171 research outputs found
A Multi-Sensor and Modeling Approach for Mapping Light Under Sea Ice During the Ice-Growth Season
Arctic sea ice is shifting from a year-round to a seasonal sea ice cover. This substantial
transformation, via a reduction in Arctic sea ice extent and a thinning of its thickness,
influences the amount of light entering the upper ocean. This in turn impacts underice algal growth and associated ecosystem dynamics. Field campaigns have provided
valuable insights as to how snow and ice properties impact light penetration at fixed
locations in the Arctic, but to understand the spatial variability in the under-ice light
field there is a need to scale up to the pan-Arctic level. Combining information from
satellites with state-of-the-art parameterizations is one means to achieve this. This study
combines satellite and modeled data products to map under-ice light on a monthly
time-scale from 2011 through 2018. Key limitations pertain to the availability of satellitederived sea ice thickness, which for radar altimetry, is only available during the sea ice
growth season. We clearly show that year-to-year variability in snow depth, along with
the fraction of thin ice, plays a key role in how much light enters the Arctic Ocean. This
is particularly significant in April, which in some regions, coincides with the beginning
of the under-ice algal bloom, whereas we find that ice thickness is the main driver of
under-ice light availability at the end of the melt season in October. The extension to the
melt season due to a warmer Arctic means that snow accumulation has reduced, which
is leading to positive trends in light transmission through snow. This, combined with a
thinner ice cover, should lead to increased under-ice PAR also in the summer month
Elastic and Raman scattering of 9.0 and 11.4 MeV photons from Au, Dy and In
Monoenergetic photons between 8.8 and 11.4 MeV were scattered elastically and
in elastically (Raman) from natural targets of Au, Dy and In.15 new cross
sections were measured. Evidence is presented for a slight deformation in the
197Au nucleus, generally believed to be spherical. It is predicted, on the
basis of these measurements, that the Giant Dipole Resonance of Dy is very
similar to that of 160Gd. A narrow isolated resonance at 9.0 MeV is observed in
In.Comment: 31 pages, 11 figure
Photon data shed new light upon the GDR spreading width in heavy nuclei
A global study of the electric dipole strength in and below the isovector
giant dipole resonance (GDR) is presented for mass numbers A>80. It relies on
the recently established remarkably good match between data for the nuclear
photo effect to novel photon scattering data covering the region below the
neutron emission threshold as well as by average resonance neutron capture
(ARC). From the wide energy coverage of these data the correlation of the GDR
spreading width with energy can be studied with remarkable accuracy. A clear
sensitivity to details of the nuclear shape, i.e. the beta- and
gamma-deformations, is demonstrated. Based hereon a new parameterization of the
energy dependence of the nuclear electric-dipole strength is proposed which -
with only two new parameters - allows to describe the dipole strength in all
heavy nuclei with A>80. Although it differs significantly from previous
parameterizations it holds for spherical, transitional, triaxial and well
deformed nuclei. The GDR spreading width depends in a regular way on the
respective resonance energy, but it is independent of the photon energy.Comment: accepted by Phys. Lett. B after minor modification
The role of -induced reactions on lead and iron in neutrino detectors
We have calculated cross sections and branching ratios for neutrino induced
reactions on ^{208}Pb and ^{56}Fe for various supernova and
accelerator-relevant neutrino spectra. This was motivated by the facts that
lead and iron will be used on one hand as target materials in future neutrino
detectors, on the other hand have been and are still used as shielding
materials in accelerator-based experiments. In particular we study the
inclusive ^{56}^{56}Co and ^{208}^{208}Bi cross
sections and calculate the neutron energy spectra following the decay of the
daughter nuclei. These reactions give a potential background signal in the
KARMEN and LSND experiment and are discussed as a detection scheme for
supernova neutrinos in the proposed OMNIS and LAND detectors. We also study the
neutron-emission following the neutrino-induced neutral-current excitation of
^{56}Fe and ^{208}Pb.Comment: 23 pages (including 7 figures
White paper: CeLAND - Investigation of the reactor antineutrino anomaly with an intense 144Ce-144Pr antineutrino source in KamLAND
We propose to test for short baseline neutrino oscillations, implied by the
recent reevaluation of the reactor antineutrino flux and by anomalous results
from the gallium solar neutrino detectors. The test will consist of producing a
75 kCi 144Ce - 144Pr antineutrino source to be deployed in the Kamioka Liquid
Scintillator Anti-Neutrino Detector (KamLAND). KamLAND's 13m diameter target
volume provides a suitable environment to measure energy and position
dependence of the detected neutrino flux. A characteristic oscillation pattern
would be visible for a baseline of about 10 m or less, providing a very clean
signal of neutrino disappearance into a yet-unknown, "sterile" state. Such a
measurement will be free of any reactor-related uncertainties. After 1.5 years
of data taking the Reactor Antineutrino Anomaly parameter space will be tested
at > 95% C.L.Comment: White paper prepared for Snowmass-2013; slightly different author
lis
CeLAND: search for a 4th light neutrino state with a 3 PBq 144Ce-144Pr electron antineutrino generator in KamLAND
The reactor neutrino and gallium anomalies can be tested with a 3-4 PBq
(75-100 kCi scale) 144Ce-144Pr antineutrino beta-source deployed at the center
or next to a large low-background liquid scintillator detector. The
antineutrino generator will be produced by the Russian reprocessing plant PA
Mayak as early as 2014, transported to Japan, and deployed in the Kamioka
Liquid Scintillator Anti-Neutrino Detector (KamLAND) as early as 2015.
