Systematics of the odd-even effect in the resonance ionization of Os and Ti

Measurements of the odd-even effect in the mass spectrometric analysis of Ti and Os isotopes by resonance ionization mass spectrometry have been performed for ΔJ = + 1, 0 and -1 transitions. Under saturating conditions of the ionization and for ΔJ = + 1 transitions odd-even effects are reduced below the 0.5% level. Depending on the polarization state of the laser large odd isotope enrichments are observed for ΔJ = 0 and -1 transitions which can be reduced below the 0.5% level by depolarization of the laser field

Laser-induced isotopic selectivity in the resonance ionization of Os

Isotope selective effects in resonance ionization mass spectrometry (RIMS) pose a potentially serious limitation to the application of this technique to the precise and reproducible measurement of isotope ratios. In order to identify some of the underlying causes of isotope selectivity in RIMS and to establish procedures for minimizing these effects, we investigated laser-induced isotope selectivity in the resonance ionization of Os. A single-color, one-photon resonant ionization scheme was used for several different transitions to produce Os photoions from a thermal atomization source. Variations in Os isotope ratios were studied as a function of laser parameters such as wavelength, bandwidth, power and polarization state. Isotope selectivity is strongly dependent on laser power and wavelength, even when the bandwidth of the laser radiation is much larger than the optical isotope shift. Variations in the ^(190)Os/^(188)Os ratio of ≈20% for a detuning of 0.8 cm^(−1) were observed on a transition with a small oscillator strength. Large even—odd isotope selectivity with a 13% depletion of ^(189)Os was observed on a ΔJ = +1 transition at low laser intensity; the odd mass Os isotopes are systematically depleted. For ΔJ = −1 and 0 transitions the isotope selectivity was reduced by polarization scrambling and for strongly saturating conditions. A technique employing the wavelength dependence of even—even isotope selectivity as an internal wavelength standard was developed to permit accurate and reproducible wavelength adjustment of the laser radiation. This technique provides control over laser-induced isotope selectivity for single-color ionization and enabled us to obtain reproducible measurements of ^(192)Os/^(188)Os and ^(189)Os/^(190)Os ratios in the saturation regime for a ΔJ = +1 transition with a precision of better than 0.5%. The application of this wavelength-tuning procedure should significantly improve the quality of RIMS isotope ratio data for many elements

Design and commissioning of a timestamp-based data acquisition system for the DRAGON recoil mass separator

The DRAGON recoil mass separator at TRIUMF exists to study radiative proton and alpha capture reactions, which are important in a variety of astrophysical scenarios. DRAGON experiments require a data acquisition system that can be triggered on either reaction product ($\gamma$ ray or heavy ion), with the additional requirement of being able to promptly recognize coincidence events in an online environment. To this end, we have designed and implemented a new data acquisition system for DRAGON which consists of two independently triggered readouts. Events from both systems are recorded with timestamps from a $20$ MHz clock that are used to tag coincidences in the earliest possible stage of the data analysis. Here we report on the design, implementation, and commissioning of the new DRAGON data acquisition system, including the hardware, trigger logic, coincidence reconstruction algorithm, and live time considerations. We also discuss the results of an experiment commissioning the new system, which measured the strength of the $E_{\text{c}.\text{m}.} = 1113$ keV resonance in the $^{20}$Ne$\left(p, \gamma \right)^{21}$Na radiative proton capture reaction.Comment: 11 pages, 7 figures, accepted for publication in EPJ A "tools for experiment and theory

An experimental study of Mg self-diffusion in spinel

Mg isotope heterogeneity, both between coexisting spinel and silicates and among spinels, is a prominent feature of Plagioclase-Olivine Inclusions (POIs) (1). The preservation of isotopic heterogeneity and relict spinel (Sp) in inclusions with igneous textures indicates that the thermal event which partially melted the precursor material either had too low a temperature or was too brief to allow Mg isotope homogenization between Sp and the melt. Since the temperature history required to homogenize Mg isotopes depends on the diffusion rate of Mg in Sp, we designed experiments using an isotope tracer method to determine this critical rate (2)

Fremdlinge in Leoville and Allende CAI – Clues to Post-Formation Cooling and Alteration

Fremdlinge are perhaps the most exotic and least understood objects in CAI and their very existence places severe constraints regarding formation and cooling histories of the host CAI. Following the discovery and description of Willy, which appears to be an "Ur-Fremdling" or prototype for smaller Fremdlinge in CAI, we have begun a systematic study of CAI of different petrographic types to see if the Fremdlinge are consistent with a common mode of formation and differing degrees of reprocessing. Fifteen type B I, B2, and compact A CAI from Allende and Leoville were selected. The relative abundance of Fremdlinge varies dramatically among CAI, however some CAI of each type and from each meteorite contain abundant Fremdlinge. The range of phase assemblages and mineral chemistries of Fremdlinge from Allende and Leoville is very similar suggesting that the parent sources for Fremdlinge were quite similar. Chemically and texturally, Fremdlinge grade continuously from complex, heterogeneous Willy-like objects to altered, homogeneous metal nuggets. Some complex Fremdlinge like Willy were found in B1 CAI; none were observed in B2 CAI

Mg Isotopic studies of Leoville "compact" type a CAI

One long-standing problem in the application of Al-Mg isotopic systematics to the chronology of CAI is the enigmatic Mg isotopic record of hibonite. Hibonite (ideally, CaAI_(12)O_(19)) is one of the first major element bearing phases to appear in the condensation sequence [1] and occurs as a major constituent only in CAI whose bulk composition is considerably more refractory than Allende Type Bl CAI