Basic Cryogenics

Cryogenics is defined as production and study of temperature range below 120 K. The cryogenic gases are those gases whose boiling points are below 120 K. They include most common atmospheric gases : nitrogen , oxygen and argon and also include the rarer atmospheric gases : neon, krypton, and xenon. Of other gases the cryogenic gases include helium , hydrogen , methane and chlorine and may be said to include ethylene which is a border line case , boiling at 169 K. The four which are available in the greatest quantities, and which account for most of the cryogenic research and applications are given major attention in this paper . They are oxygen, nitrogen , helium and hydrogen . These four major cryogenic gases may be divided in two groups , characterized as cold and very cold . the components of air boil at about 83 K which is certainly cold , and then hydrogen and helium carry us down to the very cold range of 3 K to 23 K. In this paper we have considered only helium and it's isotopes for simplicity.