60Fe and 244Pu deposited on Earth constrain the r-process yields of recent nearby supernovae.

Half of the chemical elements heavier than iron are produced by the rapid neutron capture process (r-process). The sites and yields of this process are disputed, with candidates including some types of supernovae (SNe) and mergers of neutron stars. We search for two isotopic signatures in a sample of Pacific Ocean crust-iron-60 (60Fe) (half-life, 2.6 million years), which is predominantly produced in massive stars and ejected in supernova explosions, and plutonium-244 (244Pu) (half-life, 80.6 million years), which is produced solely in r-process events. We detect two distinct influxes of 60Fe to Earth in the last 10 million years and accompanying lower quantities of 244Pu. The 244Pu/60Fe influx ratios are similar for both events. The 244Pu influx is lower than expected if SNe dominate r-process nucleosynthesis, which implies some contribution from other sources.

Neutron Capture on the s-Process Branching Point

The neutron capture cross sections of several unstable nuclides acting as branching points in the s process are crucial for stellar nucleosynthesis studies. The unstable ^{171}Tm (t_{1/2}=1.92 yr) is part of the branching around mass A∼170 but its neutron capture cross section as a function of the neutron energy is not known to date. In this work, following the production for the first time of more than 5 mg of ^{171}Tm at the high-flux reactor Institut Laue-Langevin in France, a sample was produced at the Paul Scherrer Institute in Switzerland. Two complementary experiments were carried out at the neutron time-of-flight facility (n_TOF) at CERN in Switzerland and at the SARAF liquid lithium target facility at Soreq Nuclear Research Center in Israel by time of flight and activation, respectively. The result of the time-of-flight experiment consists of the first ever set of resonance parameters and the corresponding average resonance parameters, allowing us to make an estimation of the Maxwellian-averaged cross sections (MACS) by extrapolation. The activation measurement provides a direct and more precise measurement of the MACS at 30 keV: 384(40) mb, with which the estimation from the n_TOF data agree at the limit of 1 standard deviation. This value is 2.6 times lower than the JEFF-3.3 and ENDF/B-VIII evaluations, 25% lower than that of the Bao et al. compilation, and 1.6 times larger than the value recommended in the KADoNiS (v1) database, based on the only previous experiment. Our result affects the nucleosynthesis at the A∼170 branching, namely, the ^{171}Yb abundance increases in the material lost by asymptotic giant branch stars, providing a better match to the available pre-solar SiC grain measurements compared to the calculations based on the current JEFF-3.3 model-based evaluation.

Production and separation of 163Ho for nuclear physics experiments.

This paper describes the production and chemical separation of the 163Ho isotope that will be used in several nuclear physics experiments aiming at measuring the neutrino mass as well as the neutron cross section of the 163Ho isotope. For this purpose, several batches of enriched 162Er have been irradiated at the Institut Laue-Langevin high flux reactor to finally produce 6 mg or 100 MBq of the desired 163Ho isotope. A portion of the Er/Ho mixture is then subjected to a sophisticated chemical separation involving ion exchange chromatography to isolate the Ho product from the Er target material. Before irradiation, a thorough analysis of the impurity content was performed and its implication on the produced nuclide inventory will be discussed.

Separation of weighable amounts of 10Be from proton irradiated graphite.

Large amounts of 10Be are produced at the PSI muon production facility by high-energy proton spallation in polycrystalline graphite. For the extraction of 10Be out of large amounts of carbon, pyrolysis followed by chemical purification has been performed. Approx. 270g of graphite from Target E92, which had received a total proton charge of 29 Ah between 2002 and 2005, have been burned at 1000°C in a stream of oxygen. The volatile radioactive oxidation product 3H2O was trapped in 3 water bubblers connected in series. The remainder, a white hygroscopic solid material mainly consisting of 7Li2O, 9/10BeO and 10/11B2O3, was dissolved in HF and subsequently purified by ion exchange chromatography. Radioactive impurities such as 22Na, 44Ti, 54Mn, 60Co, 101Rh, 133Ba and 172Hf have been separated from the final product. The purified material represents a mixture of approx. 6.5mg 9Be and 3.5mg (3.3MBq) 10Be. It is ready to be used for scientific investigations requiring large amounts of this precious isotope.

Neutron capture cross section of unstable 63Ni: implications for stellar nucleosynthesis.

The 63Ni(n,γ) cross section has been measured for the first time at the neutron time-of-flight facility n_TOF at CERN from thermal neutron energies up to 200 keV. In total, capture kernels of 12 (new) resonances were determined. Maxwellian averaged cross sections were calculated for thermal energies from kT=5-100 keV with uncertainties around 20%. Stellar model calculations for a 25M⊙ star show that the new data have a significant effect on the s-process production of 63Cu, 64Ni, and 64Zn in massive stars, allowing stronger constraints on the Cu yields from explosive nucleosynthesis in the subsequent supernova.

