Diffusion-type gas sample chamber

An improved diffusion-type gas sample chamber for transmitting radiation through gases present in the chamber by ambient pressure diffusion, comprising in combination

• a) an elongated hollow tube having an inner wall and having a closed end and an open end, composed of a gastight material and having a specularly-reflective surface on the inner wall and on the inwardly-facing side of the closed end;
• b) said tube including a plurality of filtering apertures arrayed along said tube for improving the diffusion into and out of the space within said tube;
• c) a sheet of a semipermeable membrane covering each of said plurality of filtering apertures, said semipermeable membrane permitting gases to diffuse through it under ambient pressure into and out of the space within said tube and preventing airborne particles larger than a predetermined size from entering said space;
• d) a source of radiation;
• e) a detector of radiation;
• and,
• f) means for mounting both said source of radiation and said detector of radiation proximate said open end and facing said closed end, whereby some of the radiation emitted in various directions from said source of radiation is conducted by at least one reflection from the specularly-reflective surface on the inner wall to the specularly-reflective surface on the inwardly-facing side of the closed end and from the latter by at least one reflection from the specularly-reflective surface on the inner wall to said detector of radiation.