Cosmogenic-nuclide production by primary cosmic-ray protons

The production rates of cosmogenic nuclides were calculated for the primary protons in the galactic and solar cosmic rays. At 1 AU, the long-term average fluxes of solar protons usually produce many more atoms of cosmogenic nuclide than the primary protons in the galactic cosmic rays (GCR). Because the particle fluxes inside meteorites and other large objects in space include many secondary neutrons, the production rates and ratios inside large objects are often very different from those by just the primary GCR protons. It is possible to determine if a small object, was small in space or broken from a meteorite. Because heliospherical modulation and other interactions change the GCR particle spectrum, the production of cosmogenic nuclides by the GCR particles outside the heliosphere will be different from that by modulated GCR primaries

Cosmic-ray exposure records and origins of meteorites

The cosmic-ray records of meteorites are used to infer much about their origins and recent histories. The methods used to interpret meteorites' cosmic-ray records, especially identifying simple or complex exposure histories, often are inadequate. Spallogenic radionuclides, stable nuclides, and measurements of products that have location-sensitive production rates, such as the tracks of heavy cosmic-ray nuclei or neutron-capture nuclides, are very useful in accurately determining a meteorite's history. Samples from different, known locations of a meteorite help in studying the cosmic-ray record. Such extensive sets of meteorite measuremetns, plus theoretical modeling of complex histories, improves the ability to predict the production of cosmogenic nuclides in meteorites, to distinguish simple and complex exposure histories, and to better determine exposure ages

Measurements of induced radioactivity in some LDEF samples

Twenty-six stainless steel trunnion samples, five aluminum end support retainer plate samples, two aluminum keel plate samples, and two titanium clips were analyzed. The shielded high purity germanium detectors used had efficiencies of 33, 54, and 80 percent at 1332 keV. Detector efficiencies as a function of energy and corrections for self-absorption in the samples were determined with calibrated sources and unactivated control samples. Several measurements were made on most samples. In the trunnion samples, Mn-54 and Co-57 were seen and limits were obtained for other isotopes. The results agree well with 1-D activation calculations for an anisotropic trapped proton model. In the aluminum and titanium samples, Na-22 was detected. Other results are presented

Workshop on Cosmogenic Nuclides

Abstracts of papers presented at the Workshop on Cosmogenic Nuclides are compiled. The major topic areas covered include: new techniques for measuring nuclides such as tandem accelerator and resonance mass spectrometry; solar modulation of cosmic rays; pre-irradiation histories of extraterrestrial materials; terrestrial studies; simulations and cross sections; nuclide production rate calculations; and meteoritic nuclides

Solar particle history: 1983 version

It has long been known that the great majority of nuclear active solar particles are emitted in a few large storms in each 11 year cycle. A single storm in August 1972 dominated the fluence of particles of energy >10 MeV. Such storms can occur, it seems, at any time within the more active half ot the cycle. On a time scale long compared to 11 years, the knowledge comes from two sources. Terrestrial C-14 sets limits on the largest proton bursts that can have taken place in the 8000 years. Lunar surface samples have yielded data on mean fluxes on a time scale from the C-14 to the Mn-53 mean life. A mean flux was found of 70 protons >10 MeV and a rigidity constant R sub o = 100 MV to be robust on the 1,000,000 to 10,000,000 year time scale. Over the shorter periods represented by C-14 and Kr-81 the fluxes seem to have been higher by a factor of roughly three. Some examples of dating are discussed

Simulation of cosmic irradiation conditions in thick target arrangements

One approach to simulate 2-pi irradiation conditions of planetary surfaces which has been widely applied in the past are bombardments of so called thick targets. A very large thick target was exposed recently to 2.1 GeV protons at the Bevatron-Bevalac in Berkeley. In a 100x100x180 cm steel-surrounded granodiorite target radioactive medium and high energy spallation products of the incident primary and of secondary particles were analyzed along the beam axis down to depths of 140 g/cm(2) in targets such as Cu, Ni, Co, Fe, T, Si, SiO2 and Al. Activities of these nuclides were exclusively determined via instrumental gamma-ray spectroscopy. Relative yields of neutron capture and spallation products induced in Co and Cu targets during the thick target bombardment are shown as a function of depth. The majority of the medium energy products such as Co-58 from Co targets exhibit a maximum at shallow depths of 40-60 g/cm(2) and then decrease exponentially. In a comparable 600 MeV proton bombarded thick target such a slight maximum for medium energy products was not observed. Rather, Co-58 activities in Co decreased steadily with the highest activity at the surface. The activities of the n-capture product Co-60 increase steadily starting at the surface. This indicates the rapidly growing flux of low energy neutrons within the target

Simulation experiments for gamma-ray mapping of planetary surfaces: Scattering of high-energy neutrons

