Method and apparatus for measurement of radioactivity over an extended range

An apparatus is described for measuring radioactivity over an extended range of activity levels comprising: (a) a body of scintillator material; (b) a photomultiplier tube mounted adjacent to the scintillator body to receive light flashes therefrom and having an anode, a cathode, and a plurality of dynodes; (c) means for biasing the anode, cathode and dynodes of the photomultiplier tube to provide an acceleration voltage for electrons from the cathode across the dynodes to the anode; (d) means for selectively measuring the current flowing from the anode of the photomultiplier tube resulting from scintillation events in the scintillator body sufficient to cause a measurable current to flow from the anode; and (e) means for selectively counting the rate of electron pulses in the photomultiplier tube resulting from scintillation events in the scintillator body. The means for measuring anode current and the means for counting the electron pulse rate are capable of doing so simultaneously over an intermediate rate range of scintillation events