoporosis [10] to quantifying volcanic eruption timescales. [11]
The decay of 40 K to 40 Ar is used in potassium-argon dating of rocks. Minerals are dated by measurement of the concentration of potassium and the amount of radiogenic 40 Ar that has accumulated. Typically, the method assumes that the rocks contained no argon at the time of formation and all subsequent radiogenic argon (i.e., 40 Ar) was retained.
Allura Red AC, also known as FD&C Red 40 or E129, is a red azo dye commonly used in food. It was developed in 1971 by the Allied Chemical Corporation, who gave the substance its name. [1] [2] It is usually supplied as its red sodium salt but can also be used as the calcium and potassium salts. These salts are soluble in water.
The most common isotope 40 Ca is also doubly magic and could undergo double electron capture to 40 Ar, but this has likewise never been observed. Calcium is the only element with two primordial doubly magic isotopes. The experimental lower limits for the half-lives of 40 Ca and 46 Ca are 5.9 × 10 21 years and 2.8 × 10 15 years respectively. [30]
For other isotopes, the isotopic mass is usually within 0.1 u of the mass number. For example, 35 Cl (17 protons and 18 neutrons) has a mass number of 35 and an isotopic mass of 34.96885. [7] The difference of the actual isotopic mass minus the mass number of an atom is known as the mass excess, [8] which for 35 Cl is –0.03115.
Zirconium is a chemical element; it has symbol Zr and atomic number 40. First identified in 1789, isolated in impure form in 1824, and manufactured at scale by 1925, pure zirconium is a lustrous transition metal with a greyish-white color that closely resembles hafnium and, to a lesser extent, titanium.
The amount that the ratio of atomic masses to mass number deviates from 1 is as follows: ... (40) 6 Li: 1.002 520 481 24 (26) 12 C: 1 14 N: 1.000 219 571 732 (17) 16 ...