The concentration and distribution of certain elements in surface layers of planetary objects specify constraints on models of their origin and evolution. This information can be obtained by means of remote sensing gamma-ray spectroscopy, as planned for a number of future space missions, i.e., Mars, Moon, asteroids, and comets. To investigate the gamma-rays made by interactions of neutrons with matter, thin targets of different composition were placed between a neutron-source and a high-resolution germanium spectrometer. Gamma-rays in the range of 0.1 to 8 MeV were accumulated. In one set of experiments a 14-MeV neutron generator using the T(d,n) reaction as neutron-source was placed in a small room. Scattering in surrounding walls produced a spectrum of neutron energies from 14 MeV down to thermal. This complex neutron-source induced mainly neutron-capture lines and only a few scattering lines. As a result of the set-up, there was a considerable background of discrete lines from surrounding materials. A similar situation exists under planetary exploration conditions: gamma-rays are induced in the planetary surface as well as in the spacecraft. To investigate the contribution of neutrons with higher energies, an experiment for the measurement of prompt gamma radiation was set up at the end of a beam-line of an isochronous cyclotron

Analysis of Drawdown for Three Ground Water Projects in Roberts County, Texas and Comparison to the 50-Percent Goal

Three water production projects have been proposed in and adjacent to Roberts County, Texas, and are in various stages of planning, permitting, construction, and implementation. The projects are referred to as the Amarillo, Mesa, and Canadian River Municipal Water Authority (CRMWA) projects. The total pumping from the Ogallala aquifer in these projects is anticipated to be more than 280,000 acre-feet/year. Additional permit applications for groundwater development in the Roberts County area are expected. This study was performed at the request of the Panhandle Groundwater Conservation District to evaluate whether these projects, at an average pumping rate of 1 acre-foot/acre per year or at some lower average pumping rate, might meet District aquifer management goals. These projects were evaluated in various combinations. Three scenarios treated each project by itself. Three more scenarios combined the three projects in pairs. A seventh scenario analyzed all three as simultaneous projects. An eighth scenario evaluated hypothetical production from the entire Roberts County area. The scenarios were evaluated using a groundwater flow model of the Ogallala aquifer developed for the Panhandle Regional Water Planning Group.Bureau of Economic Geolog

Evaluation of Electromagnetic Induction as a Noninvasive Technique for Monitoring Water Movement into and Beneath Waste Disposal Facilities

The purpose of this study was to evaluate the use of electromagnetic induction to noninvasively monitor water content in waste disposal facility cover soils. We compared apparent electrical conductivity measurements monitored with the EM38 ground conductivity meter with water content monitored with a neutron probe at 20 locations over an 18-month period from August 1998 to January 2000. Two cover designs were monitored: a gel/asphalt barrier at 1.3 m depth and a capillary barrier at 2.0 m depth. The EM38 instrument was operated in both the vertical and horizontal dipole modes with the instrument resting on the ground surface and all data were normalized to 25°C. Linear regression techniques were applied to analyze the survey data. Water content to a depth of 0.75 m was correlated with horizontal dipole mode data and water content to depths of 1.1 m and 1.5 m was correlated with vertical dipole mode data. Initially higher water content values decreased by an average of 0.10 m^3/m^3 in the top 0.75 m and an average of 0.07 m^3/m^3 in the top 1.5 m over the course of the study. The regression model of the EM38 vertical dipole mode data with water content to the 1.5 m depth for all locations monitored on the capillary barrier design resulted in a standard deviation of 0.016 m^3/m^3. Horizontal dipole mode data correlated with water content to the 0.75 m depth had a standard deviation of 0.022 m^3/m^3 for all locations on both barrier designs. Models at individual survey locations generally exhibited much smaller standard deviations, ranging from 0.005 to 0.018 m^3/m^3 and averaging 0.010 m^3/m^3. The smaller standard deviations and general similarity of regression slope values of the models at individual locations indicate that this technique is more accurate as an indicator of changes in water content than as an indicator of the absolute value of water content at a given location. Sources of variability were attributed to horizontal and vertical variation in soil salinity, the vertical distribution of water at the time of a particular survey, and subtle differences in topsoil thickness and surface roughness. Results indicate that electromagnetic induction is useful for evaluating infiltration. The EM technique resulted in standard deviation values for water content similar to those of the neutron probe method but is capable of monitoring larger areas much more rapidly and at a lower cost.Bureau of Economic Geolog

Critical performativity in the field: Methodological principles for activist ethnographers

© The Author(s) 2017. It has been proposed that engagement with activism might make critical organizational scholarship more relevant to practitioners. However, there is a lack of systematic inquiry into how such engagement might be undertaken, which this article redresses. We propose activist ethnography as a suitable methodological framework for critical organizational scholarship, drawing on organizational ethnography, militant ethnography, and participatory action research, to construct a theoretical framework which we use to analyze four ethnographic vignettes of our own experiences of research with activists. Our contribution is to (a), assess the methodological challenges and opportunities of engagement with activism, (b) give an account of our own experiences as activist ethnographers for others to learn from, and (c) propose strategies whereby the challenges of academic activism might be negotiated and the opportunities maximized