Activity Ratios Range Research Articles

Study on the behavior of radionuclides in geologic samples from fault zone, Gabal Um Hamd, southwestern Sinai, Egypt

The present study concerned with the activity concentrations of natural radionuclides (238U, 234U, 230Th, 226Ra, 232Th, 40K and, 235U) in ten sedimentary rock samples collected from fault zone, Gabal Um Hamd, southwestern Sinai, Egypt. These samples were investigated to study their behavior during a part of geologic time. The activity concentrations were measured using γ-ray spectrometry (HPGe detector). The investigated samples were analyzed for major oxides using the XRF technique. The results demonstrated high average activity concentrations of 238U, 234U, 230Th, 226Ra, 232Th, 40K and, 235U than the worldwide average values as reported by UNSCEAR 2008. Theil diagram showed that there are accumulation and leaching of uranium in some samples in the two sides of the fault zone. It is noticed that the ages of uranium depositions for the samples collected from the downthrown of the fault zone vary from 121.5 to 440.1 ky, while for the sample collected from the upthrown of the fault is 210.9 ky. The 230Th/232Th activity ratios range between 4.55 and 91.04 for downthrown samples and between 4.75 and 6.05 for upthrown samples which are smaller than 20 except for two samples, indicating a contamination of the samples by detrital 230Th. After subtraction of the detrital 230Th, the corrected ages for downthrown samples vary from 119.1 to 231.7 ky while for upthrown samples vary from 164.4 to 390 ky.

Simultaneous determination of gross alpha/beta activities in water by liquid scintillation counting and its applications in the environmental monitoring

Based on the standards of ISO11704-2018 and ASTM D7283-17, a method for simultaneous determination of gross alpha and gross beta activity concentrations in water by liquid scintillation counting (LSC) was established, which can be applied to various types of water samples in routine monitoring, such as drinking water, groundwater, geothermal water, seawater, and radioactive wastewater. The sample’s pH value and concentrated volume must be controlled to avoid quenching as much as possible. The validation tests show that the deviations of gross alpha and gross beta activities can satisfy quality control requirements in a wide range of activity ratios from 1:102 to 67:1. For the actual samples, the measurement results of the LSC method are in good agreement with those of the thick source method, in which the relative deviations of gross alpha and gross beta are both less than 15% for these two methods. Moreover, the LSC method performs better in detection limit and has a simpler pretreatment process than the thick source method.

Image reconstruction using small-voxel size improves small lesion detection for positron emission tomography.

BackgroundPET/CT imaging is widely used in oncology and provides both metabolic and anatomic information. Because of the relatively poor spatial resolution of PET, the detection of small lesions is limited. The low spatial resolution introduces the partial-volume effect (PVE) which negatively affects images both qualitatively and quantitatively. The aim of the study was to investigate the effect of small-voxel (2 mm in-line pixel size) vs. standard-voxel (4 mm in-line pixel size) reconstruction on lesion detection and image quality in a range of activity ratios.Materials and methodsThe National Electrical Manufacturers Association (NEMA) body phantom and the Micro Hollow-Sphere phantom spheres were filled with a solution of [18F]fluorodeoxyglucose ([18F]FDG) in sphere-to-background ratios of 2:1, 3:1, 4:1 and 8:1. In all images reconstructed with 2 mm and 4 mm in-line pixel size the visual lesion delineation, contrast recovery coefficient (CRC) and contrast-to-noise ratio (CNR) were evaluated.ResultsFor smaller (≤ 13 mm) phantom spheres, significantly higher CRC and CNR using small-voxel reconstructions were found, also improving visual lesion delineation. CRC did not differ significantly for larger (≥ 17 mm) spheres using 2 mm and 4 mm in-line pixel size, but CNR was significantly lower; however, lower CNR did not affect visual lesion delineation.ConclusionsSmall-voxel reconstruction consistently improves precise small lesion delineation, lesion contrast and image quality.

