1. Cosmic-Ray Fluxes Present and Past
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
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 Antarctic Data 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 Antarctic Data 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 Calibration Lake Bonneville Shorelines

22. Lake Bonneville, Utah

23. Tabernacle Hill

24. Bonneville & Provo Shorelines