Mache (symbol ME from German Mache-Einheit, plural Maches) is a unit of volumic

radioactivity Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is conside ...

named for the Austrian physicist Heinrich Mache. It was defined as the quantity of

radon Radon is a chemical element; it has symbol Rn and atomic number 86. It is a radioactive noble gas and is colorless and odorless. Of the three naturally occurring radon isotopes, only Rn has a sufficiently long half-life (3.825 days) for it to b ...

(ignoring its daughter isotopes; in practice, mostly radon-222) per litre of air which ionises a sustained current of 0.001 esu (0.001 StatAmpere). 1 ME = 3.64 Eman = 3.64×10⁻¹⁰ Ci/L = 13.4545 Bq/L.

References

Units of radioactivity Obsolete units of measurement {{measurement-stub