January 9, 2007
The New Wave staff
A Tulane University physics professor was a leader in a recent experiment that made the first laboratory observation of radiative -- or light-emitting -- neutron decay. Neutron decay, which creates other subatomic particles, played a key role in the formation of matter in the universe during the first few minutes after the Big Bang, says Fred Wietfeldt, assistant professor of physics.
"This 'radiative neutron decay' has been long predicted by theory but never before observed," Wietfeldt says. "To detect this very dim light is to find the proverbial needle in the haystack. This discovery is important because it gives scientists a new window for viewing and understanding the basic forces of nature."
Neutrons lurk deep inside most atoms and act as glue to hold the atomic nucleus together. Without neutrons, the elements that make up everyday matter would not be stable.
The experiment took place at the National Institute of Standards and Technology (NIST) Center for Neutron Research in Gaithersburg, Md.
Tulane postdoctoral scientist Brian Fisher and undergraduate student Isaac Kremsky took part in the experiment in collaboration with NIST scientists and other university researchers. An intense, cold neutron beam was passed through a strong superconducting magnet so that the decay electron and proton were transported efficiently to a particle detector some distance away.
The scientists placed a novel, "homemade" photon detector close to the beam. To separate the tiny signal from the much larger background radiation, the scientists exploited the unique time signature of radiative decay events -- the photon and electron moved so fast that they were detected almost instantaneously, even though their detectors were far apart, while the proton drifted slowly to the particle detector.
This timing trick eliminated almost all of the background photons and revealed the scarce radiative neutron decays, says Wietfeldt. The findings were published in the Dec. 21, 2006, issue of the journal Nature.
The scientists are working on the next step, which is to develop a larger and more sophisticated photon detector and repeat the experiment to study the radiative decay process in greater detail. Eventually they plan to conduct a series of experiments to precisely measure various aspects of radiative neutron decay.
"This will help shed valuable light on the weak nuclear force," Wietfeldt says.
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