Focussing optics for molybdenum radiation: an intense home laboratory source for small molecule crystallography

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Description/Abstract

Recent developments in synchrotron science have led to small molecule crystallographers being able to study increasingly small crystals at dedicated centralised facilities, such as Station 9.8 (SRS, UK) [1]. The chemical sciences have benefited greatly from these advances in instrumentation, which have in many cases enabled studies to be performed that otherwise would have been impossible. This has led to a large difference in the capabilities of the home laboratory when compared to synchrotron facilities. In addition these centralised facilities are exceedingly expensive to run and maintain and in some cases access to them can be difficult and time consuming to obtain.
Macromolecular crystallographers have been in this situation for some time now and their laboratory system of choice is a rotating anode generator equipped with focussing mirrors [2] (and refs therein). It is now clear that the small molecule crystallography community requires such advances in instrumentation in order to reduce the workload on oversubscribed synchrotron facilities and better screen candidate samples.
The requirements of small molecule work are different from the macromolecular community in that a shorter wavelength radiation is necessary (Mo-k as opposed to Cu-k). Mo-k has a lower scattering power than Cu-k and a much worse efficiency (from the source) than Cu-k. Moreover, the required Bragg angles are half that of Cu-k, which reduces the capture angle of the x-rays from the source onto the optic. Until recently the technology to address this issue has not been available.
This poster reports the performance of a graded multilayer focussing optic arranged in a side by side geometry and designed specifically for a rotating anode generator with a molybdenum target. The increase in intensity is shown to be in excess of 5-fold from comparative experiments.
In conclusion focussing optics are now enabling us to investigate crystals in the home laboratory with sizes of the order of 10-20microns and provide a much more effective screening mechanism for synchrotron candidates. Moreover, for small crystals of slightly more routine dimensions (ca 50-100microns), a 5-fold increase in intensity has a concomitant decrease in collection time, thus increasing the throughput of the instrument.