Our ECD consists of
a stainless steel cylinder containing radioactive Nickel-63. The Nickel-63
emits beta particles (electrons) which collide with the carrier gas molecules,
ionizing them in the process. This forms a stable cloud of free electrons
in the ECD cell. When electro-negative compounds enter the cell, they
immediately combine with some of the electrons, temporarily reducing the
number remaining in the electron cloud. The detector electronics, which
maintain a constant current (about 1 nanoampere) through the electron
cloud, are forced to pulse at a faster rate to compensate for the decreased
number of free electrons. The pulse rate is converted to an analog output,
which is connected to the data system.
Because it contains
only 5 millicuries of Nickel-63, the ECD is covered by a "general
license," which requires a periodic wipe test and the filing of a
form with your state's Department of Health or Radiation Safety. In most
states, no annual fee is required.