Papers by Keyword: Positronium

Paper TitlePage

Fundamental Experiments with Positronium Confined in Micro-Cavities and Emitted into Vacuum with the New Bunched Positron Beam at the Antimatter Lab of Trento
Authors: Sebastiano Mariazzi, Ahmad Chehaimi, Luca Penasa, Ruggero Caravita, Roberto Sennen Brusa
Abstract: A new bunched positron (e+) beam is currently under final development at the AntiMatter Laboratory (AML) of the University of Trento. The positron beam has been designed to deliver bunches containing up to a few 105 positrons compressed to durations of less than 2 ns and with a tunable energy range between 1 and 21 keV. Thanks to the specifications of this new apparatus, different experiments based on the production of positronium (Ps) in nanostructured e+/Ps converters have been planned. A silicon target with nanochannels connected to laser-written buried micro-cavities is under development. The intent is to produce Ps atoms in the nanochannels and collect them in the micro-cavities to explore the mechanisms of Ps/cavity walls interaction and Ps/Ps interaction. Moreover, Ps clouds emitted into vacuum after implantation of e+ bunches in nanochanneled e+/Ps converters will be employed to perform measurements of the entanglement of the three annihilation gamma-rays of Ps and the inertial sensing on Ps. In this work, the characteristics of the new positron beam at the AML of Trento will be presented and the scheduled experiments will be illustrated.
13
Quantum Monte Carlo in Positron Physics
Authors: Ilja Makkonen
Abstract: The development of algorithms and simulation codes as well as the ever increasing comput ing power available have have enabled many-body simulations to emerge as a viable alternative to the two-component density-functional theory to study positron states and annihilation in solids, defects and on solid surfaces. One practical many-body method is quantum Monte Carlo. This article will aim to present the practitioners of positron annihilation methods the basic ideas of the variational and diffusion quantum Monte Carlo, provide examples of their past and recent applications in positron physics of atomic/molecular and solid-state systems as well as an outlook into the future.
155
The Science Enjoyed by Professor Alec T. Stewart
Authors: Toshio Hyodo
Abstract: Late Professor Stewart initiated and shaped the International Conference on Positron Annihilation (ICPA) series. As a first-generation experimental positron-annihilation scientist, he made full use of the angular correlation of annihilation radiation (ACAR) method. He applied this method to study Fermi surfaces of metals, positron wave-functions in crystals, positron-electron and -phonon many-body interactions, and the vacancy formation energy in solids. He also studied with this method positronium in liquids and solids (T. Hyodo, J. Phys. Conf. Series, 618 (2015) 012002). All these studies enjoyed by Professor Stewart will long be remembered by the positron study community.
3
New Precision Measurement of Hyperfine Splitting of Positronium
Authors: Akira Ishida
Abstract: Positronium is an ideal system for precision tests of bound-state quantum electrodynamics (QED). One of the most precisely tested quantities of positronium is the ground-state hyperfine splitting (HFS). Recent progress on theoretical calculation revealed that there was a 16.0 ± 3.5 ppm (4.5 σ) discrepancy between the old experimental value and the theoretical calculation. We performed a new measurement which took into account the positronium thermalization effect for the first time. The result was HFS = 203.3942 ± 0.0016 (stat., 8.0 ppm) ± 0.0013 (syst., 6.4 ppm) GHz, which was consistent with the QED calculation within 1.1 σ, whereas it disfavored the old experimental values by 2.6 σ. It also showed that the positronium thermalization effect on HFS was as large as 10 ± 2 ppm, which was consistent with the discrepancy level within 1.5 σ, which could be the reason of the discrepancy. We are planning to preform a new experiment which uses a slow positron beam and perform HFS measurement in vacuum, instead of using gas as all of the other precision measurements. It will be completely free from material effect on HFS, including the thermalization effect. In this proceeding, summary of our previous work and details of the future new experiment are discussed.
75
Asymmetric Positron Interactions with Chiral Quartz Crystals?
Authors: J. David van Horn, Fei Wu, Gerald Corsiglia, Yan Ching Jean
Abstract: We have studied the interaction of the positron with chiral left-or right-handed quartz crystals. In Doppler-broadening experiments, using a mono-energetic positron beam there is a differential depth profile for positrons implanted in LH or RH z-cut quartz as identified by a shape parameter (S). Further, in bulk positron annihilation lifetime spectroscopy (PALS) experiments, the lifetime (τ 2) attributed to free annihilation of the positron interacting with the chiral lattice exhibits a larger value for the LH quartz, and the associated intensity (I2) is also significantly different—RH quartz is consistently 10% greater than the LH crystal. The τ 3 lifetime and its intensity, I3, attributed to positronium interacting with defects in the quartz, also appears to exhibit differences between the enantiomeric sets of crystals. These observations may demonstrate chiral recognition using a positron annihilation technique, pave the way for a broad range of positron experiments, and may help inform hypotheses of chirality recognition, selection, or induction by beta radiation.
