Abstract: Gas density variations between two electrodes are controlled by directing a gas stream into the region between the electrodes. Inside a vacuum chamber there are suitably arranged electrodes in the form of a cathode and an anode, and also a pulse gas source, as well as, preferably, a suitable winding.

Abstract: Apparatus for light flux attenuation particularly for additional quenching of scintillations in the determination of radionuclide activity comprising a body provided with a counting chamber containing a counting vial which is optically coupled with photomultipliers and between which is disposed a cylindrical spring. The opposite ends of the spring are secured in the body and the spring extends in surrounding relation with a rotatable bush mounted in the body. The bush is provided with a ring having a hole through which the cylindrical spring passes such that the ring divides the spring into a first portion surrounding the counting vial and a second portion surrounding the rotatable bush.