Cosmic-Ray Fluxes Present and Past

1. Nathaniel Lifton, Marek Zreda, Darin Desilets, John Clem Background Objectives Present-Day Fluxes Instrumental Measurements Modeling Time-Integrated Fluxes In Situ 14C in Saturated Surfaces Cosmic-Ray FluxesPresent and Past CRONUS-Earth

2. Background • Production Rates Well-Established at Few Sites • Scaling Models Predict Production Rates Elsewhere • Current Scaling Models Based on Modern Cosmic-Ray Measurements • Lal, 1991; Stone, 2000; Dunai, 2000, 2001; Desilets & Zreda, 2003; Lifton et al., in prep • Neutron Monitors (NM) • Other Instruments/Techniques • Problems • Need to Tie CR Measurements to CN Production in Rocks • Limited Empirical Testing of Models Over Millenial Time Scales • Scarcity of Samples of Well-Established Age CRONUS-Earth

3. Objectives • Relate NM Measurements to CN Production Rates • Global NM Network Data, Published Surveys CRONUS-Earth

4. Global Neutron Monitor Network CRONUS-Earth

5. Global Neutron Monitor Network CRONUS-Earth

6. Objectives • Relate NM Measurements to CN Production Rates • Global NM Network Data, Published Surveys • Selected Low-Energy Neutron Detector Measurements • Using NM Data as a Basis for CN Scaling • Can a Single Scaling Model Apply to the Entire Neutron Energy Spectrum? • Detailed NM Response to Secondary Cosmic Rays? • NMs More Sensitive to High Energies • Are Rocks as Well? • Physically Relate NM Response and CN Production in Rock • Test Scaling Models over Millenial Time Scales • In Situ 14C in Saturated Surfaces CRONUS-Earth

7. Present-Day Fluxes • Measurements (Zreda, Desilets) • Modeling (Zreda, Desilets, Clem) CRONUS-Earth

8. Time-Integrated Scaling From In Situ 14C Production Rates • Short Half-Life • 5,730 yr • Secular Equilibrium by About 25 kyr • Insensitive to Moderate Erosion Rates • Many Geomorphic Settings Suitable for Production Rate Determinations CRONUS-Earth

9. In Situ Cosmogenic 14C(In Situ 14C) • Extract From Quartz • Opportunity for Thorough Empirical Testing of Scaling Models • Integrated Over Millenial Time Scales CRONUS-Earth

10. Existing Altitude Transects CRONUS-Earth

11. In Situ 14C Production Rate Scaling • Produced by Nucleons and Muons • 83% spallation, 15% slow muon, 2% fast muon(Heisinger et al, 2002) • Preliminary AntarcticData Suggest Low Muogenic Production CRONUS-Earth

12. Antarctic Altitude Transect CRONUS-Earth

13. In Situ 14C Production Rate Scaling • Produced by Nucleons and Muons • 83% spallation, 15% slow muon, 2% fast muon(Heisinger et al, 2002) • Preliminary AntarcticData Suggest Low Muogenic Production • Scale to SL, High Latitude • Time-integrated production rate • Account for geomagnetic and solar variability • Test atmospheric models • Test For Bias With Sample Altitude and Latitude CRONUS-Earth

14. Identifying Scaling Model Biases CRONUS-Earth

15. Uncertainties • Scatter in Preliminary Data CRONUS-Earth

16. Observed Scatter CRONUS-Earth

17. Uncertainties • Scatter in Preliminary Data • Low Values = Geologic Factors • Address with Many Analyses • High Values = Inadequate Pretreatment? • Identify and Minimize Lab Sources of Scatter • Different Workers • Different Sample Prep Techniques • Different Degrees of Etching? • Objective Indicator of Etching Amount • Ba, Al, Zr? CRONUS-Earth

18. Stepwise Dissolution CRONUS-Earth

19. Uncertainties • Scatter in Preliminary Data • Low Values = Geologic Factors • Address with Many Analyses • High Values = Inadequate Pretreatment? • Identify and Minimize Lab Sources of Scatter • Different Workers • Different Sample Prep Techniques • Different Degrees of Etching? • Objective Indicator of Etching Amount • Ba, Al, Zr? • Spallogenic/Muogenic Production Proportions • Antarctic Altitude Transect • 5-10 m Drill Cores from Geological Calibration CRONUS-Earth

20. Timeline and Deliverables • Year 1 • Identify Global Sample Set for Saturated 14C Analysis • Already Collected by Other Investigators • Evidence for 14C Saturation • Stable/Long-Lived CN Data • Geomorphic/Geologic Indicators • Years 1-5 • Analyses • Year 5 • Results Compared with Other CRONUS Data • Geomagnetic & Solar Variation Effects • Atmospheric Effects • Spallogenic/Muogenic Production • Incorporate into Parameter Estimation Model • Write Papers CRONUS-Earth

21. Geological CalibrationLake Bonneville Shorelines

22. Lake Bonneville, Utah

23. Tabernacle Hill

24. Bonneville & Provo Shorelines