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X-ray photos, First light

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Proud Mary

Tue Feb 07 2012, 08:09PM

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

climatex wrote ...

I've seen some of the Svetlana monster x-ray tubes, could you show a photo of yours? Or, have you got some nice realtime fluoroscope with it? With 60 kilovolts and 5mA that should be a cinch.

Yes, there is already a link to it in my post above - click the green arrow! I give further details of this tube and other Svetlana devices which I own in the What are the most interesting vacuum tubes in your collection? thread in the General Chatting section of this forum.

I haven't tried my BSV-25-Ag yet, and perhaps I never will - not at the full 60 kV anyway. In the UK, there is a reduced safety specification for X-ray sources using less than 50 kV, and devices using less than 5 kV are not regulated at all. Beryllium windows can transmit X-ray photons right down to ~ 1 keV - depending on the window thickness - though 2 keV is more typical.

These low energy 'ultra-soft' X-rays are very suitable for differential absorption radiography of small biological structures like jellyfish polyps and amoeba. Such ultra-soft rays have scarcely enough energy to penetrate even the top coat on X-ray screens and films, so over the last year I have been trying to develop other means for imaging with them.

climatex

Mon Dec 24 2012, 10:42AM

Registered Member #2012 Joined: Sat Mar 07 2009, 10:22AM
Location: Slovakia
Posts: 45

Alright men, did a new X-ray setup, quite a while ago, with a twin flyback ZVS driver (thanks goes to Dr. Kilovolt) and a U.S. x-ray tube with a big fluoroscopic beryllium window. Some dosimetry and hand radiography included!

radhoo

Tue Dec 25 2012, 09:18PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 699

climatex wrote ...

Now, for radiation intensity measurementsâ€¦ As mentioned previously in the Chirana article, classic Geiger counters are very insensitive to soft X-rays, and will show readings 10 to 10 000 times lower than they actually are.

you got it all wrong . but the pics are nice.

climatex

Wed Dec 26 2012, 11:49AM

Registered Member #2012 Joined: Sat Mar 07 2009, 10:22AM
Location: Slovakia
Posts: 45

radhoo wrote ...
you got it all wrong

radhoo

Fri Jan 11 2013, 08:12PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 699

Energy response of GM tubes below 150keV is very non-linear so your actual dose rate may be smaller than your "dosimetry" results.

Here is an example, plotted for the 6993 geiger tube:
6993 Energy Curve 800

So the actual dose is most likely smaller, and not 10 to 10 000 times bigger, as you wrongly assumed

Proud Mary

Sat Jan 12 2013, 12:48AM

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

Absolutely correct, Radhu. All GM energy response curves follow that basic shape. Sometimes the slope is steeper, sometimes less steep, but the basic shape is always the same. It's an intrinsic property of the device, and that's all there is to it.

climatex

Sat Jan 12 2013, 03:32PM

Registered Member #2012 Joined: Sat Mar 07 2009, 10:22AM
Location: Slovakia
Posts: 45

I used the Radpro calculator to get an estimate of 12kR/h from a distance of 30cm (beryllium window, 800uA, 50 kV), compared with an ionisation chamber based meter, calibrated in 2006, which did show an intensity of 150 R/h at the same distance.
With an old Soviet GM-tube-based device (calibration 1990), a value of 1.2 R/h was measured.

Both meters have been previously probed on a Sr-90 source, with the former meter switched on the Geiger tube instead. Including the fact that the source was old, and a beta emitter, so the roentgen-gauged scale of both meters did not quite apply, they did show comparative intensity ratings (5 mR/h and 7 mR/h respectively). Gamma shields open.
Similar readings were obtained from a small piece of pitchblende, with gamma shields closed on both meters (2 mR/h and 1.5 mR/h).

Somehow, 12000 divided by 1.2 or 120 yields indeed 10000 or 100... If I'm wrong then please correct me at this.

I know a Russian who built his own X-ray device with a special crystallography tube and a 35-40 kilovolt multiplier supply, and irradiated his fingers for about a minute from close proximity (the anode-beam window was grounded and used negative high voltage for cathode).
Needless to say, on his fingers he suffered 3rd degree burns, got erythema in under 2 days and lost sensitivity in them.
Doctors estimated his fingers dose to about 500-1000 rad and after surgical treatment they survived.
Since early transient erythema starts from an estimated dose of 200 rad, I'd believe the simple math of few tens of thousands R/h divided by 60 seconds (minute) would equal his doctor's estimate..

Yet his Geiger counter based meter did show just a few R's per hour from the same distance he had his fingers in.

Just saying - of course it's all open for speculations, graphs, debates.

radhoo

Sat Jan 12 2013, 04:29PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 699

climatex wrote ...

Just saying - of course it's all open for speculations, graphs, debates.

Actually, it is the lack of knowledge that makes place for speculations and debates.

climatex

Sat Jan 12 2013, 08:46PM

Registered Member #2012 Joined: Sat Mar 07 2009, 10:22AM
Location: Slovakia
Posts: 45

And sometimes an assumed theory does not correspond with the practical results ;)

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