The design of the main accelerator for a pulsed positron beam

Abstract The pulsed positron beam at the Helsinki University of Technology is designed for the end energy of 3-30 keVand grounded target. This is achieved with a constant voltage acceleration followed by an adjustable deceleration. In the design of this accelerator-decelerator the possibility for electrical breakdowns and partial discharges must be eliminated. For designing the electrode and insulator structures for accelerator-decelerator configuration electric field simulations were carried out with the finite element analysis program. In this paper we present the design of the accelerator-decelerator and the results of the electric field simulations. The results of high voltage tests will also be presented and compared with the simulations.

Stability and Performance Characteristics of a Digital Positron Lifetime Spectrometer

We summarize the setup and performance tests of a digital positron lifetime spectrometer presently in routine use at HUT/Laboratory of Physics. The performance of the spectrometer is found to be equal to or better than that of an analog spectrometer with similar detectors. We present also results on measuring the stability of the system, which is found to be similar to that of analog spectrometers: variation in the time-zero of the spectrometer is found to be ≈ 10 ps/week. We suggest that the remaining instabilities of the spectrometers originate primarily from the detectors

Stability and Performance Characteristics of a Digital Positron Lifetime Spectrometer

We summarize the setup and performance tests of a digital positron lifetime spectrometer presently in routine use at HUT/Laboratory of Physics. The performance of the spectrometer is found to be equal to or better than that of an analog spectrometer with similar detectors. We present also results on measuring the stability of the system, which is found to be similar to that of analog spectrometers: variation in the time-zero of the spectrometer is found to be ≈10 ps/week. We suggest that the remaining instabilities of the spectrometers originate primarily from the detectors

DENSITY PROFILES FOR ELECTRON AND POSITRONIUM BUBBLES IN HELIUM

A partir des fonctionnelles de densité nous calculons les propriétés des bulles d'électrons et de positronium dans l'hélium. Les profils de densité ont été testés par des mesures de temps de vie de positron.Density functional calculations have been performed on electron and positronium bubbles in helium. Density profiles of positronium bubbles have been tested by positron lifetime measurements