Production of negatively charged radioactive ion beams

Abstract

Beams of short-lived radioactive nuclei are needed for frontier experimental research in nuclear structure, reactions, and astrophysics. Negatively charged radioactive ion beams have unique advantages and allow for the use of a tandem accelerator for post-acceleration, which can provide the highest beam quality and continuously variable energies. Negative ion beams can be obtained with high intensity and some unique beam purification techniques based on differences in electronegativity and chemical reactivity can be used to provide beams with high purity. This article describes the production of negative radioactive ion beams at the former holifield radioactive ion beam facility at Oak Ridge National Laboratory and at the CERN ISOLDE facility with emphasis on the development of the negative ion sources employed at these two facilities.

The measurement and impact of negative oxygen ions during reactive sputter deposition

“…Essential issues are the mechanisms of the negative ion generation and destruction, the influence of negative ions on transport properties of charged species (ambipolar diffusion), the structure of the plasma sheath (Bohm velocity), and finally the chemical interactions between neutrals and negative ions [74]. These topics have been investigated in the context of the usage of electronegative gases in the technology of plasma-surface processing, and the production of negative ion beams [75]. Some of the most important topics will be discussed in this section.…”

“…Despite the wealth of information produced under these driving forces, there is still no theoretical model that can predict the secondary ion probability with sufficient accuracy [75]. Hence, a full description will probably not be possible for each oxide and/or oxygen/plasma exposed surface.…”

PUMA, antiProton unstable matter annihilation

“…This has been applied to light nuclei from helium to chlorine [242] but also the efficiency for heavier isotopes like arsenic, selenium, tin, strontium and rubidium has been investigated at HRIBF at ORNL [243]. Using this technique, a conversion efficiency of 41% for tin beams was reported [244], putting exotic tin beams onto the list of possible candidates for experiments with PUMA either using the positive or the negative mixing scheme with the p. Furthermore, a dedicated development program is ongoing at ISOLDE to increase the variety of negative ion beams [244][245][246], which established astatine and resulted in the first measurement of its electron affinity [247].…”

Focus on sources of negatively charged ions

“…To achieve the mandatory isobaric purity expected in rare and exotic radioisotopes physics experiments; negative ionization of radioactive ions proved a very successful approach. Liu et al [6] review the latest achievements of these techniques based on differences in electronegativity and chemical reactivity and applied to provide high purity beams.…”