The Nuclear Lightouse Effect

The Nuclear Lightouse Effect is a newly discovered phenomenon that is helping physicists get a peek at the often extreme environments that nuclei experience in various materials. The effect derives its name from the sweeping beam of x-rays emitted by a rotating sample after it has been irradiated by intense synchrotron light. Fluctuations of the beam as it swings past a detector are a beacon of information about the nuclei that emitted the x-rays.

To create a nuclear lighthouse, researchers mount a sheet of sample material on the inside wall of a small cylinder. They then spin the cylinder at several thousand revolutions per second by pushing it with jets of pressurized air. Once the cylinder and sample are up to speed, the researchers must excite atoms in the sample with a burst of x-rays, such as those produced by circulating beams of high energy electrons in the Advanced Photon Source at the Argonne National Laboratory. The sample atoms then emit x-rays of their own in the few billionths of seconds after they are excited, which is enough time for the cylinder to rotate a few degrees and create the sweeping x-ray beam (see diagram at /png).

Researchers from the Universität Rostock in Germany (R. Röhlsberger, roehle@physik1.uni-rostock.de, 011-49-381-4981732), who discovered the effect last year, have now used it to analyze samarium oxide. Samarium is an important material for new permanent magnets, but is difficult to study with conventional methods (such as Mossbauer spectroscopy). The group has also studied iron atoms with the technique, and expects the nuclear lighthouse effect to shed new light on numerous other materials in the near future. (R. Röhlsberger et al, Physical Review Letters, 23 July 2001; text at Physics News Select.)