- 2015 – Feburary
Physicists reach new milestone measuring half-life of iron-60
A team of physicists affiliated with institutions in Australia, Switzerland and Austria has made the most accurate measurement to date of the half life of iron-60. In their paper published in the journal Physical Review Letters, the team describes their approach and note that their efforts will now allow the isotope to be used to date astronomical events.
On most places on Earth, iron is found as iron-56, a stable element. Elsewhere in the universe, however, it is found with four additional neutrons which make it a radioactive isotope—iron-60. The isotope is considered by cosmologists to be a radionuclide which has gone extinct—they believe it was created by multiple processes in the early stages of the development of our solar system. Bits of the isotope have been found to exist naturally on Earth only on ocean beds, and are believed to have got there as part of meteorites.
Over the years, scientists have tried various techniques to measure the half-life of the isotope, but have not been able to do so with enough precision to make the results useful. In 1984, for example, a team made the attempt and found it to be roughly 1.5 million years, while another effort in 2009 led to an estimate of 2.6 million years—such a discrepancy has prevented the use of iron-60 being used as a chronometer. In this new effort, the researchers started by using the same technique as the team in 1984, accelerator mass spectrometry.
Our result of (2.50±0.12)×106 yr clearly favors the recently reported value (2.62±0.04)×106 yr, and rules out the older result of (1.49±0.27)×106 yr.
New reset button discovered for circadian clock
The discovery of a new reset button for the brain’s master biological clock could eventually lead to new treatments for conditions like seasonal affective disorder, reduce the adverse health effects of working the night shift and possibly even cure jet lag.
“We found we can change an animal’s sleep/wake rhythms by artificially stimulating the neurons in the master biological clock, which is located in an area of the brain called the suprachiasmatic nucleus (SCN), with a laser and an optical fiber,” said Douglas McMahon, Stevenson Professor of Biological Sciences at Vanderbilt University who directed the study.
Until now, neuroscientists had thought that the firing rate of SCN neurons was strictly an output of the biological clock’s activity. They did not think altering the level of neuronal activity could affect how the clock operates. But the Vanderbilt researchers have shown that stimulating and suppressing the SCN’s neurons in a fashion that emulates their day and night activity levels can force the clock to reset.
The study was done using mice. Neuroscientists have found that mice possess a biological clock nearly identical to that of humans with the exception that it is tuned for a nocturnal lifestyle.
The researchers used a new technique called optogenetics to manipulate the firing rate of the SCN neurons. The technique inserts genes that express optically sensitive proteins into target cells in order to make the cells respond to light.
“This puts clock neurons under our control for the first time,” said doctoral student Jeff Jones, who conducted the study with fellow doctoral student Michael Tackenberg.
The project involved genetically engineering two strains of mice. The neurons in the brain of one strain contained an optically sensitive protein that triggers neuronal activity when exposed to light. The neurons in the brain of the other had a similar protein that suppressed neuronal activity when exposed to light.
A close call of 0.8 light years
A group of astronomers from the US, Europe, Chile and South Africa have determined that 70,000 years ago a recently discovered dim star is likely to have passed through the solar system’s distant cloud of comets, the Oort Cloud. No other star is known to have ever approached our solar system this close – five times closer than the current closest star, Proxima Centauri.
The star’s trajectory suggests that 70,000 years ago it passed roughly 52,000 astronomical units away (or about 0.8 light years, which equals 8 trillion kilometers, or 5 trillion miles). This is astronomically close; our closest neighbor star Proxima Centauri is 4.2 light years distant. In fact, the astronomers explain in the paper that they are 98% certain that it went through what is known as the “outer Oort Cloud” – a region at the edge of the solar system filled with trillions of comets a mile or more across that are thought to give rise to long-term comets orbiting the Sun after their orbits are perturbed.