AEgIS (Antimatter Experiment: Gravity, Interferometry, Spectroscopy) experiment in progress at CERN has planned to produce antihydrogen ( ) by using the resonant charge exchange process between ...orthopositronium (o-Ps) and antiproton ( ). Its primary goal is the realization of a cold beam for the first measurement of the Earth's gravitational acceleration on antimatter. A demanding condition for large o-Ps - cross section is the cooling of o-Ps at temperatures lower than at least 160 K. We will present recent results of o-Ps formation and cooling at cryogenic temperatures in a novel silicon positron/Ps converter in which oxidized nano-channels perpendicular to the surface were produced. The possibility to tune the nano-channels dimension to optimize o-Ps kinetic energy emission and to avoid o-Ps quantum confinement is discussed.
The structural evolution of nanoporous silica thin films was studied by Doppler broadening spectroscopy (DBS), 2–3 gamma ratio of positronium (3γ-PAS) and Fourier transform infrared spectroscopy ...(FT-IR). Four series of silica films with thickness in the 300–600
nm range were deposited by spin coating on Si substrate changing the content of sacrificial porogen in the sol precursors. The effect on the porosity of different amount of porogen and of the thermal treatments in the 400–900
°C temperature range have been highlighted. The evolution of the porosity is discussed considering the removal of porogen and of the silanol Si–OH groups by thermal treatments as pointed out by FT-IR. Pores with size from less than 1
nm up to sizes larger than 2.0
nm have been detected. In samples with maximum porogen load oPs escaping was observed indicating onset of connected porosity. At temperatures higher than 700
°C a decrease of the porosity due to a progressive pore collapsing was evidenced. A strong correlation was found between the shift of the Si–O–Si transversal optical (TO
3) mode in the FT-IR spectra and the pore size in the porous silica films as revealed by DBS and 3γ-PAS.
La sífilis es una de las enfermedades infectocontagiosas de transmisión sexual más frecuentes, que presentadiferentes estadios en su evolución clínica. El estadio secundario se caracteriza por un ...gran polimorfismolesional, que compromete la piel, las mucosas y los anexos cutáneos, motivo por el cual se la conoce como“la gran simuladora”. Es importante el conocimiento de todas sus manifestaciones para su sospecha,diagnóstico y oportuno tratamiento.
A magnetic transport line, a magnetic field terminator and a positron buncher were designed and built to focus low-energy positron pulses from a Surko-type accumulator on a porous target. The 25 ...electrodes buncher, which produces a parabolic potential, was designed to implant 5 ns positron bunches with a spot of 3 mm into a target held at cryogenic temperature. These pulses will be used to obtain cooled Ps clouds into vacuum for laser excitation in spectroscopy experiments. By using high-voltage fast switches and a proper mu-metal shield the requirement to form Ps in a free (magnetic and electric) field region was satisfied compatibly with the request of injecting positrons at energies of 5-9 keV. The optical design, the electrical circuitry of the buncher and the construction solutions of the whole apparatus will be presented and explained.
A positronium Time of Flight (TOF) apparatus, conceived to work with continuous positron beams of intensity up to ~10
6
positrons/s, was developed. The geometry of the TOF chamber and the acquisition ...chain are described in detail. The performances of the set up were preliminary tested with a laboratory positron beam of ~5 × 10
3
positrons/s by measuring the Time of Flight of Ps emitted from oxidized nanochannels produced in a Si single crystal. A TOF spectrum of ~10
4
events was collected in 9 days with a time resolution of 8 ns. The analysis of the TOF spectrum is discussed. This apparatus is going to be assembled at the intense positron source NEPOMUC at FRM-II reactor, where the measurement time of each spectrum will be reduced to less than 2 h, making this TOF system appropriate to investigate positronium emission after cooling in porous materials held at cryogenic temperature.
The AEgIS experiment is an international collaboration with the main goal of performing the first direct measurement of the Earth's gravitational acceleration on antimatter. Critical to the success ...of AEgIS is the production of cold antihydrogen (Hmacr) atoms. The FACT detector is used to measure the production and temperature of the Hmacr atoms and for establishing the formation of a Hmacr beam. The operating requirements for this detector are very challenging: it must be able to identify each of the thousand or so annihilations in the 1 ms period of pulsed Hmacr production, operate at 4 K inside a 1 T solenoidal field and not produce more than 10 W of heat. The FACT detector consists of two concentric cylindrical layers of 400 scintillator fibres with a 1 mm diameter and a 0.6 mm pitch. The scintillating fibres are coupled to clear fibres which transport the scintillation light to 800 silicon photomultipliers. Each silicon photomultiplier signal is connected to a linear amplifier and a fast discriminator, the outputs of which are sampled continuously by Field Programmable Gate Arrays (FPGAs).
We present here a new application of silicon sensors aimed at the direct detection of antinucleons annihilations taking place inside the sensor׳s volume. Such detectors are interesting particularly ...for the measurement of antimatter properties and will be used as part of the gravity measurement module in the AEg¯IS experiment at the CERN Antiproton Decelerator. One of the goals of the AEg¯IS experiment is to measure the gravitational acceleration of antihydrogen with 1% precision. Three different silicon sensor geometries have been tested with an antiproton beam to investigate their properties as annihilation detection devices: strip planar, 3D pixels and monolithic pixel planar. In all cases we were successfully detecting annihilations taking place in the sensor and we were able to make a first characterization of the clusters and tracks.
New Ps spectroscopy measurements, formation of antihydrogen for antimatter-matter comparison experiments, production of Ps beams require the efficient production of cooled positronium in vacuum. At ...present the most efficient positron-positronium converters are silica based ordered or disordered porous materials, in which formed Ps decreases its kinetic energy by collisional cooling. Recently new positron-positronium converters based on oxidized nanochannels in silicon were found to be very promising because of the tunability of the nanochannel size, which allows to overcome the limits imposed to the Ps cooling by the quantum confinement. With these converters, Ps with temperatures as low as 150 K was detected in vacuum by a TOF apparatus. The Ps formation, quantum confinement, collisional cooling and emission into vacuum from nanochanneled silicon will be discussed in light of recent results.
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