Possible C-forbidden transitions between 23S1 and 21P1 states of positronium are investigated. Limits are placed on the CP-violating state-mixing matrix element:|〈21P1|HH̷CP| 23P1〉| < 65MHz. Zeeman induced transitions yield the first observation of 21P1 states and measurement of the 23S1 to 21P1 transition frequency, v0=11181 ± 13 MHz, verifying QED calculations.

We review recent measurements of the orthopositronium decay rate, λT, and present results of a new 230‐ppm measurement using the vacuum technique. It corroborates, at the 6.2 sigma level, the discrepancy between theory and a recent 200‐ppm measurement of λT in gases.

The orbital ${\mathrm{\ensuremath{\mu}}}_{\mathit{L}}$\ensuremath{\cdot}B and diamagnetic ${\mathit{A}}^{2}$ interactions of electrons and positrons with an external magnetic field lead to a small quadratic Zeeman shift in the L=0, ${\mathit{m}}_{\mathit{S}}$=\ifmmode\pm\else\textpm\fi{}1 states of positronium, which, unlike the ${\mathit{m}}_{\mathit{S}}$=0 states, are not affected by the usual, spin-induced Zeeman shifts. For the n=1 states, this shift would be about 2 kHz in a field of 1000 G. These additional shifts are the same in all spin states for L=0 but do depend on n.

Positron re-emission microscopes (PRMs) are distinctly different from electron microscopes in the physical origin of their image contrasts. In a PRM, positrons of several keV energy are implanted into a sample and those positrons that are subsequently re-emitted at several eV are accelerated, focused and imaged. Contrast is produced by any process that affects the transport to, or re-emission from, the sample surface. After an introduction to the basic features of positron microscopy, applications of a PRM in four broad areas of research will be considered. These areas include: materials research, surface catalysis, microelectronic devices and biological systems.

A focused beam of 700-eV positrons is used to form orthopositronium (o-Ps) in evacuated, MgO-lined cavities of different sizes. The o-Ps decay rate ${\ensuremath{\lambda}}_{\mathit{T}}$ is determined to be 7.0482\ifmmode\pm\else\textpm\fi{}0.0016 \ensuremath{\mu}${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$ after extrapolation to infinite cavity size. This 230-ppm result is 4 times more accurate than previous measurements utilizing the vacuum technique. Subject to radically different systematic effects, it corroborates at the 6.2\ensuremath{\sigma} level the discrepancy between theory and a recent 200-ppm measurement of ${\ensuremath{\lambda}}_{\mathit{T}}$ in gases.

The production of antihydrogen by merging beams of antiprotons and positrons is described. Both beams, kept in storage devices, are continuously recirculated. Antihydrogen is formed by radiative recombination of positrons and antiprotons. Production rates of a few thousand per second are expected. The semi-relativistic atomic beam of antihydrogen would have a divergence of less than 1 mrad and a beam diameter of a few millimeter. The possibilities to increase these rates by induced recomtination are discussed. The scheme of antihydrogen production in overlapping beams is compared to other approaches.

The vacuum decay rate ${\ensuremath{\lambda}}_{T}$ of orthopositronium (${1}^{3}$${S}_{1}$) formed in a gas has been measured to be ${\ensuremath{\lambda}}_{\mathit{T}}$=7.0514\ifmmode\pm\else\textpm\fi{}0.0014\ensuremath{\mu}${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$. Measurements of ${\ensuremath{\lambda}}_{T}$ in four different gases, all in agreement, are averaged to obtain this result. As systematic tests, two entirely separate digital timing systems are simultaneously used throughout the experiment; the cross section for collisional quenching of the long-lived 2 $^{3}S_{1}$ excited state is determined; ${\ensuremath{\lambda}}_{T}$ is redetermined in two of the gases (${\mathrm{N}}_{2}$ and Ne) using only high-gas-density measurements; and the collisional quenching rate of water vapor, the major residual gas contaminant, is directly measured. The final value of ${\ensuremath{\lambda}}_{T}$ from this gas experiment, which represents a factor of 4 improvement in accuracy over previous measurements, is 9.4 experimental standard deviations above the theoretical value.

We propose a scheme to stack and accumulate positrons, emitted randomly from a radioactive source. The positrons are moderated and accumulated at low energy.

In this paper we briefly review all positronium (Ps) decay rate measurements (including those of the excited states and the Ps negative ion) that have been completed to date. The results are compared with theoretical values. The Ps system represents the most rigorous confrontation with theoretical decay rate calculations for any QED system.

The generation and applications of monoenergetic, high intensity, spin-polarized positron (e+) beams are reviewed. Techniques for obtaining highly polarized beams are discussed. Applications include studies of surface and bulk magnetism, studies of optically active molecules, tests of discrete symmetries, and polarized antiproton production.