Recent uranium mobilization of late neoproterozoic El Sela sheared granites, South Eastern Desert, Egypt

The sheared granite of El Sela represents one of the most promising uranium mineralization in the southern part of the eastern desert, in Egypt. The present work concerned in detailed with El Sela shear zone through ENE-WSW and NNW-SSE trends as a perfect way for ascending hydrothermal solutions and meteoric water that led to leaching of uranium from its bearing minerals and redeposit them in the altered granites. Activities of radionuclides were identified for 238U, 235U, 234U, 230Th, 232Th, 226Ra, 214Bi, 214Pb, 210Pb, and 40K in the studied samples by hyper-pure germanium detector. Furthermore, activity ratios 234U/238U, 230Th/238U, 230Th/234U, 226Ra/238U, 226Ra/230Th, 238U/235U, and 234U/235U were calculated. Additionally, the 238U/235U activity ratios range were evaluated from 20.99 to 22.4 with an average of 21.69 indicating a slight deviation from the natural ratio (21.7). The 234U/235U activity ratios range recorded from 4.866 to 121.39 with a reported average of 63.13 uranium migration (out / in). Finally, the age of uranium mobilization in the studied samples was calculated from 18.83 to 43.25 kyr. suggested a recent uranium mineralization.

Tracing changes in mantle and crustal influences in individual cone-building stages at Mt. Shasta using U–Th and Sr isotopes

230Th-excess is rare in most arc lavas, but common in the Cascades, yet the origin of such excesses remains unclear. At Mt. Shasta, age-corrected (230Th/232Th) and (238U/232Th) activity ratios range from 1.108 to 1.290 and from 0.987 to 1.309 (27.3% 230Th-excess to 6.1% 238U-excess), respectively. Although small degrees of zircon crystallization (<0.3%) may yield high (230Th/238U)0 in derivative magmas, high Zr contents, the lack of zircon as a liquidus phase, and low Th/U ratios in Mt. Shasta lavas argue against zircon fractionation. Instead, melting models suggest 230Th-excesses are imparted on lavas through mixing mantle-derived magmas with partial melts of a mafic amphibolite lower crust where garnet was produced in the residuum through amphibole and plagioclase destabilization. The hot nature of Cascade magmas suggests that high intrusion temperatures promoted dehydration melting in the deep crust.At Mt. Shasta, the destruction of the ancestral cone (Sand Flat) was followed by four cone-building stages, three of which lie in the age range of U-series geochronology. Lavas within individual eruptive stages have relatively constant (230Th/232Th)0 ratios that are interpreted to reflect specific mixtures of mantle (m) and lower crustal (lc) melts that are characteristic of a specific stage (Mm:lc). High (230Th/232Th)0 ratios identify higher proportions of lower crust in the Misery Hill stage (Mm:lc=∼85:15), whereas low (230Th/232Th)0 ratios reflect the more mantle-like composition of the Shastina lavas (Mm:lc=∼95:5); in the case of Shastina lavas, very low 87Sr/86Sr ratios, down to 0.7029, support a substantial mantle contribution. Changes in (230Th/232Th)0 ratios correlate with eruptive volume, where the most voluminous stage (Misery Hill) is inferred to have the largest proportion of crustal melt and highest (230Th/232Th)0 ratios. Variable (230Th/238U)0 ratios within, and between, eruptive groups likely reflect a combination of residence time in the lower crust and differential assimilation of bulk, non-garnet-bearing crust that had (230Th/238U) = 1. The volume-(230Th/232Th)0 relations are accompanied by correlations with 87Sr/86Sr ratios, where the most radiogenic Sr is associated with the largest eruptive volumes, indicating that the largest magmatic episodes produced the largest amount of lower crustal interaction.The new U–Th and Sr isotope measurements of this study, along with U-series data for other Cascade centers suggest that interaction with the lower crust exerts greater control on Cascade magma chemistry than previously recognized. Indeed, the relatively dry nature of the Cascades may offer a unique opportunity to better understand the influence of the deep crust in young continental arcs, as larger subduction components in other settings may overprint any lower crustal signature and produce lavas with large 238U-excesses.

Timescales of degassing and conduit dynamics inferred from 210 Pb– 226 Ra disequilibria in Volcán de Colima 1998–2010 andesitic magmas

Abstract Determining the timescales of magma degassing is essential for understanding the mechanisms controlling the eruption style and the dynamics of magmatic systems. Towards this end, we measured 210 Pb– 226 Ra disequilibria in andesite lavas erupted from Volcán de Colima between 1998 and 2010. ( 210 Pb/ 226 Ra) 0 activity ratios range from 0.86 to 1.09, and are best explained in terms of 222 Rn degassing and accumulation. The range in 210 Pb deficits indicates that the timescales of 222 Rn degassing did not exceed 11 years. 210 Pb excesses are rare and small (&lt;10%), which signifies that 222 Rn degassing is more effective than 210 Pb accumulation in this intermediate system despite the relatively low gas output at the surface. The absence of significant 210 Pb excesses strongly suggests that the volcanic activity results from episodic ascent of small magma batches through the vapour-saturated section of the magmatic system. Overall, the degassing models based on 210 Pb– 226 Ra disequilibrium suggest an open and complex subvolcanic magmatic system comprising several conduits in which multiple magma batches reside for up to 10 years. Shifts from effusive to explosive Vulcanian eruptive phases are not related to changes in degassing mode on timescales resolvable using 210 Pb– 226 Ra disequilibria.

