Advanced spectroscopy experiments and new physics experiments with positronium atoms in vacuum will benefit from positronium production in an environment free of magnetic and electrostatic fields. ...Here, we present a novel scheme for generating a bunched positron beam. The positron bunches are prebunched before extraction from a buffer-gas trap, nonadiabatically extracted from a 700 G magnetic field, energy elevated up to 20 kV, and bunched on a target in a free field. According to simulations of the system, 60% of cooled positrons in the buffer-gas trap are extracted and focused on the target in a time spread of 2.5 ns full width tenth maximum (FWTM) and a spot of about 4 mm FWTM for positron implantation energy higher than 3 keV. These performance numbers are achieved in the same apparatus through a combination of several innovative beam manipulations.
A novel method for the measurement of the number of positrons contained in intense positron bunches is presented. The technique is based on the Poisson distribution of the number of gamma rays ...emitted by many simultaneous positron–electron annihilations in a small solid angle. The results have been found in good agreement with those achieved with a calibrated CsI(Tl) detector coupled to a photodiode. The small dimension of the required equipment and the reduced constraints of the technique open the possibility of monitoring, in complex positrons systems, the number of positrons at different positions that are too difficult to reach with other devices.
The precise measurement of forces is one way to obtain deep insight into the fundamental interactions present in nature. In the context of neutral antimatter, the gravitational interaction is of high ...interest, potentially revealing new forces that violate the weak equivalence principle. Here we report on a successful extension of a tool from atom optics--the moiré deflectometer--for a measurement of the acceleration of slow antiprotons. The setup consists of two identical transmission gratings and a spatially resolving emulsion detector for antiproton annihilations. Absolute referencing of the observed antimatter pattern with a photon pattern experiencing no deflection allows the direct inference of forces present. The concept is also straightforwardly applicable to antihydrogen measurements as pursued by the AEgIS collaboration. The combination of these very different techniques from high energy and atomic physics opens a very promising route to the direct detection of the gravitational acceleration of neutral antimatter.
Positron annihilation lifetime spectroscopy is employed to measure the size of the interstitial void spaces characterizing the structure of a set of permanently densified SiO2 glasses. The average ...volume of the voids is markedly affected by the densification process and linearly shrinks by almost an order of magnitude after a relative density variation of 22%. In addition, x-ray diffraction shows that this change of density does not modify appreciably the short range order, which remains organized in SiO4 tetrahedra. These results strongly suggest a porous medium description for v-SiO2 glasses where the compressibility and the medium range order are dominated by the density variation of the voids volume up to densities close to that of α-quartz.
A low cost 2/3 of 4π detector for the study of Ps decay Pino, F.; Fontana, C.L.; Lunardon, M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2019, Letnik:
942
Journal Article
Recenzirano
A large area low-cost detector for detailed studies of ortho-Positronium formation and decay is being designed. The detector will be made of four modules each consisting of a thin slab of YAP(Ce) ...scintillator read out by a multi-anode flat panel photomultiplier tube. The proposed configuration will provide a position sensitive detector capable of recording, on an event-by-event basis, both the 2γ and the 3γ decay channels, for immediate information on the 2γ/3γ ratio. It will as well provide a 3D density distribution of the decay vertexes, thus enabling angular and velocity distribution measurements. In this paper we present the results of measurements performed on one module of the detector using conventional electronics, as well as Monte Carlo simulations on the performances of the system. Using a series of laboratory gamma sources we deduced values of energy and spatial resolution.
•Low-cost detector for detailed studies of ortho-Positronium formation.•YAP:Ce slap coupled to a multi-anode photomultiplier as position sensitive detector.•Center-of-mass based method to reconstruct the position of the photon interaction.•Spatial and energy resolution studies of a position sensitive detector.•Distribution of photon interaction points by Monte Carlo simulations.
Abstract
We present a hybrid imaging/timing detector for force sensitive inertial measurements designed for measurements on positronium, the metastable bound state of an electron and a positron, but ...also suitable for applications involving other low intensity, low energy beams of neutral (antimatter)-atoms, such as antihydrogen. The performance of the prototype detector was evaluated with a tunable low energy positron beam, resulting in a spatial resolution of
≈
12 mm, a detection efficiency of up to 40% and a time-resolution in the order of tens of ns.
•Depth profiling PAS techniques allowed the detection and identification of point defects in UO2+x sputtered thin films.•Experimental evidences on the presence of U vacancies in vacancy clusters were ...found.•PAS results revealed the presence of the theoretically predicted O related defects.
We experimentally studied the formation of vacancy clusters and oxygen related defects in uranium oxide (UOx) thin films (<70 nm) changing the stoichiometry in the x = 2.2–3.5 range. Films were deposited on Si(001) by DC magnetron sputtering varying the substrate temperature (room temperature, 400 °C and 600 °C) and different relative O2 partial pressures in the argon-oxygen mixture. The different species of vacancy-like defects are identified by the combination of depth dependent positron annihilation techniques and by comparison of the experimental data with ab-initio calculations. In samples growth up to 400 °C substrate temperature, di- and tri- vacancies were formed whereas at higher temperature, hexa-vacancies and larger vacancy clusters appear. Film growth at increasing oxygen partial pressure was found not to be correlated with an increase of oxygen defects, but with the formation of more complex vacancy clusters. The presence of oxygen related defects is revealed by identifying preferential positron annihilations with oxygen electrons. Moreover, uranium vacancies inside vacancy clusters are identified by localization of positrons, in agreement with ab-initio calculations.
PDF
