Scientists should never use figures. They spoil the very best ideas.
The appended diagram made by the spreadsheet (change its .pdf to .xls) tells the opacity of the target materials versus X-ray photon energy
. Multiply the cm2
/g of an element by how much g/cm3
the material contains, and you get the contribution to the exponential attenuation factor. Many thanks to Nisthttp://physics.nist.gov/PhysRefData/XrayMassCoef/tab3.htmlhttp://physics.nist.gov/PhysRefData/XrayMassCoef/tab4.html
The navy peaks locate the (set of) emission line added by an element to the continuous background when it serves as an anode. This transition to the K level, or also L on the diagram, is the reciprocal process to the stronger absorption of photons exceeding an energy threshold, except that the electron source is more diverse. X-ray tubes can have an exit filter of an element but heavier than the anode to attenuate energies beyond the threshold and dampen the less penetrating lower energies. I've put the refractory (semi-) metals, including those expensive or hard to separate, and as they operate in vacuum, even the easily corroded ones. The exit filter at room temperature accepts compounds of varied elements.
is easily detected in the target polymer chips.
- W emits at 12.1keV by its transition to L1. Re, Os or Ir can filter it.
- Br absorbs stronger above 13.5keV by its K electrons.
- Pt emits at 13.7keV, Au can filter. Or Au/Y for 14.2keV.
- Polyethylene attenuates 12.1keV as exp(-x/8.6mm), nearly perfect for chips supposedly 2-3mm thick. Air is nearly transparent.
- 1wt% Br attenuates 1.5× more than PE at 13.7keV but 0.2× more at 12.1keV. Other elements follow the usual slope. Compare both attenuations, done.
The irregular chips must keep their orientation between the measurements. A conveyor belt, not a free fall. The sources and detectors calibrate when no chip is present.Antimony
is less easily detected.
- At 24.1keV from Pd/Ag, 1% Sb adds 0.39 and 1% Cl 0.12 to PE's attenuation.
- At 42.0keV from Pr/Gd, 1% Sb adds 0.90 and 1% Cl 0.20.
- At 65.4keV from Hf/Ta, 1% Sb adds 0.28 and 1% Cl 0.02. This system is not too badly conditioned.
- 3mm PE attenuate 65.4keV ×0.95, so the signal is in the ×0.05 variation, uncomfortable.
An expert would possibly prefer to use the continuous spectrum of W filtered by Sn and by Te. Despite being more fuzzy, the spectra may give information more specific to Sb.PVC
chips are easy to recognize. At 8.3keV from Ni/Cu, they are 12× as opaque as PETP, accepting some tolerance on the thickness. A vertical line of sight, with a thin belt, eases that. Or check the attenuation ratio between 12.1keV and 65.4keV.
presents no usable threshold. Its K absorption starts at 2.8keV, where 3mm PE attenuates by 1010
. The knee between 20keV and 50keV seems most informative, as described for antimony.
Did I maybe perhaps write "detect nitrogen and oxygen from PA and ABS"? No usable K threshold allows that. Some information is hidden in the 20keV to 50keV knee if measuring at several energies there. This system isn't well conditioned, so the chip must not move, and the detectors be well aligned. Not simple.
doesn't need the photons to traverse the full chip, so it can use more varied energies. Flame-retardant chlorine is easily detected. An expert would probably have have chosen that right from the beginning.
Marc Schaefer, aka Enthalpy