The Packard Topcount NXT is a fully contained benchtop model microplate scintillation counter and luminescence detector. The ability to accommodate microplate stackers makes this instrument well designed for high throughput. These external stackers allow up to 15,000 samples (for the HTS model) to be handled at once without any further operator input. Additionally, an open front-loading sample chamber allows for easy robotics integration and permits unlimited sample loading and processing. Rapid counting is also accomplished with a range of 2 to 12 wells being monitored at a time for scintillation counting, and 12 well monitoring for the HTS model. For luminescence, 2 wells can be monitored at a time. The combination of this counting ability and the accommodation of large volumes of samples gives the NXT high throughput capabilities. It is a versatile counting system that not only executes beta, gamma, and luminescence counting, but also Cerenkov counting, liquid and solid scintillation, among others.
Forming the foundation of the scintillation counter is the single photomultiplier tube (PMT). One of these PMTs is located on each counter. High sensitivity is provided with these counters because of low intrinsic backgrounds for each of these photomultiplier tubes. A unique characteristic of this specific PMT is an ability to distinguish scintillation events from the background during decay periods. This ability is called time resolved liquid scintillation counting (TR-LSC). Given the additional ability of single photon counting, this instrument is well suited for applications in low count rate samples. With the monitoring of samples in an isothermal counting chamber where temperatures can be controlled, electronic drift and data noise are virtually eliminated, ensuring accuracy and reproducibility of results. All processes are controlled by a Windows NT operating system via computer interface.