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A General and Predictive Understanding of Thermal Transport from 1D- and 2D-Confined Nanostructures : Theory and Experiment
Altres ajuts: Acord transformatiu CRUE-CSICHeat management is crucial in the design of nanoscale devices as the operating temperature determines their efficiency and lifetime. Past experimental and theoretical works exploring nanoscale heat transport in semiconductors addressed known deviations from Fourier's law modeling by including effective parameters, such as a size-dependent thermal conductivity. However, recent experiments have qualitatively shown behavior that cannot be modeled in this way. Here, we combine advanced experiment and theory to show that the cooling of 1D- and 2D-confined nanoscale hot spots on silicon can be described using a general hydrodynamic heat transport model, contrary to previous understanding of heat flow in bulk silicon. We use a comprehensive set of extreme ultraviolet scatterometry measurements of nondiffusive transport from transiently heated nanolines and nanodots to validate and generalize our ab initio model, that does not need any geometry-dependent fitting parameters. This allows us to uncover the existence of two distinct time scales and heat transport mechanisms: an interface resistance regime that dominates on short time scales and a hydrodynamic-like phonon transport regime that dominates on longer time scales. Moreover, our model can predict the full thermomechanical response on nanometer length scales and picosecond time scales for arbitrary geometries, providing an advanced practical tool for thermal management of nanoscale technologies. Furthermore, we derive analytical expressions for the transport time scales, valid for a subset of geometries, supplying a route for optimizing heat dissipation
Measurement of double beta decay of ¹⁰⁰Mo to excited states in the NEMO 3 experiment
The double beta decay of ¹⁰⁰Mo to the 0_{1}^{+} and 2_{1}^{+} excited states of ¹⁰⁰Ru is studied using the NEMO 3 data. After the analysis of 8024 h of data the half-life for the two-neutrino double beta decay of ¹⁰⁰Mo to the excited 0_{1}^{+} state is measured to be T_{1/2}^{2v} = [5.7_{-0.9}^{+1.3} (stat.) ± 0.8 (syst.)] x 10²⁰ y. The signal-to-background ratio is equal to 3. Information about energy and angular distributions of emitted electrons is also obtained. No evidence for neutrinoless double beta decay to the excited 0_{1}^{+} state has been found. The corresponding half-life limit is T_{1/2}^{0v} (0⁺→0_{1}^{+}) > 8.9 x 10²² y (at 90% C.L.). The search for the double beta decay to the 2_{1}^{+} excited state has allowed the determination of limits on the half-life for the two neutrino mode T_{1/2}^{0v} (0⁺→2_{1}^{+}) > 1.1 x 10²¹ y (at 90% C.L.) and for the neutrinoless mode T_{1/2}^{0v} (0⁺→2_{1}^{+}) > 1.6 x 10²³ y (at 90% C.L.)
Interpreting Reactor Antineutrino Anomalies with STEREO data
Anomalies in past neutrino measurements have led to the discovery that theseparticles have non-zero mass and oscillate between their three flavors whenthey propagate. In the 2010's, similar anomalies observed in the antineutrinospectra emitted by nuclear reactors have triggered the hypothesis of theexistence of a supplementary neutrino state that would be sterile i.e. notinteracting via the weak interaction. The STEREO experiment was designed tostudy this scientific case that would potentially extend the Standard Model ofParticle Physics. Here we present a complete study based on our full set ofdata with significantly improved sensitivity. Installed at the ILL (InstitutLaue Langevin) research reactor, STEREO has accurately measured theantineutrino energy spectrum associated to the fission of 235U. Thismeasurement confirms the anomalies whereas, thanks to the segmentation of theSTEREO detector and its very short mean distance to the core (10~m), the samedata reject the hypothesis of a light sterile neutrino. Such a directmeasurement of the antineutrino energy spectrum suggests instead that biases inthe nuclear experimental data used for the predictions are at the origin of theanomalies. Our result supports the neutrino content of the Standard Model andestablishes a new reference for the 235U antineutrino energy spectrum. Weanticipate that this result will allow to progress towards finer tests of thefundamental properties of neutrinos but also to benchmark models and nucleardata of interest for reactor physics and for observations of astrophysical orgeo-neutrinos.<br
Improved FIFRELIN de-excitation model for neutrino applications
The precise modeling of the de-excitation of Gd isotopes is of great interest
for experimental studies of neutrinos using Gd-loaded organic liquid
scintillators. The FIFRELIN code was recently used within the purposes of the
STEREO experiment for the modeling of the Gd de-excitation after neutron
capture in order to achieve a good control of the detection efficiency. In this
work, we report on the recent additions in the FIFRELIN de-excitation model
with the purpose of enhancing further the de-excitation description.