221
Positron Manipulation and Positronium Laser Excitation in AEgIS
Authors: Sebastiano Mariazzi, Ruggero Caravita, Stefano Aghion, Claude Amsler, Akitaka Ariga, Tomoko Ariga, Germano Bonomi, Philippe Bräunig, Johan Bremer, Roberto S. Brusa, Luis Cabaret, Massimo Caccia, Fabrizio Castelli, G. Cerchiari, Karl Chlouba, Simone Cialdi, Daniel Comparat, Giovanni Consolati, Andrea Demetrio, Lea di Noto, Michael Doser, Alexey Dudarev, Antonio Ereditato, Craig Evans, Rafael Ferragut, Julian Fesel, Andrea Fontana, Ola K. Forslund, Sebastian Gerber, Marco Giammarchi, Angela Gligorova, Sergei Gninenko, Francesco Guatieri, Stefan Haider, Helga Holmestad, Torkjell Huse, Ine L. Jernelv, Elena Jordan, Thomas Kaltenbacher, Alban Kellerbauer, Mitsuhiro Kimura, Torsten Koetting, Daniel Krasnicky, Vittorio Lagomarsino, Pierre Lansonneur, Patrice Lebrun, Sebastian Lehner, Joanna Liberadzka, Chloe Malbrunot, Lisa Marx, Viktor Matveev, Zeudi Mazzotta, Giancarlo Nebbia, Patrick Nedelec, Markus Oberthaler, Nicola Pacifico, Davide Pagano, Luca Penasa, Vojtech Petracek, Ciro Pistillo, Francesco Prelz, Marco Prevedelli, Luca Ravelli, Laura Resch, Benjamin Rienäcker, Ole M. Røhne, Stefan Rosenberger, Alberto Rotondi, Michele Sacerdoti, Heidi Sandaker, Romualdo Santoro, Paola Scampoli, Fiodor Sorrentino, Michal Spacek, James Storey, Izabela M. Strojek, Gemma Testera, Ingmari Tietje, Stefan Vamosi, Eberhard Widmann, Pauline Yzombard, Sandra Zavatarelli, Johann Zmeskal
Abstract: Production of antihydrogen by using the charge exchange reaction, as proposed by AEgIS (Antimatter Experiment: gravity, Interferometry, Spectroscopy), requires the formation of a dense cloud of positronium atoms excited to Rydberg states. In this work, the recent advances in AEgIS towards this result are described. Namely, the manipulation of positrons to produce bunches containing more than 108 particles and the laser excitation of positronium to Rydberg states, using n=3 as intermediate level, are presented.
11
Positron Annihilation Lifetime Spectroscopy Application to In Situ Monitoring of n-Heptane Sorption in Mesopores
Authors: Radosław Zaleski, Marek Gorgol, Agnieszka Kierys
Abstract: The dynamics of n-heptane adsorption and desorption on two silicas (Si-A and SBA-15) with different porosity was studied using positron annihilation lifetime spectroscopy (PALS). Simplified method of spectra analysis consisting in the summation of counts in the long-lived part of PALS spectra was used. It allowed to observe changes occurring in the minute time scale. The dependence of the number of counts on time could be fairly well approximated by exponential functions. It was found that the time required for reaching equilibrium in long cylindrical pores is up to ten times longer than in bell-mouthed interconnected ones. The longest time constants (ca. 5 min in Si-A and ca. 60 min in SBA-15) were observed for desorption in both samples.
288
Observation of a Low Energy Component of Positronium Emitted from Alkali-Metal Coated Polycrystalline Tungsten Surfaces
Authors: Shimpei Iida, Hiroki Terabe, Takayuki Tachibana, Ken Wada, Izumi Mochizuki, Akira Yagishita, Toshio Hyodo, Yasuyuki Nagashima
Abstract: We have studied the emission of ortho-positronium from alkali-metal coated polycrystalline tungsten surfaces. The positronium time-of-flight spectra show that the yield of the 5 eV positronium component increases by alkali-metal coating. In addition, a low energy positronium component appears by Cs or K coating. We suggest that this component is due to positron energy loss by inter-band transition or surface plasmon excitation.
309
On the Limits of Sensitivity of PALS to Incorporated Free Volume Holes in Polymeric Membranes and Sorbents: Effect of sc-CO2 in Polyhexafluoropropylene
Authors: Victor P. Shantarovich, Valentin Bekeshev, Nikolai Belov, Irina Kevdina, Mikhail Filimonov, Irina Ronova, Aleksandr Nikolaev
Abstract: Positron annihilation lifetime spectroscopy (PALS) is a recognized instrument for the studies of size-distribution of nanopores (intrinsic free volume holes FVH) in polymers, particularly membrane materials. The limits of this application in the case of “alien” pores, produced by swelling of poly (hexafluoro propylene) PHFP in the gas (CO2) in super-critical (sc-) state are discussed. The obtained conclusions are controlled by measurements of low temperature gas (N2) sorption (LTGS) and by comparison of the data with the results on permeation of various gases through the PHFP membrane. Attention is payed to relaxation with time of the newly created FVH in the PHFP membrane.
261
Enegretics of the Ps Formation: Role of the Solvated Electron
Authors: Sergey V. Stepanov, Vsevolod Byakov, Dmitry Zvezhinskiy, Gilles Duplâtre
Abstract: Taking liquid water as an example, we have considered energetics of the positronium formation. It is shown that quasi-free Ps as well as the Ps localized in a bubble cannot decay into hydrated electron and positron. The most probable value of the positron work function in water, V0+, is 1.5…2 eV. Ps formation from the hydrated electron and positron is energetically possible. By the end of thermalization major fraction of positrons escapes the blob and hydrates outside. The low-mobile е+aq has no time to diffuse back and form Ps with intrablob e-. These е+aq mostly annihilate as “free positrons”. Positrons, which are thermalized within the blob, recombine with the quasi-free intrablob electrons and form Ps.
17
Showing 1 to 10 of 173 Paper Titles