Sheilding for PMT

[Tim Mitchell]

This is my first detector and learning lots along the way, and wondered if I could get some answers to a few questions. I am trying to keep the budget low but the quality high, we will see how that progresses....

I have an R6233 PMT which is coupled to a 63mm x 63mm NaI/Ti detector, which seems to be quite a good match size wise. I have secured them together with a complete covering of black Norton duct tape (high quality wide electrical tape) as I couldn't find a good quality aluminium foil tape, and have constructed a light proof housing for the unit out of thin walled spun aluminum fuel bottle and drink bottle containers. I will be using closed cell foam probably to make the unit fit snugly in the housing. The smaller bottle was set into the larger bottle very tightly with the edge peened over inside and glued with RTV Cement... still waiting for it to cure... hopefully before next christmas. I will probably give the unit a nice coat of paint, we will see. I have been able to remove the printing on the silver section so it does look ok so I may just paint the red area.

I have been considering the subject of magnetic shielding and using a mu-metal shield, but I wanted to find out with the R6233 which is a 3 inch stepped shape of PMT, how do you shield it? Do you just place shielding around the thinner portion of the tube and not the large portion, and is there a problem from not shielding the back connector side of the tube? Also is there something that regularly uses Mu-metal which I can scrounge a large enough piece from?

I am also wondering where to get a high voltage wire to make the HV cable, is there anyone who makes their own HV cables? (EDIT:I just found a thread about cabling from last year, so that question is answered...)

Thanks for your thoughts in advance,
Regards,
Tim.

[Sesselmann]

Tim,

Yes, clever idea to look for ready made products which can be converted to a casing.

For the HV cable eBay is your friend.

http://www.ebay.com/itm/10m-meter-Black ... xyd5tRyQqb

[Tim Mitchell]

Thanks Steven, I appreciate the link. What are your thoughts about the Mu metal shielding? Do I need to shield the whole PMT or just the thinner section? Shielding around a step like that would not be fun....

[Paul McK]

Tim

The photocathode is on the face of the PMT so from there onwards there is an electron beam so I guess you need the Mu metal shield to cover the full length of the tube as opposed to only the dynode assembly within the 2" straight section? Maybe someone can comment on the effectiveness of only shielding the dynode assembly, I would be interested to know?

A4 Mu metal sheets are available on ebay but these are adhesive backed and best stuck to a loose fitting cardboard former that can be removed if you need to dismantle everything. You may be able to work out a way to stick the shield to the inside of the housing you have made. The shield also needs to be electrically connected leave a small tab to solder a lead to.

Did you mean HV coax lead? These are on ebay as "BNC to BNC RG174 coax"? It's also easy to cut down one of these to wire from the divider to the BNC socket instead of buying a long length of coax.

Like the design of the housing it's going to look good when spray painted.

[Tim Mitchell]

Thanks Paul, I may have to get creative with the Mu metal shielding. The I did mean the coax, I already have high quality wire for the internals, thanks for the pointer on those.

I was concerned about how I would attach the smaller bottle to the larger bottle, but peening the edge over inside and then using silicone worked really well. It helped having a tight fit to begin with.