154 research outputs found
An active transverse energy filter to differentiate low energy particles with large pitch angles in a strong magnetic field
We present the idea and proof of principle measurements for an angular-selective active filter for charged particles. The motivation for the setup arises from the need to distinguish background electrons from signal electrons in a spectrometer of MAC-E filter type. While a large fraction of the background electrons exhibit predominantly small angles relative to the magnetic guiding field (corresponding to a low amount of kinetic energy in the motion component transverse to the field lines, in the following referred to as transverse energy) and pass the filter mostly unhindered, signal electrons from an isotropically emitting source interact with the active filter and are detected. The concept is demonstrated using a microchannel plate (MCP) as an active filter element. When correctly aligned with the magnetic field, electrons with a small transverse energy pass the channels of the MCP without interaction while electrons with large transverse energies hit the channel walls and trigger an avalanche of secondary electrons that is subsequently detected. Due to several drawbacks of MCPs for an actual transverse energy filter, an alternative detection technique using microstructured Si-PIN diodes is proposed
Dpes massless QCD have vacuum energy?
It is widely thought that this question has a positive answer, but we argue
that the support for this belief from both experiment and theory is weak or
nonexistent. We then list some of the ramifications of a negative answer.Comment: 8 pages, no figures, version to appear in NJ
Infrared Properties of QCD from Dyson-Schwinger equations
I review recent results on the infrared properties of QCD from
Dyson-Schwinger equations. The topics include infrared exponents of
one-particle irreducible Green's functions, the fixed point behaviour of the
running coupling at zero momentum, the pattern of dynamical quark mass
generation and properties of light mesons.Comment: 47 pages, 19 figures, Topical Review to be published in J.Phys.G, v2:
typos corrected and some references adde
KATRIN background due to surface radioimpurities
The goal of the KArlsruhe TRItrium Neutrino (KATRIN) experiment is the determination of the effective electron antineutrino mass with a sensitivity of 0.2 eV/c at 90 % C.L.. This goal can only be achieved with a very low background level in the order of 10 mcps in the detector region of interest. A possible background source are α-decays on the inner surface of the KATRIN Main Spectrometer. Rydberg atoms, produced in sputtering processes accompanying the α-decays, are not influenced by electric or magnetic fields and freely propagate inside the vacuum of the Main Spectrometer. Here, they can be ionized by thermal radiation and the released electrons directly contribute to the KATRIN background. Two α-sources, Ra and Th, were installed at the Main Spectrometer with the purpose of temporarily increasing the background in order to study α-decay induced background processes. In this paper, we present a possible background generation mechanism and measurements performed with these two radioactive sources. Our results show a clear correlation between α-activity on the inner spectrometer surface and background from the volume of the spectrometer. Two key characteristics of the Main Spectrometer background – the dependency on the inner electrode offset potential, and the radial distribution – could be reproduced with this artificially induced background. These findings indicate a high contribution of α-decay induced events to the residual KATRIN background
Metabolic Signatures of Lung Cancer in Biofluids: NMR-Based Metabonomics of Blood Plasma
In this work, the variations in the metabolic profile of blood plasma from lung cancer patients and healthy controls were investigated through NMR-based metabonomics, to assess the potential of this approach for lung cancer screening and diagnosis. PLS-DA modeling of CPMG spectra from plasma, subjected to Monte Carlo Cross Validation, allowed cancer patients to be discriminated from controls with sensitivity and specificity levels of about 90%. Relatively lower HDL and higher VLDL + LDL in the patients' plasma, together with increased lactate and pyruvate and decreased levels of glucose, citrate, formate, acetate, several amino acids (alanine, glutamine, histidine, tyrosine, valine), and methanol, could be detected. These changes were found to be present at initial disease stages and could be related to known cancer biochemical hallmarks, such as enhanced glycolysis, glutaminolysis, and gluconeogenesis, together with suppressed Krebs cycle and reduced lipid catabolism, thus supporting the hypothesis of a systemic metabolic signature for lung cancer. Despite the possible confounding influence of age, smoking habits, and other uncontrolled factors, these results indicate that NMR-based metabonomics of blood plasma can be useful as a screening tool to identify suspicious cases for subsequent, more specific radiological tests, thus contributing to improved disease management.ERDF - Competitive Factors Thematic Operational ProgrammeFCT/PTDC/ QUI/68017/2006FCOMP-01-0124-FEDER-007439SFRH/BD/ 63430/2009National UNESCO Committee - L'Oréal Medals of Honor for Women in Science 200Portuguese National NMR Network - RNRM
Commissioning of the vacuum system of the KATRIN Main Spectrometer
The KATRIN experiment will probe the neutrino mass by measuring the
beta-electron energy spectrum near the endpoint of tritium beta-decay. An
integral energy analysis will be performed by an electro-static spectrometer
(Main Spectrometer), an ultra-high vacuum vessel with a length of 23.2 m, a
volume of 1240 m^3, and a complex inner electrode system with about 120000
individual parts. The strong magnetic field that guides the beta-electrons is
provided by super-conducting solenoids at both ends of the spectrometer. Its
influence on turbo-molecular pumps and vacuum gauges had to be considered. A
system consisting of 6 turbo-molecular pumps and 3 km of non-evaporable getter
strips has been deployed and was tested during the commissioning of the
spectrometer. In this paper the configuration, the commissioning with bake-out
at 300{\deg}C, and the performance of this system are presented in detail. The
vacuum system has to maintain a pressure in the 10^{-11} mbar range. It is
demonstrated that the performance of the system is already close to these
stringent functional requirements for the KATRIN experiment, which will start
at the end of 2016.Comment: submitted for publication in JINST, 39 pages, 15 figure
Precision measurement of the electron energy-loss function in tritium and deuterium gas for the KATRIN experiment
The KATRIN experiment is designed for a direct and model-independent
determination of the effective electron anti-neutrino mass via a high-precision
measurement of the tritium -decay endpoint region with a sensitivity on
of 0.2eV/c (90% CL). For this purpose, the -electrons
from a high-luminosity windowless gaseous tritium source traversing an
electrostatic retarding spectrometer are counted to obtain an integral spectrum
around the endpoint energy of 18.6keV. A dominant systematic effect of the
response of the experimental setup is the energy loss of -electrons from
elastic and inelastic scattering off tritium molecules within the source. We
determined the \linebreak energy-loss function in-situ with a pulsed
angular-selective and monoenergetic photoelectron source at various
tritium-source densities. The data was recorded in integral and differential
modes; the latter was achieved by using a novel time-of-flight technique.
We developed a semi-empirical parametrization for the energy-loss function
for the scattering of 18.6-keV electrons from hydrogen isotopologs. This model
was fit to measurement data with a 95% T gas mixture at 30K, as used in
the first KATRIN neutrino mass analyses, as well as a D gas mixture of 96%
purity used in KATRIN commissioning runs. The achieved precision on the
energy-loss function has abated the corresponding uncertainty of
[arXiv:2101.05253] in the KATRIN
neutrino-mass measurement to a subdominant level.Comment: 12 figures, 18 pages; to be submitted to EPJ
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