A method of removing22Na from Al via distillation is investigated. Distillation is rapid (≈10 minutes) and nearly quantitative. When the distilled vapor is directed by a flow of He gas the deposit may be localized fairly well and easily recovered with water.

Journal of Electron Microscopy TechniqueVolume 9, Issue 2 p. 209-210 Rapid Communication First image from a positron reemission microscope Arthur Rich, Arthur Rich Department of Physics, The University of Michigan, Ann Arbor, MI 48109Search for more papers by this authorJames van House, James van House Department of Physics, The University of Michigan, Ann Arbor, MI 48109Search for more papers by this author Arthur Rich, Arthur Rich Department of Physics, The University of Michigan, Ann Arbor, MI 48109Search for more papers by this authorJames van House, James van House Department of Physics, The University of Michigan, Ann Arbor, MI 48109Search for more papers by this author First published: June 1988 https://doi.org/10.1002/jemt.1060090207Citations: 3AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat No abstract is available for this article. References 1 Van House, J., and Rich, A. (1988) First Results of a Positron Microscope. Phys. Rev. Lett., 60: 169–172. Citing Literature Volume9, Issue2June 1988Pages 209-210 ReferencesRelatedInformation

The production and use of low-energy (100 eV to 5 keV) high-intensity, spin-polarized positron beams is reviewed. Methods for obtaining beams with high polarization are discussed. Applications include studies of the moderation process, surface and bulk magnetism, optically active molecules, and the production of polarized anti-protons.

The formation of antihydrogen (\(\overline H\)) is of interest for a variety of reasons. Properties of the \(\overline H\) such as the electronic energy levels, fine structure, Lamb shift, and hyperfine structure can be measured and compared to the corresponding quantities in hydrogen as tests of CPT invariance. Novel investigations of the interactions of \(\overline H\) with atoms and with gravitation can be undertaken. Finally, applications such as the production of polarized antiprotons or the storage of macroscopic quantities of \(\overline H\) can also be pursued.

The ${2}^{3}$${\mathrm{S}}_{1}$\ensuremath{\rightarrow}${2}^{3}$${\mathrm{P}}_{1}$ and ${2}^{3}$${\mathrm{S}}_{1}$\ensuremath{\rightarrow}${2}^{3}$${\mathrm{P}}_{0}$ transition frequencies (${\ensuremath{\nu}}_{1}$ and ${\ensuremath{\nu}}_{0}$, respectively) in positronium have been measured for the first time and an improved measurement of the ${2}^{3}$${\mathrm{S}}_{1}$\ensuremath{\rightarrow}${2}^{3}$${\mathrm{P}}_{2}$ transition frequency (${\ensuremath{\nu}}_{2}$) has been made. The results ${\ensuremath{\nu}}_{0}$=18504.1\ifmmode\pm\else\textpm\fi{}10.0\ifmmode\pm\else\textpm\fi{}1.7 MHz, ${\ensuremath{\nu}}_{1}$=13001.3\ifmmode\pm\else\textpm\fi{}3.9\ifmmode\pm\else\textpm\fi{}0.9 MHz, and ${\ensuremath{\nu}}_{2}$=8619.6\ifmmode\pm\else\textpm\fi{}2.7\ifmmode\pm\else\textpm\fi{}0.9 MHz are in reasonable agreement with the predictions of quantum electrodynamics which are, to order ${\mathrm{\ensuremath{\alpha}}}^{3}$Ry, ${\ensuremath{\nu}}_{0}$(${\mathrm{\ensuremath{\alpha}}}^{3}$)=18496.1 MHz, ${\ensuremath{\nu}}_{1}$(${\mathrm{\ensuremath{\alpha}}}^{3}$)=13010.9 MHz, and ${\ensuremath{\nu}}_{2}$(${\mathrm{\ensuremath{\alpha}}}^{3}$)=8625.2 MHz. More precise measurements are planned to test the, as yet uncalculated, order ${\mathrm{\ensuremath{\alpha}}}^{4}$ Ry corrections.

We examine one-photon transitions in positronium (Ps) as possible tests of the discrete symmetries of C (charge-conjugation) and/or P (parity) and/or T (time-reversal) invariance. We discuss two general classes of experiment. The first class consists of direct searches for transitions forbidden by a given symmetry. The second class is composed of experiments that search for an asymmetry in the rate of an allowed transition upon reversal of an externally controllable vector quantity, such as an applied magnetic field B or rf photon spin ${\mathrm{S}}_{\ensuremath{\gamma}}$. For a given symmetry, we compare limits on symmetry-violating mixings, which can reasonably be expected from these Ps experiments, with limits placed by existing atomic experiments. We conclude from this analysis, that the most promising experiments in Ps are those that search for C violation with no P violation.