A surprisingly large concentration of radioactive 7Be was observed inthe upper atmosphere at altitudes above 320 km on the LDEF satellite that was recovered in January 1990. We report on follow-up experiments on Russian spacecraft at altitudes of 167 to 370 km during the period of 1996 to 1999, specifically designed to measure 7Be concentrations in low earth orbit. Our data show a significant correlation between the 7Be concentration and the solar energetic proton fluence at Earth, but not with the overall solar activity. During periods of low solar proton fluence, the concentration is correlated with the galactic cosmic ray fluence. This indicates that spallation of atmospheric N by both solar energetic particles and cosmic rays is the primary source of 7Be in the ionosphere.

Vertical soil characterization and migration of radionuclides were investigated at four radioactively contaminated sites on Kirtland Air Force Base (KAFB), New Mexico to determine the vertical downward migration of radionuclides in a semi-arid environment. The surface soils (0–15cm) were intentionally contaminated with Brazilian sludge (containing 232Thorium and other radionuclides) approximately 40 years ago, in order to simulate the conditions resulting from a nuclear weapons accident. Site grading consisted of manually raking or machine disking the sludge. The majority of the radioactivity was found in the top 15cm of soil, with retention ranging from 69 to 88%. Two models, a compartment diffusion model and leach rate model, were evaluated to determine their capabilities and limitations in predicting radionuclide behavior. The migration rates of actinium were calculated with the diffusion compartment and the leach rate models for all sites, and ranged from 0.009 to 0.1cm/yr increasing with depth. The migration rates calculated with the leach rate models were similar to those using the diffusion compartment model and did not increase with depth (0.045–0.076, 0.0cm/yr). The research found that the physical and chemical properties governing transport processes of water and solutes in soil provide a valid radionuclide transport model. The evaluation also showed that the physical model has fewer limitations and may be more applicable to this environment.

The Radiation Detection Section of the Naval Research Laboratory (NRL) is sponsored by the Defense Nuclear Agency (DNA) to study the feasibility of using passive cosmic-ray induced neutron signatures as a method of treaty verification. The main thrust has been to use the neutron signature as a unique method for verification of the type of missile or other treaty limited item (TLI) inside a closed container. The detector for the experiments described consisted of nine 3He neutron proportional counter tubes that were three feet long and at a pressure of ten atmospheres. The object of the experiments was to use this neutron detector to measure the neutron signature of a semi-realistic mock-up of a generic missile. Clear variations in the neutron signal at different points over the mock-up are shown, demonstrating that measurable neutron signatures do exist

The feasibility was investigated of a solid-state neutron detector/dosemeter based on single-event upset (SEU) effects in dynamic random-access memories (DRAMs), commonly used in computer memories. Such a device, which uses a neutron converter material to produce a charged particle capable of causing an upset, would be light-weight, low-power, and could be read simply by polling the memory for bit flips. It would have significant advantages over standard solid-state neutron dosemeters which require off-line processing for track etching and analysis. Previous efforts at developing an SEU neutron detector/dosemeter have suffered from poor response, which can be greatly enhanced by selecting a modern high-density DRAM chip for SEU sensitivity and by using a thin 10B film as a converter. Past attempts to use 10B were not successful because the average alpha particle energy was insufficient to penetrate to the sensitive region of the memory. This can be overcome by removing the surface passivation layer before depositing the 10B film or by implanting 10B directly into the chip. Previous experimental data show a 10(3) increase in neutron sensitivity by chips containing borosilicate glass, which could be used in an SEU detector. The results are presented of simulations showing that the absolute efficiency of an SEU neutron dosemeter can be increased by at least a factor of 1000 over earlier designs.

A surprisingly large concentration of radioactive 7Be was observed in the upper atmosphere at altitudes above 320 km on the LDEF satellite that was recovered in January 1990. We report on follow‐up experiments on Russian spacecraft at altitudes of 167 to 370 km during the period of 1996 to 1999, specifically designed to measure 7Be concentrations in low earth orbit. Our data show a significant correlation between the 7Be concentration and the solar energetic proton fluence at Earth, but not with the overall solar activity. During periods of low solar proton fluence, the concentration is correlated with the galactic cosmic ray fluence. This indicates that spallation of atmospheric N by both solar energetic particles and cosmic rays is the primary source of 7Be in the ionosphere.

