Featured Research

from universities, journals, and other organizations

Uranium Isotope Ratios Are Not Invariant, Researchers Show

Date:
October 25, 2007
Source:
University of Illinois at Urbana-Champaign
Summary:
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 unequivocally show this ratio actually does vary significantly in Earth materials.

Research by Craig Lundstrom, professor of geology, and graduate student Charles Bopp supports the belief that the ratio of uranium's two long-lived isotopes, U-235 and U-238, varies significantly. With improved precision from state-of-the art instrumentation, the new measurements "could represent the first evidence of the nuclear field shift found in nature," Bopp said.
Credit: Photo L. Brian Stauffer

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."


Story Source:

The above story is based on materials provided by University of Illinois at Urbana-Champaign. Note: Materials may be edited for content and length.


Cite This Page:

University of Illinois at Urbana-Champaign. "Uranium Isotope Ratios Are Not Invariant, Researchers Show." ScienceDaily. ScienceDaily, 25 October 2007. <www.sciencedaily.com/releases/2007/10/071023103947.htm>.
University of Illinois at Urbana-Champaign. (2007, October 25). Uranium Isotope Ratios Are Not Invariant, Researchers Show. ScienceDaily. Retrieved August 31, 2014 from www.sciencedaily.com/releases/2007/10/071023103947.htm
University of Illinois at Urbana-Champaign. "Uranium Isotope Ratios Are Not Invariant, Researchers Show." ScienceDaily. www.sciencedaily.com/releases/2007/10/071023103947.htm (accessed August 31, 2014).

Share This




More Matter & Energy News

Sunday, August 31, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Australian Airlines Relax Phone Ban Too

Australian Airlines Relax Phone Ban Too

Reuters - Business Video Online (Aug. 26, 2014) Qantas and Virgin say passengers can use their smartphones and tablets throughout flights after a regulator relaxed a ban on electronic devices during take-off and landing. As Hayley Platt reports the move comes as the two domestic rivals are expected to post annual net losses later this week. Video provided by Reuters
Powered by NewsLook.com
Hurricane Marie Brings Big Waves to California Coast

Hurricane Marie Brings Big Waves to California Coast

Reuters - US Online Video (Aug. 26, 2014) Huge waves generated by Hurricane Marie hit the Southern California coast. Rough Cut (no reporter narration). Video provided by Reuters
Powered by NewsLook.com
Chinese Researchers Might Be Creating Supersonic Submarine

Chinese Researchers Might Be Creating Supersonic Submarine

Newsy (Aug. 26, 2014) Chinese researchers have expanded on Cold War-era tech and are closer to building a submarine that could reach the speed of sound. Video provided by Newsy
Powered by NewsLook.com
Breakingviews: India Coal Strained by Supreme Court Ruling

Breakingviews: India Coal Strained by Supreme Court Ruling

Reuters - Business Video Online (Aug. 26, 2014) An acute coal shortage is likely to be aggravated as India's supreme court declared government coal allocations illegal, says Breakingviews' Peter Thal Larsen. Video provided by Reuters
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins