The transmission target in a X-ray transmission tube is composed by a very thin film. This layer has a thickness of 1 - 10 microns, depending on the application of the X-ray tube. My question is if the electron beam hitting the target is completely absorbed or if some electrons are transmitted along with the x-ray beam.
For x-rays, the mass-attenuation coefficients are easily calculated :
http://physics.nist.gov/PhysRefData/XrayMassCoef/chap2.html
Electrons have more complicated formulas:
http://www.jsrr.in/Volume%202%20Number%202%20April%2012/CSMahajan21-27.pdf
In general, electrons have very shallow penetration depths for energies 400 keV and less - this is why samples must be very thin for TEM work.
To answer your question, you can apply the formulas for the energies, materials, and thicknesses of interest. NIST has reference tables and calculators for this:
http://www.nist.gov/pml/data/star/index.cfm
well, it feels not many of them can escape. But it depends on the energy of the beam.
Alf
You can get an indication by looking up the electron interaction volumes calculated for SEM work. the following lecture notes give a simple equation for penetration depths:
http://www4.nau.edu/microanalysis/microprobe/Interact-Volume.html
A colleague of mine developed software for Monte-Carlo calculations of interaction volumes, including for more complicated targets (multilayered/tilted etc) but this is probably more than you need (if you do need this, let me know and I can put you in touch with him).
Usually mean free paths of elecrtons are smaller, than mean free paths of photons with the samw energy.
I am designing, building, and testing several transmission target anode type x-ray sources and e-beam sources. As already pointed out, the absorption of electrons and attenuation of X-rays in matter is relatively straightforward to estimate or calculate.
Keep in mind... the thin substrate must serve to mitigate the erosion of the film that is deposited onto the substrate for the intention of generating X-rays. And for example, this film might be 5 um of Tungsten deposited on Beryllium or CVD Diamond. In this case, the electron range is shallow at lower energies, say... up to 70 KV. So the electrons are unlikely to escape based on the target material thickness alone, much less pass through the thin membrane of Beryllium or Diamond. And in this case, for a robust X-ray target substrate, 150 um of Beryllium or Diamond is suitable.
If you want to intentionally produce electrons from the vacuum device into atmosphere the target material must but sufficiently thin. Typical X-ray targets are not thin enough in combination with the substrates as described, even using typical energies up to 130 KV for example...
But certainly is is possible to get electrons to pass through both thin film and the substrate is enough energy is applied to the beam.
For reference, 10 um of freestanding CVD diamond will pass 34% of the incident beam at 65 KV. But, the intention would be to pass electrons, not to produce X-rays... Beryllium has good transmission at thickness below 25 um, but the challenge then becomes how to maintain the hermetic seal...
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