Sunday, 5 April 2015

Packard 1000 TR Liquid Scintillation Analyser - Part 3 Photomultipliers

The next phase in the teardown is the photomultipliers and sample chamber.

The two PMTs are installed into a long bright silvery metallic tube, i'm not sure if this is just steel or some more exotic alloy for magnetic shielding and background radiation shielding working in combination with the external lead.  It's not like Mu-metal at all but it is paramagnetic. Although lead absorbs much of the background radiation i will also emit secondary radiation due to this absorption. So additional materials can be used specifically to absorb these secondary emissions. Maybe i need a x-ray fluorescence spectrometer to discover what this metal is made from!

PMT & Sample Chamber Assembly

The PMTs are easily removed, they simply slide into the metal tube with plush velour to provide light blocking.

Inside the metal tube there are two metalized plastic reflectors to improve effeciency of the overall process. They attach in the centre of the tube, the PMTs push up against them.

The large photomultipliers are Hammamatsu model R331-08, featuring a frosted concave quartz window. They are 12 stage PMTs running at 1600v. Well below their 2500v rating. They appear to be designed for use in Liquid Scintillation Analysis.

The PMTs plug into a socket which is housed in a brass case with a brazed end. At the moment i dont have a neat way to desolder this so i will look at doing this in the future. Inside the case will be the resistor divider network and connections for the third cable which i am uncertain as it's use.