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

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

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

Global Neutron Monitor Network CRONUS-Earth

Global Neutron Monitor Network CRONUS-Earth

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

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

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

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

Existing Altitude Transects CRONUS-Earth

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

Antarctic Altitude Transect CRONUS-Earth

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

Identifying Scaling Model Biases CRONUS-Earth

Uncertainties Scatter in Preliminary Data CRONUS-Earth

Observed Scatter CRONUS-Earth

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

Stepwise Dissolution CRONUS-Earth

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

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

Geological Calibration Lake Bonneville Shorelines

Lake Bonneville, Utah

Tabernacle Hill

Bonneville & Provo Shorelines