A review of time-interval measurements in the sub-nanosecond regime is presented and the various methods are compared as to their precision, stability, resolution, and other essential parameters. Calibration methods, stabilization, and correction for time walk are also discussed.

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Review of Sub-Nanosecond Time-Interval Measurements

Recent developments in measuring short time intervals by time-to-amplitude converters.

The progress of research into the behavior of the positronium in molecular substances in the last several years is reviewed. The Ps atom can be treated as a solute in a liquid. The repulsive exchange force is the dominant force which reacts against the van der Waals attractive force. One of the most useful general relationships found is the one between the pick-off quenching rate and the surface tension of the liquid. The pick-off quenching rate is found, in general, to be an additive property of the functional groups of a molecule. The quenching of theo-Ps atom by an active quenching agent in an inert solvent has been found to be primarily diffusion controlled. Some deviations from the simple Arrhenius equation have been found. For gases, more theoretical work on the collision problems of Ps with atoms or molecules is needed. For amorphous molecular solids, it is likely that the property of pick-off quenching ofo-Ps is similar to that in liquids. However, in crystalline molecular solids, the situation is quite different. A few definite cases have been found where a Ps atom does not form or exist. Further work in this area should be very interesting. The foregoing leads us to believe that positronium or positron annihilation can be useful in the study of fundamental properties of molecular liquids and solids.

Positronium in molecular substances

Timing system for high resolution time spectroscopy

High resolution time-of-flight measurement with large area counters.

A transistorized time-to-amplitude converter

In order to investigate the behavior of positronium in water, magnetic quenching measurements have been performed at various temperatures from 0 to 45 °C and with applied fields up to 12.5 kG. From these measurements it has been possible to evaluate the effect of the water. In fact, while for the positronium-free atom in the ground state the hyperfine structure energy splitting is ΔW0 = 8.34 × 10−4 eV, for positronium in water we find two consistent values, ΔW = (6.32 ± 0.20) × 10−4 eV and ΔW = (7.30 ± 0.80) × 10−4 eV, obtained by considering the magnetic-field effect on the positronium component which decays by pickoff and on its decay rate.

Hyperfine energy splitting of positronium measured in water

A new method for determining the amount of magnetic quenching of the orthopositronium atom is described. This method, still using angular correlation techniques, allows a direct measure of the quantities which the orthopositronium magnetic quenching deals with. By this way, an experimental measurement has been performed, as a check, in water at temperature T = 20 °C and with a magnetic field H = 10 kG. The obtained value ΔIs = (1.73 ± 0.22)% is in very good agreement with the theoretical one.

G. Iaci

Papers

A transistorized time-to-amplitude converter

Hyperfine energy splitting of positronium measured in water

A New Experimental Method Allowing a Quantitative Measure of Orthopositronium Magnetic Quenching

Magnetic quenching of orthopositronium in ice

A fast-slow coincidence system