Low Level Alpha Counter 7287


The 7287 system has been developed principally for thermoluminescence (and similar) dating where the counting rate is small and a very low background is essential.

Each 7287 system can have up to eight scintillation/photomultiplier assemblies. Samples of material to be tested are put onto scintillator film and placed in an acrylic holder that is put on the top the photomultiplier in a light tight housing. When an alpha particle is emited by the sample it generates a flash of light on the scintillator which is detected by the photomultiplier.

A 7287 system comprises of one control unit and up to 8 photomultiplier scintillation counter units. The control unit is connected to the standard IP computer network via an RJ45 connector. The photomultiplier units connect to the control unit via a RS485 serial bus. The user controls the system via a web interface in the control unit.

Each photomultiplier tube has its own individually adjustable high voltage supply and discriminator circuit. The output pulses from the discriminator circuits are fed into an internal microprocessor which keeps track of the total number of counts and also the number of times counts occur within 4mSec of each other (called fast pairs) and those that occur between 20 and 400mSec apart (slow pairs). The pair counts allow estimates of the thorium and uranium content to be calculated by the system.
The microprocessor can be set to accumulate counts over any period from 10 to 65,000 seconds. At the end of this period the number of counts and the number of slow and fast pairs are saved and a new period is started. At the end of a specified number of periods data collection stops. Accumulated data can be viewed at any time via the built in web interface using any JavaScript compatible web browser (Recent versions of Internet Explorer, Google Chrome, Mac Safari, IPad etc). Results can be downloaded in a variety of formats for further processing.
The 7287 system needs a computer to start/stop data collection and display results but it does not necessarily need a dedicated computer. The 7287 is connected to the local computer network and any other computer on that network would be able to control the system using its web browser (Internet explorer, Apple Safari etc). This control computer could be next to the 7287, in the operators' office, even in another country if the 7287 is connected to the internet. Up to 20 control computers can be connected at the same time allowing several users to download results as required. The system will go on working if the control computer is turned off/disconnected. The control computer(s) can be any device with a network connection and a modern web browser, eg PC, laptop, Mac, Smartphone, IPad, Android tablet etc. No special software is required.
Three separate levels of password security are provided that allow overall control, Starting/stopping of data collection or just monitoring of results.