A Part Per Trillion Isotope Ratio Analysis of 90Sr/88Sr using Energy-Filtered Thermal ionization mass spectrometry

Strontium-90 is a major radioactive nuclide released by nuclear accidents and discharge waste. Input of such radioactive nuclide into earth surface environment causes potential threat of long-term internal exposure when taken up by organism. Rapid and precise measurement of 90Sr in variety of environmental sample is important to understand the distribution and dynamics of 90Sr in the local environment after the accident and to assess the effect of radioactive nuclide inputs on bodies. However, previous 90Sr measurement techniques have drawbacks such as long measurement times for radiometry and high detection limits for mass spectrometry. Here we present a technique to accurately measure a significantly small amount of 90Sr in natural environmental samples using an energy-filtered thermal ionization mass spectrometry. Our technique achieved a 90Sr detection limit of 0.23 ag, which corresponds to a 90Sr activity of 1.2 µBq. The detection limit was lowered by two orders of magnitude compared with the previous mass spectrometric 90Sr analyses. The ability of our technique will expand the applicability of mass spectrometric 90Sr survey not only to the rapid 90Sr survey upon nuclear accidents but also to study a long-term environmental diffusion of radioactive materials using size-limited environmental and biological samples.

Late Paleoproterozoic mafic magmatism and the Kalahari craton during Columbia assembly

The 1.87–1.84 Ga Black Hills dike swarm of the Kalahari craton (South Africa) is coeval with several regional magmatic provinces used here to resolve the craton’s position during Columbia assembly. We report a new 1850 ± 4 Ma (U-Pb isotope dilution–thermal ionization mass spectrometry [ID-TIMS] on baddeleyite) crystallization age for one dike and new paleomagnetic data for 34 dikes of which 8 have precise U-Pb ages. Results are constrained by positive baked-contact and reversal tests, which combined with existing data produce a 1.87–1.84 Ga mean pole from 63 individual dikes. By integrating paleomagnetic and geochronological data sets, we calculate poles for three magmatic episodes and produce a magnetostratigraphic record. At 1.88 Ga, the Kalahari craton is reconstructed next to the Superior craton so that their ca. 2.0 Ga poles align. As such, magmatism forms part of a radiating pattern with the coeval ca. 1.88 Ga Circum-Superior large igneous province.

Load Carriage Exercise Increases Calcium Absorption and Retention in Healthy Young Women

Objectives Aerobic exercise (EX) reduces circulating ionized Ca (iCa) and increases parathyroid hormone (PTH), but the cause and consequences on Ca handling are unknown. The objective of this study was to determine the effects of EX on Ca kinetics using dual stable Ca isotopes. Methods Twenty-one healthy women (26.2 ± 6.7 yr; BMI: 22.8 ± 2.1 kg/m2) completed a randomized, crossover study consisting of two 6 day iterations separated by ≥2 wk. One iteration consisted of 3 d of load carriage EX 2 h after breakfast (1 hr treadmill walking at 65% VO2max wearing a vest weighing 30% body wt) on days 0, 2, 4, and the other a no-EX control (CON). Diet was controlled during each iteration, and matched to the volunteer's usual intake. On day 0, volunteers received one IV bolus of 42Ca, and oral 44Ca with each meal (0600,1200, and 1700). Serial blood draws and 3 urine pools (U1: 0600–1000, U2: 1000–2000, U3: 2000–0800) were collected on day 0; spot urines were collected on days 1–5. Ca isotope ratios were analyzed by Thermal Ionization Mass Spectrometry and total Ca by Siemens Dimension; fractional Ca absorption (FCA) was measured and kinetic modeling determined, rates of Ca deposition (VO+) and resorption (VO–) from bone, and bone Ca balance (Vbal). Circulating PTH and iCa were also measured before, during and after exercise. Data were analyzed by paired T-test or linear mixed models using SPSS. Results On day 0, PTH increased 45 min into EX as compared to pre (+36 pg/ml, P < 0.001) with max increases 15 min post EX (+70.5 pg/ml, P < 0.001). No changes were observed during CON. Compared to pre-EX, iCa decreased at 45 min into EX (-0.14 mmol, P = 0.01) with max 15 min post EX (–0.273 mmol, P < 0.001). Urinary Ca (UCa) was lower during EX in the U1 pool (25 ± 11 mg) vs. CON (38 ± 16 mg, P = 0.001) with no differences in U2 and U3 (P > 0.05). FCA was greater during EX (26.6 ± 8.1%) compared to CON (23.9 ± 8.3%, P < 0.05). Vbal was less negative during EX (–61.3 ± 111 mg) vs. CON (–108 ± 23.5 mg, P < 0.05), but VO+ (574 ± 241 vs. 583 ± 260 mg) and VO– (–636 ± 243 vs. –692 ± 252 mg) were not different (P > 0.05). Conclusions During EX, an increase in FCA and decrease in UCa resulted in a positive shift in Ca balance. The rapid reduction in circulating iCa may be due to a change in the miscible Ca pool, resulting in increased PTH and changes in intestinal and renal Ca handling that support a more positive Ca balance. Funding Sources Defense Health Program.

Constraining the duration of the Tarim flood basalts (northwestern China): CA-TIMS zircon U-Pb dating of tuffs

The Early Permian Tarim large igneous province (LIP) in northwestern China comprises voluminous basaltic lava flows, as well as ultramafic and silicic intrusions. The age and duration of the Tarim LIP remains unclear, and thus the rate of magma production and models of potential environmental effects are uncertain. Here we present high-precision chemical abrasion−isotope dilution−thermal ionization mass spectrometry zircon U-Pb ages for three newly discovered tuff layers interlayered with lava flows in the Kupukuziman and Kaipaizileike formations in the Keping area (Xinjiang, northwest China). The volcanism of the Kupukuziman Formation is constrained to a short duration from 289.77 ± 0.95 to 289.41 ± 0.52 Ma. An age for the overlying Kaipaizileike Formation is 284.27 ± 0.39 Ma, bracketing the duration of the entire eruptive phase of the Tarim flood basalts at ∼5.5 m.y. The low eruption rate and relatively long duration of magmatism is consistent with a plume incubation model for the Tarim LIP.