X-ray imaging to characterize MeV electronics propagation through plastic targets Page: 4 of 7
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direct measure of the beam propagation in dense plasmas; one which can be used away
from sample surfaces.
The low x-ray cross-section of car on relative to higher Z elements offers a possible
solution to this problem. At 1 ke, the minimum detectable x-ray energy for the pin hole
camera , the x-ray absorption length is -6 pm in CH, rapidly increasing with energy
; high Z elements absorb up to 60 times more strongly (See Table 1), that enables the
use of films so thin that their low resistance will not perturb the high energy electrons or
their return current . A film of gold only 0.1 pm thick is already 30% opaque, and will
emit 30% of black body radiation. This radiation would be only slightly attenuated in
exiting the CH film. Moreover, A second buried film would be visible under the first
with only another 30% attenuation of its signal (see Figure 1).
Table 1: 1 keV X-ray absorption lengths for selected elements. A foil of e.g. Au only a
few tenths of a micron thick could radiate brightly through 100 microns of CH. (CH
absorption calculated assuming a C density of 1 g/cc.)
Element Absorption length
1 2 4 keV
CH 5 33 270 pm
Aluminum 3.1 1.2 10.0
Molybdenum 0.2 1.0 1.0
Iron 0.1 0.8 4.8
Tantalum 0.1 0.2 0.6
Silver 0.1 0.7 0.7
Manganese 0.2 0.9 6.0
Nickel 0.1 0.5 3.4
Copper 0.1 0.5 3.1
Gold 0.1 0.5 0.4
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Key, M H; Stephens, R B; Koch, J & Pennington, D. X-ray imaging to characterize MeV electronics propagation through plastic targets, article, September 3, 1999; California. (https://digital.library.unt.edu/ark:/67531/metadc623302/m1/4/: accessed March 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.