Evaluation of New Geological Reference Materials for Uranium-Series Measurements: Chinese Geological Standard Glasses (CGSG) and Macusanite Obsidian

Recent advances in high-resolution, rapid, in situ microanalytical techniques present numerous opportunities for the analytical community, provided accurately characterized reference materials are available. Here, we present multicollector thermal ionization mass spectrometry (MC-TIMS) and multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) uranium and thorium concentration and isotopic data obtained by isotope dilution for a suite of newly available Chinese Geological Standard Glasses (CGSG) designed for microanalysis. These glasses exhibit a range of compositions including basalt, syenite, andesite, and a soil. Uranium concentrations for these glasses range from ∼2 to 14 μg g(-1), Th/U weight ratios range from ∼4 to 6, (234)U/(238)U activity ratios range from 0.93 to 1.02, and (230)Th/(238)U activity ratios range from 0.98 to 1.12. Uranium and thorium concentration and isotopic data are also presented for a rhyolitic obsidian from Macusani, SE Peru (macusanite). This glass can also be used as a rhyolitic reference material, has a very low Th/U weight ratio (around 0.077), and is approximately in (238)U-(234)U-(230)Th secular equilibrium. The U-Th concentration data agree with but are significantly more precise than those previously measured. U-Th concentration and isotopic data agree within estimated errors for the two measurement techniques, providing validation of the two methods. The large (238)U-(234)U-(230)Th disequilibria for some of the glasses, along with the wide range in their chemical compositions and Th/U ratios should provide useful reference points for the U-series analytical community.

Distinguishing lower and upper crustal processes in magmas erupted during the buildup to the 7.7 ka climactic eruption of Mount Mazama, Crater Lake, Oregon, using 238U–230Th disequilibria

Uranium-series isotope ratios determined for 35 volcanic rocks and 4 glass separates erupted from ~36 to 4.8 ka at Mt. Mazama, Crater Lake, Oregon, identify both 230Th-excess and 238U-excess components. U–Th isotope compositions cover a wide range, exceeding those previously measured for the Cascade arc. Age-corrected (230Th/232Th) and (238U/232Th) activity ratios range from 1.113 to 1.464 and from 0.878 to 1.572 (44.4 % 230Th-excess to 8.8 % 238U-excess), respectively. The most distinctive aspect of the data set is the contrast in U–Th isotope ratios between low and high Sr (LSr, HSr) components that have been previously identified in products of the 7.7 ka caldera-forming climactic eruption and preclimactic rhyodacite lavas. The LSr component exclusively contains 238U-excess, but the HSr component, as well as more primitive lavas, are marked by 230Th-excess. 230Th-excesses such as those recorded at Mt. Mazama are commonly observed in the Cascades. Melting models suggest that high 230Th-excesses observed in the more primitive lavas evolved through mixing of a mantle melt with a partial melt of a mafic lower crustal composition that contained garnet in the residuum that was produced through dehydration melting of amphibolite that was initially garnet free. Dehydration melting in the lower crust offers a solution to the “hot-slab paradox” of the Cascades, where low volatile contents are predicted due to high slab temperatures, yet higher water contents than expected have been documented in erupted lavas. The 238U-excess observed at Mt. Mazama is rare in Cascade lavas, but occurs in more than half of the samples analyzed in this study. Traditionally, 238U-excess in arc magmas is interpreted to reflect slab fluid fluxing. Indeed, 238U-excess in arcs is common and likely masks 230Th-excess resulting from lower crustal interaction. Isotopic and trace element data, however, suggest a relatively minor role for slab fluid fluxing in the Cascades. We propose that 238U-excess reflects melting and assimilation of young, hydrothermally altered upper crust. The processes related to generating 238U-excess are likely important features at Mt. Mazama that accompanied development of a large-scale silicic magma chamber that led to the caldera-forming eruption.

