[Noisebridge-discuss] x-ray machine

Jake jake at spaz.org
Fri Mar 15 18:11:31 UTC 2013


Jof,

there is nothing radioactive inside this xray machine.  Just a transformer 
and a vacuum tube, which contains copper and other ordinary metals.  The 
90 KeV xrays that come out are a result of 90 kilovolts coming from the 
transformer and getting rectified in the vacuum tube.

The machine is designed for 90KeV because that energy provides good 
contrast for dental work, however it can be dialed up or down for looking 
through different kinds of material and contrasting between different 
material densities.  By the way, 25MeV (as in Therac 25) is 278 times 
higher energy than the 90KeV setting of the machine i have.

Therac 25 was a high-energy radiation therapy machine with poorly written 
software controlling patient dosages.  I agree that it is an interesting 
historical reminder that software should be written carefully so that 
operators don't accidentally program it to release 100X the amount of 
radiation that the patient needs, but i don't think it has any relavence 
at all to the equipment that I have acquired (which has mechanical 
controls)

We should talk instead about what types of film or scintillators we might 
use (thanks Tony) so that we can prepare shielding for whatever energy of 
x-rays we expect to be using.  Since we won't be scanning anything alive 
(except ditzydoo) we can use lower energies for longer times to get 
details, instead of higher energies which are harder to shield.  I think.

The xray machine that me and Mike Kan made with a vacuum tube and a Taser 
was pretty low energy - i'm guessing 20 or 30 KeV, which is easily 
shielded by the metal garbage can we put around it.  to xray an unhatched 
duck egg (stillborn, couldn't peck its way out of the egg) we would not 
need much higher than that, i think, and shielding would not be a problem.

When xraying teeth or bones for details, it is necessary to use 
higher-energy xrays to penetrate more of the solid matter, and then 
shielding becomes more of a problem.  We can wait to get to that point.

We should be talking about energy levels and intensities and shielding and 
CT scanning objects and 3D printing them rather than PDP-11 software 
errors from the 80's.

also, "scary" is good, we are hackers and we should be opening up things 
and playing with 120V and blowing fuses and makin geiger counters chirp.

-jake


On Fri, 15 Mar 2013, Jonathan Lassoff wrote:

> That is just scary to have. All potential hackers should get a talking
> to about the history of Therac 25 before beginning. :p
>
> Does it still have an active x-ray source?
>
> Cool find!
>
> Cheers,
> jof
>
> On Fri, Mar 15, 2013 at 12:09 AM, Jake <jake at spaz.org> wrote:
>> you guys know i got an xray machine?  it's a 90KeV dental xray machine by
>> ritter, gas-cooled with sulfur hexaflouride.
>>
>> http://www.ritterdental.com/Story/TheGoldenYears/1950sX-RayF.htm
>>
>> anyway, we should take some REAL xray pictures.  that means we need a
>> phosphor screen, like an "x ray cassette" as seen on ebay.  Those cassettes
>> are basically a mechanical envelope that you put the film in, and they have
>> phosphor screens in there that expose the film when xrays land on the
>> phosphors.
>>
>> http://www.ebay.com/itm/Ortho-Curix-MR800-X-Ray-Cassette-with-screen-30x35cm-Low-Price-/300789089608?pt=LH_DefaultDomain_0&hash=item46086d4548
>> http://www.ebay.com/itm/JPI-xray-cassette-8x10-used-xray-intesifying-screen-/271169903159?pt=LH_DefaultDomain_0&hash=item3f22fc5a37
>>
>> if possible we should get an image intensifier, which would allow us to see
>> through things in real time, without waiting for film to develop. basically
>> the output goes to a video camera, so it would be like the enlarge-o-scope
>> we made except dangerous.
>>
>> http://en.wikipedia.org/wiki/X-ray_image_intensifier
>>
>> actually it only takes like 1mm thick lead to stop all the rays that come
>> out of this thing so we can and will build a box for it, so it's safe.
>>
>> of course, if anyone can get ahold of a Flat Panel x-ray detector, we should
>> get that.  it would allow much better x-ray pictures with less radiation.
>> but i hear they're really expensive.
>>
>> http://en.wikipedia.org/wiki/Flat_panel_detectors
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