A comparison of an HPGe planar detector and an HPGe coaxial detector, both with short length-to-diameter ratios, provides empirical evidence for the advantage of the coaxial configuration in measurements of actinide radionuclides. The principal advantage is related to the lower capacitance of a coaxial detector relative to that of a planar detector, both with large active frontal areas. In addition, the higher interaction probability (efficiency) of Ge versus Si underscores the advantages of Ge for measurements of samples with -ray energies from 5 to 200 keV (235U and241Pu). The advantages are also dependent on the presence of other higher-energy -rays collimated versus diffuse-sample geometry, and (for bioassay applications) the intervening scattering mediums of bone and tissue.
Three hundred ancient Turkish potsherds were analyzed by instrumental neutron activation analysis, and the resulting data analyzed by several techniques of multivariate statistical analysis, some only recently developed. The programs AGCLUS, MASLOC, and SIMCA were sequentially employed to characterize and group the samples by type of pottery and by site of excavation or collection. Comparison of the statistical analyses by each method provided archaeological insight into the site/type relationships of the samples and ultimately evidence relevant to commercial relations between the ancient communities and to specialization of pottery production over time. The techniques used for statistical analysis were found to be of significant potential utility in the future analysis of other archaeometric data sets.
The Californium User Facility for Neutron Science has been established at Oak Ridge National Laboratory (ORNL). The Californium
Use Facility (CUF) is a part of the larger Californium Facility, which fabricates and stores compact252Cf neutron sources for worldwide distribution. The CUF can provide a cost-effective option for research with252Cf sources. Three projects at the CUF that demonstrate the versatility of252Cf for biological and biomedical neutron-based research are described: future establishment of a252Cf-based neutron activation analysis system, ongoing work to produce miniature high-intensity, remotely afterloaded252Cf sources for tumors therapy, and a recent experiment that irradiated living human lung cancer cells impregnated with experimental
boron compounds to test their effectiveness for boron neutron capture therapy.
Among other objectives, forest inventories are aimed to identify ecological communities and to correlate community composition with environmental variables. The identification of different communities would require several forest inventories, each covering small sampling areas with relatively homogeneous environmental conditions. The multiple plot sampling method, traditionally used in local inventories of tropical forests, cannot assure such homogeneity, since even small sampling areas would show environmental heterogeneity influencing vegetation. In this paper we assessed the consequences of this heterogeneity for sampling by quantifying the variability of species abundance ranks for species sampled with 10 or more individuals in a set of plots covering a small sampling area. The species reference abundance ranks were obtained from a sample of 100 plots of 10 m × 10 m each randomly set in a sampling area of 6.5 ha in a tropical forest fragment (Southeastern Brazil). For each species we used resamplings (30 trials) to obtain the species abundance ranks in sub-samples, considering different sampling intensities (n = 25, 50 and 75 plots), and compared these ranks with the species reference rank (n = 100 plots). Then, we compared the species ranks in sub-samples of 50 plots (10.000 trials) with the reference rank and assessed the frequency and extent of rank displacements. Species rank was highly variable across resampling trials for the sampling intensities of n = 25 and n = 50, but decreased considerable with a sampling intensity of n = 75 plots. The mean rank variability and especially the maximum displacement raised significantly from the seventh most abundant species on, and some species occupied quite discrepant abundance ranks in up to 10% of the 10.000 resampling trials. This high internal variability of forest samples may impair the search for floristic patterns as scale lessens, say, to the meso-scale (1–100 km2). We discussed some possible ways to increase internal homogeneity of tropical forest samples with the multiple plot sampling method. Among these, objective entitation, based on an ancient phytosociological procedure, is suggested as the most appropriate for use on the hilly relieves of the Atlantic forest biome.
What factors influence the relationship between the academic research and the knowledge- transfer activities of academics, in particular in ‘catch-up’ countries like South Korea? To address this research question, after first conducting a critical review of existing theoretical and empirical studies, we put forward a conceptual framework based on the twin concepts of ‘synergy’ and ‘separation’ modes, together with a number of accompanying hypotheses. These hypotheses, along with others that emerged from subsequent interviews, are then tested using various statistical models. After taking into account the specific characteristics of scientific communities in rapidly catching-up counties such as Korea, we find that not only are individual characteristics (such as the gender, age, discipline, and patenting activity) of academics significantly related to the generation of a ‘synergy mode’ (i.e. a positive relationship between academic research and knowledge-transfer activities) among academics, but so too are a number of contextual characteristics (e.g. laboratory size and type of university).
Authors:R. Cielo Filho, F.R. Martins, and A. Gneri
The species abundance distribution of ecological communities has been represented through several mathematical models, of which the most common are: geometric series, logseries, lognormal, and a type of broken stick, this latter found only in animal communities. There is no consensus on the underlying biological processes, but initial observations on plant communities related these models to equilibrium and high richness (lognormal), stress or disturbance and low richness (logseries and geometric series). Recently the value of these relationships was challenged, and other descriptors were considered better predictors of richness, disturbance and stress. We aimed at investigating how these models and their parameters, as well as dominance and evenness are related with species richness, stress and disturbance in six tropical forest communities, SE Brazil: two well-conserved fragments, two disturbed by fire, and two swampy forests (anoxic stress). The models did not show consistent relationships with richness, disturbance or stress. The parameters and indices of diversity a (logseries) and l (lognormal) varied closely with richness, and the dominance was larger in the communities submitted to stress or disturbance. Our results indicate the need of further studies in order to validate (or refute) the use of abundance distribution models for detection of patterns related to richness, stress or disturbance in tropical arboreal communities. On the other hand, richness and dominance did respond to disturbance and stress.
Authors:J. Colbert, R. Martin, S. Manahan, and J. Morris
A experimental method to measure the fate and distribution of a variety of radionuclides under the ChemChar gasification process
has been developed. The elements studied were arsenic, mercury, thorium, protactinium, uranium and neptunium. Results indicate
that the ChemChar gasification system quantitatively retains these elements. In all of the cases except mercury the radiotracer
was found to reside on the char matrix with small amounts (<1%) being found downstream in the condensation trap and char filter.
Mercury, presumably as vapor, was entrained and distributed in significant amounts (≈40%) to the downstream char filter and
its pre-filter. A methodology was developed to account for char height differences in quantifying the radiotracer on the char
prior and subsequent to gasification. These results demonstrate the efficacy of using relatively short-lived radiotracers
to characterize the behavior of hazardous elements during waste treatment via gasification.
Authors:A. Murray, R. Marten, A. Johnston, and P. Martin
The analytical potential of low level, high resolution gamma-ray spectrometry for naturally occurring radionuclides at environmental levels is described, with particular emphasis on detector background levels and sensitivity. Comparisons are drawn between the performance of a specially designed low background detector system, and that of standard off the shelf devices. Sample characteristics, calibration procedures and checks, are described, and empirical minimum detection limits of between 0.4 Bq·kg–1 (226Ra,228Th) and 10 Bq·kg–1 (210Pb) are derived for soil or sediment samples of about 250 g. Representative analyses of a variety of environmental samples, including water, plant material, animal tissue and sediment, are given to illustrate the routine use of the spectrometer.