Cross-sections for Cl-36 from Ti at E-p=35-150 MeV: Applications to in-situ exposure dating

We have measured the low-energy yield of Cl-36 from Ti for proton energies from 35 to 150 MeV. Thin Ti foil irradiations were performed at the Harvard University Cyclotron Laboratory and Cl-36 concentrations were determined u sing the ANTARES AMS facility at ANSTO. Cross-sections ranged smoothly with energy from 0.32 +/- 0.05 mb at 35 MeV to 5.3 +/- 0.4 mb at 150 MeV, Resul ts for E < 110 MeV are new, while the upper region from 110 to 150 MeV agre es well with overlapping data from other studies. The in-situ production ra te for Cl-36 from Ti at the earth's surface and high latitude based on this excitation function and calculations of Masarik and Reedy (normalised to t he mean measured yield of Cl-36 from Ca) is estimated at <similar to>(13 +/ - 3) atoms Cl-36 (g Ti yr)(-1) We thus conclude that in Ti-rich, Ca-poor ro cks or in typical basalts, Cl-36 yield from Ti can amount to similar to5-10 % of total. This is similar to the contribution from slow muon capture on C a-40 and in some cases, from thermal neutron capture on native Cl. (C) 2000 Elsevier Science B.V. All rights reserved.