Abstract: A system for in-situ measurement of the radioactivity of multiple samples while the samples are in a multiple-well sample tray, with a scintillator in each sample-containing well for producing light pulses in response to radiation from the respective samples. Multiple photomultiplier tubes are positioned adjacent to the sample wells containing the scintillator for simultaneously measuring the radioactivity of multiple samples with only a single photomultiplier tube sensing the scintillations from each well and converting the sensed scintillations into corresponding electrical pulses. The electrical pulses from each photomultiplier tube are processed to discriminate between pulses attributable to sample events within the wells and pulses attributable to non-sample events such as photomultipler tube noise.

Abstract: An improved method and apparatus is provided for performing high sensitivity fluorescence measurements. A liquid sample contained within a cuvette is exposed to exciting radiation in such a way that the radiation is introduced directly to the sample and is restricted from reaching the container walls. The sample container is in the form of a cylindrical cuvette provided with reflector means on the bottom so that any unabsorbed exciting radiation reaching the cuvette bottom is reflected back through the sample solution. Fluorescent radiation emitted by the sample is collected by an ellipsoidal reflector which substantially surrounds the sample container and focuses radiation incident thereupon onto a small area from which it is efficiently sensed by a photodetetor. The optical arrangement realizes significantly improved signal-to-noise and signal-to-background ratios.