We report a new measurement of the positronium (Ps) 2^{3}S_{1}→2^{3}P_{0} interval. Slow Ps atoms, optically excited to radiatively metastable 2^{3}S_{1} level, flew through microwave radiation field tuned drive transition short-lived 2^{3}P_{0} which was detected via time spectrum subsequent ground state annihilation radiation. After accounting for Zeeman shifts we obtain frequency ν_{0}=18501.02±0.61 MHz, is not in agreement with theoretical value ν_{0}=18498.25±0.08 MHz.

We report the results of a new measurement positronium 2 ^{3}S_{1}→2 ^{3}P_{2} (ν_{2}) interval. Using modified experimental arrangement we have significantly reduced effects microwave reflections, which in previous experiments resulted shifts and asymmetric line shapes. With improved apparatus obtain an value ν_{2}=8627.94±0.95 MHz, is within 1.3σ theoretical 8626.71±0.08 MHz.

We report new measurements of the positronium (Ps) $2^{3}S_{1}\ensuremath{\rightarrow}2^{3}P_{J}$ fine-structure intervals, ${\ensuremath{\nu}}_{J}$ ($J=0,1,2$). In experiments, Ps atoms, optically excited to radiatively metastable $2^{3}S_{1}$ level, flew through microwave radiation fields tuned drive transitions short-lived $2^{3}P_{J}$ levels, which were detected via time spectrum subsequent ground-state annihilation radiation. Both ${\ensuremath{\nu}}_{1}$ and ${\ensuremath{\nu}}_{2}$...

We present a range of cross section measurements for the low-energy scattering positrons from pyridine, incident positron energies less than 20 eV, as well independent atom model with screening corrected additivity rule including interference effects calculation, dipole rotational excitations accounted using Born approximation. Comparisons are made between experimental and theoretical calculations. For positronium formation section, we also compare results recent empirical model. In general,...

We report measurements of the positronium (Ps) $2^{3}S_{1}\ensuremath{\rightarrow}2^{3}P_{2}$ interval in which atoms traveling free space were irradiated with microwave radiation generated using a horn antenna. Previous this transition, performed waveguides, exhibited asymmetric and shifted line shapes. In free-space we here, much smaller line-shape asymmetry was observed, but large frequency shifts that varied orientation Our observations are supported by simulations demonstrate variations...

The direct single-ionization cross section for Ar by positron impact has been measured in the region above first ionization threshold. These measurements are compared to semiclassical calculations which give rise a power law variation of threshold region. experimental results appear be disagreement with extensions Wannier theory applied ionization, smaller exponent than that calculated most previous works. In fact, this work, we see no difference behavior between and electron cases. Possible...

Absolute measurements of elastic differential cross sections for positron scattering from argon at energies 2--50 eV are presented as well total and inelastic 2--20 eV. Comparisons the current data, previous experimental theoretical models using convergent close-coupling relativistic optical potential methods made.

Abstract We report experiments in which positronium (Ps) atoms were created a thick layer of MgO smoke powder deposited on thin silicon nitride substrate. The experimental arrangement was such that positron beam could be implanted directly into the top or transmitted through substrate, allowing Ps to produced within ≈100 nm 30 μ m powder-vacuum interface. transverse kinetic energy emitted vacuum measured via Doppler broadening 1 3 S <?CDATA ${}_{1}\,\to {2}^{3}$?> <mml:math...

Experimental determinations of the absolute differential positronium-formation cross sections near ${0}^{\ensuremath{\circ}}$ for Ne, Ar, Kr, and Xe are presented compared with theory. The degree forward collimation, expressed by ratios differential-to-integral sections, is also computed theories other targets. Trends among targets structures at low energies emerge when considered as a function reduced total energy.

Abstract We describe an experimental arrangement suitable for performing microwave spectroscopy measurements of the positronium (Ps) $$n=2$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>n</mml:mi> <mml:mo>=</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:math> fine structure using Ramsey interferometry. Simulations are presented concerning production energetic $$2\,^3S_1$$ <mml:msup> <mml:mspace /> <mml:mn>3</mml:mn> </mml:msup> <mml:msub> <mml:mi>S</mml:mi>...

We describe the experimental production of a beam 23S1 positronium (Ps) atoms obtained from charge-exchange collisions between positron and Xe held in gas cell. The angular divergence emitted Ps was recorded using two position sensitive detectors located at different distances fraction produced level measured via change count rate after driving → 23P2 transition with microwave radiation; optimal parameters, we estimate that up to 10% is formed state. properties were used evaluate feasibility...

We report numerical simulations of positronium experiments designed to measure the $n=2$ fine-structure intervals. The include all possible interference effects between 20 states in $n=1$ and laser-excited manifolds as well representations electric magnetic fields present waveguides used experiments. find that rf wave reflection from vacuum chamber walls is a explanation previously observed line-shape distortions shifts. also characterized several systematic effects, including those arising...

Abstract We report measurements of low energy positron scattering from neon, with the first absolute differential cross sections (DCSs) and state-selective electronic excitation. These are compared to calculations using relativistic optical potential (ROP) technique, as well other recently published theoretical calculations. At lowest energies, experimental DCS data fitted extract phase shifts, which can be values also used generate over full angular range. For most part we find good accord...

We report a measurement of the annihilation decay rate positronium (Ps) atoms, . Ground state atoms optically excited to radiatively metastable states were quenched via Stark mixing by application time-delayed electric field. Rapid radiative mixed ground state, followed self-annihilation, was observed radiation time spectrum, and used determine number remaining at different times, hence rate. obtain , in broad agreement with Zeeman-shifted theoretical value

Abstract We report experiments in which radiatively metastable $2\,^{3}\mathrm {S}_{1}$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mn>2</mml:mn> <mml:msup> <mml:mrow> <mml:mspace/> </mml:mrow> <mml:mn>3</mml:mn> </mml:msup> <mml:msub> <mml:mi>S</mml:mi> <mml:mn>1</mml:mn> </mml:msub> </mml:math> positronium (Ps) atoms entered a waveguide whose internal surfaces were lined with smoked magnesium oxide (MgO) powder. The was built such that time-delayed microwave radiation...

Abstract Experimental determinations of the detection efficiency for positrons impacting a channel electron multiplier with incident energies between 0–1400 eV are presented. A log-normal dependence energy is established and used to compute positron-to-positronium ratio as function positronium energy, required determining quantities involving positron rates. energy-dependence also observed in results previous work electrons, protons ions.

Abstract This paper presents measurements of low energy electron scattering from pyridine. The positron beamline at the Australian National University was used for these measurements, with a change in operational parameters allowing measurement processes. We have collected data total cross section scattering, as well differential sections electrons up to 3 eV impact energy. operation will be briefly outlined and are compared R -matrix Schwinger multichannel theoretical calculations, previous...

Synopsis Data will be presented for positron scattering from neon. As a “simple” target, neon provides useful target the testing and exploration of our fundamental understanding processes. The low-energy, high-resolution beamline based at Australian National Universitywas used to measure elastic differential cross sections total electronic ionization low energy positrons experimental data compared several recent theoretical calculations.