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An experimental set-up is described for the precise measurement of the recoil energy spectrum of the daughter ions from nuclear beta decay. The experiment is called WITCH, short for Weak Interaction Trap for CHarged particles, and is set up at the ISOLDE facility at CERN. The principle of the experiment and its realization are explained as well as the main physics goal. A cloud of radioactive ions stored in a Penning trap serves as the source for the WITCH experiment, leading to the minimization of scattering and energy loss of the decay products. The energy spectrum of the recoiling daughter ions from the ¬-decays in this ion cloud will be measured with a retardation spectrometer. The principal aim of the WITCH experiment is to study the electroweak interaction by determining the beta-neutrino angular correlation in nuclear ¬-decay from the shape of this recoil energy spectrum. This will be the first time that the recoil energy spectrum of the daughter ions from ¬-decay can be measured for a wide variety of isotopes, independent of their specific properties. IntroductionThe standard model of the electroweak interaction is very successful in describing the interaction both qualitatively and quantitatively. However, it contains many free parameters and ad hoc assumptions. One of these is that from the five possible types of weak interactionsvector (V), axial-vector (A), scalar (S), tensor (T) and pseudoscalar interaction (P) -just V and A interactions are present at a fundamental level. Together with maximal parity violation this has led to the well known V A structure of the weak interaction. Most experimental limits for the S and T coupling constants in the charged current sector are rather weak, though [1,2,3,4],

In this paper we reported the first results of a novel symmetry test performed to check the standard model's prediction of maximal parity violation in nuclear P decay. The experiment measured the ratio R of the polarization of positrons emitted in opposite directions with respect to the nuclear spin and compared the result with the standard model prediction Ro. We have since come to realize that the small transverse components of the positron polarization accepted by the polarimeter make a non-negligible contribution to Ro. Our corrected result, which is presented in detail elsewhere[1], is (b+g) =0.0003~0.0058. This correction increases our 90% confidence level lower bound on the mass of an eventual right-handed gauge boson from 225 to 250 GeV/c, leaving our main conclusions unchanged.We thank Dr. J. Govaerts for calculations which show that the rotation of the positron spin in the magnetic fields of the apparatus has a negligible eAect on the final result.

In this article the vibration behavior of a flexible cylinder subjected to an axial flow is investigated numerically. Therefore a methodology is constructed, which relies entirely on fluid-structure interaction calculations. Consequently, no force coefficients are necessary for the numerical simulations. Two different cases are studied. The first case is a brass cylinder vibrating in an axial water flow. This calculation is compared to experiments in literature and the results agree well. The second case is a hollow steel tube, subjected to liquid lead-bismuth flow. Different flow boundary conditions are tested on this case. Each type of boundary conditions leads to a different confinement and results in different eigenfrequencies and modal damping ratios. Wherever appropriate, a comparison has been made with an existing theory. Generally, this linear theory and the simulations in this article agree well on the frequency of a mode. With respect to damping, the agreement is highly dependent on the correlation used for the normal friction coefficients in the linear theory.

The presence of isospin mixing in the T = 5/2 ground state of 71 As was studied via anisotropic positron emission from oriented nuclei. A small isospin-forbidden Fermi component in the predominantly Gamow-Teller β decay was established, corresponding to an isospin mixing probability of (13 ± 4) × 10 −6 . The sign of the magnetic moment of 71 As was determined to be positive.

In this article, the fluid forces and the dynamics of a flexible clamped-clamped cylinder in turbulent axial flow are computed numerically. In the presented numerical model, there is no need to tune parameters for each specific case or to obtain coefficients from experiments. The results are compared with the dynamics measured in experiments available in literature. The specific case studied here consists of a silicone cylinder mounted in axial water flow. Computationally it is found that the cylinder loses stability first by buckling. The threshold for buckling is in quantitative agreement with experimental results and weakly-nonlinear theory. At higher flow speed a fluttering motion is predicted, in agreement with experimental results. It is also shown that even a small misalignment between the flow and the structure can have a significant impact on the dynamical behavior. To provide insight in the results of these fluid-structure interaction simulations, forces are computed on rigid inclined and curved cylinders, showing the existence of two different flow regimes. Furthermore it is shown that the inlet turbulence state has a non-negligible effect on these forces and thus on the dynamics of the cylinder.

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