1. Comparing 36Cl Production Rates from Stone et al (1996) and Caffe, Swanson (2001)

2. Cosmogenic Isotope Dating Overview
Exposure dating technique
Based on secondary cosmic rays
Spallation
Neutron capture
Muon capture
36Cl
300,000 yr t ½
Useful from 1000 to 1,000,000 years

3. Caffe, Swanson (2001) Attempt to refine 36Cl production rates
Uses exposed surfaces on Whidbey and Fidalgo islands
Well-constrained deglaciation timeline
Measures spallation and neutron-capture
Ring Creek lava flow, Vashon, Sumas, and interior British Columbia sites used for calibration

4. Range of Measured Production Rates

5. FIG. 5. Individual ground-level secondary neutron production rate Pf(0) values inferred from thermal neutron absorption by 35Cl show a bimodal distribution
suggesting that the thermal neutron absorption rate is at least ~40% greater for the samples possessing high water content (serpentinized samples) compared with
those samples possessing relatively low water content. The calculated mean secondary neutron production rate in air [Pf(0)] ±1σ error for the low water calibration
samples is 762±28 fast neutrons (g air)-1 yr-1.

6. Stone, Et. Al (1996) Measurement of Calcium spallation
Calcium Feldspars analyzed
High yield
Low chlorine content = minimal neutron capture production
Tabernacle Hill Basalt 17.3±0.3 Ka (absolute)

7. Conclusions
Significant difference in production rates due to Calcium spallation ~60%
Well-constrained ages for calibration surfaces
Whole rock vs. mineral separates
Altitude scaling