Mache (symbol ME from German Mache-Einheit, plural Maches) is an obsolete unit of volumic radioactivity named for the Austrian physicist Heinrich Mache. It was defined as the quantity of radon (ignoring its daughters; 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
Mache (unit) Wikipedia(Text) CC BY-SA