Sr90 Concentration Research Articles

GM検出器を用いたY-90β線測定による水中のSr-90濃度の高感度・簡便測定法

Strontium-90/Y-90 are major radionuclides observed in the water samples tested recently at the site of the Fukushima Daiichi Nuclear Power Station of Tokyo Electric Power Company. A simple method of evaluating Sr-90 concentration in these water samples by measuring β rays from Y-90 with a GM-detector setup was developed. By applying the precipitation method, Sr-90 and Y-90 were separated and quantitatively collected with a filter. β rays from Y-90 in the filter were measured two times at appropriate intervals by inserting a polyethylene plate of 2 mm thickness as a β-ray absorber. The contribution of γ rays from Cs-134 and Cs-137 to the Y-90 count rates was quantitatively evaluated using a 10-mm-thick acrylic resin plate. From the parent-daughter relationship between Sr-90 and Y-90, the Sr-90 concentration was evaluated using the conversion coefficient of Y-90 count rate (cps) to Sr-90 concentration (Bq/cm3). It was verified that Sr-90 concentration of below 0.01 Bq/cm3 in water samples can be correctly measured by this simple method.

Baseline concentrations of strontium and 90Sr in seawater from the northern Gulf

Baseline concentration of strontium and Sr-90 in Gulf is presented. The strontium concentration is much higher than reported for other oceanic waters, while the Sr-90 concentration is low at 0.7–1.0mBql−1, that represents the background level following nuclear tests and can be used as an effective tracer in case of any radioactive release in the region. The strontium concentration is primarily related to the increasing salinity off the Gulf coast.

Aquatic Assessment of the Chernobyl Nuclear Accident and Its Remediation

This modeling study evaluated the aquatic environment affected by the Chernobyl nuclear accident and the effectiveness of remediation efforts. The study results indicate that radionuclide concentrations in the Pripyat and Dnieper rivers were well above the drinking water limits immediately after the Chernobyl accident but have decreased significantly in subsequent years due to flushing, burying, and decaying. Because high concentrations of Sr90 and Cs137 , the major radionuclides affecting human health through the aquatic pathways, are associated with flooding, two earthen dikes were constructed along the Pripyat River. The left-bank dike alone was successful in reducing the Sr90 concentration in the river by half. The 100-m -high, movable New Safe Confinement (NSC), which will cover the current Chernobyl Shelter, will reduce radionuclide contamination further in these rivers and nearby groundwater. If the Chernobyl Shelter should collapse before the NSC is built, the resulting peak radionuclide concentra...

An unexpected rise in strontium-90 in US deciduous teeth in the 1990s

For several decades, the United States has been without an ongoing program measuring levels of fission products in the body. Strontium-90 (Sr-90) concentrations in 2089 deciduous (baby) teeth, mostly from persons living near nuclear power reactors, reveal that average levels rose 48.5% for persons born in the late 1990s compared to those born in the late 1980s. This trend represents the first sustained increase since the early 1960s, before atmospheric weapons tests were banned. The trend was consistent for each of the five states for which at least 130 teeth are available. The highest averages were found in southeastern Pennsylvania, and the lowest in California (San Francisco and Sacramento), neither of which is near an operating nuclear reactor. In each state studied, the average Sr-90 concentration is highest in counties situated closest to nuclear reactors. It is likely that, 40 years after large-scale atmospheric atomic bomb tests ended, much of the current in-body radioactivity represents nuclear reactor emissions.

Uncertainty and sensitivity analysis of chronic exposure results with the MACCS reactor accident consequence model

Uncertainty and sensitivity analysis techniques based on Latin hypercube sampling, partial correlation analysis and stepwise regression analysis are used in an investigation with the MACCS model of the chronic exposure pathways associated with a severe accident at a nuclear power station. The primary purpose of this study is to provide guidance on the variables to be considered in future review work to reduce the uncertainty in the important variables used in the calculation of reactor accident consequences. The effects of 75 imprecisely known input variables on the following reactor accident consequences are studied: crop growing-season dose, crop long-term dose, water ingestion dose, milk growing-season dose, long-term groundshine dose, long-term inhalation dose, total food pathways dose, total ingestion pathways dose, total long-term pathways dose, total latent cancer fatalities, area-dependent cost, crop disposal cost, milk disposal cost, population-dependent cost, total economic cost, condemnation area, condemnation population, crop disposal area and milk disposal area. When the predicted variables are considered collectively, the following input variables were found to be the dominant contributors to uncertainty: dry deposition velocity, transfer of cesium from animal feed to milk, transfer of cesium from animal feed to meet, ground concentration of Cs-134 at which the disposal of milk products will be initiated, transfer of Sr-90 from soil to legumes, maximum allowable ground concentration of Sr-90 for production of crops, fraction of cesium entering surface water that is consumed in drinking water, groundshine shielding factor, scale factor defining resuspension, dose reduction associated with decontamination, and ground concentration of I-131 at which disposal of crops will be initiated due to accidents that occur during the growing season. Reducing the uncertainty in the preceding variables was found to substantially reduce the uncertainty in the predicted variables under consideration. For total number of latent cancer fatalities, the dominant variable was dry deposition velocity, with small effects indicated for a large number of additional variables.

