I need an advice regarding PMT, voltage divider etc.

[Vit Ladanyi]

Hello guys,
I have several questions which I am trying to solve. I hope that you can help me.

I am trying to find datasheet for old PMT – RCA 4254/VI from sixties. This PMT with preamplifier is a part of scintillation probe with well-type NaI(Tl) detector. My search is still unsuccesfull. Do you have someone some informations for this PMT? The probe comes from old device (Nuclear-Chicago corp.) which no longer exist...

Light guide balm between the RCA PMT and NaI(Tl) crystal is dry, the PMT could not be separated from the crystal. Could help me to separate the PMT from the crystal heating or use of any organic solvent?

Rather general question – the voltage divider of this PMT has 4.3 MΩ resistance (contains thirteen 332 kΩ resistors + one 27 kΩ). If I wanted to increase the divider resistance, it is possible to prepend ahead of divider for example 10 MΩ resistor or I have to use as divider thirteen resistors with higher resistance?

Thanks!

Vit

[valentin]

Hi Vit,

I do not have a data sheet either, but you can tell the pin layout by looking at the current resistor chain. By prepending a 10M resistor you would just reduce the voltage across the detector to about 30% of the voltage provided by your HV supply. So you have to replace the resistors in the divider chain.

Valentin

PS: be careful when removing the crystal. Sodium Iodide is corrosive and the Thallium is poisonous.

[Sesselmann]

Rather general question – the voltage divider of this PMT has 4.3 MΩ resistance (contains thirteen 332 kΩ resistors + one 27 kΩ). If I wanted to increase the divider resistance, it is possible to prepend ahead of divider for example 10 MΩ resistor or I have to use as divider thirteen resistors with higher resistance?

Vit,

As valentin says above you need to change all the resistors in the divider, so wherever you have 332 kΩ you can change it with a 1MΩ metal film resistor.

Steven

[Vit Ladanyi]

Thank you Valentine and Steven!