An ion source with storage capability for bunched beam release and controlled chemical separation

Abstract

A discharge ion source of the FEBIAD-type is described which allows accumulation of various elements in a cooled trap and release of the stored atoms after a preselected time in a defined bunch. This bunching effect is systematically investigated for the elements CuGe, PdSb and AuBi as a function of temperature and of the trap materials graphite, zirconium, niobium, molybdenum and tantalum. The accumulation/release characteristics and the underlying adsorption/desorption mechanism are qualitatively explained in terms of the temperature and enthalpy of adsorption; the measured sequences of the elements may, with some reservation, be used to test theoretical predictions. Utilizing the differences in accumulation efficiency and release profile for neighbouring elements, a high degree of chemical selectivity may be achieved. This feature, important for mass-separation on-line, is illustrated by a test in which neutron-deficient Sn isotopes were investigated γ-spectroscopically with substantially reduced isobaric contamination of In, Cd and Ag. Additionally, the bunching itself strongly increases the peak-to-noise ratio in collinear laser spectroscopy, permitting the study of isotopes hitherto inaccessible due to low production rates. The extension of this new method to other elements and to higher release speed is outlined.