51 research outputs found
Time and position sensitive single photon detector for scintillator read-out
We have developed a photon counting detector system for combined neutron and
gamma radiography which can determine position, time and intensity of a
secondary photon flash created by a high-energy particle or photon within a
scintillator screen. The system is based on a micro-channel plate
photomultiplier concept utilizing image charge coupling to a position- and
time-sensitive read-out anode placed outside the vacuum tube in air, aided by a
standard photomultiplier and very fast pulse-height analyzing electronics. Due
to the low dead time of all system components it can cope with the high
throughput demands of a proposed combined fast neutron and dual discrete energy
gamma radiography method (FNDDER). We show tests with different types of
delay-line read-out anodes and present a novel pulse-height-to-time converter
circuit with its potential to discriminate gamma energies for the projected
FNDDER devices for an automated cargo container inspection system (ACCIS).Comment: Proceedings of FNDA 201
Interatomic Coulombic Decay following Photoionization of the Helium Dimer: Observation of Vibrational Structure
Using synchrotron radiation we simultaneously ionize and excite one helium
atom of a helium dimer (He_2) in a shakeup process. The populated states of the
dimer ion (i.e. He^[*+](n = 2; 3)-He) are found to deexcite via interatomic
coulombic decay. This leads to the emission of a second electron from the
neutral site and a subsequent coulomb explosion. In this letter we present a
measurement of the momenta of fragments that are created during this reaction.
The electron energy distribution and the kinetic energy release of the two He^+
ions show pronounced oscillations which we attribute to the structure of the
vibrational wave function of the dimer ion.Comment: 8 pages, 5 figure
Single photon double ionization of the helium dimer
We show that a single photon can ionize the two helium atoms of the helium
dimer in a distance up to 10 {\deg}A. The energy sharing among the electrons,
the angular distributions of the ions and electrons as well as comparison with
electron impact data for helium atoms suggest a knock-off type double
ionization process. The Coulomb explosion imaging of He_2 provides a direct
view of the nuclear wave function of this by far most extended and most diffuse
of all naturally existing molecules.Comment: 10 pages, 5 figure
Ultrasonically enhanced low-temperature drying of apple: Influence on drying kinetics and antioxidant potential
[EN] Low-temperature air drying represents an alternative means to hot air drying of better retaining the
sensory, nutritional and functional properties of foods. However, reducing the air temperature to figures
below the product s freezing point involves low drying rates, which largely places constraints on any
further industrial application. The main aim of this work was to evaluate the feasibility of using power
ultrasound to improve the low-temperature drying of apple, considering not only the kinetic effects
but also the influence on the antioxidant potential of the dried apple.
For that purpose, apple (Malus domestica cv. Granny Smith) cubes (8.8 mm side) were dried (2 m/s and
a relative humidity of under 10%) at low temperatures ( 10, 5, 0, 5 and 10 C) with (20.5 kW/m3) and
without ultrasound application. The drying kinetics were modeled by considering the diffusion theory,
negligible shrinkage and cubic geometry. In the dried apple, total phenolic and flavonoid contents and
antioxidant capacity were measured.
The application of power ultrasound sped up the drying kinetics at every temperature tested, achieving
drying time reductions of up to 77%, which was linked to the improvement in diffusion and convective
mass transport. In overall terms, ultrasound application involved a greater degradation of polyphenol
and flavonoid contents and a reduction of the antioxidant capacity, which was related to the cell
disruption caused by the mechanical stress of acoustic waves.The authors acknowledge the financial support of the Spanish Ministerio de Economia y Competitividad (MINECO), the European Union (FEDER) and the Generalitat Valenciana (from the projects DPI2012-37466-CO3-03, DPI2012-37466-CO3-02, PROMETEO/2010/062 and the FPI fellowship granted to J.V. Santacatalina).Santacatalina Bonet, JV.; RogrĂguez, Ă.; Simal, S.; CĂĄrcel CarriĂłn, JA.; Mulet Pons, A.; GarcĂa PĂ©rez, JV. (2014). Ultrasonically enhanced low-temperature drying of apple: Influence on drying kinetics and antioxidant potential. Journal of Food Engineering. 138:35-44. https://doi.org/10.1016/j.jfoodeng.2014.04.003S354413
Photo double ionization of helium 100 eV and 450 eV above threshold: II. Circularly polarized light
We present a joint experimental and theoretical study of the fully differential cross section of the photo double ionization of helium with left and right circularly polarized light at E exc= 100 eV and 450 eV above the threshold. We analyse angular distributions for the slow electron and the normalized circular dichroism for various energy sharings of the excess energy between the two electrons. The experimental results are well reproduced by convergent close coupling calculations
Partial photoionization cross sections and angular distributions for double excitation of helium up to the N=13 threshold
Partial photoionization cross sections ÏN(EÎł) and photoelectron angular distributions ÎČN(EÎł) were measured for the final ionic states He+(N>4) in the region between the N=8 and N=13 thresholds (EÎł>78.155ââeV) using the cold target recoil ion momentum spectroscopy technique (COLTRIMS). Comparison of the experimental data with two independent sets of theoretical predictions reveals disagreement for the branching ratios to the various HeN+ states. The angular distributions just below the double ionization threshold suggest an excitation process for highly excited N states similar to the Wannier mechanism for double ionization
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