| 摘要 |
Radioactive specimens are placed in the well (12) of a plastic scintillator body (11), and the light flashes from the scintillator body (11) are picked up by a photomultiplier tube (13). The anode (44) and dynodes (43) of the photomultiplier tube (13) are electrically isolated and a selected biasing voltage is provided across the cathode (42) and dynodes to operate the photomultiplier tube in its linear range at the activity level of the specimen. At high activity levels, the current flowing from the anode (44) is measured by an electrometer (21) to determine a value which is directly related to the activity of the specimen, whereas at lower activity levels where anode current is not accurately measurable, the pulses at the last dynode (50) are counted to determine the scintillation rate and thereby the activity level of the specimen.
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