Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Uranium isotope ratios are not invariant

24.10.2007
For years, the ratio of uranium’s two long-lived isotopes, U-235 and U-238, has been considered invariant, despite measurements made in the mid-1970s that hinted otherwise. Now, with improved precision from state-of-the-art instrumentation, researchers at the University of Illinois unequivocally show this ratio actually does vary significantly in Earth materials.

The new findings are in line with recent findings in other high-mass isotope systems – such as thallium or mercury – that had been assumed to be invariant. Additionally, the new measurements “could represent the first evidence of the nuclear field shift found in nature,” said U. of I. graduate student Charles J. Bopp, who led the study.

What, exactly, causes the variance is not yet clear, though, Bopp said.

There are two basic types of uranium ore deposits: magmatic, which develop due to hydrothermal effects; and sedimentary, which develop by chemical reduction of uranium in groundwater in subsurface aquifers.

In 1976, scientists George Cowan and Hans Adler analyzed gas mass spectrometry results of uranium hexafluoride (before artificial isotopic enrichment processes took place) derived from uranium ores around the world. This assessment revealed a slight offset in the distribution of the ratio of U-235 to U-238, with magmatic-type deposits having on average higher U-235 percentage weight and sandstone-type deposits having lower.

However, the precision of individual analyses remained approximately 3 per mil (3 parts per thousand) while the average offset between deposit types was less than this.

With the higher precision now obtainable in the UI geochemistry laboratory, Bopp and UI geology professor Craig Lundstrom have observed the same offset between uranium ores from different geologic settings.

The researchers used a technique called multiple-collector inductively coupled plasma-mass spectrometry to measure the ratio of U-235 to U-238 in three sandstone-type and three magmatic-type uranium ores provided by the Smithsonian Institution.

“Repeated analysis of the ore samples shows the sandstone-type ores to be consistently depleted in U-235 relative to magmatic-type ores by approximately 1 per mil, which is a significant amount of variation,” said Bopp, who will present the findings at next week’s annual meeting of the Geologic Society of America.

The observed depletion of U-235 is most likely the result of a nuclear field shift effect as isotopes partition between the water and the reduced uranium ore mineral, Bopp said. But what uranium reduction process – biotic or abiotic – is responsible is not yet clear.

“We can’t parse that apart at this stage,” Bopp said. “We observe a depletion, and we know there are microbes present in these types of deposits, but we can’t say for sure who’s doing what without a much more in-depth study of a single locality.”

James E. Kloeppel | EurekAlert!
Further information:
http://www.uiuc.edu

More articles from Earth Sciences:

nachricht New research calculates capacity of North American forests to sequester carbon
16.07.2018 | University of California - Santa Cruz

nachricht Scientists discover Earth's youngest banded iron formation in western China
12.07.2018 | University of Alberta

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: First evidence on the source of extragalactic particles

For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.

To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...

Im Focus: Magnetic vortices: Two independent magnetic skyrmion phases discovered in a single material

For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.

Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...

Im Focus: Breaking the bond: To take part or not?

Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.

A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...

Im Focus: New 2D Spectroscopy Methods

Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.

"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....

Im Focus: Chemical reactions in the light of ultrashort X-ray pulses from free-electron lasers

Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.

Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Conference on Laser Polishing – LaP: Fine Tuning for Surfaces

12.07.2018 | Event News

11th European Wood-based Panel Symposium 2018: Meeting point for the wood-based materials industry

03.07.2018 | Event News

 
Latest News

Subaru Telescope helps pinpoint origin of ultra-high energy neutrino

16.07.2018 | Physics and Astronomy

Barium ruthenate: A high-yield, easy-to-handle perovskite catalyst for the oxidation of sulfides

16.07.2018 | Life Sciences

New research calculates capacity of North American forests to sequester carbon

16.07.2018 | Earth Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>