Cosmogenic nuclides in early solar system materials

Glynn Edward Bricker, Purdue University

Abstract

The overall goal of this research was to assess early solar system processes, particularly ancient proto-solar activity. This goal was addressed on two fronts. First, a model was developed to explain the provenance of now extinct radionuclides in early solar system materials, namely the refractory inclusions termed CAIs (Calcium-Aluminum-Inclusion) found in carbonaceous chondrites. As CAIs are believed to be the first solids to condense in the solar system and are also believed to have formed close to the proto-Sun, a model which explains the now extinct radionuclides found in CAIs constrains early solar system processes. Secondly, a series of measurements were performed on samples of the early solar system, namely chrondritic meteorites and the inclusions called chondrules, often contained within these meteorites. Chondrules, which are often a chief constituent of these meteorites, are believed to have originated close to the proto-Sun. As such, these materials should contain clues about solar processes at the beginning of the solar system. We propose a model for the incorporation of SLRs (short lived radionuclide) within CAIs in primitive carbonaceous meteorites. In this model SLRs are produced by energetic particle reactions in the proto-solar atmosphere of a more active proto-Sun characterized by proton fluxes higher than contemporary particle fluxes. These SLRs are entrained in the solar wind that is then implanted into CAI precursor material. This production mechanism is operational in the contemporary solar system and is responsible for implantation of 10 Be, 14C and other nuclides in lunar materials. We utilize contemporary experimental solar wind production rates for 10Be and 14 C and theoretical ancient production rates for 7Be, 10Be, 14C, 26Al, 36Cl, 41Ca, and 53Mn. Using a ∼ 105 enhancement in SEPs (solar energetic particles) and hence production rates in conjunction with an accepted refractory mass inflow rates close to the proto-Sun, we model the SLR concentrations in CAI precursors. The model predictions are consistent with measurements of 7Be, 10Be, 36Cl, 41Ca, and 53Mn, but fails by two orders of magnitude to account for 26Al. We also predict the 14C content in CAIs, which to date has not been measured. The implantation model will be presented at the 2009 Meteoritical Society Conference in Nancy, France in July. Several chondritic meteorites have been processed for ICP-OES (inductively coupled plasma-optical emission spectrometry), AMS (accelerator mass spectrometry), and noble gas analysis. Bulk analysis has been performed on the chondritic meteorites Bjurbole, Dhajala, and Sena through the use of ICP-OES. The radionuclides 10Be (T1/2 = 1.36 MYR), 26Al (T1/2 = 0.71 MYR), and 36Cl (T1/2 = 0.30 MYR) have been measured in chondrules and matrix material from Bjurbole and Dhajala using AMS at Primelab (Purdue Rare Isotope Measurement Lab). In order to unravel the complex exposure scenario for these materials, especially chondrules, shielding information must be obtained. 10Be data from AMS in conjunction with production rate calculations for three Bjurbole chondrules indicates that the location of the chondrule samples was close to the surface of the meteorite. 36Cl data from AMS in conjunction with production rate calculations indicates the size of the meteoroid to be ∼ 35 cm in radius. For Dhajala, 26Al saturation activity in concert with 26Al production rate calculations indicate our samples were located inside the meteoroid of radius > 100cm, at a depth of ∼ 60 cm. The 10Be activity and production rate for pre-atmospheric radius and depth characterized by 26Al data indicate a recent cosmic ray exposure age of > 7 MYR for Dhajala. 36Cl saturation activity and 36Cl production rate calculations show that production rate model for 36Cl in large bodies with radii > 100cm at depth ∼ 60cm underestimates the production rate for 36Cl by 15-30%.

Degree

Ph.D.

Advisors

Caffee, Purdue University.

Subject Area

Astronomy

COinS