C. S. Galovich

Effects of backsputtered material on gallium liquid metal ion source behavior

Backsputtered material is demonstrated to be a major factor in determining gallium liquid metal ion source (LMIS) lifetimes and I‐V characteristics during operation in ultrahigh vacuum. The behavior of LMIS emission current is extremely sensitive to the type of material backsputtered onto the source tip, shaft, and reservoir. The assimilation of sputtered material is important in maintaining stable ion emission and is found to depend on the miscibility of the contaminant material in gallium. Materials which do not form solid phases when mixed with liquid gallium have the least effect on ion currents.

Polarized gas jet targets

Abstract A polarized neutral hydrogen gas jet produced by an atomic beam source has been used as a nuclear target for the first time in a crossed beam experiment. The nuclear polarization in the gas jet was measured by elastic scattering of α particles and found to be 37%, which is 74% of the maximum possible value. Polarized beams of nitrogen and fluorine have also been produced.

A new method for improving gallium liquid metal ion source stability

The influence of backsputtered molybdenum and tin on gallium liquid metal ion source emission and focused currents is examined. In a typical ion gun arrangement, extractor and aperture surfaces act as sources of contaminant material. By selecting appropriate materials for the construction of these components, the stability of focused gallium ion currents is substantially improved. Materials which form a lower melting point solution when mixed with gallium, i.e., indium and tin, yield stable source operation and longer lifetimes. The implications of the long‐term use of these materials in an ion gun are discussed, as well as the increased ability to analyze the effects of residual gases and secondary electrons on source operation.

Design and performance of an electron-positron pair detector

Abstract An electron-positron pair spectrometer with nearly 4π acceptance is described. The spectrometer can detect e + e − emission from nuclear 0 → 0 transitions and can be operated in coincidence with (backscattered) particles from a reaction exciting the pair-emitting state. The spectrometer has a cylindrical design with the target at the center. A cylinder of thin plastic scintillator divided into four segments identifies the electrons and positrons ( ΔE ) and is surrounded by a cylinder of thicker plastic scintillator also segmented into four quadrants to determine the total pair energy ( E ). The four ΔE scintillators are rotated 45° relative to the four thick E scintillators to increase the probability of identifying both members of the electron-positron pair. The efficiency of the spectrometer is determined at two different pair energies from measurements of the pair branches (100%) of the 0 2 + → 0 1 + transitions in 40 Ca and 16 O. Pair detection efficiencies of (23.6±0.3)% and (36.3±0.7)% are obtained for the 3.35 MeV, 40 Ca and 6.05 MeV, 16 O transitions, respectively.