1. The fission process generates many krypton and xenon isotopes both directly and as aconsequence of radioactive decay of their precursors.

2. Helium isotops are among the products of thermonuclear reactions.

3. Neutrons generated by the detonation interact with components of the explosive, and of the surrounding medium, to create noble gas isotopes through nuclear reaction processes.

4. The detonation itself vaporizes, melts, and fractures the medium surounding it, causing the release of soil gases to the chimney voids.

5. Air normally enters the chimney region to replace the condensing steam during the cooling process, and in doing so introduces an often significant quantity of noble gases that may be generally termed "background"


C.F.Smith, Utilization of the noble gasses in studies of underground nuclear detonations, Symposium on noble gases, 1973