Detection of 135Cs & 137Cs in environmental samples by AMS

The detection of low abundances of 135Cs in environmental samples is of significant interest in different fields of environmental sciences, especially in combination with its shorter-lived sister isotope 137Cs. The method of Ion–Laser InterAction Mass Spectrometry (ILIAMS) for barium separation at the Vienna Environmental Research Accelerator (VERA) was investigated and further improved for low abundance cesium detection. The difluorides BaF2- and CsF2- differ in their electron detachment energies and make isobar suppression with ILIAMS by more than 7 orders of magnitude possible. By this method, samples with ratios down to the order of 135,137Cs/133Cs ˜10-11 are measurable and the 135Cs/137Cs ratios of first environmental samples were determined by AMS

Upper limits for the existence of long-lived isotopes of roentgenium in natural gold

A sensitive search for isotopes of a superheavy element (SHE) in natural gold materials has been performed with accelerator mass spectrometry at the Vienna Environmental Research Accelerator, which is based on a 3-MV tandem accelerator. Because the most likely SHE in gold is roentgenium (Rg, Z=111), the search concentrated on Rg isotopes. Two different mass regions were explored: (i) For the neutron-deficient isotopes Rg261 and Rg265, abundance limits in gold of 3×10-16 were reached (no events observed). This is in stark contrast to the findings of Marinov, who reported positive identification of these isotopes with inductively coupled plasma sector field mass spectrometry in the (1-10)×10-10 abundance range. (ii) Theoretical models of SHEs predict a region of increased stability around the proton and neutron shell closures of Z = 114 and N = 184. We therefore investigated eight heavy Rg isotopes, ARg, A=289, 290, 291, 292, 293, 294, 295, and 296. For six isotopes no events were observed, setting limits also in the 10-16 abundance range. For Rg291 and Rg294 we observed two and nine events, respectively, which results in an abundance in the 10-15 range. However, pileup of a particularly strong background in these cases makes a positive identification as Rg isotopes-even after pileup correction-unlikely

Ultrasensitive search for long-lived superheavy nuclides in the mass range A=288 to A=300 in natural Pt, Pb, and Bi

Theoretical models of superheavy elements (SHEs) predict a region of increased stability around the proton and neutron shell closures of Z = 114 and N = 184. Therefore a sensitive search for nuclides in the mass range from A = 288 to A = 300 was performed in natural platinum, lead, and bismuth, covering long-lived isotopes of Eka-Pt (Ds, Z = 110), Eka-Pb (Z = 114), and Eka-Bi (Z = 115). Measurements with accelerator mass spectrometry (AMS) at the Vienna Environmental Research Accelerator (VERA) established upper limits for these SHE isotopes in Pt, Pb, and Bi with abundances of <2×10-15, <5×10-14, and <5×10-13, respectively. These results complement earlier searches for SHEs with AMS at VERA in natural thorium and gold, which now amounts to a total number of 37 SHE nuclides having been explored with AMS. In none of our measurements was evidence found for the existence of SHEs in nature at the reported sensitivity level. Even though a few events were observed in the window for Ek293a-Bi, a particularly strong pileup background did not allow a definite SHE isotope identification. The present result sets limits on nuclides around the center of the island of stability, essentially ruling out the existence of SHE nuclides with half-lives longer than ∼150 million years

Anthropogenic ²³⁶U in Danish Seawater: Global Fallout versus Reprocessing Discharge

This work focuses on the occurrence of ²³⁶U in seawater along Danish coasts, which is the sole water-exchange region between the North Sea−Atlantic Ocean and the Baltic Sea. Seawater collected in 2013 and 2014 were analyzed for ²³⁶U (as well as ²³⁸U and ¹³⁷Cs). Our results indicate that ²³⁶U concentrations in Danish seawater are distributed within a relatively narrow range of (3.6–8.2) × 10⁷ atom/L and, to a certain extent, independent of salinity. ²³⁶U/²³⁸U atomic ratios in Danish seawater are more than 4 times higher than the estimated global fallout value of 1× 10^–9. The levels of ²³⁶U/²³⁸U atomic ratios obtained are comparable to those reported for the open North Sea and much higher than several other open oceans worldwide. This indicates that besides the global fallout input, the discharges from the two major European nuclear reprocessing plants are dominating sources of ²³⁶U in Danish seawater. However, unexpectedly high ²³⁶U/²³⁸U ratios as well as high ²³⁶U concentrations were observed at low-salinity locations of the Baltic Sea. While this feature might be interpreted as a clue for another significant ²³⁶U input in the Baltic Sea, it may also be caused by the complexity of water currents or slow turnover rate

