Radiochronology


Some more information on the story from August:

It’s nuclear physics 101: Radioactivity proceeds at its own pace. Each type of radioactive isotope, be it plutonium-238 or carbon-14, changes into another isotope or element at a specific, universal, immutable rate. This much has been known for more than a century, since Ernest Rutherford defined the notion of half-life—the time it takes for half of the atoms in a radioactive sample to transmute into something else. So when researchers suggested in August that the sun causes variations in the decay rates of isotopes of silicon, chlorine, radium and manganese, the physics community reacted with curiosity, but mostly with skepticism.

In one experiment, a team at Purdue University in West Lafayette, Ind., was monitoring a chunk of manganese-54 inside a radiation detector box to precisely measure the isotope’s half-life. At 9:37 p.m. on December 12, 2006, the instruments recorded a dip in radioactivity. At the same time, satellites on the day side of the Earth detected X-rays coming from the sun, signaling the beginning of a solar flare.

The sun’s atmosphere was spewing out matter, some of which would reach Earth the day after. Charged particles would contort the planet’s magnetic field, disrupt satellite communications and pose a threat to astronauts on the International Space Station.

But that dip in the manganese-54 radioactivity was not a coincidental experimental fluke, nor was it the solar flare discombobulating the measurements, the Purdue researchers claim in a paper posted online (arxiv.org/abs/0808.3156). In West Lafayette the sun had set while X-rays were hitting the atmosphere on the other side of the globe, and the electrically charged matter that created electromagnetic disturbances worldwide was still in transit. After a solar flare has begun, “the charged particles arrive several hours later,” points out theorist Ephraim Fischbach, coauthor of the paper with his Purdue colleague Jere Jenkins….

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As for the first commenter:

“I’m concerned – however – that a garbled abstract of this scientific curiousity will end up in the hands of Creationists, who try to prove the Universe is only 8000 years old…..”

What are you “concerned” about? Is it a problem when someone points out inconsistencies between scientific theories and observational data? We’ll have to see where this goes, it is far from having been demonstrated conclusively and will have to be duplicated in subsequent experiments still – if it does prove to be a valid observation, then we’ll have to take time to hash out what it means, exactly.

CHAMPAIGN, Ill. – 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…

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…

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.”

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31 July 2006 (PhysicsWeb.org) – A group of physicists in Germany claims to have discovered a way of speeding up radioactive decay that could render nuclear waste harmless on timescales of just a few tens of years. Their proposed technique – which involves slashing the half-life of an alpha emitter by embedding it in a metal and cooling the metal to a few degrees kelvin – could therefore avoid the need to bury nuclear waste in deep repositories, a hugely expensive and politically difficult process. But other researchers are sceptical and believe that the technique contradicts well-established theory as well as experiment.

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