In 1990 an unexpectedly high concentration of Be-7 was discovered on the LDEF satellite surface, facing in the RAM direction. The search for an explanation of this high concentration of Be-7 which is in thermal equilibrium in the upper atmosphere, led the researchers to the hypothesis of Be-7 transport by vertical turbulent fluxes from deeper layers in the Earth's atmosphere, where Be-7 is produced as a result of nuclear reactions between solar energetic protons (which penetrated there after a solar flare) and terrestrial atmosphere elements. The experiments carried out during 1995-1999 on 'Resource F1' and 'Cosmos' satellites not only confirmed the existence of high Be-7 concentrations at altitudes of about 200 km, but also permitted to establish correlation between the concentration of Be-7 in the upper atmosphere and flare activity on the Sun. More detailed analysis of the whole set of experimental data on Be-7 measurements at satellite altitudes showed, that the appearance of high Be-7 concentrations in the upper atmosphere of the Earth is a more complicated phenomenon. Two more mechanisms , explaining the observed effect can be indicated. Firstly, the observed concentrations could be associated with direct penetration of energetic Be-7 nuclei, originating in flares, into the terrestrial atmosphere. Calculations show, that in solar cosmic rays the flux of Be-7 nuclei should be maximum in comparison to the fluxes of other Beryllium isotopes. Secondly, the high concentration of Be-7 in the upper atmosphere of the Earth could be explained by solar wind penetration through the polar zones. Theoretical analysis of active processes including flares, occurring in the solar atmosphere, leads to the conclusion, that radioactive Beryllium is constantly present in the solar atmosphere, and, possibly, is the main isotope of solar Beryllium.

A pilot program has been initiated at Kirtland AFB, New Mexico to study new methods of environmental characterization and restoration of sites contaminated with potential mixed wastes. The initial program studied four sites whose primary radioactive contaminant was thorium. Geophysical, nuclear, and chemical analyses were performed during the initial phase, with the program currently expanding to include biochemical studies. The entire program was conducted on-site to eliminate public health concerns about hazardous waste movement and to provide a more efficient and effective way to collect and process characterization samples. Chemical analyses showed no significant chemical contamination by metals, semi-volatile organic compounds, and total petroleum hydrocarbons by EPA standards and thus indicated that the soil would not have to be treated as mixed waste. Radioactivity analysis showed a 232Th activity that ranged from background levels to over 1000 pCi/g. Additionally, using dry sieving, a correlation was found between sample radiation content and soil grain size. It is planned to exploit this effect later in the program when site remediation strategies are developed.

This paper considers the problem of the origin of the pollution level in the Yenisey river estuary which is located in north-central Siberia and empties into the Kara sea. In the framework of this problem, a joint American–Russian environmental and hydrophysical expedition to the Angara and Yenisey rivers of Siberia was accomplished in the summer of 1995. Using the results of the pollution measurements taken during this expedition, it becomes possible to begin the synthesis of the spatial mathematical model for pollution transport in the Angara–Yenisey river system. The model includes blocks describing the flows of pollutants from biogeochemical, hydrophysical and anthropogenic sources. The influence of soil–plant formations are considered. The model is designed for interactive use in the mode of a computer experiment. The results of model calculations and of the expedition are given.

: This progress report covers field work and laboratory analysis efforts for quantifying the environmental threat of radioactive waste released in the Arctic seas adjacent to the former Soviet Union and for studying the various transport mechanisms by which this radioactivity could effect populations of the U.S. and other countries bordering the Arctic. We obtained water, sediment, biological samples and oceanographic data from several cruises to the Kara Sea and adjacent waters and conducted detailed laboratory analyses of the samples for radionuclides and physical biological properties. In addition, we obtained water and sediment samples and conducted on site low level radionuclide analysis on the Angara, Yenisey River system which drains a major part of the Siberian industrial heartland and empties into the Kara Sea. We report on radionuclide concentrations, on radionuclide transport and scrubbing by sediments, on adsorption by suspended particles, on transport by surface and benthic boundary layer currents, on the effects of benthic and demersal organisms, on studies of long term monitoring in the Arctic and on an interlaboratory calibration for radionuclide analysis.

