Raymond Davis Jr. (1914-2006)

Although astronomy covers the very big, sometimes you have to examine the very small to find out more about our universe. These days this cross-over between disciplines is called astroparticle physics and is a very exciting field. One of the pioneers was Raymond Davis Jr. who started off as a physical chemist and found his way into the study of neutrinos in around 1948. He died on 31st May 2006 at the age of 91.

Neutinos are pretty strange, almost massless, particles that are created in various nuclear reactions. Neutrinos don't really interact with other matter - i.e. the stuff that makes us up - and there are trillions of them passing through our bodies every second. The Sun is our largest, local source of neutrinos producing a few hundred trillion trillion trillion of them per second. As normal matter is pretty transparent to them, they quickly escape and get a head start on the particles of light (photons) which have a very long random walk to the surface of the Sun.

Detecting these solar neutrinos was the focus of one of Ray's early experiments at the Homestake Gold Mine in South Dakota. There, almost a mile underground, he helped construct a 100,000 gallon tank of cleaning fluid with which to attempt to detect the ghostly neutrinos. Over the years, with many improvements in the methods, the experiment was found to detect only one third the number of neutrinos that were expected. This lack of neutrinos became known as the solar neutrino problem and was a pretty huge question in physics. It has only been in the last few years that other experiments such as SuperKamiokande and the Sudbury Neutrino Observatory (SNO) have been able to show that the problem is caused by neutrinos changing into one of the three different types of neutrinos; those early detectors could only detect one of the types (the electron-neutrinos). Nowadays neutrino detectors are becoming astronomical observatories, not only detecting neutrinos from the Sun but those emitted from stars in the last moments before they explode as supernovae. For more on neutrinos listen to the Planetary Society's programme about the SNO.

In 2002, Ray Davis was presented with the Nobel Prize for Physics for "pioneering contributions to astrophysics, in particular for the detection of cosmic neutrinos". As well as studying neutrinos, he had an interest in other things astronomical. He found ages for meteorites from the decay of Chlorine into Argon and he also analysed the composition of lunar rocks brought back by the Apollo astronauts.

My belated condolences and sympathy go to his family.

Posted in astro blog by Stuart on Tuesday 20th Jun 2006 (10:20 CEST) | Permalink
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