240 research outputs found
Time-of-flight spectroscopy of ultracold neutrons at the PSI UCN source
The ultracold neutron (UCN) source at the Paul Scherrer Institute (PSI)
provides high intensities of storable neutrons for fundamental physics
experiments. The neutron velocity spectrum parallel to the beamline axis was
determined by time-of-flight spectroscopy using a neutron chopper. In
particular, the temporal evolution of the spectrum during neutron production
and UCN storage in the source storage volume was investigated and compared to
Monte Carlo simulation results. A softening of the measured spectrum from a
mean velocity of 7.7(1) m s to 5.1(1) m s occurred within the
first 30 s after the proton beam pulse had impinged on the spallation target. A
spectral hardening was observed over longer time scales of one measurement day,
consistent with the effect of surface degradation of the solid deuterium
moderator
The Design of the n2EDM Experiment
We present the design of a next-generation experiment, n2EDM, currently under construction at the ultracold neutron source at the Paul Scherrer Institute (PSI) with the aim of carrying out a high-precision search for an electric dipole moment of the neutron. The project builds on experience gained with the previous apparatus operated at PSI until 2017, and is expected to deliver an order of magnitude better sensitivity with provision for further substantial improvements. An overview is of the experimental method and setup is given, the sensitivity requirements for the apparatus are derived, and its technical design is described
Characterization of ultracold neutron production in thin solid deuterium films at the PSI UCN source
We determined the ultracold neutron (UCN) production rate by superthermal
conversion in the solid deuterium (sD) moderator of the UCN source at the
Paul Scherrer Institute (PSI). In particular, we considered low amounts of less
than mol of D, deposited on the cooled moderator vessel surfaces in
thin films of a few mm thickness. We measured the isotopic () and isomeric () purity of the deuterium
to conclude that absorption and up-scattering at K have a negligible
effect on the UCN yield from the thin films. We compared the calculated UCN
yield based on the previously measured thermal neutron flux from the heavy
water thermal moderator with measurements of the UCN count rates at the
beamports. We confirmed our results and thus demonstrate an absolute
characterization of the UCN production and transport in the source by
simulations
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Carbon stable isotope analysis of cereal remains as a way to reconstruct water availability: preliminary results
Reconstructing past water availability, both as rainfall and irrigation, is important to answer questions about the way society reacts to climate and its changes and the role of irrigation in the development of social complexity. Carbon stable isotope analysis of archaeobotanical remains is a potentially valuable method for reconstructing water availability. To further define the relationship between water availability and plant carbon isotope composition and to set up baseline values for the Southern Levant, grains of experimentally grown barley and sorghum were studied. The cereal crops were grown at three stations under five different irrigation regimes in Jordan. Results indicate that a positive but weak relationship exists between irrigation regime and total water input of barley grains, but no relationship was found for sorghum. The relationship for barley is site-specific and inter-annual variation was present at Deir ‘Alla, but not at Ramtha and Khirbet as-Samra
Avaliação da relação seca/produtividade agrícola em cenário de mudanças climáticas.
As mudanças climáticas alertam para um possível aumento de eventos meteorológicos extremos em todo o mundo, sendo crescente a preocupação de como o clima pode mudar o ambiente e afetar a produção das culturas agrícolas. Este estudo investiga a relação entre a produtividade agrícola e a seca em algumas mesorregiões do estado de Minas Gerais, em cenários de mudanças climáticas. Foram utilizados dados meteorológicos diários projetados pelo modelo ECHAM5/MPI-OM, para o período de 2008 a 2020 para o cenário A1B. Utilizou-se a metodologia da zona agroecológica (AEZ) para estimar a produtividade futura do milho. Empregou-se o índice de seca Z de Palmer em um modelo de regressão linear com a produtividade do milho estimada pela metodologia da AEZ. O desempenho dos modelos foi verificado por meio das estatísticas: coeficiente de determinação (r2), raiz do erro quadrático médio(RMSE), erro absoluto médio (MAE) e índice de concordância de Willmott (d). Os resultados do índice de concordância de Willmott variaram entre 0,48 e 0,90, e os valores de r2 foram pouco expressivos.Contudo, a produtividade estimada pela metodologia AEZ projetou maiores perdas na produtividade do milho devido a limitações por água para os anos agrícolas de 2008/2009, 2009/2010, 2014/2015,2018/2019 para as mesorregiões Triângulo/Alto Paranaíba, Central Mineira e Jequitinhonha
The very large n2EDM magnetically shielded room with an exceptional performance for fundamental physics measurements.
We present the magnetically shielded room (MSR) for the n2EDM experiment at the Paul Scherrer Institute, which features an interior cubic volume with each side of length 2.92 m, thus providing an accessible space of 25 m3. The MSR has 87 openings of diameter up to 220 mm for operating the experimental apparatus inside and an intermediate space between the layers for housing sensitive signal processing electronics. The characterization measurements show a remanent magnetic field in the central 1 m3 below 100 pT and a field below 600 pT in the entire inner volume, up to 4 cm to the walls. The quasi-static shielding factor at 0.01 Hz measured with a sinusoidal 2 μT peak-to-peak signal is about 100 000 in all three spatial directions and increases rapidly with frequency to reach 108 above 1 Hz
Search for an interaction mediated by axion-like particles with ultracold neutrons at the PSI
We report on a search for a new, short-range, spin-dependent interaction
using a modified version of the experimental apparatus used to measure the
permanent neutron electric dipole moment at the Paul Scherrer Institute. This
interaction, which could be mediated by axion-like particles, concerned the
unpolarized nucleons (protons and neutrons) near the material surfaces of the
apparatus and polarized ultracold neutrons stored in vacuum. The dominant
systematic uncertainty resulting from magnetic-field gradients was controlled
to an unprecedented level of approximately 4 pT/cm using an array of
optically-pumped cesium vapor magnetometers and magnetic-field maps
independently recorded using a dedicated measurement device. No signature of a
theoretically predicted new interaction was found, and we set a new limit on
the product of the scalar and the pseudoscalar couplings (95% C.L.) in a range of for the monopole-dipole interaction. This new result confirms
and improves our previous limit by a factor of 2.7 and provides the current
tightest limit obtained with free neutrons
Desenvolvimento de modelo agrometeorológico espectral para estimativa de rendimento do milho na Província de Manica-Moçambique
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