Abstract: A process for producing an encapsulated detector operating in an ultra high vacuum (UHV) for gamma (.gamma.) spectroscopy, wherein a detector is placed into a detector chamber portion of a detector containment pot and a lid is placed into the containment pot and both are joined by electron beam welding under vacuum at their top in such a way, that the detector is not exposed to excessive heat and that the vapors generated during welding are condensed before they can reach the detector chamber, whereby a detector capsule capable of maintaining an ultra high vacuum can be produced.