Regolith production rates calculated with uranium-series isotopes at Susquehanna/Shale Hills Critical Zone Observatory

In the Critical Zone where rocks and life interact, bedrock equilibrates to Earth surface conditions, transforming to regolith. The factors that control the rates and mechanisms of formation of regolith, defined here as material that can be augered, are still not fully understood. To quantify regolith formation rates on shale lithology, we measured uranium-series (U-series) isotopes ( 238U, 234U, and 230Th) in three weathering profiles along a planar hillslope at the Susquehanna/Shale Hills Observatory (SSHO) in central Pennsylvania. All regolith samples show significant U-series disequilibrium: ( 234U/ 238U) and ( 230Th/ 238U) activity ratios range from 0.934 to 1.072 and from 0.903 to 1.096, respectively. These values display depth trends that are consistent with fractionation of U-series isotopes during chemical weathering and element transport, i.e., the relative mobility decreases in the order 234U > 238U > 230Th. The activity ratios observed in the regolith samples are explained by i) loss of U-series isotopes during water–rock interactions and ii) re-deposition of U-series isotopes downslope. Loss of U and Th initiates in the meter-thick zone of “bedrock” that cannot be augered but that nonetheless consists of up to 40% clay/silt/sand inferred to have lost K, Mg, Al, and Fe. Apparent equivalent regolith production rates calculated with these isotopes for these profiles decrease exponentially from 45 m/Myr to 17 m/Myr, with increasing regolith thickness from the ridge top to the valley floor. With increasing distance from the ridge top toward the valley, apparent equivalent regolith residence times increase from 7 kyr to 40 kyr. Given that the SSHO experienced peri-glacial climate ∼ 15 kyr ago and has a catchment-wide averaged erosion rate of ∼ 15 m/Myr as inferred from cosmogenic 10Be, we conclude that the hillslope retains regolith formed before the peri-glacial period and is not at geomorphologic steady state. Both chemical weathering reactions of clay minerals and translocation of fine particles/colloids are shown to contribute to mass loss of U and Th from the regolith, consistent with major element data at SSHO. This research documents a case study where U-series isotopes are used to constrain the time scales of chemical weathering and regolith production rates. Regolith production rates at the SSHO should be useful as a reference value for future work at other weathering localities.

Uranium-Series Constraints on Radionuclide Transport and Groundwater Flow at the Nopal I Uranium Deposit, Sierra Peña Blanca, Mexico

Uranium-series data for groundwater samples from the Nopal I uranium ore deposit were obtained to place constraints on radionuclide transport and hydrologic processes for a nuclear waste repository located in fractured, unsaturated volcanic tuff. Decreasing uranium concentrations for wells drilled in 2003 are consistent with a simple physical mixing model that indicates that groundwater velocities are low ( approximately 10 m/y). Uranium isotopic constraints, well productivities, and radon systematics also suggest limited groundwater mixing and slow flow in the saturated zone. Uranium isotopic systematics for seepage water collected in the mine adit show a spatial dependence which is consistent with longer water-rock interaction times and higher uranium dissolution inputs at the front adit where the deposit is located. Uranium-series disequilibria measurements for mostly unsaturated zone samples indicate that (230)Th/(238)U activity ratios range from 0.005 to 0.48 and (226)Ra/(238)U activity ratios range from 0.006 to 113. (239)Pu/(238)U mass ratios for the saturated zone are <2 x 10(-14), and Pu mobility in the saturated zone is >1000 times lower than the U mobility. Saturated zone mobility decreases in the order (238)U approximately (226)Ra > (230)Th approximately (239)Pu. Radium and thorium appear to have higher mobility in the unsaturated zone based on U-series data from fractures and seepage water near the deposit.

Determination of 234U/238U ratio: comparison of multi-collector ICPMS and ICP-QMS for water, hair and nails samples, and comparison with alpha-spectrometry for water samples

The (234)U/(238)U ratio in water, hair and nails samples was determined by multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) and inductively coupled plasma quadrupole mass spectrometry (ICP-QMS) and by alpha-spectrometry for the water samples only. A correlation of 0.99 was found between the two ICPMS methods and of 0.98 with alpha-spectrometry. The range of activity ratios was between 0.9 and 2.6 according to the MC-ICPMS measurements. The reproducibility of both ICPMS techniques was better than 4% for water samples containing 1 mug l(-1) of uranium and a (234)U/(238)U atom ratio of 54.9 x 10(-6). Sample preparation for the ICPMS consisted of dilution of water samples containing >10 microg l(-1) of uranium and measurement time was approximately 1 min, while alpha-spectrometry involved pre-concentration and separation of the uranium and counting times of 1,000 min.

