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Potassium-40 undergoes four different types of radioactive decay, including all three main types of beta decay: electron emission (β −) to 40 Ca with a decay energy of 1.31 MeV at 89.6% probability, positron emission (β + to 40 Ar at 0.001% probability [1], electron capture (EC) to 40 Ar * followed by a gamma decay emitting a photon [Note 1 ...
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While 40 K comprises only 0.001167% of total potassium mass, 40 Ca makes up 96.9821% of total calcium mass; thus, 40 K decay leads to significantly greater 40 Ca enrichment than any other isotope. [8] The decay constant for the decay to 40 Ca is denoted as λ β and equals 4.962 × 10 −10 yr −1; the decay constant to 40
This involves electron capture or positron decay of potassium-40 to argon-40. Potassium-40 has a half-life of 1.3 billion years, so this method is applicable to the oldest rocks. Radioactive potassium-40 is common in micas, feldspars, and hornblendes, though the closure temperature is fairly low in these materials, about 350 °C (mica) to 500 ...
The Bateman equation predicts the relative quantities of all the isotopes that compose a given decay chain once that decay chain has proceeded long enough for some of its daughter products to have reached the stable (i.e., nonradioactive) end of the chain. A decay chain that has reached this state, which may require billions of years, is said ...
The daughter nuclide of a decay event may also be unstable (radioactive). In this case, it too will decay, producing radiation. The resulting second daughter nuclide may also be radioactive. This can lead to a sequence of several decay events called a decay chain (see this article for specific details of important natural decay chains ...
The decay scheme of a radioactive substance is a graphical presentation of all the transitions occurring in a decay, and of their relationships. Examples are shown below. It is useful to think of the decay scheme as placed in a coordinate system, where the vertical axis is energy, increasing from bottom to top, and the horizontal axis is the proton number, increasing from left to right.
Some nitrogen-14 is radiogenic, coming from the decay of carbon-14 (half-life around 5700 years), but the carbon-14 was formed some time earlier from nitrogen-14 by the action of cosmic rays. Other important examples of radiogenic elements are radon and helium, both of which form during the decay of heavier elements in bedrock. Radon is ...