Re: Airport and Building X-Ray machines and Digital Cameras
- From: Clark Martin <cmnews@xxxxxxxxx>
- Date: Wed, 05 Oct 2005 01:33:49 GMT
In article <4329a0fe$1_1@xxxxxxxxxxxxxxxxxx>,
"Richard Tomkins" <tomkinsr@xxxxxxxxx> wrote:
> Wait a second here.
>
> CCD's respond to visible and near visible light, aka, photons, also known as
> non-ionizing radiation.
>
> X-Ray's do not contain photons, so a CCD would not respond at all. X-Ray's
> are known as ionizing radiation.
X-Rays are photons, it's not just visible light. Photons are the
particle representation of any E-M wave.
>
> Now in an Digital X-Ray system, in order to be able to visualize what the
> X-Rays are penetrating, you need an intermediary between the course of the
> X-Rays and the CCD. This is a fluorescent material of some kind, that when
> X-Rays strike the material, the material in turns emits photons that the CCD
> can pick up.
>
> The lifetime of these extremely physically large CCD sensors is in fact
> several years or more and thus it is unlikely X-Rays would in fact damage a
> CCD Sensor, even over many exposures over time.
Sometimes, at least, the optical sensor sees the fluorescent screen
through a mirror.
>
> Systems that emit X-Ray radiation for medical purposes do not splash X-Rays
> all over the place. If they did, you'd be exposing the folks on the floor
> above and below and beside the treatment room. They emit a constrained beam
> of X-Rays at the diagnostic area.
>
> http://www.canon.com/technology/interview/xray/xray_p4.html
>
It's not a diagnostic area if it's therapeutic X-Rays.
Therapy machines produce x-rays in single direction at a time but the
machine rotates through 360 degrees. The parts of the room thus exposed
to the primary beam are shielded to reduce the X-Ray intensity to
permissible levels. The entire room though is shielded as an X-Ray beam
will scatter, particularly when hitting metal. And at 200 Rads/S even a
little bit of that scattered is still a fair amount. And yes the beam
can point up, down and to either side. This is why they usually (but
not always) are in the basement. I've spent more than a few hours in
such basements.
--
Clark Martin
Redwood City, CA, USA Macintosh / Internet Consulting
"I'm a designated driver on the Information Super Highway"
.
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