Hans Kraus

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:

The scintillation light response and the decay time constant of Bi4Ge3O12 (BGO) were measured down to a temperature of 6 K using a multi-photon counting technique. The light response of BGO was confirmed to be temperature independent below 100 K and an estimate of the light yield was made, giving a value of 23,700±2600 ph/MeV. The temperature dependence of the scintillation decay time constant is interpreted using a simple three-level model for the emission centre which agrees well with the experimental data over the temperature range investigated. © 2008 Elsevier B.V. All rights reserved.

Abstract:

The importance of luminescent tungstates and molybdates in several technological applications motivated the study of the structural, luminescence and scintillation properties of the MgWO4-MgMoO4 system. X-ray diffraction studies allowed the identification of three main types of structures in the pseudo-binary MgWO4-MgMoO4 system (sanmartinite β-MgMoO4, cuprosheelite α-MgMoO4, and wolframite MgWO4) and the refinement of the parameters of the crystal lattice. It is found that the single-phase solid solution MgMo 1-xWxO4 with a β-MgMoO4 structure is created only at x<0.10, while for a higher tungsten content a mixture of different phases is formed. The x-ray luminescence spectra of a series of samples of the MgWO4-MgMoO4 system are measured at T = 8 K. The principal emission bands are assigned to the main structural phases as follows: β-MgMoO4, 520 nm; α-MgMoO4, 590 nm; MgWO4 (wolframite), 480 nm. The phase composition of the sample determines the actual shape of the observed spectra. Possible relations between the crystal structure and luminescence properties of different phases are discussed in terms of a configuration coordinate model. Of all the compounds under test, MgWO4 is found to have the best scintillation response for particle excitation (0.90 0.15 that of ZnWO4 at T = 295 K). Further, the light yield also remains high with decreasing temperature, which makes this material potentially useful for cryogenic applications. © 2008 IOP Publishing Ltd.