U–Th–Pa–Ra systematics for the Grande Comore volcanics: melting processes in an upwelling plume

High precision TIMS Pa-U disequilibrium data have been obtained on a series of recent samples from the Karthala and La Grille volcanoes, Grande Comore. We use this data together with U–Th–Ra and Sr isotope, major and trace element data to constrain melting-induced fractionation of the U series nuclides. ( 231Pa/ 235U) activity ratios range between 1.7 and 1.9 for the historical Karthala volcanics and are around 2.0 for two recent La Grille samples. While the Karthala magmas could have been generated in the upwelling asthenosphere, the La Grille lavas are thought to involve some lithospheric melting. The Karthala data is best explained by a model of slowly upwelling mantle during 230Th and 231Pa grow in from their parent nuclides. Pb isotope data is consistent with a recent fractionation of 230Th/ 232Th induced by a slow melting process in the source of the Karthala. The upwelling velocity of the mantle plume is constrained to be a few cm per year. The La Grille data can be explained by interaction of the Karthala melts with the lithosphere. The degree of melting of the lithosphere still needs to be small to preserve the U-series fractionation. The higher 231Pa/ 235U in the La Grille lavas probably reflects a higher cpx/garnet mode than for the Karthala.

Concentration of global fallout 99Tc in rice paddy soils collected in Japan

Analysis of global fallout 99Tc in environmental samples should provide useful information for predicting the nuclide behaviour under natural conditions which is important from the viewpoint of radioecology. Concentrations of 99Tc in rice paddy soils collected in Japan have been studied. After chemical separation, 99Tc in the final solution was measured by ICP-MS. The activity ratio of 99 Tc 137 Cs was used to understand the 99Tc behaviour in the environment because the fission yields of 99Tc and 137Cs from 235U or 239Pu are almost the same. The theoretical activity ratio from fission which is calculated now is about 3.0×10 −4. Our results showed that the range of activity ratios of 99 Tc 137 Cs in the soil samples was (2.0−5.2)×10 −3; these ratios were one order of magnitude higher than the theoretical one. 99Tc has been accumulating in rice paddy soil like 137Cs has, although their mechanisms might differ. One of the reasons for the high ratio in the surface soil might be the ratios in the atmospheric samples, which have increased from the order of 10 −3 to 10 −2 (García-León et al., 1993).

Ridge-hotspot interaction along the Mid-Atlantic Ridge between 37°30′ and 40°30′N: the U [sbnd]Th disequilibrium evidence

This study reports U Th disequilibrium data obtained by mass spectrometry for basaltic glasses collected along the Azores platform portion of the Mid-Atlantic Ridge (37°30′–40°30′N), a region characterized by both a geochemical and bathymetric gradient. High Th and U concentrations, as well as Th/U ratios, document an enriched geochemical signature. ( 230Th 238U ) activity ratios range from 1.20 to 1.35 and are thus systematically larger than most EPR MORBs reported in the literature. ( 230Th 232Th ) activity ratios show remarkable homogeneity for multiple samples taken from single dredge hauls. Additionally, samples with the highest Th concentrations (2.4 ppm) have among the highest Th isotope ratios. Taken together, these observations rule out assimilation of 230Th-rich sediment as an explanation for the 230Th 238U systematics. The relatively large 230Th excesses in the erupted lavas may be related to the influence of the enriched Azores mantle plume source. The lack of observed correlations between 230Th excess and trace element and isotopic indices of source enrichment, however, rules out source composition as an explanation for the variations in ( 230Th 238U ). Excess 230Th is correlated with the axial depth of the ridge in the study area, with the shallowest portions showing the largest extents of disequilibrium. This may reflect more melting in the presence of garnet for the shallow segments, and suggests that melting begins well within the garnet peridotite stability field (∼ 35 kbar) in the mantle beneath the Azores segment of the MAR. At the ridge segment scale, 230Th excesses tend to be smaller near segment boundaries. This could reflect differences in the melting process or less frequent magmatism in these zones. These results demonstrate the potential for U Th systematics to constrain the depth and degree of melting as well as the rate of mantle upwelling, even in the presence of source chemical heterogeneity.