Analysis of strontium-90 in the bones of brown trout ( Salmo trutta) from Lake Ontario

Whereas fallout from atomic weapons testing has greatly diminished, nuclear generating capacity along the shores of the Great Lakes has increased 100-fold since 1963. Radionuclides such as Sr-90, mainly from liquid effluent releases from nuclear power generating facilities, can contaminate water and biota. Lake Ontario ultimately receives the outflow from each of the other Great Lakes. In the work reported, brown trout ( Salmo trutta) were captured from Lake Ontario and their entire skeletal bone material analyzed for Sr-90. They showed an average concentration of Sr-90 approximately four times greater than control brown trout captured from nearby Cayuga Lake in Central New York State which has no nuclear generating facilities. The results are discussed considering fallout and hydrographic considerations.

Effect of high-power gamma-radiation on the90Sr distribution in the ground

This paper examines the effect of gamma-radiation on the Sr-90 distribution in argillaceous soil. For the irradiated argillaceous ground specimens, the authors investigated the ion-exchange capacity and the Sr-90 distribution coefficient concentration in the solid phase to the Sr-90 concentration in the contacting equilibrium solution. The investigation of the irradiated ground samples has shown that the ion-exchange capacity remains virtually unchanged up to a total dose of 2.3 x 10/sup 8/ rd. The effect of gamma-radiation on the Sr-90 distribution coefficient was investigated in two series of experiments.

Strontium-90 in Surface Air and the Stratosphere: Some Interpretations of the 1963–75 Data

Stratospheric inventories of Sr-90 over the period 1963–75 yield T½* = 6–7 months for the inventory difference between Northern and Southern Hemispheres, T½N = 9–10 months for the decay of the Northern Hemispheric inventory by transfer to the troposphere and Southern Hemisphere, T½T=10–11 months for the decay of the total stratospheric inventory, and T½E=1.5–3.5 years for the decay of the Northern Hemispheric inventory by transfer to the Southern Hemisphere alone. Mean monthly concentrations of Sr-90 in surface air along the 80th meridian are computed for the years 1963–75 and presented in time-latitude cross sections. The spring maximum in the Northern Hemisphere appears first at the lowest latitude (Miraflores-Balboa, 9°N) for which data are available. The reason for this appears to be seasonal precipitation scavenging associated with seasonal migrations of the equatorial trough (ITCZ). In the tropics and subtropics, where precipitation rate shows large seasonal variations, the Sr-90 concentration in surface air is related to precipitation rate in a manner qualitatively similar to that predicted by a simple theory based on precipitation scavenging and a constant source. The standard error of the data is small in both hemispheres and similar to the pattern of SF-90 concentration. The standard error is inversely related to the precipitation rate. However, longitudinal comparisons are inadequate in the Southern Hemisphere to confirm that the Sr-90 concentrations of the 80th meridian network are representative.

The Influence of Farming and Feeding Practices on Cs137 and Sr90 Concentration in Fodder, Milk and Excreta

In a district on the west coast of Norway where the annual precipitation is about 3000 mm, the content of Gs137 in cows milk, fodder and excreta from 14 different farms have been measured during the period 1963—1966. The farms have been classified according to farming and feeding practices. There is strong correlation between extensive farming and high concentration of radionuclides. The average content of Cs137 in milk samples from the most extensively worked farms is about 3.5 nGi/1, while the corresponding value for the relatively well-worked farms is 0.4 nCi/1. Similar variations are found for Sr90. The seasonal variation in the radionuclide content is large, the highest values being found during the grazing period.

