[en] When subjected to radiation overload existing geiger-mueller counters may give an erroneously low reading, resulting in possible hazard to personnel. The instant invention discloses simple and inexpensive apparatus to remedy this dangerous shortcoming. Depending on the geometry of the detector tube, two possible failure modes have been identified, and circuitry is disclosed to detect the existence of these respective failure modes. The disclosed apparatus indicates the absence of an overload condition, in addition to signaling, by both visible and audible means, the existence of excessive radiation that might result in erroneously low reading of the geiger-mueller counter

[en] A new method for detecting the positronium minus ion is described, and the possibility of a long positronium mean free path in a solid is discussed

[en] This chapter investigates the subject of intense positron beams. Some new areas of study that might become available with advanced beam technology are reviewed and the terminology is examined. The best radioactive source and moderator available are described. Some details are given on an existing time bunching apparatus and a method of beam bunching is presented. Topics considered include intensity, flux, brightness, phase space density, fluidity, Debye screening, and space charge limitation. Single positron sources are examined

[en] The present status of slow positron beams for surface studies is reviewed briefly and examples given of new experiments which should be possible soon with the introduction of a new generation of positron beams with high flux and brightness. (author)

[en] Since the pioneering work of Cherry the subject of slow positrons has been intimately connected with surfaces. The relatively high yield slow positron source of Canter et al. permitted subsequent studies in ultra-high vacuum which have given some understanding of how positrons interact with surfaces. This knowledge has enabled better slow positron moderators yielding higher beam strengths for experimentation on surfaces and solids and for studying positronium and positron-molecule scattering at low energies to be made. The present knowledge of positron and positronium work functions, the positron surface state, positron stopping and positron diffusion are reviewed. The paper concludes with a brief speculation about the experimental possibilities offered by future slow positron beams of high flux and brightness. (0uth.)

[en] With a view to finding analogies with slow muons, the physics of slow positrons at surfaces is outlined. Some possibilities for moderators that might make slow muons, thermal muonium, and the μ⁺ μ^- atom (muium) are explored. (author)

[en] This chapter reports details of the first experiment to excite optically Ps from the n=1 triplet ground state to the 2³S₁ state. Discusses the positronium source, the light source, and the experiment. Points out that an improved laser source and better laser metrology should enable a measurement with a precision comparable to or better than the hydrogen 1S-2S measurements. Improvements include a flat Fabry-Perot interferometer inside the ultra high vacuum chamber that will filter the laser output to create a nearby Fourier transform limited pulse, and precision laser metrology techniques using well known iodine and tellurium reference lines

[en] The formation of positronium by low-energy positrons incident on 'clean' metal surfaces is thermally activated by increasing temperature. The activation energy Esub(a) has been measured for a number of surfaces. Esub(a) is understood as the energy required to form positronium (binding energy 1/2Ry) from positrons bound at the surface by an energy Esub(b). Esub(a)=Esub(b)+phi-sub(-)-1/2Ry, where phi-sub(-) is the electron work function. Representative values of Esub(b) derived are Al(100): 3.03(5) eV; Al(110): 2.92(4) eV; Cu(111): 2.80(5) eV. (author)

[en] Recently it has been pointed out that annihilation terms in the effective 4x4 Hamiltonian H for n=1 positronium cause the real parts of the Zeeman eigenvalues to be shifted by terms of order lambdasub(s)/4πδν)₂ approximately 10^-₅ relative to the Breit-Rabi eigenvalues, where lambdasub(s) is the annihilation rate of the singlet state and δν is the hyperfine interval. The observation that the δν measurements might not have dealt correctly with decay has prompted the author to recalculate the Zeeman resonance lineshape. He finds that the 1975 Brandeis measurement of δν should be increased by 2.5 ppm to δν(Brandeis)=203.3875(16) GHz, and the 1975 Yale measurement should be increased by 21 ppm to δν(Yale)=203.3890(12) GHz. The weighted mean of the two corrected measurements is δν=203.3885(10) G0z. (Auth.)

[en] The capability of studying the interactions of positrons with surfaces has recently been exploited by using ultra-high-vacuum techniques. The result has been a new understanding of how positrons interact with surfaces and because of this we are now able to make much stronger fluxes of slow positrons. The higher beam strengths in turn are opening up new possibilities for experimentation on surfaces and solids and for studying the atomic physics of positronium and positron-molecule scattering at low energies. The lectures are intended to review some of the history of this subject and to outline the present state of our knowledge of experimentation with low-energy positron beams. (orig./TW)