T92 Landscape Evolution through the Lens of Cosmogenic Nuclides

Monday, 20 October 2014
8:00 AM - 12:00 PM
211

A TENFOLD INCREASE IN 26AL CURRENTS AT PRIME LAB: REVISITING OLD IDEAS AND EXPLORING NEW POSSIBILITIES WITH A GAS-FILLED-MAGNET

Paper number: T92-9
Program: Technical Sessions
Time: 10:00 AM – 10:20 AM

Authors

Abstract

The cosmogenic nuclide pair 26Al and 10Be in quartz has long been used to decipher complex exposure/erosion/burial histories of bedrock, boulders, and sediment. However, the number of applications has been limited because the nuclide pair suffers from a lopsided uncertainty, with 10Be typically measured at 3-5 times better precision than 26Al. This is because 10Be, injected into the accelerator mass spectrometer (AMS) as the molecular ion BeO-, produces ample currents, while 26Al, injected as Al-, produces notoriously poor currents. Injection of the molecular ion AlO- yields much better beam currents, but comes at the expense of interference by the isobar 26Mg. Here we report the successful implementation of a gas-filled-magnet (GFM) for measuring 26Al at PRIME Lab, which effectively eliminates the isobaric interference. Coupled with a high-output ion source, in our initial experiments we analyzed currents of up to ~10 μA on geologic samples, comparable to those we see for 10Be. Percent-level measurements are now possible for both 26Al and 10Be.

We will present several case examples illustrating before-and-after measurements of 26Al using archived sample material. We will also discuss various possibilities for future research using 26Al and the 26Al-10Be pair. In addition, by reducing isobaric interference the GFM also yields significant improvements in 10Be and 36Cl measurements, and holds promise for allowing measurement of other nuclides such as 32Si and 53Mn opening new applications for quantifying surface processes.