KamLAND's 13 m diameter target volume provides a suitable environment to
measure the energy and position dependence of the detected neutrino flux. A
characteristic oscillation pattern would be visible for a baseline of about 10
m or less, providing a very clean signal of neutrino disappearance into a
yet-unknown, sterile neutrino state. This will provide a comprehensive test of
the electron dissaperance neutrino anomalies and could lead to the discovery of
a 4th neutrino state for Delta_m^2 > 0.1 eV^2 and sin^2(2theta) > 0.05.Comment: 67 pages, 50 figures. Th. Lasserre thanks the European Research
Council for support under the Starting Grant StG-30718
A FABRY-PEROT CAVITY FOR COMPTON POLARIMETRY
A new kind of Compton polarimeter using a resonant Fabry—Pe« rot cavity as a power buildup for the photon beam is proposed. A prototype of such a cavity is described, along with the results obtained in terms of source to be used in a Compton scattering polarimeter. ( 1998 Elsevier Science B.V. All rights reserved
Measurement of Mutual Coulomb Dissociation in GeV Au+Au collisions at RHIC
We report on the first measurement of Mutual Coulomb Dissociation in heavy
ion collisions. We employ forward calorimeters to measure neutron multiplicity
at beam rapidity in peripheral collisions. The cross-section for simultaneous
electromagnetic breakup of Au nuclei at GeV is
barns in good agreement with calculations.Comment: This paper has been submitted for publication in Phys. Rev. Let
Site testing for submillimetre astronomy at Dome C, Antarctica
Over the past few years a major effort has been put into the exploration of
potential sites for the deployment of submillimetre astronomical facilities.
Amongst the most important sites are Dome C and Dome A on the Antarctic
Plateau, and the Chajnantor area in Chile. In this context, we report on
measurements of the sky opacity at 200 um over a period of three years at the
French-Italian station, Concordia, at Dome C, Antarctica. We also present some
solutions to the challenges of operating in the harsh polar environ- ment. Dome
C offers exceptional conditions in terms of absolute atmospheric transmission
and stability for submillimetre astron- omy. Over the austral winter the PWV
exhibits long periods during which it is stable and at a very low level (0.1 to
0.3 mm). Higher values (0.2 to 0.8 mm) of PWV are observed during the short
summer period. Based on observations over three years, a transmission of around
50% at 350 um is achieved for 75% of the time. The 200-um window opens with a
typical transmission of 10% to 15% for 25% of the time. Dome C is one of the
best accessible sites on Earth for submillimetre astronomy. Observations at 350
or 450 {\mu}m are possible all year round, and the 200-um window opens long
enough and with a sufficient transparency to be useful. Although the polar
environment severely constrains hardware design, a permanent observatory with
appropriate technical capabilities is feasible. Because of the very good
astronomical conditions, high angular resolution and time series (multi-year)
observations at Dome C with a medium size single dish telescope would enable
unique studies to be conducted, some of which are not otherwise feasible even
from space
SPIRAL II Project (electron option) - Preliminary Design Study
This document presents a Preliminary Design Study (PDS) of the electron option of the SPIRAL II project
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