The influence of flood source placement on radiation exposure during quality control testing.
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OBJECTIVE: This study examined the photon energy distribution and exposure rate from a 250-MBq 57Co flood source during quality control (QC) procedures as a function of source placement and measurement location. The optimum placement of the source to reduce the radiation dose to the nuclear medicine technologist during QC checks was determined. METHODS: Measurements of exposure rate were made inside and outside a camera room with the source positioned either above or below the camera head. The energy distribution of the photon field was examined at the same locations using a high-resolution gamma-ray spectrometer. Additional measures of exposure rate were made with the source at various distances from the camera face. RESULTS: The lowest exposure rates occurred when the source was lying directly on the face of the camera head. The exposure rates at locations inside the camera room increased by a factor of 4.3 +/- 3.0 when the source was placed on an imaging table below the camera head. This increase can be attributed to decreased shielding provided by the camera head. CONCLUSION: A large portion of the radiation dose received by technologists during QC checks is due to scattered radiation and x-rays produced by gamma-ray interactions within the camera. This dose can be reduced significantly if QC checks are performed with the flood source lying directly on the inverted gamma camera head rather than placing the flood source on an imaging table under the gamma camera. (+info)
Older men and women efficiently absorb vitamin B-12 from milk and fortified bread.
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Nothing is directly known about the bioavailability of vitamin B-12 from dairy products or fortified grain products. We directly studied vitamin B-12 absorption from water, milk and fortified bread in adult subjects using (58)Co-labeled vitamin B-12 and a whole body gamma-ray counter/spectrophotometer. Sixteen healthy men and women over the age of 60 y with normal serum levels of vitamin B-12 and normal basal gastric acid secretion were studied. (58)Co vitamin B-12 (0.25 microg) was administered in water, milk or fortified bread to each subject along with 185 kBq (5.0 microCi) (51)Cr as a stool marker. Whole body counting was performed 30 min after ingestion of the radioactive dose and at 7 and 14 d after dosing. Mean absorptions from water, milk and fortified bread were 55, 65 and 55%, respectively, and did not differ. The high body retention of the extrinsic vitamin B-12 label from milk and bread may warrant a greater use of such fortified products in the elderly to ensure vitamin B-12 adequacy. (+info)
Role of bacteria in bioaccumulation of mercury in the oyster Crassostrea virginica.
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An investigation of mercury-resistant bacteria was undertaken to determine their role in the accumulation of mercury in a simplified food chain. Oysters (Crassostrea virginica) were maintained in a closed system, sealed aquarium with stirred, aerated water containing 10 mug of 203-HgCl2 per liter. Uptake of 203-Hg by oysters held under control conditions was compared with that of 203-Hg uptake by oysters under similar conditions except that mercury-accumulating and mercury-metabolizing species of Pseudomonas, isolated from Chesapeake Bay, were added to the experimental oysters. After incubation for 4 days, the major portion ofthe 203-Hg in the water column was found to be associated with the microparticulate fraction, corresponding to a rise in total viable count. Mercury accumulation in the oysters was significantly higher in the gill and visceral tissue than other tissue. Mercury concentrations were 200 times greater in tissue fractions of oysters dosed with mercury-metabolizing bacteria compared with the oysters held under control conditions without mercury-metabolizing bacteria. (+info)
Global distribution of neutrons from Mars: results from Mars odyssey.
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Global distributions of thermal, epithermal, and fast neutron fluxes have been mapped during late southern summer/northern winter using the Mars Odyssey Neutron Spectrometer. These fluxes are selectively sensitive to the vertical and lateral spatial distributions of H and CO2 in the uppermost meter of the martian surface. Poleward of +/-60 degrees latitude is terrain rich in hydrogen, probably H2O ice buried beneath tens of centimeter-thick hydrogen-poor soil. The central portion of the north polar cap is covered by a thick CO2 layer, as is the residual south polar cap. Portions of the low to middle latitudes indicate subsurface deposits of chemically and/or physically bound H2O and/or OH. (+info)
Maps of subsurface hydrogen from the high energy neutron detector, Mars Odyssey.
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After 55 days of mapping by the High Energy Neutron Detector onboard Mars Odyssey, we found deficits of high-energy neutrons in the southern highlands and northern lowlands of Mars. These deficits indicate that hydrogen is concentrated in the subsurface. Modeling suggests that water ice-rich layers that are tens of centimeters in thickness provide one possible fit to the data. (+info)
Distribution of hydrogen in the near surface of Mars: evidence for subsurface ice deposits.
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Using the Gamma-Ray Spectrometer on the Mars Odyssey, we have identified two regions near the poles that are enriched in hydrogen. The data indicate the presence of a subsurface layer enriched in hydrogen overlain by a hydrogen-poor layer. The thickness of the upper layer decreases with decreasing distance to the pole, ranging from a column density of about 150 grams per square centimeter at -42 degrees latitude to about 40 grams per square centimeter at -77 degrees. The hydrogen-rich regions correlate with regions of predicted ice stability. We suggest that the host of the hydrogen in the subsurface layer is ice, which constitutes 35 +/- 15% of the layer by weight. (+info)
Environmental radionuclides in surface soils of Vietnam.
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A database on 238U, 232Th, 40K, and 137Cs in surface soils was established to provide inputs for the assessment of the collective dose to the population of Vietnam and to support soil erosion studies using 137Cs as a tracer. A total of 292 soil samples was taken from undisturbed sites across the territory and the concentrations of radionuclides were determined by gamma spectrometry method. The multiple regression of 137Cs inventories against characteristics of sampling locations allowed us to establish the distribution of 137Cs deposition density and its relationship with latitude and annual rainfall. The 137Cs deposition density increases northward and varies from 178 Bq m(-2) to 1,920 Bq m(-2). High rainfall areas in the northern and central parts of the country have received considerable 137Cs inputs exceeding 600 Bq m-2, which is the maximum value that can be expected for Vietnam from the UNSCEAR global pattern. The mean activity concentrations of naturally occurring radionuclides 238U, 232Th, and 40K are 45, 59, and 401 Bq kg(-1), respectively, which entail an average absorbed dose rate in air of 62 nGy h(-1), which is about 7% higher than the world average. (+info)
Experimental system to displace radioisotopes from upper to deeper soil layers: chemical research.
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BACKGROUND: Radioisotopes are introduced into the environment following nuclear power plant accidents or nuclear weapons tests. The immobility of these radioactive elements in uppermost soil layers represents a problem for human health, since they can easily be incorporated in the food chain. Preventing their assimilation by plants may be a first step towards the total recovery of contaminated areas. METHODS: The possibility of displacing radionuclides from the most superficial soil layers and their subsequent stabilisation at lower levels were investigated in laboratory trials. An experimental system reproducing the environmental conditions of contaminated areas was designed in plastic columns. A radiopolluted soil sample was treated with solutions containing ions normally used in fertilisation (NO3-, NH4+, PO4--- and K+). RESULTS: Contaminated soils treated with an acid solution of ions NO3-, PO4--- and K+, undergo a reduction of radioactivity up to 35%, after a series of washes which simulate one year's rainfall. The capacity of the deepest soil layers to immobilize the radionuclides percolated from the superficial layers was also confirmed. CONCLUSION: The migration of radionuclides towards deeper soil layers, following chemical treatments, and their subsequent stabilization reduces bioavailability in the uppermost soil horizon, preventing at the same time their transfer into the water-bearing stratum. (+info)