Taiyen later released a statement quoting the response of the AEC that the tested Potassium-40
is a source of natural radioactivity often found in animal and human bodies.
In all cases, however, the amounts of cesium and silver isotopes were much lower than those of naturally occurring potassium-40
in the same samples.
And although only a tiny fraction of potassium-40
is actually radioactive, and most of it has already decayed over Earth's 4.6-billion-year history, potassium still contribute up to 20 percent of the radioactive heat, Stevenson says.
For that far back, you need to measure the decay of such things as Uranium-235 or Potassium-40
mean activity (n = 65) was 83.0 Bq/kg, and varied significantly from 76.0 to 104.4 Bq/kg among locations.
Emissions of potassium-40
, a radioactive form of the element occurring naturally in the body in tiny amounts, measure mostly muscle mass, because at least 70 percent of body potassium is in the muscle, says Ellis.
An isotope of argon called argon-40 is produced from the natural decay of potassium-40
. A common technique for determining a rock's age is to heat the rock and measure the amount of argon-40 released: The more argon-40, the older a rock may be.
Yet they were still below levels of concern for humans and marine organisms and were about one-sixth the level of radiation that marine organisms receive from naturally occurring radionuclides such as potassium-40
However, in 1999, using potassium-40
atoms, Jin and her colleagues achieved a key milestone toward making a fermionic-type condensate (SN: 9/11/.99, p.
(Argon-40 results from the decay of radioactive potassium-40
, which has a half-life of 1.3 billion years; the argon accumulates at a predictable rate after each droplet solidifies into glass.)
In their experiments at JILA, DeMarco and Jin magnetically trapped batches of about 100 million atoms of potassium-40
. Their method of reducing the temperature resembles the cooling of a cup of coffee.