Development of a proton microprobe and application to chemical analysis

The goal of a proton microprobe is to determine details of the structure of small samples. Our probe consists of a collimated beam of protons which impinges upon and interacts with the sample producing x-rays characteristic of the elements present. it is a very powerful tool because it permits analysis on a micro scale rather than an analysis based on average composition thus identifying the distribution of elements in a heterogeneous sample.; The proton microprobe, in which a beam of ions of a few MeV is focused or collimated to give a spot diameter of a few microns on targets, has found increasing applications worldwide. The specific advantages of a proton microprobe are its multi-elemental capability, speed, low detection limit for small samples and accuracy. To gain the benefit of these special features, I have constructed at Brooklyn College a proton microprobe system in which a beam of protons of 3.00 MeV from the Dynamitron Accelerator is reduced in diameter (1.25 cm down to 20 {dollar}mu{dollar}m) by collimation, using a home-made multiple-stage collimator. Target samples are scanned by moving the target in both X and Y directions past the microbeam, while X-rays characteristic of each element present in the sample are recorded. The experiments are performed in a helium-filled Lucite chamber of my design. The chamber can house two detectors for simultaneous X-ray and {dollar}gamma{dollar}-ray analysis. The combination of microbeam and target scanning capability of the system provides a two dimensional map of a sample.; One interesting application of a proton microprobe is in the analysis of the trace element composition of hair. There is a strong possibility that trace element content of hair correlates with the body stores (2). Measurement of longitudinal profiles of single hair strands have been performed using the proton microprobe. By scanning a single hair strand from the root to the tip, one can obtain information about metabolic changes of many elements over a long period of time, reflecting past nutritional events. The capability of the system has also been demonstrated in the analysis of other biological and zoological samples. (Abstract shortened with permission of author.)...