A proof-of-concept experiment was performed to demonstrate the three-dimensional imaging capabilities of an all-germanium Compton camera for near-field sources. Eight high purity germanium (HPGe) coaxial detectors were configured in two planes of four detectors each. The data acquisition system was assembled from available hardware and off-the-shelf electronics using standard NIM and CAMAC modules. Sixteen-parameter data were recorded event-by-event for later analysis and image reconstruction. The energy resolution of the system was 0.3% at 1333 keV. Preliminary analysis indicates the position resolution for a source at one meter and a specific detector geometry was less than a centimeter

Cosmic ray interactions with materials result in secondary neutrons which are easily measurable. The magnitude of this neutron flux depends on geomagnetic latitude, altitude, and on the materials that constitute the local environment. In general the neutrons produced by cosmic rays in a given object depend on the atomic number, density, and total mass of the elements which constitute that object. Any massive object will have a unique “neutron signature” depending on its materials and structure. To test if this phenomenon might be used to determine if a closed canister contains a specific object, such as a missile, we conducted a proof of concept study. The study had two parts, experimental and Monte Carlo simulations. The object was to perform measurements and simulations of a “block missile mockup”. We constructed the mockup at approximately one-sixth the mass of a real missile. A clear neutron signature was observed from this mockup experimentally, and modeling predictions agreed well with the data. Predictions from our results indicate that a full sized missile should produce a very distinct signature.

We report the first complete gamma-ray survey of a large spacecraft, the Long Duration Exposure Facility (LDEF). The survey was conducted using an array of germanium detectors from the U.S. Naval Research Laboratory (NRL) and individual detectors from the Institute for Space Science and Technology (ISST) to study the accumulation and distribution of radioisotopes induced in the wide variety of materials present on LDEF. Na-22, Be-7, Mn-54, and the positron annihilation line were all strongly observed. Also observed were traces of Co-58, Co-57, and Co-60. The most striking feature of the data was the unexpected distribution of Be-7, which was predominately observed on the leading surfaces of the spacecraft. The evidence clearly indicates an accretion of the Be-7 onto the surface of the LDEF. This is the first known observation of the deposition of a radioisotope onto the surface of a spacecraft. Be-7 is a spallation product of cosmic rays on nitrogen and oxygen in the upper atmosphere[1]. To explain the surface density of 5.4 x 10(5) atoms/cm2, the light Be-7 atom must be transported up from lower altitudes.

THE Long Duration Exposure Facility (LDEF), an orbiting unmanned satellite, was recently returned to Earth after almost six years in space. From radioactivity measurements, we have found significant quantities of the isotope Be-7 on the leading edge (but only on the leading edge) of LDEF. Although the absolute atmospheric concentration of Be-7 needed to explain this detection is extremely small (10(-7) atoms cm-3), it concentration of LDEF's altitude (310 km) must be several orders of magnitude higher than in the stratosphere below, where it is produced by cosmic-ray reactions with atmospheric nitrogen and oxygen nuclei. To explain the presence of Be-7 on the surface of LDEF, it must first be rapidly and efficiently transported to high altitudes, and then adsorbed onto the surface of the spacecraft. Neither process had been expected. Our detection may therefore lead to the use of Be-7 as an exo-atmospheric tracer, as well as to studies of surface interactions in space.

The retrieval of the Long Duration Exposure Facility spacecraft in January 1990 after nearly six years in orbit offered a unique opportunity to study the long term buildup of induced radioactivity in the variety of materials on board. We conducted the first complete gamma-ray survey of a large spacecraft on LDEF shortly after its return to earth. A surprising observation was the Be-7 activity which was seen primarily on the leading edge of the satellite, implying that it was picked up by LDEF in orbit. This is the first known evidence for accretion of a radioactive isotope onto an orbiting spacecraft. Other isotopes observed during the survey, the strongest being Na-22, are all attributed to activation of spacecraft components. Be-7 is a spallation product of cosmic rays on nitrogen and oxygen in the upper atmosphere. However, the observed density is much greater than expected due to cosmic-ray production in situ. This implies transport of Be-7 from much lower altitudes up to the LDEF orbit.