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X-ray photos, First light

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Proud Mary

Tue Jan 10 2012, 10:11AM

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

Ha ha that's telling me!

Good luck to you anyway!

Wolfram

Wed Jan 11 2012, 06:43AM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

climatex wrote ...

Folks, I have been in contact with a Russian, who has made a nice fluoroscope with 40-50 kilovolts, utilising his Soviet BS-1 x-ray tube intended for crstallography (the anode had a beryllium window).

(He got 4th degree burns shortly afterwards, since he didn't shield the soft xrays, however no amputation was needed.)

I've seen that video before, and I would expect something bad like that to happen to him afterwards. Exposing yourself to a normal glass x-ray tube will result in an absorbed radiation dose, and radiation burns in extreme cases. Exposing yourself to the radiation from a beryllium window tube is almost guaranteed to result in severe skin burns.

And Anders, congrats! Perfect "FullHD" x-ray setup you've got there, hats off to that!

It's not very hard. Grab yourself a roll of ISO100-400 black/white 35mm or 120 film and some developer and fixer for it. Cut it up into small squares in a dark room and pack them individually in aluminium foil, making sure that no light can get in. Expose and develop individually. This could give very good results, with lower-ISO film giving even sharper results than the last picture I posted. The size of the objects you can x-ray will be limited with this method, but it should be very cheap and you can upgrade to bigger film if you like the results.

Steve Conner

Wed Jan 11 2012, 09:43AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

The important point is that the beryllium window tubes are not for use on living targets. The glass envelope of a medical X-ray tube actually helps by absorbing the soft x-rays. An aluminium filter is used to absorb even more of them, leaving the higher energy radiation needed for good pictures of teeth and bones.

If working with non-living specimens you can use any sort of tube you like.

The copper anode block of a medical x-ray tube has a tungsten target inside. Tungsten is chosen mainly for its high melting point, but being a heavy element, it has characteristic radiation of a decently high energy.

climatex

Wed Jan 11 2012, 10:47AM

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

Thanks Anders and Steve for your ideas. Agreed with the external shielding of those Be-windowed tubes o'doom; I already obtained some 2-3mm lead sheets for experimentation with these.

I did some research into the geometric unsharpness as Proud Mary here noted. And the results with the BX-4 tube wouldn't be satisfactory, in comparision against the BS-1 you've seen. Well, there were some Java applet calculators for that and I've seen images how concrete values of the unsharpness affect the final picture.

As per the Russian datasheet says (if anyone's interested I can upload it here to 4hv), it states a 2x4mm focal point size, or 8mm squared. As I've seen that the focal point size is usually given in length (power of 1) and not in an area (power of 2), the 8mm^2 focal point area would make a size of sqrt(8) which is 2.82mm. That's a much lower value, however it's still huge compared to microfocus tubes.

Ah well, either I'll wait for the BS-1 with a focal point size of 0.1mm or it's time to look for another medical x-ray tube. Actually I have sold the Chirana tube for 80 EUR as in to try luck with different x-ray tubes out there. Sadly, no time to do electronics at this moment, either.

I'll keep this topic updated, folks. Feel free to comment :)

radhoo

Wed Jan 11 2012, 11:16AM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

Why would anyone do a stupid thing like that?

LE, the advise you got from Proud Mary was for your own good, you really shouldn't have retaliated like that.

It seems age matters after all

climatex

Wed Jan 11 2012, 03:08PM

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

Sorry radhoo for proving her wrong. How very impolite. I have never known that her answers were always right. eh?

radhoo" wrote ...
Why would anyone do a stupid thing like that?

Why would anyone torture the 2X2, that poor vacuum rectifier, with excessive voltage...? That isn't a stupid thing to do?

Wolfram

Wed Jan 11 2012, 03:12PM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

Steve Conner wrote ...

The important point is that the beryllium window tubes are not for use on living targets.

At least not without filtering. Beryllium window tubes are commonly used in mammography, but with a rhodium or molybdenum filter to take out the lowest energy x-rays. Do not try this on yourself though.

The copper anode block of a medical x-ray tube has a tungsten target inside. Tungsten is chosen mainly for its high melting point, but being a heavy element, it has characteristic radiation of a decently high energy.

You forgot one of the most important factors, x-ray production efficiency is directly propotional to atomic number, so it has an advantage on most elements in this respect. Tungsten also has pretty good thermal conductivity, which is important. These factors, combined with the extremely high melting point, makes tungsten pretty much the only choice for medical tubes. Other anode materials are used in tubes for special purposes (mammography, crystallography) where the anode material's characteristic lines are desirable. Also, tungsten is sometimes alloyed with a bit of rhenium for increased resistance to cracking and pitting of the focal spot.

climatex

Wed Jan 11 2012, 03:14PM

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

Anders, so that huge chunk of copper in that Chirana was actually passive cooling to that tungsten (wolfram) target? Thanks.

Wolfram

Thu Jan 12 2012, 09:52AM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

Yeah, the copper part of the anode does the job of conducting the heat out of the tube. It also has a high thermal mass, so that the tube can be used with high input power for a short while without overheating.

climatex

Sat Jan 28 2012, 06:27PM

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

@Anders: Did I inspire you with the translation of "tungsten" with your nick change? :)

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