Dear Daniel,
A very good question. I have seen R_d plots jumping up and down, most often in low-symmetry space groups. I think the "mountains" are due to residual systematic differences between symmetry-related observations, differences that the scaling could not compensate for whatever reason. They are most likely associated with observations on _different_ quadrants of the detector - it is on my list of things to track down.
Summary: this tells you nothing about radiation damage. Radiation damage can be concluded from the overall slope of R_d, not from local features.
Hope this makes sense,
Kay
On Thu, 17 Oct 2013 17:48:45 +0200, Danilo Belviso <[log in to unmask]> wrote:
> Dear all,
>
> I am using xds (with graphical interface xdsgui) to process several
> diffraction data of a membrane protein that I have crystallized. At the
> end, I run XDSSTAT in order to check the statistic parameters of the
> process and my attention is captured by the R_d plot: R_d drops during
> the firsts 10-15 frames and then reaches a maximum (20-30 frames). Then,
> its value remains quite stable (I suppose due to the radiation damage
> correction performed by xds). The trend seems the same that is shown in
>
> ActaCryst. (2006). D62, 96–101 where "Some aspects of quantitative
> analysis and correction of radiation damage"
> Fig.1(a)(b)
>
> where R_d (decay R-factor) was introduced.
>
> The question is:
>
> By considering that radiation damage increases during the data
> collection due to the progressive dose of radiation to which the crystal
> is subjected, why does the R_d drop during the first period of data
> collection?
>
> Thank you in advance for your answers.
>
> Danilo
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