[en] In this report results of tritium tagging experiments in the Thar Desert, Rajasthan, India are presented. They are compared with the results obtained at Ahmedabad, a region with about three times higher rainfall than the Thar Desert but still on the fringe of the desert in the semi-arid region of NW India. The moisture content of the soil in the Thar Desert is only about 2-6% as compared with 5-15% in Ahmedabad. The two models represent basic understanding of the evapotranspiration, run-off and soil moisture movement processes in the arid regions of Thar Desert. The studies indicate that even in a very low rainfall region the groundwater recharge can be quite substantial, amounting to about 7-15%

[en] The luminescence and absorption spectra of single crystals of K₂UO₂(NO₃)₄, Rb₂UO₂(NO₃)₄ and (NH₄)₂UO₂(NO₃)₄. 2H₂O have been measured at liquid-helium temperatures. These spectra indicate a highly symmetric environment for the uranyl ion. Infrared, Raman and electronic spectra show the presence of two types of coordinated nitrate groups. The anion therefore probably has a trans-UO₂(ONO₂)₂(O₂NO) structure with both monodentate and bidentate nitrato ligands. (author)

[en] Raman, infrared, electronic absorption and luminescence spectra of Na[UO²(CH³COO)³] have been measured at temperatures down to 10 K. Multiple structure in the region of the lowest-energy electronic origin is shown to be due to the presence of a substantial concentration of defect sites. In the luminescence spectra these defect sites are populated by energy transfer from the majority species. Most of the vibrational modes of the uranyl and acetate groups have been identified and their vibronic intensity mechanism in the electronic spectra discussed. (author)

[en] Anthropogenic sources from nuclear reprocessing discharges and bomb test fallout have completely overwhelmed the natural signal on the surface of the earth in the last 50 years. However, the transfer functions in and out of environmental compartments are not well known due to temporal variations in the sources of ¹²⁹I and to a lack of knowledge regarding the forms of iodine. From a vertical profile of ¹²⁹I/¹²⁷I ratios in sediments located in the Mississippi Delta region in approximately 60 meters water depth, the ¹²⁹I input function to this region was reconstructed. Dates in the core were assigned based on the plutonium peak at 20 cm depth (assumed to have been deposited in 1963) and the excess ²¹⁰Pb profile in the same depth interval, and below that, based on the steadily decreasing ²⁴⁰Pu/²³⁹Pu ratios from a ratio of 0.18 at 22 cm to 0.05 at 57 cm depth, the 1953 horizon. Atom ratios of ¹²⁹I/¹³⁷I Cs, decay corrected to 1962, the year of maximum radionuclide production, are about 0.3, very close to the production ratios of about 0.2 during atomic bomb tests. This evidence, combined with other observations, strongly suggests that ¹²⁹I in Mississippi River Delta sediments originates from atomic bomb fallout eroded from soils of the Mississippi River drainage basin, with little alteration of the isotopic ratios during transport from watershed to coastal deposits. Based on these observations and on laboratory evidence, the authors propose a conceptual model which explains this correspondence and the low ¹²⁹I/¹²⁷I ratios. Differences in mobilities of the different chemical forms of ¹²⁹I and ¹²⁷I, as well as the variances in chemical forms of ¹²⁹I from nuclear bomb fallout versus nuclear fuel reprocessing, are proposed to have created such a correspondence between I-isotope ratios and bomb fallout nuclides, without revealing recent inputs from nuclear fuel reprocessing releases to the northern hemisphere observed in watersheds of the USA and Europe

[en] ¹⁰Be and ²⁶Al are produced by cosmic-ray-induced spallation of atmospheric constituents, and also as has recently been shown, by spallation in the rocks exposed to cosmic rays. The authors now present experimental data showing that these two isotopes can also be produced by radiation from uranium and thorium decay chain radionuclides contained within the host rocks. They have measured the ¹⁰Be and ²⁶Al concentrations in a number of shielded uranium and thorium ores using accelerator mass spectrometry. The concentrations of ¹⁰Be and ²⁶Al range from 2.8 · 10⁶ to 29.6 · 10⁶ and 1.1 · 10⁷ to 1.43 · 10¹⁰ atoms g^-1, respectively. The calculated concentrations of ¹⁰Be and ²⁶Al range from < 1 to 4,100 and 9 to 10.3 · 10⁶ atoms g^-1, respectively. Implications of these calculations are discussed. In general, the calculated amounts of radiogenically produced ¹⁰Be in geological materials are quite small and frequently negligible compared to cosmogenic production, while that of ²⁶Al are significant and sometimes the dominant source

No abstract available

[en] Precise ¹⁰Be measurements in a vertical profile of a large-diameter gravity core with uniform chemical composition from the central equatorial Pacific have not shown the expected decrease with depth. The decay-corrected ¹⁰Be activities ranged from 5.79 +- 0.21 d.p.m./kg at the top of the core to 9.88 +- 0.46 d.p.m./kg at the bottom with a mean of 7.24 +- 1.18 d.p.m./kg. This variation is attributable to the combined variations in the intensity of cosmic rays and that of the earth's magnetic field during the past 1 Ma. (Auth.)

[en] The results of ¹⁰Be and ⁹Be measurements in several sections of ten large manganese nodules are presented along with U and Th isotope data on five of them. The ¹⁰Be and ¹⁰Be/⁹Be methods yield growth rates (covering a period of 5-10 Ma) which are in excellent agreement with each other. In three cases, these rates are also in very good agreement with those derived from the ²³⁰Th methods, whereas in the other two the ²³⁰Th based rates are faster by over a factor of two. (orig./ME)

[en] Soil moisture movement in the arid region of Thar desert, Rajasthan, has been studied using the tritium tagging method. It was found that groundwater recharge in the area varies between 6-14% of the precipitation input. The important factors which control the groundwater recharge are: i) vegetation cover; ii) nature of surface soil; and iii) topography. It was found that groundwater recharge is higher in the regions of shifting unconsolidated sands as compared to stabilised sand dunes having vegetation cover. In addition, a slight inclination of the land surface results in considerable reduction in the soil moisture transfer as compared to flat areas or areas which are situated in slight depression. A simple conceptual model has been employed to understand the mechanism of soil moisture movement. The model involves estimation of precipitation excess for individual months taking into account the requirement of soil moisture storage and evapotranspiration. Using this model, the computed groundwater recharge for the semi-arid regions of Gujarat has been found to be in very good agreement with the experimental values obtained by the tritium tagging method. (author)

[en] Radiocarbon dates of around 18 Kyr for palaeosols in Kashmir, indicative of warm-humid climate, have been an enigma as this period is regarded as the last glacial maximum (LGM) globally. In case of aeolian deposits such as loess in Kashmir, which can be assumed to have been exposed to solar radiation before deposition, thermoluminescence (TL) method is also being used for estimating the period since burial. Until a few years ago, when only limited number of measurements were available, it was believed that the dates of Kashmir palaeosols by the radiocarbon and TL methods were apparently not in agreement with each other. In this note, we use all the available organic fraction radiocarbon and TL dates for the top two palaeosol horizons (S9 and S10) from Kashmir loess-palaesol sections and show that the dates obtained by the two methods are concordant within the limits of uncertainties of the two methods. (author). 18 refs., 2 figs