The WITCH experiment: Acquiring the first recoil ion spectrum

The standard model of the electroweak interaction describes beta-decay in the well-known V-A form. Nevertheless, the most general Hamiltonian of a beta-decay includes also other possible interaction types, e.g. scalar (S) and tensor (T) contributions, which are not fully ruled out yet experimentally. The WITCH experiment aims to study a possible admixture of these exotic interaction types in nuclear beta-decay by a precise measurement of the shape of the recoil ion energy spectrum. The experimental set-up couples a double Penning trap system and a retardation spectrometer. The set-up is installed in ISOLDE/CERN and was recently shown to be fully operational. The current status of the experiment is presented together with the data acquired during the 2006 campaign, showing the first recoil ion energy spectrum obtained. The data taking procedure and corresponding data acquisition system are described in more detail. Several further technical improvements are briefly reviewed.Comment: 11 pages, 6 figures, conference proceedings EMIS 2007 (http://emis2007.ganil.fr), published also in NIM B: doi:10.1016/j.nimb.2008.05.15

First detection and energy measurement of recoil ions following beta decay in a Penning trap with the WITCH experiment

The WITCH experiment (Weak Interaction Trap for CHarged particles) will search for exotic interactions by investigating the beta-neutrino angular correlation via the measurement of the recoil energy spectrum after beta decay. As a first step the recoil ions from the beta-minus decay of 124In stored in a Penning trap have been detected. The evidence for the detection of recoil ions is shown and the properties of the ion cloud that forms the radioactive source for the experiment in the Penning trap are presented.Comment: 9 pages, 6 figures (9 figure files), submitted to European Physical Journal

A GEANT4 Monte-Carlo Simulation Code for precision beta spectroscopy

The measurement of the beta asymmetry parameter in nuclear beta decay is a potentially very sensitive tool to search for non V-A components in the charge-changing weak interaction. To reach the required precision (percent level) all effects that modify the emission pattern of the beta radiation, i.e. the geometry of the setup, the effect of the magnetic field on the trajectories of beta particles as well as (back)scattering in the source, on the sample holder and on the detector, have to be correctly taken into account in the analysis of the data. A thorough study of these effects and a new method based on detailed GEANT4 Monte-Carlo simulations that was developed for this purpose is presented here. The code was developed for beta asymmetry measurements by means of the Low Temperature Nuclear Orientation (LTNO) method, but can in principle be generalized to other experimental setups using other polarization techniques

WITCH: a recoil spectrometer for weak interaction and nuclear physics studies

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 $\beta$--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 $\beta$--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 $\beta$--decay can be measured for a wide variety of isotopes, independent of their specific properties

New limits on nucleon decays into invisible channels with the BOREXINO Counting Test Facility

The results of background measurements with the second version of the BOREXINO Counting Test Facility (CTF-II), installed in the Gran Sasso Underground Laboratory, were used to obtain limits on the instability of nucleons, bounded in nuclei, for decays into invisible channels ($inv$): disappearance, decays to neutrinos, etc. The approach consisted of a search for decays of unstable nuclides resulting from $N$ and $NN$ decays of parents $^{12}$C, $^{13}$C and $^{16}$O nuclei in the liquid scintillator and the water shield of the CTF. Due to the extremely low background and the large mass (4.2 ton) of the CTF detector, the most stringent (or competitive) up-to-date experimental bounds have been established: $\tau(n \to inv) > 1.8 \cdot 10^{25}$ y, $\tau(p \to inv) > 1.1 \cdot 10^{26}$ y, $\tau(nn \to inv) > 4.9 \cdot 10^{25}$ y and $\tau(pp \to inv) > 5.0 \cdot 10^{25}$ y, all at 90% C.L.Comment: 22 pages, 3 figures,submitted to Phys.Lett.

