Method FW1/4/5M allows for quick Grain Size Distribution (GSD) calculation. You need to specify two peak widths: measured at 1/5 and 4/5 of maximum of the diffraction peak (FW1/5M and FW4/5M, respectively). The metod takes into account only size-broadening of the diffraction maxima. Therefore the following phenomena are not considered:
The method in the most basic form (as presented here) is accurate for nanocrystals of size not greater than 200-300Å (no corrections are required in this range). Peak widths are expected to be given in scattering vector q=4πsin(θ)/λ units (hence standard 2θ diffraction data must be scaled accordingly). You may convert your standard two-theta data using on-line converter.
For usage details please consult manual either in HTML or PDF form.
For full diffraction theory involved and credits please refer to:
"Dyfrakcyjne badania mikrostruktury nanokryształów poddawanych działaniu wysokiego ciśnienia" (eng."Diffraction studies of microstructure of nanocrystals exposed to high pressure"), PhD. Thesis University of Warsaw, Department of Physics, Roman Pielaszek (firstname.lastname@example.org), 2003 (see in PDF)