Search results for "rex"
showing 10 items of 701 documents
Production and characterization of a custom-made 228Th source with reduced neutron source strength for the Borexino experiment
2012
A custom-made 228Th source of several MBq activity was produced for the Borexino experiment for studying the external background of the detector. The aim was to reduce the unwanted neutron emission produced via (alpha,n) reactions in ceramics used typically for commercial 228Th sources. For this purpose a ThCl4 solution was converted chemically into ThO2 and embedded into a gold foil. The paper describes the production and the characterization of the custom-made source by means of gamma-activity, dose rate and neutron source strength measurements. From gamma-spectroscopic measurements it was deduced that the activity transfer from the initial solution to the final source was >91% (at 68%…
Constraining neutrino magnetic moment with solar and reactor neutrino data
2004
We use solar neutrino data to derive stringent bounds on Majorana neutrino transition moments (TMs). Such moments, if present, would contribute to the neutrino-electron scattering cross section and hence alter the signal observed in Super-Kamiokande. Using the latest solar neutrino data, combined with the results of the reactor experiment KamLAND, we perform a simultaneous fit of the oscillation parameters and TMs. Furthermore, we include data from the reactor experiments Rovno, TEXONO and MUNU in our analysis, improving significantly the current constraints on TMs. A comparison with previous works shows that our bounds are the strongest and most general results presented up to now. Finally…
Neutrinos from the primary proton–proton fusion process in the Sun
2014
International audience; In the core of the Sun, energy is released through sequences of nuclear reactions that convert hydrogen into helium. The primary reaction is thought to be the fusion of two protons with the emission of a low-energy neutrino. These so-called pp neutrinos constitute nearly the entirety of the solar neutrino flux, vastly outnumbering those emitted in the reactions that follow. Although solar neutrinos from secondary processes have been observed, proving the nuclear origin of the Sun's energy and contributing to the discovery of neutrino oscillations, those from proton-proton fusion have hitherto eluded direct detection. Here we report spectral observations of pp neutrin…
Supersymmetry does not imply mass degeneracy
2004
Abstract It is commonly believed that unbroken supersymmetry (SUSY) implies that all members of a supermultiplet have the same mass. We demonstrate that this is not true, by exhibiting a simple counterexample. We employ the formalism of homeotic fermions, in a simple model where CPT conjugate fermions have different masses. This model can be supersymmetrized to a hypermultiplet of fields which form a representation of the conventional N=2 SUSY algebra. Nevertheless, CPT conjugate states in this hypermultiplet have different masses. These surprising results do not violate either the CPT theorem or the Haag–Lopuszanski–Sohnius theorem.
Three-flavour neutrino oscillation update
2008
We review the present status of three-flavour neutrino oscillations, taking into account the latest available neutrino oscillation data presented at the Neutrino 2008 Conference. This includes the data released this summer by the MINOS collaboration, the data of the neutral current counter phase of the SNO solar neutrino experiment, as well as the latest KamLAND and Borexino data. We give the updated determinations of the leading 'solar' and 'atmospheric' oscillation parameters. We find from global data that the mixing angle $\theta_{13}$ is consistent with zero within $0.9\sigma$ and we derive an upper bound of $\sin^2\theta_{13} < 0.035 (0.056)$ at 90% CL (3$\sigma$).
A calorimeter for the precise determination of the activity of the 144Ce-144Pr anti-neutrino source in the SOX experiment
2018
We describe the design and the performance of a high precision thermal calorimeter, whose purpose was the measurement of the total activity of the 144Ce-144Pr anti-neutrino source of the SOX (Short distance neutrino Oscillation with BoreXino) experiment. SOX aimed at the search for eV-scale sterile neutrinos by means of the Borexino detector at the Laboratori Nazionali del Gran Sasso in Italy and of a very powerful artificial anti-neutrino source located at 8.51 m from the detector center. In order to obtain the required sensitivity, the activity of the source (approximately 150 kCi) had to be known at 1% precision. In this work we report the design of the experimental apparatus and the res…
Superspin glass phase and hierarchy of interactions in multiferroic PbFe1/2Sb1/2O3: an analog of ferroelectric relaxors?
2014
We have fabricated new perovskite multiferroic PbFeSbO3 with a high degree (up to 0.9) of chemical ordering and unexpectedly high-temperature magnetic relaxor properties, which can barely be described within concepts of conventional spin glass physics. Notably, we found that the field-temperature phase diagram of this material, in the extremely wide temperature interval, contains the de Almeida–Thouless-type critical line, which has been the subject of long debates regarding its possible experimental realization. We explain our findings by the creation, at high temperatures of not less than 250 K, of giant superspins (SSs), owing, curiously enough, to the antiferromagnetic superexchange int…
Experimental searches on sterile neutrinos
2015
While neutrino oscillations among the three active neutrino flavors are by now well established, several anomalies observed at relatively short baselines in oscillation experiments hint towards the existence of one or more additional sterile neutrino flavors. As a consequence, several experiments are in preparation that are dedicated to test the sterile neutrino hypothesis. The present contribution gives an overview of the on-going experimental efforts, highlighting the two projects that are foreseen to start in 2015: SOX deploying a radioactive neutrino source at short distance from the BOREXINO detector at LNGS, and STEREO searching for sterile neutrino oscillations at short distance from…
Magnetic transitions in double perovskiteSr2FeRe1−xSbxO6(0⩽x⩽0.9)
2006
The double perovskites ${\mathrm{Sr}}_{2}\mathrm{Fe}M{\mathrm{O}}_{6}$ $(M=\mathrm{Re},\mathrm{Mo})$ belong to the important class of half-metallic magnetic materials. In this study we explore the effect of replacing the electronic $5d$ buffer element Re with variable valency by the main group element Sb with fixed valency. X-ray diffraction reveals ${\mathrm{Sr}}_{2}{\mathrm{FeRe}}_{1\ensuremath{-}x}{\mathrm{Sb}}_{x}{\mathrm{O}}_{6}$ $(0lxl0.9)$ to crystallize without antisite disorder in the tetragonally distorted perovskite structure (space group $I4∕mmm$). The ferrimagnetic behavior of the parent compound ${\mathrm{Sr}}_{2}{\mathrm{FeReO}}_{6}$ changes to antiferromagnetic upon Sb subst…
Electrically switchable magnetic exchange in the vibronic model of linear mixed valence triferrocenium complex
2018
In this article, we report our development of a vibronic model for the electric-field control of antiferromagnetic superexchange in the mixed-valence (MV) triferrocenium complex FeIII-FeII-FeIII proposed as a possible candidate for the molecular implementation of a quantum logic gate. Along with the electronic interactions, such as electron transfer between the iron ions in different oxidation degrees and Coulomb repulsion of the extra holes, the proposed model of the triferrocenium complex also takes into account the vibronic coupling as an inherent ingredient of the problem of mixed valency. The latter is described by the conventional Piepho-Krauzs-Shatz (PKS) model adapted to the linear …