<* $Id: xnd_faq.html,v 2001/02/05 11:30:00 berar Exp $ *> <em>xnd</em> F A Q.

xnd_faq F A Q.

xnd top Next file Previous file

To be filled

From scale factors to absolutes intensities and/or percentage.

It is easy to have an idea of the intensity received by the sample when we known the scale factor. Following Suorti (Acta Cryst 85, A41 p413) and knowning expression used in xnd, the number of photons received by the sample for measuring each data point is :

No = 32 Scale Pi^2 Mu Vc^2 / (180 Eff RSlits VDiv Re^2 Lamda^3)

in which (using Al(OH)3 measured on a laboratory difractometer as an exemple ) :
Re 2.82 e-15 m electron radius
Vc425 e-30 m^3 cell volume
Lambda 1.54 e-10 mwave length
RSlits5 e-4 radreceiving slits
VDiv4 e-2 radvertical (axial) divergency
Eff~1counter efficiency, air absorption
Mu5.7 e3 m^-1sample absorption length
Scale1 e-6xnd scale factor
No3.10 e6Number of incoming photons on the sample
Assuming that we can neglect correction associated micro-absorption. We can calculate the amount of each phase in a mixture. In the above formula, there is only two coefficients which depend on the phase : the cell volume and the scale factor. Then in volume the amount of each phase in the sample is proportional to Scale Vc^2.

xnd top Next file Previous file

JFB March 5th, 2001