The most likely explanation is that you have a cracked crystal or your
crystal has split from radiation damage around the frame 70.

If you had a cracked crystal from the start, the spot overlap between
crystals would change when the sample was rotated. In such cases, it may
happen that the program starts refining a different subgroup of crystals
as the one that defines crystal parameters. If these crystals are
isomorphous to each other, the scaling can correct for such a variable
exposure/integration. If the crystals are not isomorphous, which sometimes
happens, you have a problem. In such a case it would probably be better to
restrict the scaling to the initial 70 frames. Sometimes it helps to
reprocess the data with different spot integration size. There are two
opposing strategies that could be beneficial:
1) reduce the spot integration size to narrow down the integration to a
single crystal
2) increase the spot integration size to integrate diffraction from a
group of crystals with similar orientation. If these are uniformly
integrated, the phasing signal should be still preserved.

If your crystal has split from radiation damage, the strategy 2 may help,
but frequently the cracking induced by radiation damage is a very bad sign
(crystal lattice has changed so the crystal is no longer isomorphous with
its initial state).

Scaling provides the ultimate diagnostic of the problem's seriousness.
Statistics from integration that you provided are secondary, but may help
in pinpointing the source of the problem. One can disregard them if the
scaling is good.

The presence of iodine creates additional factors. It increases X-ray
absorption and so the radiation damage, but iodine is also a quencher of
radicals and tends to reduce structural changes induced by radiation.

Hope that helps,
Zbyszek Otwinowski
>
> Hi all,
>
> I have collected one iodine soaked data in our home source, and processing
> the data using HKL2000. Exposure time per frame is 5min/1 degree.
> While processing I have noticed that the Chisq values, cell parameters and
> rotation change Vs frame are deviating like anything. Please find the
> picasa link to see the carves. I will be benefited if anyone kindly
> suggest me the possible cause of these deviations.
>
> https://picasaweb.google.com/118341875228875389610/Mar252011?authkey=Gv1sRgCJXe6-ncmt6KmwE#
>
> Thank you all for your suggestions,
>
> Sincerely,
>
> Debajyoti


Zbyszek Otwinowski
UT Southwestern Medical Center at Dallas
5323 Harry Hines Blvd.
Dallas, TX 75390-8816
Tel. 214-645-6385
Fax. 214-645-6353