The HP-100B is equivalent to the Ludlum 43-143, 100 cm² Gas Flow Proportional Detector which is used for alpha/beta contamination measurements wherever a steady supply of P10 counting gas is available.    It has an MHV connect.   The gas is supplied up through the detector signal cable so no additional gas feed lines are needed making its use just like any other external probe.  Another nice feature of this design is the removable faceplate which simply slides off to facilitate quick replacement of the window anytime it’s needed.