Transport of radioactivity in rain and air across the trade wind inversion at Hawaii

Radiochemical analyses of aerosols and precipitation collected along the slopes of Mauna Loa volcano in Hawaii show that the concentration of radioactivity in aerosols generally increases with height across the trade wind inversion. The time variations of the vertical distribution of radioactivity concentration and moisture mixing ratio were inversely correlated; intrusions of dry air having higher concentrations of radioactivity accompanied vertical oscillations in the upper boundary of the moist surface layer. The concentration of Sr90 in rain along the slopes generally decreased with altitude above the cloud base. This decrease is attributed to the continuous depletion of condensation nuclei through rainout while remaining droplets in the air parcels continue to grow as they move upslope.

Sr90 CONCENTRATION IN DEEP- AND SHALLOW-ROOTING SPECIES AS AFFECTED BY PLACEMENT OF Sr90 AND FERTILIZER TN THE SOIL

In greenhouse experiments involving the placement of Sr90 and fertilizer in the soil, marked reductions in Sr90 concentration were found for timothy and wheat when the Sr90 was placed deep in the soil compared with the results found for shallow placement. Fertilization of the soil above the zone of Sr90 contamination led to further decreases in Sr90 concentration in timothy and wheat.Results for alfalfa differed from the results for timothy and wheat. A combination of shallow fertilization and shallow placement of Sr90 caused the highest concentration of Sr90 in plants. Deep placement of Sr90 did not reduce the Sr90 concentration in the first cutting of alfalfa, but as the plant matured, there was a reduction caused by deep placement of Sr90. Deep placement of Sr90 combined with deep placement of fertilizer caused an increase in the Sr90 concentrations in alfalfa compared with deep placement of Sr90 alone. The greatest reductions in Sr90 in the plants were found where the deep placement of Sr90 was combined with shallow placement of the fertilizer. Surface or subsurface watering of the crop did not affect the main conclusions with regard to placement of Sr90 and fertilizer.

INFLUENCE OF RATE OF Sr90 ADDED TO SOIL AT DIFFERENT PHOSPHATE LEVELS ON THE CONCENTRATION OF Sr90 IN PLANTS

In a greenhouse experiment designed to show the effects of monocalcium phosphate and rate of Sr90 added to soil on the concentration of Sr90 in oats and alfalfa, a reduction in Sr90 concentration in oats of about 50% was effected on Grenville soil by the addition of 0.546 g P per [Formula: see text] soil. It is believed that the reduction was caused partly by the effect of calcium in the fertilizer and partly by the dilution caused by a very large increase in yield from the application of the fertilizer. Similar reductions in Sr90 concentration were not found for alfalfa. A wetting and drying pretreatment of the soil caused slight decreases in Sr90 concentration in alfalfa but not in oats compared with samples which received no pretreatment, indicating that the phosphate fixed some Sr90. In one series of treatments Sr90 was added to the soils in doses ranging 1000-fold in concentration. The concentration of Sr90 in oats and alfalfa was generally proportional to applied dose, although it was found in some instances to be proportionately higher at the lowest dose added to soil.

ASSESSMENT OF THE RADIATION DOSE TO CANADIANS FROM FALLOUT

Sr89, Sr90, Cs137, and plutonium in precipitation collected at Deep River, Ontario, have been measured for the 10-year period ending December 1962. The accumulated deposit, in mc/km2, amounted to 34 mc of Sr90, 53 mc of Cs137, and 0.5 mc of plutonium. The mean concentration of Sr90 in rain (and snow) for the same period was 4.2 pc/l. Using these results, the 30-year infinite plane γ-dose from fallout deposited prior to 1963 was calculated to be 27 mrem. It is shown that this calculation applies to all of southern Canada.

THE EFFECT OF POTASSIUM FERTILIZATION ON THE Sr90 CONTENT OF CROPS

Three soils were used in greenhouse experiments to determine the effect of KCl and K2CO3 on the Sr90 concentration in oats, alfalfa, and timothy. In addition soils were moist incubated to determine the effects of similar potassium treatments on water soluble Sr90, calcium, and potassium.The general trend of results found in the greenhouse experiments was that increasing levels of added potassium caused decreases in calcium, magnesium, and Sr90 contents and increases in potassium contents of the crops. The decreases of Sr90 were frequently greater when potassium was applied as the carbonate compared with its addition as the chloride. There were some exceptions to these trends. For instance, Sr90 concentrations in oat grain increased with the addition of KCl to two of the soils. Increases in Sr90 content were also found for timothy grown in one of the soils when KCl was applied.The greater apparent effectiveness of K2CO3 in reducing Sr90 content of crops compared with the addition of the chloride is explained in part by the results of incubation experiments, where KCl caused increases in water soluble Sr90 whereas K2CO3 caused either smaller increases or decreases.

