Q 
Integrated reflection from a crystal of unit volume 

Volume of crystal element 
e, m 
Electronic charge and mass 
c 
Speed of light 
λ 
Wavelength of radiation 
μ 
Linear absorption coefficient for Xrays or total attenuation coefficient for neutrons 
2θ 
Angle between incident and diffracted beams 

In (b) and (c), as defined; in (h), latitude of reciprocallattice point relative to axis of rotation 
V 
Volume of crystal, or of irradiated part of powder sample 
N 
Number of unit cells per unit volume 
ξ 
In (b) and (c), as defined; in (h), radial coordinate xi used in interpreting Weissenberg photographs 
I_{0} 
Energy of radiation falling normally on unit area per second 
hkl 
Indices of reflection 
F 
Structure factor of hkl reflection 

Distribution function of the mosaic blocks at angular deviation from the average reflecting plane 
σ 
Diffraction cross section per unit volume 
σ_{0} 
Diffraction cross section per unit volume at 
b 
Asymmetry parameter 
τ 
Reduced thickness of the crystal slab 
P_{H}/P_{0} 
Reflection power ratio, i.e. the ratio of the diffracted power to the incident power 
ρ 
Integrated reflection power ratio from a crystal element 
ρ′ 
Integrated reflection power ratio, angular integration of reflection power ratio 
p′ 
Multiplicity factor for singlecrystal methods 
p′′ 
Multiplicity factor for powder methods 