<* \$Id: xnd_faq.html,v 1.1.1.1 2001/02/05 11:30:00 berar Exp \$ *> <em>xnd</em> F A Q.

## xnd_faq F A Q.

### 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 Vc 425 e-30 m^3 cell volume Lambda 1.54 e-10 m wave length RSlits 5 e-4 rad receiving slits VDiv 4 e-2 rad vertical (axial) divergency Eff ~1 counter efficiency, air absorption Mu 5.7 e3 m^-1 sample absorption length Scale 1 e-6 xnd scale factor No 3.10 e6 Number 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.

JFB March 5th, 2001