Potassium potential and potential buffering capacity of torripsamments in the United Arab emirates

Abstract Eighteen surface soil samples from five locations were collected to represent the Torripsamments in the United Arab Emirates. The quantity‐intensity (Q/I) relationships were determined for the soils. They were linear over the range of activity ratios commonly encountered in the studied soils. The soil solution potassium (K) activity relative to the calcium (Ca) + magnesium (Mg) at equilibrium (ARKe) ranged between 0.0034 and 0.0396 (M/L)0.5. The readily exchangeable K (Kre) values ranged between 0.009 and 0.069 cmolc/kg which represented an average of 23% of the exchangeable K. A negative relation was found between K‐feldspars and Kre values (r = ‐ 0.573∗∗), indicating that K‐feldspars contributed little to available K in the studied soils. The soils showed low capacity to maintain the potential of K against depletion, as they showed very low potential buffering capacity #OPPBCK#CP [1.21–5.68 (cmoLc/kg)/(M/L)0.5].

Radium-thorium disequilibrium and zeolite-water ion exchange in a Yellowstone hydrothermal environment

Whole rock samples of hydrothermally altered Biscuit Basin rhyolite from Yellowstone drill cores Y-7 and Y-8 were analyzed for 226Ra and 230Th to determine the extent of radioactive disequilibrium and its relation to the rates and mechanisms of element transport in the shallow portion of an active hydrothermal system. The ( 226 Ra 230 Th ) activity ratios range from 0.73 to 1.46 and are generally correlated with Th-normalized Ba concentrations (Ba N). Values of ( 226 Ra 230 Th ) and Ba N > 1 were found in samples containing large modal fractions of clinoptilolite; whereas values of ( 226 Ra 230 Th ) and Ba N < 1 were found in samples containing large modal fractions of mordenite. Composition clinoptilolite and mordenite in these samples are consistent with ion exchange equilibrium between zeolites and coexisting thermal waters. Average K d mineral-water Ba values are 1.0·10 5 mL/g for clinoptilolite and 1.4·10 4 mL/g for mordenite. Apparent diffustvities through matrix porosity estimated for Ra and Ba range from ∼10 −12 to ∼10 −10 cm 2s −1 in thoroughly zeolitic rhyolite; these rates of diffusion are too low to account for the observed distance scale of ( 226 Ra 230 Th ) disequilibrium. The correlated values of ( 226Ra 230 Th ) disequilibrium and Ba N represent zeolite-water ion exchange equilibrium that is caused by porous flow of water through the rock matrix and by the relatively rapid diffusion of cations within the zeolite lattices. A water flux of at least ∼2.5 ( cm water 3 cm rock 3 ) yr −1 is required to produce measurable ( 226 Ra 230 Th ) disequilibrium, whereas at least ∼23 ( cm water 3 cm rock 3 ) yr −1 is r for the sample exhibiting the most extreme ( 226 Ra 230 Th ) disequilibrium; these fluxes are much higher than those that can be inferred from net mass transfers of stable species. The zeolite-water ion exchange process appears to have been operating for at least 8000 yr in the environment of the Y-7 and Y-8 drill holes.

Uranium and thorium isotopic disequilibrium in Venezuelan hot springs.

Deviations from the natural isotopic composition of the 234U/238U and 228Th/232Th activity ratios have been determined for nine different hot spring water samples from Venezuela. The 234U/238U activity ratios range from 1.13 ± 0.07Ci/Ci to 9.94 ± 2.53 Ci/Ci in the samples Quebrada la Colonia and Aguas Calientes Ure=a, respectively. The 228Th/232Th activity ratios range from 3.20 ± 0.25 Ci/Ci to 21.60 ± 1.81 Ci/Ci in the Quebrada la Colonia and Las Trincheras hot spring samples. A linear relationship was found between 228Th/232Th activity ratio and the amount of dissolved SiO2 in mg/l which follows the relationship 228Th/232Th=0.2397 SiO2 + 0.5402. The wide deviations in the activity ratios measured were attributed to mechanisms of differential solubility of the intermediate short lived daughters in the decay chain of uranium and thorium (234Th, 234Pa, 229Ra, 228Ac) and to the effect of recoil of the decaying nuclei during alpha and beta emissions.

Evaluation of the selectivity of alpha-adrenoreceptor blocking drugs for postsynaptic alpha 1- and alpha 2-adrenoreceptors in a simple animal model.

