G.K.Williamson and W.H.Hall (Acta Metall. 1, 22-31 (1953)) has given a method that the approximate formulae for size broadening, β, and strain broadening, βe , vary quite differently with respect to Bragg angle, θ:
β = Kλ/D cosθ
βe = 4ε tanθ
I want some light on strain part of this method from experts. How "4" is coming into picture? also why only strain part is included etc? Any book or reference suggested is highly appreciated.
Regards