Dear CCP4bb,

I have a few questions concerning SANS data recently collected that I'm having trouble analyzing. The data was collected at 2 different detector distances (4m, 2.5m) to achieve higher q-range, but I worry that the curves don't overlap enough at intermediate q, which might indicate a problem with the data. The links below are pictures of the corresponding datasets, before truncating the 4m high-q data and merging them into one. Is there a problem evident with the data, or am I imagining a problem?

http://postimg.org/image/qb00y20qr/

http://postimg.org/image/jzuthmzib/

My second question concerns the values obtained in the analysis of the final scattering curves. The second sample in my experiment shows serious deviation in the values obtained for I(0) and Rg by Guinier analysis compared to the values obtained by the P(r) analysis. In other words, either the P(r) values match the Guinier and the P(r) fit is terrible, or else the P(r) fit is good but doesn't match the Guinier at all (5-10 difference in Rg, 2x difference in I(0)). I've checked to make sure the buffer subtraction algorithm was OK, and I'm pretty certain that the buffers were exact matches, so I don't know how to explain this variation. There's no evidence of aggregation or polydispersity to throw off the values, either. Does anyone know how this can happen?