It seems to me that if there is no internationally accepted definition of signal to noise ratio in powder diffraction, then let me suggest that this forum might be a way to define it once and for all. How about this? SNR = (P-B)/SQRT(B).
Of course this would only give a value for a single peak. I suppose one could also define a global SNR as a sum over all Global SNR = sum over peaks (P-B)/SQRT(B). Does this make sense? Mike -----Original Message----- From: Van der Lee [mailto:[EMAIL PROTECTED] Sent: 19 February 2008 09:09 To: rietveld_l@ill.fr Subject: Re: advice on new powder diffractometer Michael Glazer wrote the following on 19/02/2008 09:42: > > Or else one could take the peak intensity divided by the square root of the background: this at least would improve with measurement time. > > For instance suppose we have a peak above background of 10000 counts and a background of 1000 counts, this would give a signal to noise ratio of roughly 322. If we measure ten times longer, the peak intensity becomes 100000 and the background becomes 10000, giving a signal to noise ratio of 1000, an improvement! > So my question remains: what is the definition of signal to noise ratio that is accepted for powder diffraction? > > This at least coincides with data collection practice in single crystal diffraction: there it is said that in order to improve the 'signal to noise' ratio with a factor of two you have to count 4 times longer, or, alternatively, double the generator power. Arie