Upgrade of the UML 5.5-MV Van de Graaff ion microprobe*

Ion microprobes are used to deliver a highly focused charged-particle beam with a diameter of a few microns to a sample. Applications include elemental imaging, probing microelectronics, material analysis, and cellular radiotherapy on the micron scale, for example. The upgraded UML Van de Graaff microprobe is planned to be used for detector characterization, as the small beam spot allows for precise mapping of the spatial response of position-sensitive detectors. The microbeam line was upgraded with a new modular vacuum chamber, with customizable ports, from IdealVac systems to improve sample manipulation and facilitate additional spectroscopy capabilities. This upgrade also allows for multiple detectors to be mounted concurrently within the chamber. The system is composed of a set of two four-jaw slits (object and emittance) that collimate the beam. An XY scanning magnet controlled by a function generator rasters the beam which is transported through a quadrupole doublet magnet that focuses the beam at the sample location in the chamber. To characterize the system a 3-MeV proton beam was used to probe a resolution test target. Two detectors were utilized; a Si charged-particle detector at backward angles to measure elastically scattered protons and a HPGe detector to measure characteristic X-rays from gold, glass, and chromium on the target. The data were analyzed to produce an image of the features on the target. An overview of the upgraded system and the results of the test runs will be presented.