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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.

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.

The U-Pb and Sm-Nd dating of garnet are important tools for understanding rates of tectonometamorphic processes and have been widely applied in studies of metamorphic terranes. However, the budgets of uranium, lead, samarium, and neodymium in garnet separates from metamorphic rocks may be dominated by contributions from inclusions of monazite or zircon. A combined fission track and stepwise dissolution technique is proposed for evaluating the role of inclusions of monazite and zircon in the budgets of uranium, lead, samarium, and neodymium in garnets used for U-Pb and Sm-Nd chronology. Variations of Th/U, U/Nd, and Sm/Nd ratios between successive dissolution steps reveal the contributions of monazite and zircon inclusions. The stepwise dissolution procedure does not induce any apparent artifacts on 207Pb-206Pb and Sm-Nd ages. The technique has been applied to garnets from three metamorphic terranes. Almandine garnet samples from the high grade Pikwitonei Granulite Domain (Manitoba, Canada) and the Wind River Range (Wyoming, USA) have the majority of their uranium, samarium, neodymium, and radiogenic lead (Pb*) hosted by micrometer-scale inclusions of monazite. Fission track densities reveal that uranium is 108 times more abundant in inclusions than in garnets. Stepwise dissolution of the samples shows that neodymium and uranium are associated with the dissolution of monazite. In contrast, grossularandradite garnets from Cascade Slide (Adirondack Highlands, NY, USA) show little variation in fission track density and similar isotopic ratios between dissolution steps, indicating that the budgets of uranium, samarium, neodymium, and Pb* are not significantly influenced by inclusions. The demonstrated success of these techniques leads us to recommend similar procedures as a routine matter in U-Pb and Sm-Nd garnet geochronology of metasedimentary rocks.

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.

When using the nuclear track technique for multi-element detection and spatial mapping, the presence of moderate to high concentrations of boron or lithium results in a large number of (n,α) reactions when using the high thermal neutron fluences required to map trace amounts of uranium. When chemically etched, tracks generated by a large number of alpha particles cannot be spatially resolved, and are manifested instead by large-scale depressions in the detector surface. High Li and B concentration samples have the most pronounced topographic development in both CR-39 and CN detectors. Samples with low concentrations of Li and B or high concentrations of Gd, Sm or Eu developed moderate depressions. These depressions can affect uranium quantitation, but simultaneously, they provide useful information about the sample. This paper is a preliminary study of observations of etched bulk depressions, variations in track revelation time, and the mapping of samples containing elements with high thermal neutron absorption cross sections such as gadolinium.