Stellar and thermal neutron capture cross section of ⁹Be

The neutron capture cross section of ⁹Be for stellar energies was measured via the activation technique using the Karlsruhe Van de Graaff accelerator in combination with accelerator mass spectrometry at the Vienna Environmental Research Accelerator. To characterize the energy region of interest for astrophysical applications, activations were performed in a quasistellar neutron spectrum of kT = 25 keV and for a spectrum at En = 473 ± 53 keV. Despite the very small cross section, the method used provided the required sensitivity for obtaining fairly accurate results of 10.4 ± 0.6 and 8.4 ± 1.0 μb, respectively. With these data it was possible to constrain the cross section shape up to the first resonances at 622 and 812 keV, thus allowing for the determination of Maxwellian-averaged cross sections at thermal energies between kT = 5 and 100 keV. In addition, we report a new experimental cross section value at thermal energy of σth = 8.31 ± 0.52 mb.This work was partly funded by the Austrian Science Fund (FWF), Projects No. P20434 and No. I428, and by the Australian Research Council, Projects No. DP140100136 and No. DP180100496

Limits on Supernova-Associated Fe 60/Al 26 Nucleosynthesis Ratios from Accelerator Mass Spectrometry Measurements of Deep-Sea Sediments

We searched for the presence of Al26 in deep-sea sediments as a signature of supernova influx. Our data show an exponential dependence of Al26 with the sample age that is fully compatible with radioactive decay of terrigenic Al26. The same set of samples demonstrated a clear supernova Fe60 signal between 1.7 and 3.2 Myr ago. Combining our Al26 data with the recently reported Fe60 data results in a lower limit of 0.18-0.08+0.15 for the local interstellar Fe60/Al26 isotope ratio. It compares to most of the ratios deduced from nucleosynthesis models and is within the range of the observed average galactic Fe60/Al26 flux ratio of (0.15±0.05).This work was funded in part by the Austrian Science Fund (FWF), Projects No. P20434 and No. I428 (EUROCORES project EuroGENESIS, subproject CoDustMas), by BMBF Project No. 05K2016, DAAD (56266169), and by the University of Vienna

Developing Accelerator Mass Spectrometry Capabilities for Anthropogenic Radionuclide Analysis to Extend the Set of Oceanographic Tracers

Recent major advances in Accelerator Mass Spectrometry (AMS) at the Vienna Environmental Research Accelerator (VERA) regarding detection efficiency and isobar suppression have opened possibilities for the analysis of additional long-lived radionuclides at ultra-low environmental concentrations. These radionuclides, including $^{233}$U, $^{135}$Cs, $^{99}$Tc, and $^{90}$Sr, will become important for oceanographic tracer application due to their generally conservative behavior in ocean water. In particular, the isotope ratios $^{233}$U/$^{236}$U and $^{137}$Cs/$^{135}$Cs have proven to be powerful fingerprints for emission source identification as they are not affected by elemental fractionation. Improved detection efficiencies allowed us to analyze all major long-lived actinides, i.e., $^{236}$U, $^{237}$Np, $^{239,240}$Pu, $^{241}$Am as well as the very rare $^{233}$U, in the same 10 L water samples of a depth profile from the northwest Pacific Ocean. For this purpose, a simplified and very flexible chemical purification procedure based on extraction chromatography (a single UTEVA® column) was implemented which can be extended by a DGA® column for Am purification. The procedure was validated with the reference materials IAEA-381/385. With the additional increase in ionization efficiency expected for the extraction of actinides as fluoride molecules from the AMS ion source, a further reduction of chemical processing may become possible. This method was successfully applied to an exemplary set of air filter samples. In order to determine the quantitative $^{237}$Np concentration reliably, a $^{236}$Np spike material is being developed in collaboration with the University of Tsukuba, Japan. Ion-Laser Interaction Mass Spectrometry (ILIAMS), a novel technique for the efficient suppression of stable isobaric background, has been developed at VERA and provides unprecedented detection sensitivity for the fission fragments $^{135}$Cs, $^{99}$Tc, and $^{90}$Sr. The corresponding setup is fully operational now and the isobar suppression factors of >10$^{5}$ achieved, in principle, allow for the detection of the mentioned radionuclides in the environment. Especially for $^{90}$Sr analysis, this new approach has already been validated for selected reference materials (e.g., IAEA-A-12) and is ready for application in oceanographic studies. We estimate that a sample volume of only (1-3) L ocean water is sufficient for $^{90}$Sr as well as for $^{135}$Cs analysis, respectively

金融发展对经济增长的影响——来自APEC国家1981-2000年的证据

本研究使用修正的增长模型，考察APEC（APEC）国家1981-2000年的金融发展是否促进了经济增长。本文主要关注金融发展的三个方面对经济增长的影响：股票市场、银行业和资本流动。为了降低国别因素的影响，本模型把研究对象区分为发达成员国与发展中成员国以进行更深入的分析。结果显示，在上述三个方面中，只有股票市场的发展对经济增长产生了显著的增强效应，特别是在发达的成员国中。这一正相关关系即使在控制同步偏差（simultaneity bias）后仍然十分显著。因此，无证据表明，金融体系的发展水平一定会影响本研究中金融-增长的总体关系。译者单位：厦门理工学院外语#厦门大学外文学院(36100#361024