Status and Perspectives for a Slow Positron Beam Facility at the HH—NIPNE Bucharest

Abstract

The development of a positron annihilation spectroscopy laboratory at the HH‐NIPNE Bucharest‐to be used for material studies and applications was started in the last 10 years. In the framework of a national research project extended over the last 3 years, was designed a low energy positron accelerator, as a high‐vacuum dedicated beam line with two options: a 25 mCi 22NaCl source and in line with the NIPNE‐cyclotron or a new intense compact cyclotron. The construction of the beam line was planned as a sequence of modules: source‐ moderator system; magnetical filter for fast positrons in order to select the positrons energies in the range 0.8–1 keV; a modular system for focusing, transport and acceleration of monoenergetic positrons in the energy range 0.8–50 keV and a CDBS analysis chamber. The moderator proposed—is tungsten as a foil of about 3 μm prepared at the Optoelectronics Institute were put into a thermal treatment vacuum chamber and bombarded with electrons from a 100 W electron gun After the treatment, they were tested for changes of elemental composition of the surface and structure at the Polytechnic University. The structure tests were performed on a DRON 3 M diffractometer, with a Co tube (λKα = 1.7903 A)—the angular regions studied were around 34° (1 0 0) and 69° (2 0 0). In the present time, the trajectories of the positron are going to be simulated with dedicated software (an ion and electron optics simulator). For the coincidence measurements (CDBS) set‐up we used a home‐made 22NaCl source, by separation without carrier from a metallic Mg target irradiated with 12 MeV protons and separated by columnar cation exchange. A home‐ made biparametric system for CDBS measurements will be reported, also.

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