Hans Kraus

Abstract:

Temperature is a very important parameter when aiming to minimize radiation damage to biological samples during experiments that utilise intense ionising radiation. A novel technique for remote, non-contact, in situ monitoring of the protein crystal temperature has been developed for the new I23 beamline at the Diamond Light Source, a facility dedicated to macromolecular crystallography (MX) with long-wavelength X-rays. The temperature is derived from the temperature-dependant decay time constant of luminescence from a minuscule scintillation sensor (<0.05 mm3 ) located in very close proximity to the sample under test. In this work we present the underlying principle of cryogenic luminescence lifetime thermometry, discuss the features of the detection method, the choice of temperature sensor and demonstrate how the temperature monitoring system was integrated within the viewing system of the end-station used for the visualisation of protein crystals. The thermometry system was characterised using a Bi4Ge3O12 (BGO) crystal scintillator that exhibits good responsivity of the decay time constant as function of temperature over a wide range (8 – 270 K). The scintillation sensor was calibrated and the uncertainty of the temperature measurements over the primary operation temperature range of the beamline (30 – 150 K) was assessed to be ±1.6 K. It has been shown that the temperature of the sample holder, measured using the luminescence sensor, agrees well with the expected value. The technique was applied to characterise the thermal performance of different sample mounts that have been used in MX experiments at the I23 beamline. The thickness of the mount is shown to have the greatest impact upon the temperature distribution across the sample mount. Altogether these tests and findings demonstrate the usefulness of the thermometry system in highlighting the challenges that remain to be addressed for the in-vacuum MX experiment to become a reliable and indispensable tool for structural biology.

Abstract:

The paper describes an original technique for non-contact in situ monitoring of the temperature developed for experiments in a vacuum environment at the tender X-ray beamline I23 of the Diamond Light Source. The sample temperature is established by determining the luminescence decay constant of a Bi4Ge3O12 (BGO) scintillation sensor. BGO is ideally suited for a temperature range of 30 K to 130 K, in which its decay constant shows a strong temperature dependence. The principle of the method, system design and application examples are discussed and the performance and potential of the technique is assessed.

Abstract:

We present a measurement of the cosmogenic activation in the cryogenic germanium detectors of the EDELWEISS III direct dark matter search experiment. The decay rates measured in detectors with different exposures to cosmic rays above ground are converted into production rates of different isotopes. The measured production rates in units of nuclei/kg/day are 82 ± 21 for 3H, 2.8 ± 0.6 for 49V, 4.6 ± 0.7 for 55Fe, and 106 ± 13 for 65Zn. These results are the most accurate for these isotopes. A 90% C.L. lower limit on the production rate of 68Ge of 71 nuclei/kg/day is also presented. They are compared to model predictions present in literature and to estimates calculated with the ACTIVIA code.