I think that care has to be taken when defining B=noise. In many cases, B contains some amorphous material scattering, air scattering, TDS, etc which one might account for using a proper model. So they will scale with time while the error part of noise will not.
miguel On 19 Feb 2008 at 9:21, Michael Glazer wrote: > 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 > > > -- Miguel Gregorkiewitz Dip Scienze della Terra, Università via Laterina 8, I-53100 Siena, Europe fon +39'0577'233810 fax 233938 email [EMAIL PROTECTED]
