J. Van House

Beta decay and the origin of biological chirality: New experimental results

The proposed connection between the parity-violating handedness of beta particles in radioactive decay and the sign (L) of biological chirality (the Vester-Ulbricht [V-U] hypothesis) is being investigated by measuring the theoretically predicted asymmetry in the formation of triplet positronium in amino acid enantiomers by low energy positrons under reversal of the helicity of the positrons. We find the asymmetry in leucine to be (0.8±1.0)×10−4, i.e. consistent with the theoretical, prediction of 10−6 to 10−7. The apparatus is now sensitive enough to test the predicted asymmetry in optically active molecules which have heavy atoms at their chiral centers. The connection between these results and asymmetry in radiolysis by beta-decay electrons is made, and the implications of our limits for the V-U hypothesis discussed. Although the above limits are 106 times lower than direct measurements of radiolysis, they are still not small enough to allow us to rule out the V-U hypothesis.

Spin-polarized low-energy positron beams and their applications

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.

Antihydrogen: Production and Applications

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.

Proposed new reactor-activated positron source for intense slow e+ beam production

Abstract A novel method is suggested for producing a new positron (e+) emitting isotope in a nuclear reactor with application to slow e+ beams. The initial radiated sample is 124Xe which is transformed to 126I by two neutron absorptions and an intermediate decay. Over 25 Ci of positrons with a specific activity of 25 Ci gm can be produced by this technique, allowing the generation of a slow e+ beam of over 4 × 107 e + cm 2 −s. As discussed in the conclusion, specific activities approaching 200 Ci gm should be for activation cells are presented, one with Xe in the gas phase, the other with solid Xe. Both designs allow the easy separation of the 126I from other contaminants, permitting the production of a pure, high specific activity source.

Development of intense, long-lived positron sources

Abstract There are many important applications for very intense positron beams (≥ I Ci of e + ); however, the radioactive sources needed to produce these beams are not readily available. Two separate processes for fabricating inexpensive, intense positron sources from 22 Na and 58 Co have been investigated. Both procedures have been successfully tested with low levels (mCi) of activity.

Positron accumulation and storage for antihydrogen production

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

Limits on asymmetric orthopositronium formation in high Z optically active molecules

AbstractThe proposed connection between the parity violating handedness of beta particles in radioactive decay and the sign (L) of biological chirality (the Vester-Ulbricht [V-U] hypothesis) is experimentally tested. The theoretically predicted asymmetry in triplet positronium formation (APs) is measured in several highZ optically active molecules using low energy positrons with a net helicity. We findAPs<3×10−4 in selenocystine (Z=34) and thyroxine (Z=53), excluding part of the theoretically predicted range of 4×10−3> APs>2×10−6 in these molecules. The connection between these limits and limits on asymmetric radiolysis (AR) is made, with a new limit ofAR>10−9 being placed. This limit onAR, which is thirty times lower than a previous measurement in the amino acid leucine (Z=6), is still not small enough to rule out the V-U hypothesis.

Positron re-emission microscopy and its applications

Abstract 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.

Production and applications of monoenergetic polarized positron beams

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.

Isolation of22Na for intense positron sources

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.