Adsorbate-induced transition between different mechanisms of laser-stimulated desorption

2 were measured as a function of laser fluence, number of laser pulses, and oxygen exposure. If the laser fluence exceeds 10 mJ/cm² desorption from clean particles occurs as a thermal reaction. Oxygen exposure as low as 1 L causes a strong decrease in the number of desorbed atoms and dimers. For larger oxygen coverages desorption of Na₂O molecules is observed and, surprisingly, the atom signal recovers. At this stage, the underlying mechanism is substantially different from that for clean particles. The results can be explained by a model that takes into account the formation of a Na₂O layer around a Na core and diffusion of Na atoms through the oxide layer prior to desorption. Received: 15 December 1997/Accepted: 16 December 1997     

Experimental plant for investigation of the possibility of linac-based production of medicine-intended isotopes

We describe a technique of obtaining radioactive ^99mTc isotope by irradiation of molybdenum with high-intensity beam of bremsstrahlung photons from the electron beam of the linear electron accelerator (LUE50) of the Alikhanyan National Science Laboratory (ANSL, former Yerevan Physics Institute). We have elaborated and created an experimental plant for development of ^99mTc production technology. Upgrading of linac has been performed aimed at raising the beam intensity and density. A system of automated control of the parameters of the plant and accelerator was built up. We carried out preliminary studies of ^99mTc obtaining technique and give quantitative and qualitative results.