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Proud Mary

Wed Mar 09 2016, 01:03AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Wastrel wrote ...

I've found the raw 25um PGS for sale at mouser and other places but it looks like the 10um isn't normally sold outside of a more manufactured product like a laminated tape. I'm thinking of ordering some of that too and trying to delaminate or degrade the non graphite layer but 25um would still be a lot better than an aluminium foil window I thought I'd be forced to use.

Farnell have Panasonic Industrial 25Î¼m PGS, but their website is temporarily down for repair.

I found this YouTube vid which gives a hands-on presentation about the 25 Î¼m sheet. As you'll see, the material can be heated to red heat without smoking or deforming and you can cut it up with scissors, all of which is a good sign for our purposes:

Proud Mary

Wed Mar 09 2016, 01:31AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Wastrel, Panasonic Industrial graphite only sheet - which they call 'S-type' - goes down to only 25Î¼m as you pointed out, but I still think it could be good for x-ray windows, though not for the very softest rays as I had hoped. By comparison, the minimum thickness at which beryllium windows can be gas tight is generally given as 8Î¼m

1457487094 543 FT175675 Panasonic Graphite Sheet

Conundrum

Wed Mar 09 2016, 06:26AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059

Interesting note.
A Geiger tube, IR LED and two other components (thanks PM for the HVPSs) can make a device that has about a 2 foot range and sends many if not all counts over infrared to a remote TV 3 pin 38KHz receiver.

I found that about a 9.076nF and 2.691mH works, but due to the low quality parts is not that reliable so a polyester (eg tuning circuit) capacitor is recommended here.
The receiver inside the 3 pin is very selective indeed and a good test is to connect the prospective LED and resonant circuit to a 3V coin cell via a small resistor to limit current, if it activates tweak the circuit for maximum range.

The GM tube is connected in series with a 10M resistor, as per recommendations.

Wastrel

Wed Mar 09 2016, 07:14PM

Registered Member #4095 Joined: Thu Sept 15 2011, 03:19PM
Location: England.
Posts: 122

I checked farnell and can't quite work it out. Are those prices for packs of 5 or 10 sheets? If not they are massively expensive.

Proud Mary

Wed Mar 09 2016, 08:05PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Wastrel wrote ...

I checked farnell and can't quite work it out. Are those prices for packs of 5 or 10 sheets? If not they are massively expensive.

I've had a second look, and it does seem to be 'price each.' I must admit I was very pleased to see that I would be able to afford the smallest sheet of the 25 Î¼m - 90 x 115mm @ Â£22.88 + VAT - from which I could make quite a few detector and soft x-ray tube windows which will be just 10-15mm diameter after all. The cost of high vacuum epoxy for sealing the windows down is much more fearsome!

Wastrel

Wed Mar 09 2016, 08:32PM

Registered Member #4095 Joined: Thu Sept 15 2011, 03:19PM
Location: England.
Posts: 122

The large sheets are Â£5 at mouser, the small ones are half that. There is a factor of 10 between the prices. This is consistent over the product range. 10 is also the minimum order for the large sheets, it might be a supply or packaging multiple. Nothing I could see on the farnell page let me to think you'd get more than one sheet though.

I will be placing a mouser order shortly. Just in case. They've lowered the minimum order for free shipping too. I've ordered from both in the past but I'm doing much more price cross checking. I ordered a bunch of stuff from future electronics recently which undercut mousers prices by half (very limited range).

Proud Mary

Wed Mar 09 2016, 09:49PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

I've never ordered anything from Mouser, though I've often heard folk mention it.

Farnell's prices are on occasion eye-watering, but perhaps they have made a cataloguing error here and are actually quoting for a pack price, rather than for individual sheets.

I see that Digi-Key are selling the 25 Î¼m sheets 115X180MM @ Â£5.44 each + VAT - and that 25 Î¼m is the thinnest sheet that is made without an adhesive or polymer backing.

Wastrel

Thu Mar 10 2016, 01:32AM

Registered Member #4095 Joined: Thu Sept 15 2011, 03:19PM
Location: England.
Posts: 122

"10 is also the minimum order for the large sheets", I meant in the Panasonic literature. Mouser is selling them individually. I checked FE, and they are selling at Farnell like prices AND they have a minimum order of 10. So there seems to be a big split between companies. Fingers crossed Digikey and Mouser have it right and keep selling them individually, this is really cheap for an effective beryllium substitute.

My current experiments only need it to be light tight but I'll think about vacuum sealing. I wonder if high vacuum wax would work if it's kept at room temperature. How do people normally seal to graphite, is it a nightmare?

When I can find some 10um laminate in stock I'll get some and have a play.

Conundrum

Thu Mar 10 2016, 01:16PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059

wonder if its possible to erode a thicker windows with RF discharges or laser etc?

Proud Mary

Thu Mar 10 2016, 05:25PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Wastrel wrote ...

Fingers crossed Digikey and Mouser have it right and keep selling them individually, this is really cheap for an effective beryllium substitute.

It may even be superior in the applications I have in mind. One of the limiting factors in high intensity low energy X-ray production is destructive heating of the beryllium exit window. The lower the energy of the X-rays the more they are absorbed as heat in the window. (X-ray production by devices having less than 5 kV PD across them is completely unregulated by UK and EU law, creating a happy hunting ground in the Grenz ray domain for amateur scientists like me!) As PGS is designed first and foremost with heat dissipation in mind, it could turn out to be a perfect choice for windows.

A second problem with Be windows is their permeability to, and general dislike of, helium gas, a real problem in home-made glow discharge x-ray sources of the type that interests me. Pressures that can easily be reached with an inexpensive rotary pump, and 2 kV @ 0.1 mA on the anode, so no hissing, rickety, sagging, voltage multipliers required. Perfect:

]x-ray_-_compact_glow_discharge_x-ray_tube..pdf[/ file]

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