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Background radiation and radioactive sources have been measured with laser-scanned phosphor imaging plates using an image processing method that produces spectra. This enables distinction between ambient background radiation, alpha and beta radionuclides and provides a means for quantitation. The background counts span a broad spectral continuum, whereas counts resulting from alpha and beta activity are restricted to certain regions within the background continuum spectrum. The alpha-counting spectral region has a background count rate of −2 h −1 . The beta-counting region has a count rate of −2 h −1 . One region of the background spectrum is attributed to heavy ions from cosmic rays and has a count rate of −2 day −1 . With regard to imaging spectrometry, beta-particles from 3 H ( E max =0.0186 MeV) could be distinguished from higher energy beta-particles such as those from 14 C ( E max =0.157 MeV) and 40 K ( E max =1.33 MeV). Beta-particles can be distinguished from alpha-particles, and radionuclide counts can be distinguished from the background. The spectral characterization of the background, alpha-particles and beta-particles is expected to support applications in cosmic ray, heavy ion, radionuclide and electron studies.

Phosphor imaging plate technology has made it possible to directly image the distribution of primary beam electrons and scattered electrons in the environmental scanning electron microscope. The phosphor plate is exposed under electron scattering conditions in the microscope chamber. When processed, the electron intensity distribution is displayed as a digital image. The image is a visual representation of the electron probe and skirt and may provide the basis for a more accurate model.

Recent advances in instrumentation provide the capability to measure size, count rate, type of radiation, and the chemical composition of radioactive particles. We present a demonstration of these capabilities, using a laser-scanned phosphor imaging system and a charge injection device system for digital autoradiography, light and electron microscopy, energy dispersive X-ray spectrometry, and conventional radionuclide spectrometry. Response characteristics of the phosphor system that support these efforts are presented.

The need to locate “hot particles” during environmental radioactivity characterization benefits from autoradiography. Three detectors are compared for the evaluation of point-source alpha emitters. 238 PuO 2 particles were used to compare a detector based on a pixel array, a phosphor imaging plate system, and a track-etch detector. The pixel-array detector is based on a charge injection device (CID) having nominally 14 μm sized pixels in a 7 mm × 9 mm array. Processing at a 30 frames per second rate allows real-time display of results. Background interference is minimal even in long-duration exposures. The phosphor imaging plate system is subject to background accumulation. Track overlap makes single-event discrimination and quantification impractical, but a large exposure area and ease of use are distinct advantages. A system having a pixel size of 50 μm was used. Track-etch detectors have the largest potential exposure area and best spatial resolution, the latter being limited by the amount of material etched, resolving power of the reading system, and the number of tracks recorded per source. Readout, however, can be time-consuming, and track overlap can make quantification difficult. The best apatial resolution, 10 μm, was obtained with the track-etch detector, with a precision in location of 1 μm. The phosphor plate system was capable of detecting 0.002 Bq sources in 2 d, whereas the track-etch and semiconductor pixel array were capable of detecting 0.0002 Bq sources in 2 d. The track-etch method was the most difficult, whereas the most rapid results were obtained with the real-time display of the semiconductor pixel array.

A focusing neutron lens using glass polycapillary fibers has been introduced successfully into a prompt gamma activation analysis (PGAA) instrument placed at the exit of a cold neutron guide. The neutron current density gain of the lens is 80, averaged over the focused beam size of 0.53 mm diameter. PGAA measurements have been made on submillimeter particles of gadolinium and cadmium. The results indicate that elemental sensitivities of measurements are increased by ∼ 60, and that particles of sizes smaller than 0.5 mm can be discerned using the focusing lens. The measured gain in prompt gamma signals for these particles is less than anticipated, probably due to alignment difficulties. Gamma ray background associated with the lens is discussed and improvements are suggested.

This work provides examples of some of the imaging capabilities of environmental scanning electron microscopy applied to easily charged samples relevant to particle analysis. Environmental SEM (also referred to as high pressure or low vacuum SEM) can address uncoated samples that are known to be difficult to image. Most of these specimens are difficult to image by conventional SEM even when coated with a conductive layer. Another area where environmental SEM is particularly applicable is for specimens not compatible with high vacuum, such as volatile specimens. Samples from which images were obtained that otherwise may not have been possible by conventional methods included fly ash particles on an oiled plastic membrane impactor substrate, a one micrometer diameter fiber mounted on the end of a wire, uranium oxide particles embedded in oil-bearing cellulose nitrate, teflon and polycarbonate filter materials with collected air particulate matter, polystryene latex spheres on cellulosic filter paper, polystyrene latex spheres “loosely” sitting on a glass slide, and subsurface tracks in an etched nuclear track-etch detector. Surface charging problems experienced in high vacuum SEMs are virtually eliminated in the low vacuum SEM, extending imaging capabilities to samples previously difficult to use or incompatible with conventional methods. © 1993 Wiley-Liss, Inc.