RESUMO
New neutron rich isotopes 267107Bh and 266107Bh were produced in bombardments of a 249Bk target with 117-MeV and 123-MeV 22Ne ions at the Lawrence Berkeley National Laboratory 88-Inch Cyclotron. Identification was made by observation of correlated alpha-particle decays between the Bh isotopes and their Db and Lr daughters using a rotating wheel system. 267Bh was produced with a cross section of approximately 70 pb and decays with a 17(+14)(-6) s half life by emission of alpha particles with an average energy of 8.83+/-0.03 MeV. One atom of 266Bh was observed, decaying within 1 s by emission of a 9.29-MeV alpha particle.
RESUMO
We have studied the catastrophic relaxation in superfluid 3He-B as a function of magnetic field for a sample pressure of 31 bars. "Catastrophic relaxation" refers to a novel magnetic relaxation process which rapidly disrupts the homogeneous precession of nuclear spins in NMR experiments on the B phase. The catastrophe was observed through its effect on the evolution of a long-lived coherent dynamic state, the homogeneously precessing domain. Our measurements reveal that the onset of catastrophic relaxation is suppressed to lower temperatures by a strong magnetic field.
RESUMO
A model stream ecosystem evaluation of the non-commercial alcohol ethoxylate 25-6 alcohol ethoxylate (AE) was performed in 1994. Algal, heterotrophic microbial, protozoan, and invertebrate communities were assessed over an 8-week exposure period that followed an 8-week colonization period. Streams were exposed to nominal concentrations of 0, 12, 37, 111, 333 and 1000 µg AE/l. Confirmed concentrations (8-week means) were 7 (at the detection limit), 13, 36, 76, 259, and 760 µg AE/l as measured at the head of streams on a weekly basis. Microbial communities were initially enhanced by AE exposure (first 2 weeks of exposure), but by the conclusion of the study autotrophic and heterotrophic microbial communities were similar across treatments. In contrast, invertebrate populations and communities responded strongly to AE exposure with adverse effects indicated at 259-760 µg/l by 4 weeks and at 36-760 µg/l by 8 weeks. Key affected groups were the sensitive mayfly, stonefly, and caddisfly fauna. Species richness and abundance of selected populations such as Stenonema (mayfly), Chimarra (caddisfly), and Corbicula (Asiatic clam) were affected. These data indicated a model ecosystem no-observed effect concentration of 13 µg/l for 25-6 AE. In contrast to other published AE model ecosystem studies, 25-6 appears more toxic. Structure-activity-relationships at the model ecosystem level still demonstrate good relationships across a range of surfactants with calculated K(ow)s of 3-6. Importantly, the collective information on fate and effects measured in laboratory and field systems confirms low risk to the environment.
