1,342 research outputs found
Effect of an electric field on superfluid helium scintillation produced by alpha-particle sources
We report a study of the intensity and time dependence of scintillation
produced by weak alpha particle sources in superfluid helium in the presence of
an electric field (0 - 45 kV/cm) in the temperature range of 0.2 K to 1.1 K at
the saturated vapor pressure. Both the prompt and the delayed components of the
scintillation exhibit a reduction in intensity with the application of an
electric field. The reduction in the intensity of the prompt component is well
approximated by a linear dependence on the electric field strength with a
reduction of 15% at 45 kV/cm. When analyzed using the Kramers theory of
columnar recombination, this electric field dependence leads to the conclusion
that roughly 40% of the scintillation results from species formed from atoms
originally promoted to excited states and 60% from excimers created by
ionization and subsequent recombination with the charges initially having a
cylindrical Gaussian distribution about the alpha track of 60 nm radius. The
intensity of the delayed component of the scintillation has a stronger
dependence on the electric field strength and on temperature. The implications
of these data on the mechanisms affecting scintillation in liquid helium are
discussed.Comment: 17 pages, 23 figure
The environment effect on operation of in-vessel mirrors for plasma diagnostics in fusion devices
First mirrors will be the plasma facing components of optical diagnostic
systems in ITER. Mirror surfaces will undergo modification caused by erosion
and re-deposition processes [1,2]. As a consequence, the mirror performance may
be changed and may deteriorate [3,4]. In the divertor region it may also be
obscured by deposition [5-7]. The limited access to in-vessel components of
ITER calls for testing the mirror materials in present day devices in order to
gather information on the material damage and degradation of the mirror
performance, i.e. reflectivity. A dedicated experimental programme, First
Mirror Test (FMT), has been initiated at the JET tokamak within the framework
Tritium Retention Studies (TRS).Comment: 12th International Congress on Plasma Physics, 25-29 October 2004,
Nice (France).Submitted by B. Schunke on behalf of V. Voytseny
First test of an enriched CdWO scintillating bolometer for neutrinoless double-beta-decay searches
For the first time, a cadmium tungstate crystal scintillator enriched in
Cd has been succesfully tested as a scintillating bolometer. The
measurement was performed above ground at a temperature of 18 mK. The crystal
mass was 34.5 g and the enrichment level ~82 %. Despite a substantial pile-up
effect due to above-ground operation, the detector demonstrated a high energy
resolution (2-7 keV FWHM in 0.2-2.6 MeV energy range), a powerful
particle identification capability and a high level of internal radiopurity.
These results prove that cadmium tungstate is an extremely promising detector
material for a next-generation neutrinoless double-beta decay bolometric
experiment, like that proposed in the CUPID project (CUORE Upgrade with
Particle IDentification)
Effect of strain rate on the formation of the microstructure of a 1950/10% SiC metal matrix composite under high temperature
The paper studies the effect of strain rate on the formation of grains and low-angle boundaries in an aluminum matrix composite based on the 1950 alloy (analogous to the AA7075 alloy) with 10 vol% SiC. The deformation of the metal matrix composite, produced by a powder technique, is investigated at a temperature of 500 °C. The specimens are investigated by electron backscatter diffraction before and after deformation at strain rates ranging from 0.1 to 5.5 s-1. It has been established that continuous dynamic recrystallization occurs in the composite at 500 °C in the whole strain rate range considered. The recrystallization is followed by a decrease in the average grain diameter and an increase in the density of the low-angle boundaries with increasing strain rate. © 2017 Author(s).The work was partially financially supported rheological behavior of a metal matrix composite
Excitation-energy dependence of the mechanism for two-photon ionization of liquid H2O and D2O from 8.3to12.4eV
This is the publisher's version, also available electronically from http://scitation.aip.org/content/aip/journal/jcp/125/4/10.1063/1.2217738.Transient absorption measurements monitor the geminate recombination kinetics of solvated electrons following two-photonionization of liquid water at several excitation energies in the range from 8.3to12.4eV. Modeling the kinetics of the electron reveals its average ejection length from the hydronium ion and hydroxyl radical counterparts and thus provides insight into the ionization mechanism. The electron ejection length increases monotonically from roughly 0.9nm at 8.3eV to nearly 4nm at 12.4eV, with the increase taking place most rapidly above 9.5eV. We connect our results with recent advances in the understanding of the electronic structure of liquid water and discuss the nature of the ionization mechanism as a function of excitation energy. The isotope dependence of the electron ejection length provides additional information about the ionization mechanism. The electron ejection length has a similar energy dependence for two-photonionization of liquid D(2)O, but is consistently shorter than in H(2)O by about 0.3nm across the wide range of excitation energies studied
Observation of Crossover from Ballistic to Diffusion Regime for Excimer Molecules in Superfluid He
We have measured the temperature dependence of the time of flight of helium
excimer molecules He2* in superfluid 4He and find that the molecules behave
ballistically below 100mK and exhibit Brownian motion above 200 mK. In the
intermediate temperature range the transport cannot be described by either of
the models.Comment: 8 pages, 6 figures, submitted to the Proceedings of the International
Conference on Quantum Fluids and Solids 201
- …