The dependence of radiation damage to protein crystals at cryogenic temperatures upon the X-ray absorption cross-section of the crystal has been examined. Lysozyme crystals containing varying heavy-atom concentrations were irradiated and diffraction patterns were recorded as a function of the total number of incident photons. An experimental protocol and a coefficient of sensitivity to absorbed dose, proportional to the change in relative isotropic B factor, are defined that together yield a sensitive and robust measure of damage. Radiation damage per incident photon increases linearly with the absorption coefficient of the crystal, but damage per absorbed photon is the same for all heavy-atom concentrations. Similar damage per absorbed photon is observed for crystals of three proteins with different molecular sizes and solvent contents.

We demonstrate a novel atom chip trapping system that allows the placement and high-resolution imaging of ultracold atoms within microns from any 100 µm-thin, UHV-compatible material, while also allowing sample exchange with minimal experimental downtime. The sample is not connected to the atom chip, allowing rapid exchange without perturbing the atom chip or laser cooling apparatus. Exchange of the sample and retrapping of atoms has been performed within a week turnaround, limited only by chamber baking. Moreover, the decoupling of sample and atom chip provides the ability to independently tune the sample temperature and its position with respect to the trapped ultracold gas, which itself may remain in the focus of a high-resolution imaging system. As a first demonstration of this new system, we have confined a 700-nK cloud of 8 × 10 4 87 Rb atoms within 100 µm of a gold-mirrored 100-µm-thick silicon substrate. The substrate was cooled to 35 K without use of a heat shield, while the atom chip, 120 µm away, remained at room temperature. Atoms may be imaged and retrapped every 16 s, allowing rapid data collection.Ultracold gases trapped near cryogenic surfaces using atom chips 1 can serve as elements of hybrid quantum systems for quantum information processing, e.g., by coupling quantum gases to superconducting qubits 2 , or as sensitive, high-resolution, and wide-area probes of electronic current flow 3 , electric ac and patch fields 4 , and magnetic domain structure 5 and dynamics. Previous experiments have succeeded in trapping and imaging ultracold thermal and quantum gases of alkali atoms around carbon nanotubes 6 , near superconductors 7 at 4 K, microns from room-temperature gold wires 8 , and within a He dilution refrigerator 9 .