Qext is a strong function of the particle size but it is not easy to calculate accurately for high density particles. The key difference is the use of µabs which is the x-ray absorption efficiency instead of Qext. It is not a function of particle size or refractive indices. There is no optical correction. Notice that the decay function includes µabs. At time 0, there is 100% absorption and therefore no signal. As time progresses and absorption declines the signal is generated and produces a cumulative size distribution.
- It = Io×exp(-µabs×c×L) Io, It = Transmitted, Incident Intensity
- µabs = X-ray absorption efficiency ≠ f(dp, np/nf, λ)
- c = Mass concentration
- L = Path length (width of fluid segment in disc)
When X-rays are absorbed, they are absorbed in proportion to mass without any dependence on particle size or refractive indices. There is no optical correction. For high density materials with normally high refractive indexes, the mass weighted size distribution is quantitative.