The mechanisms responsible for changing stable isotope ratios are known in principle but seldom in detail. This results in an inability to explain fractionations found in terrestrial and extra-terrestrial samples. My thesis research is aimed at understanding iron and silicon mass-dependent fractionations: 1) by performing experiments at high pressure and temperature to determine the equilibrium iron isotopic effects of temperature and oxidation/reduction reactions, 2) by developing a laser-based sampling technique for measuring silicon isotope ratios in order to measure the silicon fractionation in natural geological samples, and 3) by calculating models for Si and Mg isotopic fractionations attending gas-liquid reactions in the early solar system.
Together with Professors Ed Young and Craig Manning, I have developed a method to identify the equilibrium iron isotopic fractionation of two minerals at high pressure and temperature. The high P-T experiments are done in the piston cylinder apparatus with an isotopically spiked starting material. We track the progress of the reaction by measuring the isotopic fractionations until we have come to equilibrium. We have recently shown that there is a resolvable fractionation between fayalite and magnetite at 800 C of approximately 0.35 permil.
The other aspect of my research is focused on silicon isotopes in the early solar system. Professor Ed Young and I have developed silicon laser ablation MC-ICPMS at UCLA and have used this technique to obtain silicon isotopic data on calcium aluminum inclusions (CAIs) in chondritic meteorites. CAIs are the oldest known objects in the solar system and can therefore tell us about the environment in which they formed and hence the early solar system. After obtaining the data, using our new technique, we have modeled the results in order to constrain the pressure, temperature, and composition of the early solar nebula, while learning about the evaporative history of each CAI.
Shahar, A., and Young, E. D., 2007, Astrophysics of CAI formation as revealed by silicon isotope LA-MC-ICPMS of an igneous CAI. Earth and Planetary Science Letters, In Press. PDF (1.1 MB)
Gounelle, M., Young, E. D., Shahar, A., Tonui, E., and Kearsley, A., 2007, Magnesium isotopic constraints on the origin of CBb chondrites. Earth and Planetary Science Letters, v. 256, p. 521-533. PDF (1.2 MB)
Van Acker, M., Shahar, A., Young, E. D., and Coleman, M., 2006, GC/Multiple Collector-ICPMS method for chlorine stable isotope analysis of chlorinated aliphatic hydrocarbons. Analytical Chemistry, v. 78, p. 4663-4667. PDF (260 KB)
Shahar, A., Bassett, W. A., Mao, H. K., Chou, I. M., and Mao, W., 2005, The stability and Raman spectra of ikaite, CaCO36H2O, at high pressure and temperature. American Mineralogist, v. 90, p. 1835-1839. Ê PDF (172 KB)
Kavner, A., Bonet, F., Shahar, A., Simon, J., and Young, E. D., 2005, The isotope effects of electron transfer: An explanation of Fe isotope fractionation in nature. Geochimica et Cosmochimica Acta, v. 69, p. 2971-2979. PDF (356 KB)
Shahar, A. and E. D. Young, 2007, Silicon isotope ratio analyses of a CAI by laser ablation MC-ICPMS and implications for the astrophysics of CAI formation. Lunar and Planetary Science Conference XXXVIII, Abstract 1445. PDF (204 KB)
Shahar, A., C. M. Manning, and E. D. Young, 2006, High Temperature Iron Isotopic Fractionation in Earth's Mantle Ð An Experimental Approach. Eos Trans. AGU, 87(52), Fall Meet. Suppl., Abstract V13E-03.
Shahar, A., and E.D. Young, 2006, LA-MC-ICPMS Analysis of Silicon Isotopes: Application to Early Solar System Materials. Geochimica et Cosmochimica Acta, v. 70 (18), A574.
Hill, P., E.A. Schauble, A. Shahar, E. Tonui, and E.D. Young, 2006, Ab Initio and Experimental Studies of Equilibrium Isotopic Fractionation in Aqueous Ferric Chloride Complexes. Geochimica et Cosmochimica Acta, v. 70 (18), A251.
Shahar, A. and E.D. Young (2006) Silicon Isotope Ratios in CAIs: In Situ Laser-Ablation MC-ICPMS Measurements and Comparisons with Magnesium Isotope Ratios. Lunar and Planetary Science Conference XXXVII, Abstract 1493.
Gounelle, M., E.D. Young, A. Shahar, and A. Kearsley, 2006 Magnesium Isotopic Composition of CAIs and Chondrules from CBb Chondrites. Lunar and Planetary Science Conference XXXVII, Abstract 2014.
Shahar, A., A. Kavner, and E.D. Young, 2005, Mechanisms of Iron Isotope Fractionation During Electrodeposition. Eos Trans. AGU, 86(52), Fall Meet. Suppl., Abstract PP31B-1538.
Van Acker, M.R., A. Shahar, E.D. Young, and M.L. Coleman, 2005, A New, Rapid, Precise, and Sensitive Method for Chlorine Isotope Analysis of Chlorinated Aliphatic Hydrocarbons. Eos Trans. AGU, 86(52), Fall Meet. Suppl., Abstract H22A-03.
Shahar, A. A. Kavner, 2004, A new laser heating and temperature measurement system. Eos Trans. AGU, 85(47), Fall Meet. Suppl., Abstract MR11A-0888.
Kavner, A., A. Shahar, F. Bonet, J. Simon, and E. Young, 2004, The isotope effects of electron transfer: An explanation of Fe isotope fractionation in nature. Eos Trans. AGU, 85(47), Fall Meet. Suppl., Abstract V51A-0512.
Shahar, A., 2004, Thermal Conductivity Measurements in the Laser-heated Diamond Anvil Cell. CA High-Pressure Geoscience Seminar, Berkeley California.
Shahar, A., W.A. Bassett, H.K. Mao, I.M. Chou, and W. Mao, 2003, The Stability of Ikaite, CaCO36H20, at High Pressure and Temperature. GSA Abstracts with Programs, 35(6).