Scaling factors for production rates of in situ produced cosmogenic nuclides: a critical reevaluation

New scaling factors are presented describing the altitude and latitudinal dependence of production rates for in situ produced cosmogenic nuclides. The new factors incorporate the influence of the non-dipole contributions to the geomagnetic field on the cosmic ray flux. The currently used scaling factors of Lal [Earth Planet. Sci. Lett. 104 (1991) 424-439] are based on the assumption of a dipole field. The overall strategy used in deriving the new scaling factors is, however, very similar to that of Lal and relies on the same and/or similar nuclear data. In this reevaluation, data are only used if the effective geomagnetic parameters (inclination, horizontal field strength) can be reconstructed for the time of measurement. The absorption free pathlengths Lambda for cosmic rays selected for this study are based on observational data at altitudes relevant for exposure age dating (sea level to 7000 m). At sea level and latitudes between 20 degrees and 40 degrees, the new factors are up to 18% lower and at high altitudes more than 30% higher than those of Lal. In addition to accounting for the influence of the effective geomagnetic field and providing more applicable estimates of Lambda, the new factors also allow for correction for the significant deviations from the standard pressure-altitude relationship that exist in the atmosphere (less than or equal to 10%). (C) 2000 Elsevier Science B.V. All rights reserved.