Energy filter

An energy filter, for enclosing a Geiger Mueller tube, comprises a copper sheath, open at one end and possessing an aperture at the other, surrounded by a discontinuous jacket of 60-40 tin-lead alloy. The latter, assisted by the copper sheath, reduces those radiant frequencies at which the Geiger Mueller tube is most sensitive, enabling the tube to produce a response which is substantially independent of the energy of the incoming radiation. 60-40 tin-lead alloy is a commercial solder of eutectic composition. Consequently the filter is readily constructed by casting the tin-lead parts, either directly onto the copper sheath, or apart from it, for later assembly. The particular configuration of the alloy jacket, comprising two axially spaced rings and one end disc, and the sheath aperture, are chosen to give a circular polar response as nearly as possible. (author)