Abstract: A scintillation detector is provided which has a scintillation member comprised of a substance which converts energy received in the form of an ionizing particle to light. The scintillation member, such as a thallium-activated alkali halide crystal, is sealed in a housing containing an atmosphere which is substantially non-reactive to the scintillation member at temperatures ranging from about 100.degree. C. to about 250.degree. C. Examples of suitable atmospheres include the noble gases including helium, neon argon, krypton, xenon and radon; nitrogen; carbon dioxide, a vacuum, and other atmospheres, such as mixtures of these or air which has been substantially depleted of oxygen. Processes for the manufacture of the detector are taught where the scintillation member is encapsulated in a non-reactive atmosphere such as ones listed above. Alternatively, the reactive atmosphere can be washed from the housing or the sealed housing can be evacuated and refilled with a non-reactive atmosphere.