1 The increase of diastolic pressure of pithed, normotensive rats was determined after i.v. administration of the alpha-adrenoreceptor agonists L-phenylephrine and B-HT 933. 2 alpha-Adrenoreceptor antagonists varied widely in their relative inhibitory effects towards either L-phenylephrine- or B-HT 933-induced vasoconstrictor responses. Prazosin displayed the highest affinity for the postsynaptic alpha-adrenoreceptor triggered by L-phenylephrine. The rank order of potency was further: phenotlamine greater than dihydroergotamine greater than clozapine greater than corynanthine greater than azapetine greater than yohimbine greater than piperoxan greater than tolazoline greater than mainserin greater than rauwolscine. On the other hand, the rank order of potency towards B-HT 933 was: dihydroergotamine greater than rauwolscine greater than yohimbine greater than phentolamine greater than piperoxan greater than prazosin greater than tolazoline greater than mainserin greater than corynanthine greater than azapetine greater than clozapine. These data are in general agreement with the classification of alpha 1-(triggered by L-phenylephrine) and alpha 2-(triggered by B-HT 933) adrenoreceptors. Both populations are present postsynaptically in vascular smooth muscle of the pithed rat and are involved in vasoconstriction. 3 The ratio of KB post alpha 2/KB post alpha 1 was calculated as a measure of selectivity for either alpha-adrenoreceptor site. The alpha-adrenoreceptor antagonists used cover a 20,000-fold range of activity ratios. The antagonists most selective for either type were prazosin (alpha 1) and rauwolscine (alpha 2). The selectivity of the alpha-adrenoreceptor antagonists for postsynaptic alpha 1- and alpha 2-adrenoreceptors in the intact circulatory system of the pithed rat is comparable with the reported selectivity of these blocking agents for alpha 1 (postsynaptic)- and alpha 2(presynaptic)-adrenoreceptors in the rabbit isolated pulmonary artery. 4 It is concluded that two distinct types of postsynaptic alpha-adrenoreceptors participate in vasoconstriction in the pithed rat. Apart from the classical alpha 1-adrenoreceptor, vascular smooth muscle of the pithed rat contains postsynaptic alpha 2-adrenoreceptors resembling those previously found mainly presynaptically. The presence of separate classes of postsynaptic alpha 1- and alpha 2-adrenoreceptors in the intact circulatory system of the pithed rat offers the possibility to use this relatively simple animal model as an in vivo test system for the pharmacological characterization of alpha-adrenoreceptors agonists and antagonists.

Disequilibrium in the 238uranium series in samples from yeelirrie, Western Australia

Uranium-series disequilibrium studies carried out on samples from the Yeelirrie uranium deposit, Western Australia, indicate that uranium and radium have been migrating within the deposit during recent times, and are actually being removed from the deposit. Samples collected for 230 Th/ 234 U age dating were found to be substantially out of equilibrium, with 230 Th/ 234 U activity ratios ranging from 0.750 to 1.345. This can be explained by a dynamic hydrologic system in which there has been, and continues to be, uranium migration caused by leaching in this arid, oxidizing environment, and a fluctuating water table. Recent, extensive 226 Ra migration ( 226 Ra/ 230 Th activity ratios range from 0.53 to 1.30), and a very low emanation factor ( E ) of 222 Rn limit the quantitative application of radon exploration techniques in this environment.

STUDIES ON SOIL POTASSIUM II. THE ‘IMMEDIATE’ Q/I RELATIONS OF LABILE POTASSIUM IN THE SOIL

SummaryThe Q/I relations of labile soil K relate its availability or intensity (I) to the amount (Q) present. The activity ratio aK/√(aCa±Mg) has already been proposed as a measure of the intensity factor (part I). The ability of a soil to maintain the activity ratio against depletion by plant roots is governed partly by the character of the pool of labile K and also by the rate of release of fixed K, and by the diffusion and transport of K ions in the soil solution. We may isolate the Potential Buffering Capacity of the pool of labile K by determining the Q/I relation over short periods. Such immediate Q/I relations have been determined for a number of soils. They are all linear over the range of activity ratios commonly encountered in agricultural soils and approximate to familiar ion‐exchange equations. At low values of the activity ratio the Q/I relations are all curved and asymptotic to the Q‐axis.The effects of drying, pH, the addition of lime or K fertilizers, and changes in temperature on the form of the Q/I relations are reported.Oven‐drying a soil, particularly if repeated, appears to cause proportionately more K than Ca to be fixed in the fine clay fraction.