A new measurement of the half-life of (166m)Ho.

The work presented here is a new and precise measurement of the half-life of (166m)Ho by determining the activity concentration, using an ionisation chamber calibrated for this nuclide, and measuring the number of (166m)Ho atoms using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). Since the isotope (166)Er interferes with the mass spectrometric measurement, Er has to be eliminated from the (166m)Ho radioactive solution. The elimination was achieved using ion-exchange chromatography with the cation exchange resin Dowex AG 50W-X8 and 2-Hydroxybutanoic acid as the mobile phase. After a first transit through the chromatographic column, the purified (166m)Ho eluate was spiked with natural Er to get a resulting Er isotopic composition close to that of natural Er at better than 99.5%, and then it underwent two further separations to eliminate the Er. The activity concentration of this Er-free radioactive (166m)Ho solution was measured in our reference ionisation chamber calibrated for this nuclide by means of the 4πß(PC)-γ and 4πß(PS)-4πγ coincidence techniques and integral counting with a well-type NaI(Tl) detector and Monte Carlo efficiencies. An aliquot of this standardized solution was sent to the Paul Scherrer Institute (PSI) for mass concentration determination using an isotope dilution MC-ICP-MS approach. The mass concentration of (166m)Ho in this solution was determined with 0.25% relative standard uncertainty. This value was corroborated by two other independent measurements. The new half-life of (166m)Ho, 1132.6(39) years (k=1), is compatible with the value determined in 1965, but is 5.6% shorter and about 43 times more precise.

New Measurement of the 60Fe Half-Life.

We have made a new determination of the half-life of the radioactive isotope 60Fe using high precision measurements of the number of 60Fe atoms and their activity in a sample containing over 10(15) 60Fe atoms. Our new value for the half-life of 60Fe is (2.62+/-0.04) x 10(6) yr, significantly above the previously reported value of (1.49+/-0.27) x 10(6) yr. Our new measurement for the lifetime of 60Fe has significant implications for interpretations of galactic nucleosynthesis, for determinations of formation time scales of solids in the early Solar System, and for the interpretation of live 60Fe measurements from supernova-ejecta deposits on Earth.

Lack of effect of rifalazil on ethinyl estradiol pharmacokinetics in healthy postmenopausal women.

Rifalazil, a second-generation rifamycin, is being evaluated for the treatment of sexually transmitted disease and gastrointestinal infections. We determined whether rifalazil influences CYP3A4 metabolism by studying the effect of a single oral, 25 mg dose of rifalazil administered to healthy postmenopausal women, on the steady-state pharmacokinetics (PK) of ethinyl estradiol (EE) during administration of Ortho-Novum 1/35 (EE/NET). Noncompartmental PK and sequential statistical analyses were performed to establish if and when subjects achieved steady-state EE plasma concentrations and to determine whether this steady state was altered by rifalazil administration. The geometric mean ratios for the difference between EE alone and following rifalazil for EE Cmax, AUC(0-24) and Cmin were 105.9, 104.4 and 105.0, respectively. The 90% confidence intervals for each ratio fell within 80 - 125% of the reference treatment indicating no significant difference in the PK of EE before or after rifalazil administration. The posterior probabilities for the true treatment differences of Cmax or AUC(0-24) being less than 20% were > 99.99% in both cases. Based on the results of this study, there is no CYP3A4-metabolic interaction between a single oral, 25 mg dose of rifalazil and EE for either induction or inhibition. Consequently, there is minimal threat of contraceptive failure when single doses of rifalazil are administered with EE/NET. A single dose of rifalazil 25 mg was well tolerated when administered concomitantly with a combination oral contraceptive (EE/NET) by healthy postmenopausal females.

Effect of food on the pharmacokinetics of rifalazil, a novel antibacterial, in healthy male volunteers.

Rifalazil is a new antibiotic structurally related to rifampin but devoid of the metabolic liabilities typically associated with the rifamycin class of antibiotics. A randomized, 3-way crossover study in healthy male volunteers (n = 12) investigated the safety and pharmacokinetics of a single 25-mg oral rifalazil dose administered under a standard breakfast containing fat as 30% of calories, a high-fat breakfast containing fat as 60% of calories, and an overnight fast of 10 hours with a 21- to 28-day washout between doses. Systemic exposure to rifalazil based on Cmax, AUC(0-Tlast), and AUC(0-infinity) was increased progressively as the fat content of the test breakfast was increased from 30% to 60% compared with fasting. The confidence intervals for both fat-containing breakfasts are outside the limits of 80% to 125% allowed for food effect bioequivalence based on Cmax, AUC(0-Tlast), and AUC(0-infinity). This food effect may be a result of increased fractional absorption with increasing dietary fat content. Another striking finding was the large reduction of the pharmacokinetic intersubject variability after rifalazil administration with food. Rifalazil was safe and well tolerated under fed and fasted conditions.