Experimental Methods in RIB Target/Ion Source Development and Characterization Page: 4 of 21
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I. Introduction
On-line target/ion source (TIS) systems for radioactive ion beam (RIB) generation must
efficiently transport and ionize short-lived radioactive species formed by light-ion bombardment
of thick target materials with minimal delay-times. Low ionization efficiencies and/or long
delay-times which result from interactions between chemically active species and the surfaces of
the TIS will result in serious reduction in RIB intensities. We have developed off-line
experimental techniques and apparatuses that permit direct measurement of effusive-flow delay-
times and ionization efficiencies for nearly any chemically reactive element in an arbitrary high-
temperature TIS at flow-rates commensurate with on-line RIB generation. Interest in generating
RIBs of 17F and '8F for the astrophysics research program [1] at the Holifield Radioactive Ion
Beam Facility (HRIBF) [2,3] was the motivating factor for studying this species. This paper
describes the experimental apparatuses and techniques used in the measurements and provides
delay-time and ionization efficiency data for fluorine and fluoride compounds in the electron-
beam-plasma target-ion source (EBPTIS) operated in both positive and negative ion extraction
modes. The EBPTIS used in these studies is very similar to sources described previously [3].
II. Ultra-Low Flow Measurement and Control apparatus
During RIB generation, the flow rates of radioactive species are typically 108 to 1013 atoms/s,
which, for most cases, is insufficient to form a monolayer on the interior surfaces of the high-
temperature TIS. Therefore, studies must be made in a flow-rate regime comparable to that2
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Welton, R. F.; Alton, G. D.; Murray, S. N. & Cui, B. Experimental Methods in RIB Target/Ion Source Development and Characterization, article, November 1, 1997; Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc697304/m1/4/: accessed April 23, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.