Evan T. Williams

PIXE analysis with external beams: Systems and applications

Abstract A survey of PIXE analytical systems and microprobe systems where the beam is extracted from the accelerator vacuum is presented. The merits of external-beam analysis are discussed and examples of experiments with these systems are given.

Quantitative analysis by proton-induced X-ray emission utilizing an inexpensive external-beam system

Abstract We describe a sensitive and convenient system for PIXE analysis in which an external beam impinges on samples in a helium-filled target chamber. Samples are presented to the beam by an ordinary slide projector, slightly modified, which can accommodate 80 slides. The numerous advantages of the system are enumerated. The sensitivity and range of detectable elements are the same as for PIXE systems employing the more usual vacuum chamber; absorption of low-energy X-rays in the helium is insignificant compared to absorption in the beryllium window of standard Si(Li) detectors.

Street level versus rooftop sampling: Carbon monoxide and aerosol in New York city

Abstract Aerosol samples were simultaneously collected with three cascade impactors for 2-h periods; two of the impactors were located at street level and the third was located on the 16th floor, all on the same city block in Manhattan. Carbon monoxide was also measured at all three sites. Particle-size distributions of the respective elements were similar, in contrast with the concentrations, which were not. The concentrations at street level, e.g. lead and CO, decreased with height as expected. On the other hand, the concentrations of particulate sulfur did not diminish with height. The results obtained from the two cascade impactors and CO monitors located around the corner from each other at street level show significantly different pollutant concentrations, thereby indicating the difficulty in obtaining representative samples at street level.

Application of particle-induced X-ray emission to research in biology and medicine.

The analytical technique of particle-induced X-ray emission (PIXE) is described, and recent applications to problems in biomedical research are surveyed.

Analysis of pottery by PIXE: Late classical and hellenistic imports to gordion

Abstract In a feasibility study, PIXE analysis was performed in an attempt to classify samples obtained at Gordion, an archaeological site in Turkey. On the basis of the work performed so far, it appears that PIXE analysis is capable of discriminating between imported and local ware and also of establishing subgroupings among certain types of pottery specimens.

PIXE studies using a target chamber with helium atmosphere

Abstract The use of a helium atmosphere in the target chamber has advantages which will be discussed. The sensitivity of the system and some recent results will be discussed.

Sulfur in aerosol versus wind direction in New York City and a nearby rural site

Abstract Analysis of aerosol samples collected simultaneously in New York City and in a rural area in New Jersey showed that concentrations of sulfur were similar at both locations. Summer measurements in New York City, five months later, showed that sulfur in aerosol was as much as ten times greater when the wind blew from the southwest quarter compared to other wind directions. We infer from these results that the bulk of particulate sulfur in New York City is transport from the west.

PIXE: A tool for research and education

Abstract The advantages of PIXE as an analytical tool are well known but the suitability of the method as an excellent educational tool for the training of students in research may not be as widely appreciated. This paper will demonstrate the latter attribute by describing research projects involving undergraduate students. The projects include PIXE analysis of: blood serum, annual-growth rings in trees, rainwater, and carbon water filters.

A small inexpensive scattering chamber constructed from commercially available components

A 6-way Dependex(tm) multicross with four 6-in. and two 4-in. ports serves as the basis for a “home-built” scattering chamber. A target assembly ladder, mounted vertically, can accommodate up to five targets. These can be aligned at angles ranging from 0 to 75° with respect to the incident beam. Both particles and photons can be measured with the appropriate solid state detectors. Special attention has been focused on the problems of accurate and reproducible charge collection. The chamber is suitable for PIXE, PIGE, RBS, atomic and nuclear cross-section determinations.

PIXE Analysis of Aerosol in the Workplace

Sampling programs of relatively limited extent can be useful for monitoring suspended particulate matter in specific locations; for example certain occupational situations. Aerosol samples were collected by cascade impactors and analyzed by PIXE at the Brooklyn College Dynamitron Laboratory. We describe the results of experiments in a metal-sculpture studio involving silver soldering, an industrial plastics-milling shop and a municipal incinerator.