Number 96, September 29, 1992 by Phillip F. Schewe and Ben Stein
FIRST OBSERVATION OF BOUND-STATE BETA DECAY . The beta decay of a nucleus in which the emitted electron becomes bound in the daughter atom was first predicted in 1947. Now scientists at the Institute of Heavy Ion Research (GSI) at Darmstadt, Germany have observed such a decay in completely ionized (+66) dysprosium atoms circulating in a storage ring. Although neutral Dy is stable, in a fully stripped form it decays via bound-state beta decay into highly ionized (+66) holmium (atomic number 67) with a halflife of 47 (+5,-4) days, a value derived from the measured storage time of the holmium daughter ions. The GSI scientists report that bound-state beta decay is of minor importance for neutral atoms but might be the predominant decay mode for highly ionized atoms, such as those inside stellar plasmas during nucleosynthesis. Studies of these decays (which are accompanied by a essentially monoenergetic antineutrino) may lead to more precise bounds on the mass of the antineutrino. (M. Jung et al., Phys. Rev. Lett., 12 Oct. 1992.)
A LASER-BASED MAGNETOMETER has been demonstrated by scientists at the University of Rennes in France (F. Bretenaker et al., Phys. Rev. Lett., 10 Aug. 1992). Their laser consists of a 60-cm long cylinder of the non-magnetic material Zerodur, filled with Ne-20, and capped with "quasi-mirrors" with a reflectivity of only 3%. In this setup, a weak external magnetic field along the laser axis causes a splitting in the neon energy levels (via the Zeeman effect); radiation at the two frequencies interferes in a characteristic way that depends on the size of the magnetic field. With this device, the French scientists have measured variations in the mean magnetic field as small as 10 microgauss. They expect that their magnetometer will be useful in prospecting, volcanology, and particularly in seismology, where the 100-picosecond response time might help in sensing earthquakes. (Nature, 17 Sept. 1992.)
TRITON'S GEYSERS AND HALLEY'S FLASH may be caused by the change of nitrogen ice from one crystalline form to another, according to Tobias Owen of the University of Hawaii. Owen believes that the venting of heat which occurs when nitrogen ice (an important ingredient in outer-solar-system object like Pluto and comets) shifts may drive the 8-km high geysers spewing from Triton's surface (as seen in 1989 by Voyager 2 on its way past Neptune) and the brightening of Comet Halley (1991) long after its swing past the Sun. (Science News, 19 Sept. 1992.)
PHYSICS NEWS UPDATE begins its third year. It is prepared by the Public Information Division of the American Institute of Physics (335 E. 45th St, New York, NY 10017) and is intended as a brief digest of physics news items appearing elsewhere in magazines, reports, journals, or newspapers. Some recent requests for inclusion on our electronic mailing list may have inadvertently been lost. If so, please make the request again to pfs2@aip.org
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