Thermal electron source
AssigneeThe Secretary of State for Defence in Her Britannic Majesty's Government of the United Kingdom of Great Britain and Northern Ireland
InventorPeter G. Simmonds
Life of this patent
Estimating the term…
Abstract
A thermal electron source suitable for use in an electron capture detector comprises a source of stable ultra-violet light, an ultra-violet transparent support member (20,31) located in the path of the ultra-violet light (41) and a thin photo-emissive metallic layer (1A, 24, 33) coated over the surface of the support member remote from the source. In one form the source is a cylindrical mercury vapor lamp (1) with the photo-emissive layer coated directly on the lamp. The coated lamp may then be enclosed within a cylindrical anode (8) with a gas flow between them and the electrical current is measured between the anode and cathode. In an alternative arrangement a planar geometrical assembly is provided. Preferably the photo-emissive material is gold and the carrier gas is an argon-methane mixture.
Claims6
An electron capture detector (ECD) including an anode and a cathode and means therebetween for passage of a gas stream including trace elements for detection wherein the cathode comprises:
- (a) a source of stable ultra-violet light having a cylindrical envelope;
- (b) a coating of photoemissive material provided over the cylindrical envelope of the source, the coating comprising a thin conducting layer of metal selected such that the work function is less than the principal irradiance of light, so that said source of stable ultra-violet light and said coating form a cathode having a photoemissive thermal electron source of cylindrical geometry;
- and
- (c) cathode connection means conductively connected to the photoemissive metallic layer such that electrical circuitry can be connected to the cathode.
An electron capture detector (ECD) including an anode and a cathode and means therebetween for passage of a gas stream including trace elements for detection wherein the cathode comprises:
- (a) a source of stable ultra-violet light having a cylindrical envelope;
- (b) a coating of photoemissive material provided over the cylindrical envelope of the source, the coating comprising a thin conducting layer of metal selected such that the work function is less than the principal irradiance of light, so that said source of stable ulta-violet light and said coating form a cathode having a photoemissive thermal electron source of cylindrical geometry;
- (c) cathode connection means conductively connected to the photoemissive metallic layer such that electrical circuitry can be connected to the cathode;
- (d) a conducting cylindrical anode having a larger diameter than and surrounding the cathode and extending along at least a portion of the length of the electron source,
- (e) means for introducing a flow of gas between the cathode and anode, and
- (f) means for measuring the current flow between the cathode and the anode.
Dependencies are inferred from the claim text.