Fast positronium formation and dissociation at surfaces

The origin of short‐lived components in the annihilation lifetime spectrum of positronium (Ps) is shown to be due to fast Ps that is collisionally dissociating at the surfaces of the surrounding confinement cavity. The results are consistent with a model of fast (10–100 eV) Ps production by backscattered positrons from the incident beam. It is found that the typical lifetime of dissociating Ps scales with the mean free path of the cavity, and the relative formation intensity depends inversely on the incident positron beam energy. This ubiquitous effect will be present in any Ps formation experiment involving a free surface and can only be eliminated at beam energies less than 10 eV. More practical methods of minimizing the undesirable systematic effects of fast Ps quenching in depth‐profiled positron lifetime spectroscopy and in precision Ps decay rate measurements will be discussed. © 1995 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70565/2/JAPIAU-78-3-1406-1.pd

Measurement of the vacuum decay rate of orthopositronium formed in an MgO-lined cavity

Orthopositronium decay rates are measured in MgO-lined cavities with various volumes and entrance apertures. Systematic effects of the entrance aperture, cavity geometry, and collisional pick-off are measured. The vacuum decay rate is determined to be 7.050 +/- 0.013 [mu]s-1.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22484/1/0000025.pd

The decay rate of orthopositronium

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.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87568/2/481_1.pd

A viable superluminal hypothesis: Tachyon emission from orthopositronium

Tachyons are hypothetical particles that travel faster than the vacuum speed of light. Previous experiments have searched for, but have not found evidence of tachyons. Long-standing, anomalous measurements of the orthopositronium (o-Ps) decay rate are interpreted as evidence for two tachyons being occasionally emitted when o-Ps decays. Restricting the coupling of tachyon pairs to a single photon (no tachyon coupling to matter) yields a new theory where tachyons are only observed in o-Ps decay and not in the previous tachyon experiments. Combining the single photon coupling theory with all previous experiments predicts that these tachyons must deposit energy while traversing scintillator detectors. A new tachyon search experiment will use this energy loss prediction to attempt to find tachyons passing through the apparatus or set limits disproving the original o-Ps to tachyon hypothesis. Viewing an intense o-Ps source, a time-of-flight spectrometer uses the superluminal property of tachyons for identification. Several months of continuous data acquisition will be necessary to completely eliminate the o-Ps to tachyon hypothesis. © 2000 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87640/2/1119_1.pd

The Promise of Prediction Markets

Prediction markets are markets for contracts that yield payments based on the outcome of an uncertain future event, such as a presidential election. Using these markets as forecasting tools could substantially improve decision making in the private and public sectors. We argue that U.S. regulators should lower barriers to the creation and design of prediction markets by creating a safe harbor for certain types of small stakes markets. We believe our proposed change has the potential to stimulate innovation in the design and use of prediction markets throughout the economy, and in the process to provide information that will benefit the private sector and government alike.Technology and Industry

Studies of the formation of slow positrons in MgO‐coated moderators

Studies have been made of the production of slow (∼1 eV) positrons by high‐energy positrons from a radioactive source. Moderators consisting of thin metallic foils coated with MgO smoke were used in the transmission mode. The thinnest foils gave the largest fluxes of slow positrons. A double moderator, consisting of a MgO‐coated grid following the MgO‐coated thin foil, gave a flux almost double that of either the foil or grid alone. The positron beam machine used is described. It has electrostatic optics for the collection, analysis, and transmission of the slow positrons.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70074/2/JAPIAU-51-2-856-1.pd

Performance of a spiralled continuous electron multiplier in a magnetic field

The gain and detection efficiency of a spiralled electron multiplier (Spiraltron) have been measured in a magnetic field. Results are presented as a function of field strength and angle between the field and detector. The multiplier is useful in fields as high as 900 G, considerably higher than the limit that has been obtained on a Channeltron curved electron multiplier.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69554/2/RSINAK-48-12-1601-1.pd

Beta-decay And The Origins Of Biological Chirality - Experimental Results

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62544/1/297639a0.pd