Samuel Henry

Abstract:

Results are presented of our latest research, aimed at the development and study of oxide scintillation crystals with high scintillation yield and low intrinsic radioactivity. We report on the improvement of these properties for conventional scintillators, as well as on new promising crystals based on metal tungstates and molybdates. The results are discussed in view of applying these materials in cryogenic experiments searching for dark matter or neutrinoless double beta decay. ©2008 IEEE.

Abstract:

High precision magnetometry is an essential requirement of the cryoEDM experiment at the Institut Laue-Langevin, Grenoble. We have developed a SQUID system for this purpose, however tests done in Oxford have been limited by the noisy electromagnetic environment inside our laboratory, therefore we have tested a smaller version of our prototype system in the very low noise environment at LSBB, Rustrel, France. We have studied the crosstalk between an array of parallel pick-up loops - where the field generated by a current in one loop is detected by the others. We monitored the magnetic field in the LSBB for over twelve hours; and after correcting these data for SQUID resets, and crosstalk, we compare it to the published values from nearby geomagnetic observatories. We have also measured the noise spectrum of our system and studied the effect that heating one of the pick-up loops into its conducting state has on the other, parallel loops. © 2008 IOP Publishing Ltd and SISSA.

Abstract:

We have measured the superconducting transition temperatures of commercial alloys Dural and titanium 6Al-4V, to assess their suitability for use in the cryoEDM neutron electric dipole moment experiment. Our sample of aluminium alloy Dural became a superconductor at 0.84 0.07K but the titanium alloy did not show any superconducting behaviour down to the experimental limit of 0.17 0.11K. © IOP Publishing Ltd.

Abstract:

CRESST (Cryogenic Rare Event Search with Superconducting Thermometers) is a low temperature experiment dedicated to the direct dark matter detection via nuclear recoil. It is located in Hall A of the Laboratori Nazionali del Gran Sasso, Italy. Scintillating CaWO4 crystals operated at a few mK are utilized as target forWIMPs (Weakly Interacting Massive Particles), which are expected to scatter predominantly on the heavy tungsten nuclei. As for background rejection, CRESST uses the phonon-light technique, where two different quantities of an interaction are recorded: the heat production in the CaWO4crystal and the simultaneous emission of scintillation light, which is monitored by a second low-temperature detector, the light detector. The information provided by both detectors allows a powerful background discrimination on an event by event basis. After a major upgrade phase, CRESST-II has now successfully completed a commissioning run during 2007, the results of which are presented in this article.

Abstract:

Following the investigations of the structure and scintillation properties of Ca-doped zinc tungstate powder [phys. stat. sol. (a) 204. 730 (2007)] a single-crystal of ZnWO4-Ca (0.5 mol%) was grown and characterised. The relative light output, energy resolution and decay characteristics were measured for pure and Ca-doped ZnWO4 scintillators. An increase in the light yield of ~40% compared with the undoped crystal, and an energy resolution 9.6% (¹³⁷Cs) were obtained for Ca-doped ZnWO4. The observed improvement is attributed to the reduction of self-absorption (bleaching) of the crystal. The cause of bleaching as well as the possible contribution of scattering is discussed. © 2008 WILEY-VCH Verlag GmbH & Co. KGaA.