[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
RE: possible sources for sheet lead and mineral/ transformer oil?
Original poster: "Jim Lux" <jimlux-at-earthlink-dot-net>
At 08:18 AM 10/7/2004 -0600, you wrote:
>Original poster: "David Trimmell" <humanb-at-chaoticuniverse-dot-com>
>Soft x-rays are significantly "reduced" by many low Z materials. By soft
>I would mean <20KeV.
Significantly reduced? Which low Z materials?
Yes, in general, low Z materials have higher absorption for low energy
Xrays than for high energy Xrays (which is actually true of most
materials), but the difference is between "not much absorption" and "almost
no absorption". This is important if you're making thermonuclear bombs
where you have gargantuan fluxes of soft xrays to manage.
It's not particularly relevant if you're trying to shield yourself for safety.
If you're detecting soft xrays at any distance from your source, you've
probably got a fairly high flux. Most detectors have very poor
efficiencies for soft Xrays because the photon energy is low... as noted in
another post, the run of the mill Geiger-Muller type counter isn't very
sensitive to low energy (<60keV) photons. For most lowish voltage
applications, the peak energy will be the voltage applied to the system,
but it's a continuous distribution from around 5keV on up, with a peak flux
at about 1/3 of the energy of the max (that is, if you apply 60 kV to the
tube, your peak will be at around 20keV).
I couldn't find any handy references to get a feel for how many xrays you
get from, say, 1 mA at 20kV. I do know that the lower the energy of the
electrons, the less efficient the generation of photons from the
bremsstrahlung process. That is, at 60 keV the efficiency is about 1% of
the efficiency at 120 keV.
Bremsstrahlung = "braking radiation", the process by which radiation is
produced when a high energy particle is stopped.
By the way, there's also the whole scattering thing to worry about. I
believe that Richard Hull discovered some "interesting" aspects to this on
one of his earlier "fusor" devices where he discovered strong soft Xray
emission in the plane of a chamber window. The usual run of the mill fusor
produces a lot more Xrays than neutrons.