Search

BSDB Spring meeting 2020Jointly with Genetics Societydate: 15-18 March 2020location: Warwickorganisers: Stefan Hoppler (GenSoc), Aziz Aboobaker (GenSoc), Tanya Whitfield (BSDB), Clare Baker (BSDB), Sally Lowell (BSDB)

Detailed experimental methods for Part 1 (length and volume measurements from SPIM) and Part 2 (cross-section diameter and cristae density from TEM), and calculation of mid-piece volume assuming the volume of a truncated cone.

Lattice sites and collective ordering of oxygen atoms in HgBa$_2$CaCu$_2$O$_{6+\delta}$ were studied using the perturbed angular correlation (PAC) technique at ISOLDE/CERN. The electric field gradients (EFG) at $^{199m}$Hg nuclei have been measured as functions of oxygen doping on the Hg planes, above and below T$_c$. In comparison with the results obtained for oxygen and fluorine doping in Hg-1201, the analysis shows a different oxygen ordering exhibited by Hg-1212. Moreover, for all studied cases, the experimental results show that at a local scale there is non-uniform oxygen distribution. A series of ab initio EFG calculations allowed to infer that at low concentrations, regions without oxygen coexist with regions where O$_{2\delta}$ dumbbell molecules are located at the center of the Hg mesh. On the other side, at high concentrations, O$_{2\delta}$ dumbbell molecules coexist with single O$_\delta$ atoms occupying the center of the Hg mesh. The present results suggest that oxygen sits on the Hg planes in the form of a molecule and not as a single atom.

The cubic spinel CdCr$_2$S$_4$ gained recently a vivid interest, given the relevance of relaxor-like dielectric behavior in its paramagnetic phase. By a singular combination of local probe techniques namely Pair Distribution Function and Perturbed Angular Correlation we firmly establish that the Cr ion plays the central key role on this exotic phenomenon, namely through a dynamic off-centering displacement of its coordination sphere. We further show that this off centering of the magnetic Cr-ion gives rise to a peculiar entanglement between the polar and magnetic degrees of freedom, stabilizing, in the paramagnetic phase, short range magnetic clusters, clearly seen in ultra-low field susceptibility measurements. Moreover, the Landau theory is here used to demonstrate that a linear coupling between the magnetic and polar order parameters is sufficient to justify the appearance of magnetic cluster in paramagnetic phase of this compound. These results open insights on the hotly debated magnetic and polar interaction, setting a step forward in the reinterpretation of the coupling of different physical degrees of freedom.

Megawatt-class molten targets, combining high material densities and good heat transfer properties are being considered for neutron spallation sources, neutrino physics facilities and radioactive ion beam production. In order to cope with the limitation of long diffusion times affecting the extraction of short-lived isotopes, a lead bismuth eutectic (LBE) target loop equipped with a diffusion chamber has been proposed and tested offline at IPUL, Latvia, by E. Noah and co-workers. To validate the concept, a molten LBE loop is now in the design phase and will be prototyped and tested on-line at CERN-ISOLDE using a 1.4-GeV proton beam. Primary focus is given to the dimensioning of the diffusion chamber. The molten LBE concept inspired a new alternative route to produce 10¹³ 18Ne/s for the Beta Beams project, where a molten salt loop would be irradiated with 7 mA, 160-MeV proton beam. The concept has been validated by testing a molten fluoride salt static unit at CERN-ISOLDE using a 1.4-GeV proton beam. The investigation of the release and production of neon isotopes allowed the first measurement of the diffusion coefficient of this element in molten fluoride salts., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

The problems of geometry and mechanics have driven forward the generalization of the concepts of number and function. This shows how application and generalization together prevent that mathematics becomes a mere formalism. Thoughts are signs and signs have meaning within a certain context. Meaning is a function of a term: This function produces a pattern. Algebra or modern axiomatic come to mind, as examples. However, strictly formalistic mathematics did not pay sufficient attention to the fact that modern axiomatic theories require a complementary element, in terms of intended applications or models, not to end up in a merely formal game.