نتایج جستجو برای: 238u
تعداد نتایج: 745 فیلتر نتایج به سال:
A method for in situ U–Pb isotopic analyses by secondary ion mass spectrometry (SIMS) has been developed for uranium minerals with a range of chemical compositions. This method combines the advantages of conventional U–Pb dating (i.e., use of concordia) and in situ analysis, and therefore is ideally suited for the study of chemically complex and fine-grained uranium oxides associated with urani...
Uranium groundwater contamination due to U mining and processing affects numerous sites globally. Bioreduction of soluble, mobile U(VI) to U(IV)-bearing solids is potentially a very effective remediation strategy. Uranium isotopes (238U/235U) have been utilized to track the progress of microbial reduction, with laboratory and field studies finding a ∼1‰ isotopic fractionation, with the U(IV) pr...
Uranium (U) concentration and the activities of 238U, 234U, and 230Th were determined for groundwaters, spring waters, and lake water collected from the Shihongtan sandstone-hosted U ore district and in the surrounding area, NW China. The results show that the groundwaters from the oxidizing aquifer with high dissolved oxygen concentration (O2) and oxidation-reduction potential (Eh) are enriche...
234U/238U mass spectrometry of corals: How accurate is the U-Th age of the last interglacial period?
Direct measurement of U and Th by mass spectrometry recently provided a spectacular improvement in the precision of coral dating by the U-Th disequilibrium method [1]. Mass spectrometric data also provide a much better resolution for the examination of subtle diagenetic effects revealed by small variations of the 234U//238U ratio. Such perturbations may strongly affect the accuracy of the U-Th ...
The production cross sections and the kinematical properties of primary residual nuclei have been studied in reactions 197Au + p, 208Pb + p,d, 238U + p,d, and 238U + 208Pb at energies around 1 A GeV. The measured kinematical properties of the residues were also used to disentangle the relevant reaction mechanisms, spallationevaporation and spallation-fission. The fragment separator FRS at GSI, ...
In order to identify radon-prone areas and evaluate radon risk level, a soil gas radon survey combined with gamma-ray spectrometry measurements was carried out in Shenzhen City, south China. Meanwhile, the statistical analysis was applied to evaluate the distribution of measured results. This paper presents the methodology of the radon risk assessment. A radon risk map was accomplished based on...
Precise momentum distributions of identified projectile fragments, formed in the reactions 238U+Pb and 238U+Ti at 1A GeV, are measured with a high-resolution magnetic spectrometer. With increasing mass loss, the velocities first decrease as expected from previously established systematics, then level off, and finally increase again. Light fragments are on the average even faster than the projec...
The fusion-fission cross sections of the 4He+238U and 6He+238U systems have been measured, at Louvain-la-Neuve, for energies around and below the Coulomb barrier, using an array of Si detectors surrounding a UF4 target. The data taken with 4He are in good agreement with previous data and with the coupled channel fusion calculation performed with ECIS. The 6He data show a regular trend with a la...
Total photofission cross sections for 238U, 235U, 233U, 237Np, 232Th, and natPb have been measured simultaneously, using tagged photons in the energy range Egamma=0.17-3.84 GeV. This was the first experiment performed using the Photon Tagging Facility in Hall B at Jefferson Lab. Our results show that the photofission cross section for 238U relative to that for 237Np is about 80% over the entire...
Background: All human beings and living organisms are exposed to natural radiations on daily basis, which is mainly due to the activity concentration of primordial radionuclides 232Th, 238U and their products of decay together with the natural radionuclide 40K present in the earth’s crust. Materials and Methods: A total of 59 soil samples were collected around the banks and surroundings of the ...
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