[plug] OT: RAM and X-Rays

[Mike from West Australia]

At 05:43 PM 17/6/2000 +0800, you wrote:
>Christian,
>it depends what kind of X-rays. The ones at airports are low-enery, and
>low intensity. They are supposed to be safe for computers and magnetic
>media. I've not heard of any problems.  But if you are in Upper Volta and
>the X-ray machine looks like a colonial relic, you might have a problem.
>   Higher enery X-rays can flip bits in RAM. Dont take your Palm into
>a CAT scanner.

Actually its not quite so simple, and is somewhat contrary to intuition ...

Higher energy means higher frequency means smaller wavefront, hence high
energy particles tend to go straight through if and only if the intensity
is low (in relative context that is).

Lower energy means lower frequency means wider (larger) wavefront means
greater chance of dislodging a particle/atom/charge/dopant etc...

For the same relative intensity lower energy X-rays (lower down the spectra
but say just above high UV) will do far more damage then high energy X-rays.

Its (a bit) like - this analogy:-

The ram is a low density peach tree, low energy X-rays could represent
baseballs, whereas high energy X-rays represent small bullets.

Its the large baseballs that have more chance of dislodging peaches
then a small bullet.

I won't stretch the analogy too far as it depends on the space density
of the peaches and velocity is an issue for baseballs not for X-rays etc.

There are other aspects too. Palm pilots with nonvol ram tend to be
static (4 or 2 transistor cells) vs drams which are 1 transitor caps etc.

Its much harder to flip a 2 or 4 transistor flip flop then a single
transistor DRAM cell - then again who puts a powered up PC through an
X-ray...

As to hard damage from atomic/ionic migration from intense X-rays reagardless
of the energy or frequency, you'd need to raise the intensity by several
hundred throusand times (of a typical scanner) before you'd do any
hard damage to ram that is not powered up ..

This is why its possible to erase eproms in plastic opaque packages if
you get the x-ray spectra right,


Kind Regards


Mike Massen

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