![]() This issue... Plants with Backbone: A Promising Mystery PLaboratory Plasmas Shed Light on the Sun Eureka! California Discovers Plutonium...Again! |
Eureka! California Discovers Plutonium...Again!by Sallie J. Ortiz Soon after plutonium's initial discovery in 1941, researchers associated with Glenn T. Seaborg's group at the University of California Radiation Laboratory began looking intensively for the lighter (neutron-deficient) plutonium isotopes. In 1951, D.A. Orth found, 232Pu, the lightest plutonium isotope known at that time and remaining so for nearly 40 years. In the early 1990s, a Russian team identified three lighter isotopes, 228,229,230Pu, leaving a vacancy in the chart of nuclides for 231Pu. This year, a team of scientists working with Carola Laue and Darleane Hoffman at Lawrence Berkeley National Laboratory filled that vacancy. The key to the challenge in identifying the long-sought 231Pu isotope was its brief half life, expected to be 3 to 30 minutes (see decay chain). Laue and Hoffman attribute their success to improvements in the research that increased the sensitivity of the experiment. The LBNL team experimented with techniques for larger production rates, developed a novel fast chemical plutonium separation technique (see flow chart), and used state of the art data acquisition and analysis that finally led them to the missing isotope. Laue and Hoffman chose the 233U(3He,5n)231Pu reaction, which was predicted to have a higher production rate for 231Pu than those previously investigated. In addition, the overall production rate was increased using a new, specially designed multiple-target system. The researchers irradiated 233Uranium targets with 48-MeV 3Helium-ions, causing nuclear reaction products to recoil out of the targets. The recoiling reaction products caught by an aerosol saturated helium stream were transported directly to the site of collection. After chemical separation, they analyzed the purified plutonium samples by alpha-spectrometry. Summing the decay data from all of the single experiments, they determined the half-life and decay modes of 231Pu. (See schematic of experimental setup.) "I would like to modify and/or automate the plutonium separation procedure to identify 230Pu, for which the alpha-decay was found [by the Russian team], but the half-life was not characterized. It is expected to be even shorter than that for 231Pu," said Laue. This research is supported by Office of Basic Energy Science. Related Information: |
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