mache unit

A unit of concentration of radioactive material, = 3.64 emans = 3.64 × 10⁻¹³ curies per cubic centimeter, defined in 1930 by the International Radium-Standards Committee¹ as that quantity of emanation from radon (i.e., alpha particles) which sets up an ionization saturation current of 0.001 cgs electrostatic units of current in air. In SI units, it is about 13.5 × 10⁻³ becquerels per cubic centimeter.

The unit is named for H. Mache (1876–1954).

1. M. Curie, A. Debierne, A. S. Eve, H. Geiger, O. Hahn, S. C. Lind, St. Meyer, E. Rutherford and E. Schweidler.
The Radioactive Constants as of 1930. Report of the International Radium-Standards Commission.
Reviews of Modern Physics, volume 3, number 3, pages 427-445 (July 1931).

Page 432: "Mache Unit (M. E.) is a concentration unit referred to the Rn content of 1 liter of water or gas, etc. It is that quantity of Rn per liter which without decay products and with complete utilization of the α-particles can maintain by its ionization of air a saturation current of 10⁻³ e.s.u..
"1 M.E. corresponds to 3.64·10⁻¹⁰ curie/liter = 3.64 Eman."