A detection system to measure muon-induced neutrons for direct Dark Matter searches

International audienceMuon-induced neutrons constitute a prominent background component in a number of low count rate experiments, namely direct searches for Dark Matter. In this work we describe a neutron detector to measure this background in an underground laboratory, the Laboratoire Souterrain de Modane. The system is based on 1 m of Gd-loaded scintillator and it is linked with the muon veto of the EDELWEISS-II experiment for coincident muon detection. The system was installed in autumn 2008 and passed since then a number of commissioning tests proving its full functionality. The data-taking is continuously ongoing and a count rate of the order of 1 muon-induced neutron per day has been achieved

The transmission problem on a three-dimensional wedge

We consider the transmission problem for the Laplace equation on an infinite three-dimensional wedge, determining the complex parameters for which the problem is well-posed, and characterizing the infinite multiplicity nature of the spectrum. This is carried out in two formulations leading to rather different spectral pictures. One formulation is in terms of square integrable boundary data, the other is in terms of finite energy solutions. We use the layer potential method, which requires the harmonic analysis of a non-commutative non-unimodular group associated with the wedge

The optimization of radiation protection composition

The purpose of the study is to develop an algorithm for designing the composition of homogeneous radiation protective materials (RPM) for the radiation protection optimization. Homogeneous radiation protective materials of the Abris type were used in the studies, the manufacturing technology for which makes it possible to obtain the required concentrations of filling agents. The attenuating capacity of a radiation protective material with the barite, lead and tungsten concentrations of 20–80% was estimated using high-precision codes. Experimental studies into the protective properties of the Abris material with different concentrations of filling agents were conducted to verify the calculation results. For the experiment, five sources of gamma radiation (60Co, 58Co, 198Au, 54Mn, 24Na) with typical radiation energies were generated in the IVV-2M research reactor. A dedicated facility and a DKS-AT1123 measuring device were also used. As the result of an integrated research, calculated dependences of the attenuation factors have been obtained for the radiation produced by typical radiation sources, and for different RPM compositions and thicknesses. This data forms the input for the optimization of radiation protection. The design of the homogeneous RPM composition is highly promising in terms of the approach to radiation protection optimization. As follows from a comparison of the investigation results for the γ-radiation dose attenuation factors for homogeneous protective materials of the Abris type, depending on composition and thickness, the experimental data differs from the values obtained by calculation by not more than 5%. The Abris-type homogeneous RPM manufacturing technology makes it possible to provide the required protective properties for particular exposure conditions (composition of radioactive contaminants)

Investigations for the substantiation of high-temperature nuclear power generation technology using fast sodium-cooled reactor for hydrogen production and other innovative applications (Part 1)

Neutronics and thermal physics studies of BN-VT reactor installation with 600-MW thermal power demonstrated the possibility in principle to achieve the required parameters of high-temperature fast reactor for production of large quantities of hydrogen on the basis, for instance, of one of thermal chemical cycles or high-temperature hydrolysis with high thermal efficiency of use of electric power. Relatively small dimensions, the type of coolant, selection of fissile material and structural materials allow developing nuclear reactor with particular inherent properties (exclusion of prompt-neutron reactor power excursions, removal of decay heat in passive mode) while ensuring enhanced nuclear and radiation safety. Composition of BN-VT reactor facility includes sodium-cooled fast reactor, three cooling loops for emergency heat removal and three sets of equipment of the secondary cooling loop for heat transfer from the reactor to chemical installations generating hydrogen or to gas-turbine plant for supplying chemical equipment with electric power. Composition of each of the cooling loops includes intermediate heat exchanger arranged inside the reactor vessel, centrifugal pump and pipeline for removal and re-introduction of sodium in the reactor core. Contemporary requirements on the safety and financial performance of future generations of nuclear reactors were taken into consideration in the development of the reactor under study. Implemented calculation studies demonstrated that penetration of hydrogen within the limits of permissible allowances produce practically no effect on the neutronics and safety parameters of the reactor. Solution of the problem of fuel pin stability was mitigated due to the selection of low thermal load on fuel pins. Application of EP-912-VD steel as a possible optional structural material was examined. Continued studies of heat-resistant materials and their behavior under irradiation are required