RESUMO
A new data acquisition system including a Field Programmable Gate Array (FPGA) based time-resolved scaler was developed for laser-induced fluorescence and beam bunch coincidence measurements. The FPGA scaler was tested in a collinear laser-spectroscopy experiment on radioactive (37)K at the BEam COoler and LAser spectroscopy (BECOLA) facility at the National Superconducting Cyclotron Laboratory at Michigan State University. A 1.29 µs bunch width from the buncher and a bunch repetition rate of 2.5 Hz led to a background suppression factor of 3.1 × 10(5) in resonant photon detection measurements. The hyperfine structure of (37)K and its isotope shift relative to the stable (39)K were determined using 5 × 10(4) s(-1) (37)K ions injected into the BECOLA beam line. The obtained hyperfine coupling constants A((2)S(1/2)) = 120.3(1.4) MHz, A((2)P(1/2)) = 15.2(1.1) MHz, and A((2)P(3/2)) = 1.4(8) MHz, and the isotope shift δν(39, 37) = -264(3) MHz are consistent with the previously determined values, where available.
RESUMO
A previous study of lead (Pb) contamination in estuarine crocodiles (Crocodylus porosus) in Kakadu National Park, Australia, found elevated Pb levels in bone and flesh from individuals caught in habitats where hunting with lead ammunition had occurred. Lead shot was suspected as the potential source of Pb in these animals. An investigation was designed to determine if crocodiles are capable of retaining and dissolving lead shot in their stomachs and absorbing the ionic Pb into the blood. Four of the six juvenile crocodiles (C. porosus) used in the experiment were fed an initial dose of five or ten lead shot each. Most of the lead shot were retained in the stomach over the 20-week experimental period, as confirmed by stomach lavage and radiography of the stomach region. From 13 to 30% of the original weight of individual lead shot had been eroded in that time. In vitro experiments confirmed that lead shot could be dissolved under conditions simulating those known for the crocodilian stomach. Blood Pb concentrations increased by an order of magnitude within a week after dosing three crocodiles with five lead shot each, and then attained steady-state equilibrium 5-20 weeks after dosing, with blood Pb steady-state levels ranging from 278 to 363 microg/dL. The blood Pb concentration-time curves in these crocodiles followed a one-compartment model with first-order loss kinetics that yielded an apparent biological half-life for Pb in blood of about 3.4 days. Throughout the experiment, the crocodiles remained in apparent good physical condition and displayed no clinical signs of Pb toxicosis. These observations, together with the very high blood Pb levels that were sustained for several months, suggest that crocodilians may possess a relatively high degree of resistance to Pb toxicity.
