Installation and testing of a focusing mirror at beamline X28C for high flux x-ray radiolysis of biological macromolecules.

The NSLS X28C white-light beamline has been upgraded with a focusing mirror in order to provide increased x-ray density and a wide selection of beam shapes at the sample position. The cylindrical single crystal silicon mirror uses an Indalloy 51 liquid support bath as both a mechanism for heat transfer and a buoyant support to counter the effects of gravity and correct for minor parabolic slope errors. Calorimetric measurements were performed to verify that the calculated more than 200-fold increase in flux density is delivered by the mirror at the smallest beam spot. The properties of the focused beam relevant to radiolytic footprinting, namely, the physical dimensions of the beam, the effective hydroxyl radical dose delivered to the sample, and sample heating upon irradiation, have been studied at several mirror angles.