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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 .
For U.S. food and dietary supplement labeling purposes, the amount in a serving is expressed as a percent of Daily Value (%DV). For potassium labeling purposes, 100% of the Daily Value was 3500 mg, but as of May 2016, it has been revised to 4700 mg. [29] [30] A table of the old and new adult Daily Values is provided at Reference Daily Intake.
Although bananas are commonly thought to contain exceptional potassium content, [112] [113] their actual potassium content is not high per typical food serving, having only 12% of the Daily Value for potassium (table). The potassium-content ranking for bananas among fruits, vegetables, legumes, and many other foods is medium.
[1] [2] [3] Minerals are one of the four groups of essential nutrients; the others are vitamins, essential fatty acids, and essential amino acids. [4] The five major minerals in the human body are calcium, phosphorus, potassium, sodium, and magnesium. [2] The remaining minerals are called "trace elements".
Included for each food is its weight in grams, its calories, and (also in grams,) the amount of protein, carbohydrates, dietary fiber, fat, and saturated fat. [1] As foods vary by brands and stores, the figures should only be considered estimates, with more exact figures often included on product labels.
Potassium is a chemical element; it has symbol K (from Neo-Latin kalium) and atomic number 19. It is a silvery white metal that is soft enough to easily cut with a knife. [9] Potassium metal reacts rapidly with atmospheric oxygen to form flaky white potassium peroxide in only seconds of exposure.
40 K occurs in natural potassium in sufficient quantity that large bags of potassium chloride commercial salt substitutes can be used as a radioactive source for classroom demonstrations. [citation needed] 40 K is the largest source of natural radioactivity in healthy animals and humans, greater even than 14 C.
Potassium forms a mixture of potassium peroxide and potassium superoxide, while rubidium and caesium form the superoxide exclusively. Their reactivity increases going down the group: while lithium, sodium and potassium merely burn in air, rubidium and caesium are pyrophoric (spontaneously catch fire in air).