Experimental transition intensities from EGAF database are now included in the
FIFRELIN cascades, in order to improve the description of the higher energy
part of the spectrum. Furthermore, the angular correlations between {\gamma}
rays are now implemented in FIFRELIN, to account for the relative anisotropies
between them. In addition, conversion electrons are now treated more precisely
in the whole spectrum range, while the subsequent emission of X rays is also
accounted for. The impact of the aforementioned improvements in FIFRELIN is
tested by simulating neutron captures in various positions inside the STEREO
detector. A repository of up-to-date FIFRELIN simulations of the Gd isotopes is
made available for the community, with the possibility of expanding for other
isotopes which can be suitable for different applications.Comment: Corrected typos on author names on arXiv metadat
Production of Radioactive Isotopes through Cosmic Muon Spallation in KamLAND
Radioactive isotopes produced through cosmic muon spallation are a background
for rare-event detection in detectors, double--decay experiments,
and dark-matter searches. Understanding the nature of cosmogenic backgrounds is
particularly important for future experiments aiming to determine the pep and
CNO solar neutrino fluxes, for which the background is dominated by the
spallation production of C. Data from the Kamioka liquid-scintillator
antineutrino detector (KamLAND) provides valuable information for better
understanding these backgrounds, especially in liquid scintillators, and for
checking estimates from current simulations based upon MUSIC, FLUKA, and
GEANT4. Using the time correlation between detected muons and neutron captures,
the neutron production yield in the KamLAND liquid scintillator is measured to
be . For other isotopes,
the production yield is determined from the observed time correlation related
to known isotope lifetimes. We find some yields are inconsistent with
extrapolations based on an accelerator muon beam experiment.Comment: 16 pages, 20 figure
Measurement of double beta decay of 100Mo to excited states in the NEMO 3 experiment
The double beta decay of 100Mo to the 0^+_1 and 2^+_1 excited states of 100Ru
is studied using the NEMO 3 data. After the analysis of 8024 h of data the
half-life for the two-neutrino double beta decay of 100Mo to the excited 0^+_1
state is measured to be T^(2nu)_1/2 = [5.7^{+1.3}_{-0.9}(stat)+/-0.8(syst)]x
10^20 y. The signal-to-background ratio is equal to 3. Information about energy
and angular distributions of emitted electrons is also obtained. No evidence
for neutrinoless double beta decay to the excited 0^+_1 state has been found.
The corresponding half-life limit is T^(0nu)_1/2(0^+ --> 0^+_1) > 8.9 x 10^22 y
(at 90% C.L.).
The search for the double beta decay to the 2^+_1 excited state has allowed
the determination of limits on the half-life for the two neutrino mode
T^(2nu)_1/2(0^+ --> 2^+_1) > 1.1 x 10^21 y (at 90% C.L.) and for the
neutrinoless mode T^(0nu)_1/2(0^+ --> 2^+_1) > 1.6 x 10^23 y (at 90% C.L.).Comment: 23 pages, 7 figures, 4 tables, submitted to Nucl. Phy
Results of the BiPo-1 prototype for radiopurity measurements for the SuperNEMO double beta decay source foils
The development of BiPo detectors is dedicated to the measurement of
extremely high radiopurity in Tl and Bi for the SuperNEMO
double beta decay source foils. A modular prototype, called BiPo-1, with 0.8
of sensitive surface area, has been running in the Modane Underground
Laboratory since February, 2008. The goal of BiPo-1 is to measure the different
components of the background and in particular the surface radiopurity of the
plastic scintillators that make up the detector. The first phase of data
collection has been dedicated to the measurement of the radiopurity in
Tl. After more than one year of background measurement, a surface
activity of the scintillators of (Tl) 1.5
Bq/m is reported here. Given this level of background, a larger BiPo
detector having 12 m of active surface area, is able to qualify the
radiopurity of the SuperNEMO selenium double beta decay foils with the required
sensitivity of (Tl) 2 Bq/kg (90% C.L.) with a six
month measurement.Comment: 24 pages, submitted to N.I.M.
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