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Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Ionisation Chamber Collector Plate
The etched face of the PTFE slab will take epoxy for glueing to the ceramic hurdles.
The self-adhesive copper foil adheres only lightly to the PTFE surface, so I carried the guard on right round the bottom and tacked the corners together with solder, so it is strapped down as well as glued now.
I used a 25W iron with Ersin Multi Core lead/tin solder for this job, and found the solder flowed quickly enough to stop the adhesive on the copper playing up, which I was afraid it might try to do, given the chance.
@Les - yes, it's wonderful that the world below 5 keV was almost ignored until quite recently - not like some wretched old lamp post upon which fifty generations of dogs have already made their mark!
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
@ Les: Yes. I realise the simplicity of the ion chamber. It's just that after PM's comments about only ~6.5% of radiation will make it into the chamber at these energy levels I was wondering if it was possible to use a pmt with suitable scintillator. I appreciate the biggest hurdle would be obtaining a suitable scintillator. Things like NaI/Tl crystals do turn up occasionally on E-bay.
@PM: Could photographic paper not be used as a simple guage of emissions @ various energy levels? (or even digital camera technology?)
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Ash Small wrote ...
@ Les: Yes. I realise the simplicity of the ion chamber. It's just that after PM's comments about only ~6.5% of radiation will make it into the chamber at these energy levels I was wondering if it was possible to use a pmt with suitable scintillator. I appreciate the biggest hurdle would be obtaining a suitable scintillator. Things like NaI/Tl crystals do turn up occasionally on E-bay.
@PM: Could photographic paper not be used as a simple guage of emissions @ various energy levels? (or even digital camera technology?)
BTW, very nice work!
Perhaps I haven't done a good job of making myself clear, Mr Ash. I intended to make clear that at 2.3 keV, only 6.5% of the total photons generated at the anode ever managed to escape through the beryllium window of the Grenz generator. And these survivors suffered a further 35% loss just traveling through 1 cm of air, so that only 4.2% of the original photons were available to interact with whatever kind of detector you put there.
One advantage the free air ionisation chamber has over almost all other detectors - including NaI/Tl* - is that it doesn't need a window of any kind that would produce further losses.
I will be looking at direct digital imaging when all the basic apparatus and instruments have been taken care of. I have to make everything up as I go along, so don't hold your breath!
*NaI/Tl is hygroscopic, so must be operated in an anhydrous atmosphere with a beryllium or aluminium window.
Registered Member #1134
Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351
Ash Small wrote ...
Could photographic paper not be used as a simple guage of emissions @ various energy levels? (or even digital camera technology?)
Sure! In fact I use small piece of photographic paper all the time to test at these low kVp levels. It has the added advantage providing you with a beam profile too, which is very handy as far as imaging goes.
Film may be faster, however my shed is far from dark enough, paper is fast enough, and the white background provides good contrast for making quick observations.
As far as silicon is concerned, I suspect it would make a wholly suitable detector, since all of the photons that arrive at the chip, will deposit their energy at the surface. I would guess even the bare silicon layer of a photodiode, or solar cell, would make an adequate detector.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Proud Mary wrote ...
Perhaps I haven't done a good job of making myself clear, Mr Ash. I intended to make clear that at 2.3 keV, only 6.5% of the total photons generated at the anode ever managed to escape through the beryllium window of the Grenz generator. And these survivors suffered a further 65% loss just traveling through 1 cm of air, so that only 4.2% of the original photons were available to interact with whatever kind of detector you put there.
One advantage the free air ionisation chamber has over almost all other detectors - including NaI/Tl* - is that it doesn't need a window of any kind that would produce further losses.
I will be looking at direct digital imaging when all the basic apparatus and instruments have been taken care of. I have to make everything up as I go along, so don't hold your breath!
*NaI/Tl is hygroscopic, so must be operated in an anhydrous atmosphere with a beryllium or aluminium window.
Aaah, that certainly clarifies things, PM.
I simply wondered what the obstacles were to using a PMT @ these low energy levels, compared to the ionization chamber, or other methods.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Haha, I didn't make myself clear at all!
When I wrote that
"I intended to make clear that at 2.3 keV, only 6.5% of the total photons generated at the anode ever managed to escape through the beryllium window of the Grenz generator. And these survivors suffered a further 65% loss just traveling through 1 cm of air, so that only 4.2% of the original photons were available to interact with whatever kind of detector you put there."
I should have said "survivors suffered a further 35% loss just traveling through 1 cm of air" i.e. that 65% got through the 1 cm of air.
I will go back and edit the original so readers aren't further mislead.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Collector Plate Assembly
The copper foil on the collector has lifted slightly around the soldering, so I have dropped 'superglue' down the triaxial feedthrough - where the semi-rigid co-ax passes through it - to forestall any movement that might result in a tear.
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Life Below 5 keV
