TOF_Powder_extinction

Description: Extinction correction for TOF neutrons

Comment: extinction for TOF powder data; value = mosaic block size in micron^2

lambda is the TOF-dependent wavelength calculated in the Lobanov TOF absorption macro

Contributed by: Pamela Whitfield

 macro TOF_Powder_extinction(c, v) {   
 #m_argu c
  If_Prm_Eqn_Rpt(c, v, min = Val-.1; max = Val+.1; del 0.001)
    local !xx = CeV(c,v) (lambda I_no_scale_pks / Get(cell_volume))^2;
    local !Eb = 1/Sqrt(1 + xx);
    local !El = If(xx < 1,
    			1 - xx/2 + xx^2/4 - (5 xx^3)/48,
    			Sqrt(2/Pi xx) (1 - 8/xx - 3/(128 xx^3) - 15/(1024 xx^5))
    			);
    scale_pks = 1/(Eb Sin(two_theta Deg_on_2)^2 + El Cos(two_theta Deg_on_2)^2);
 }