Searching for a Supernova Trigger for Solar System Formation Using High Precision Nickel Isotope Measurements of Fe-Ni Metal in Meteorites
Authors:   , Andrews Kimberly Tethera 
Published: July 2022

<p>This thesis presents high precision Ni isotope data for Fe-Ni metal with subchondritic Fe/Ni ratios from two non-magmatic irons, five magmatic irons, two main group pallasites and one chondrite, including some meteorites that have not previously been analysed to high precision (IAB irons). The main objectives of this thesis are: (i) to searchfor variations in 60Ni in the Fe-Ni metal phase of meteorites, which may provide evidence for the former presence of live 60Fe and, therefore, the presence and timing of a SN input into the early Solar System; and (ii) to determine if there are variations in the abundance of the neutron-rich isotope of Ni (62Ni) in Fe-Ni metal phase of meteorites with subchondritic Fe/Ni ratios, which may represent the addition of a heterogeneous SNremnant. Techniques were established and modified from previously established chemicalmethods for the isolation of Ni from Fe-Ni metal. Three chemical separation methods using TEVA spec resin, AG 1x4 anion resin and Ni spec resin were utilised. The majority of meteorites studied have been processed through all three different Ni separation techniques. Ni isotope ratios were measured with a Nu Plasma multi-collector inductively coupled plasma mass spectrometer to precisions of <+/-0.05 E (E60Ni ) and <+/-0.10 E(E62Ni) (2 se), with estimated external reproducibilities that are ca.<= to 2 times larger than the 2 se. Ni isotope ratios are corrected for instrumental mass bias using 61Ni/58Ni and the exponential mass fractionation law. E60Ni deficits were measured in magmatic irons, the carbonaceous chondrite Gujba and the main group pallasites (PMG), with E60Ni values ranging from -0.041 to -0.205. E62Ni ranges from +0.299 to -0.052, and supports several genetic associations between meteoritic groups. The majority of meteorites (Canyon Diablo (IAB), Sikhote Alin (IIAB), Henbury (IIIAB), Mundrabilla (IIICD), Gibeon (IVA), Brenham (PMG) and Esquel (PMG)) have E62Ni values within error of the terrestrial standard, indicating that the Ni isotope composition of the material their parent bodies accreted from was homogeneous. However, Toluca (IAB), Chinga (IVB) and Gujba (CBa) have significantly positive E62Ni values (+0.138+/-0.088, +0.299+/-0.075 and +0.184+/-0.082 respectively), which are attributed to preservation of nucleosynthetic effects on an asteroidal scale in the protoplanetary disk. Ni isotope data for the meteorites measured in this study are in agreementwith measurements of the same meteorites from the same groups reported by Dauphas et al.(2008), Regelous et al.(2008) and Chen et al.(2009), and are inconsistent with the data of Bizzarro et al.(2007). E60Ni deficits and 56Fe/58Ni ratios reported here for pallasites and magmatic irons are consistent with a maximum initial 60Fe/56Fe of 4 x 10-7 at the time of formation of these meteorites, which is potentially consistent with a supernova interaction with the molecular cloud fragment just prior to the formation of the Solar System.</p>