Abstract: An invention for preventing optical crosstalk in a process of counting liquid scintillation samples deposited in a sample plate, the sample plate composed of a plurality of sample wells, the optical crosstalk being caused by mutual optical affection between samples deposited in the sample wells. Sample wells are provided with tubes made of material impermeable but reflective or scattering for scintillation light generated by the samples.

Abstract: An arrangement for counting liquid scintillation samples on bottom-window multi-well sample plates in a liquid scintillation counter. The sample plates include a plurality of samples wells having light impermeable side walls and a light permeable bottom sheet which covers and forms the bottoms of said sample wells. The liquid scintillation counter includes at least one photomultiplier tube and a sample plate holder. The sample plate holder includes a device to hold sample plates of different sizes and a device to enable transporting of the sample plate holder by the scintillation counter. For preventing light passage between sample wells in the permeable bottom sheet a light permeable adhesive foil provided with black lines or other light passage preventing treatment between the sample wells is attached to the bottom side of the sample plate.