Sr90Concentration in Precipitation from Convective Showers

Analysis has been made of seven spring and summer convective showers collected at State College, Pa. The data indicate that the ground-level Sr90 concentration in the precipitation is dependent upon the extent of the vertical development of the clouds from which the precipitation originates and the distance of these clouds from the jet stream. These data are contrasted to the data obtained for precipitation resulting from large-scale uplift where the generating level is essentially constant, and the ground-level Sr90 concentration has been shown to be dependent upon the descent experience of the precipitation in failing from the cloud to the ground.

The Loss of Strontium90 from Small Cultivated Watersheds

AbstractSoil samples were taken from the plow layer of eight small watersheds and analyzed for strontium90. Two watersheds in permanent pasture, with no recorded loss soil, contained about 90 mc. per square mile, which is slightly higher than an estimated total deposit at the time of sampling.The plow layer of six watersheds under cultivation was sampled by compositing soil cores taken on contours of each watershed. The Sr90 concentration of these samples was from one‐third to two‐thirds of that in the permanent pastures.The loss of Sr90 appeared to be influenced by length of slope and cropping history. No areas of Sr90 accumulation were found within these watersheds.

Sr90Concentration in Precipitation Resulting from Large-Scale Uplift

Abstract Analysis has been made of three winter rainstorms, resulting from large-scale uplift, in which the generating level and the precipitation mechanism were essentially constant. The data show that the ground-level Sr90 concentration in the precipitation is determined by the descent experience of the precipitation in falling from the, generating cloud to the ground. The descent experience, can be expressed in terms of the height of the ceiling, which is an index of the humidity profile and depth of the lower layers of air. These parameters affect the rate of evaporation or growth of the precipitation elements and, thus, the final concentration of Sr90 reaching the ground.

THE INFLUENCE OF SOIL PROPERTIES AND SOIL AMENDMENTS ON THE SR90 CONTENT OF OATS GROWN IN SELECTED CANADIAN SOILS

Oats were grown in the greenhouse in six soils varying widely in pH, organic matter content, C.E.C., per cent saturation, and exchangeable calcium. Sr90 was added to all soils and its concentration in oats, as influenced by soil properties or soil treatment, was determined.The Sr90 content of oats grown in six soils, which included both saturated and unsaturated soils, was highly significantly correlated with the reciprocal of the exchangeable Ca contents of the soils with correlation coefficients of 0.99 for both the straw and the grain. The correlation coefficients between Sr90 concentration and the reciprocal of the C.E.C. for oat straw and oat grain were 0.65 and 0.55 respectively, which were not significant at the 5 per cent level.When calcium salts were added to three acid soils the larger applications of CaCl2 and CaSO4 lowered the soil pH, whereas CaCO3 raised the soil pH, but all three salts caused a decrease in Sr90 concentration in oats. A greater decrease in Sr90 content was effected by the addition of Ca salts to soil with low exchangeable Ca and low percentage Ca saturation than to soil with high percentage Ca saturation. It was concluded that the exchangeable Ca content, not C.E.C. or pH, was the dominant soil property upon which the Sr90 concentration in plants depended.

Fallout Sr90 in four staple U.S. foods, 1959 and 1960.

Earlier reports have noted that as a consequence of the nuclear test moratorium, the concentration of Sr90 in milk has been declining from the peak levels of mid-1959. This survey of four staple U.S, food crops indicates that the rate of decline of the Sr90 content in grain and vegetables is not as great as it is in milk. These lower levels of Sr90 in food are reflected in its reduced concentration in growing bone, specifically fetal bone.

The global distribution and stratospheric storage of debris from equatorial and high latitude nuclear explosions

The concentration of Sr90 in rain in the N. Hemisphere rises to maximum values in sub-tropical latitudes and above 60oN. There is evidence that the relative distribution varies with season. During 1959 the ratio Sr89/Sr90, and and hence the ratio of polar (high latitude) to equatorial Sr90 activity remained substantially independent of latitude. During the same period the ratio Zr95/Cs137 measured in atmospheric debris at 55oN was significantly higher in the troposphere than in the lower stratosphere. The ratio Ce144/Cs137 in tropospheric air samples (∼55oN) shows that the proportion of polar debris was ∼ 50% during 1959 until July when it fell to a lower value that was sustained during 1960. The Cs137 activities due to polar and equatorial explosions may be separated during this period by use of this ratio. The separate observations summarized above provide, in combination a set of conditions that must be satisf ed by any model of the mechanism of storage in the stratosphere and of transfer between stratosphere and troposphere. The paper was published in Nature, Vol. 192, p. 497 (1961).