International Journal of PIXE

A survey has been made of PIXE programs, updating and extending a similar one published in 1981. Significant changes have occurred in the past decade, especially in the use of focussed ion beams in PIXE microprobes, milliprobes, and external beam systems. Some programs have achieved success and even dominance in one type of application, while others continue to show innovation and flexibility in many areas. The total number of active programs has increased modestly from about 95 in 1981 to 110 in 1990, with much of the increase due to new proton microprobes.

Particle-induced X-ray emission is very well suited for the analysis of geological samples. This review discusses the characteristics for such analyses. For light-element analysis, the complimentary technique of particle-induced gamma ray emission is also discussed since the emission of gamma rays occurs simultaneously with the X-rays. Not only are exploratory investigations of PIXE's capabilities presented but also synopses of studies aimed at answering geological questions. The latter have become more and more common in the last few years, an indication of PIXE's maturity as a technique for clement analysis of geological material.

Scanning PIXE analysis using a proton beam was applied to study the distribution of elements in human kidney, cerebrum and sternum (breast bone) tissues. Relative amounts of P, Cl, K, Ca, Mn, Fe, Cu, Zn, Se, Br, Rb and Cd were determined from PIXE spectra. The distribution of these elements is discussed in relation to the histological structure of each tissue.

Elemental analysis of airborne particulates collected in a site near downtown Mexico City have been performed. The samples were taken during one week of every season in 1988, Twenty three elements, from sodium to lead, were detected by Proton Induced X-ray Emission (PIXE). In addition, soot contents was determined by laser Integrating Plate Method (LIPM). Concentrations of these elements show hourly variations during the day, with maximum values in the period from 6 to 12 A.M. An overall tendency toward maximum elemental concentrations is observed in the winter season, especially for primary anthropogenic pollutants, as was anticipated based upon the frequency of thermal inversions.

As the second part of a wide project, we have carried out a study of airborne particulates in Mexico City, collected during two time periods (from 7:00 to 11:00, and from 11:00 to 15:00 Hrs.), one day of every week between March 1988 and February 1990. Elemental concentrations were determined by Proton Induced X-ray Emission (PIXE) for elements Na to Pb, while soot content was measured by means of Laser Integrating Plate Method (LIPM). As expected, the concentrations show an increase during the months October to March, due to frequent thermal inversions and dry weather. Moreover, the pollutant levels are higher during earlier hours, while the soil and anthropogenic origin of the elements can be better determined for the mid-day period, as seen from the grouping in the respective dendograms.

The size distributions of mass concentrations for 18 elements were obtained from a PIXE analysis of the atmospheric aerosol around the Great Wall Station in the Antarctic. The enrichment factors for various elements in the aerosol relative to the earth crust and sea water with a salinity of 3.5% were calculated. Comparisons were made between the coarse, fine and ultra-fine particles in the aerosol and those over the Pacific and in Beijing.

We observed the following: The atmospheric aerosol around the Great Wall Station comes mainly from marine aerosol, which is chiefly distributed at the particle size range of 0.5–8 μm and, to a lesser extent, from the local soil dust, which is distributed at particle sizes greater than 8 μm. Particles caused by human activities also come up to some proportions, and are distributed at sizes less than 0.5 μm. We conclude from analysis of size distribution spectra for aerosol mass concentrations that ultra-fine anthropogenic particles are mainly transported to the Great Wall Station from distant continents.