Zur diskriminierung isobarer kernreaktionsprodukte mit hilfe der positiven und der negativen oberflächenionisation

Abstract

The possibility of utilizing the phenomena of positive and of negative surface ionization in connection with a mass separator for a rapid discrimination or even a selective separation of isobar nuclides of certain elements is discussed and supported by experimental results. Whereas on a clean metal surface (e.g. tungsten) only alkali elements are efficiently ionized by positive surface ionization, certain other elements may also be manipulated to have high ionization-efficiency values by increasing the work function of the substrate with a regulated coverage of electronegative ad-particles (e.g. oxygen). A preselection of such elements is thus possible if under the same surface conditions isobar nuclides of the neighbouring elements have very small values of the ionization efficiency. In the case of neighbouring elements having almost equal values of the ionization energy, other surface effects can often be utilized for an identification of the nuclides: 1) the desorption of some elements in the form of oxides under special conditions of temperature and oxygen pressure, and 2) the high desorption energy of certain elements which practically do not desorb at lower temperatures. Thus, apart from the nuclides of the alkalis, those of a variety of other elements (e.g. earth alkalis and elements of the IIIb group) may be identified with the help of positive surface ionization. The negative surface ionization can be used for a selective separation of the elements of the halogen group. In this case high values of the ionization efficiency can be obtained only at low values of the work function. Preliminary results which have been obtained by a deposition of electropositive ad-layers on a tungsten surface are reported.