3he helium age dating
30 atoms g-1 yr-1), and those between 7000 and 10,000 years (127 ?? The minimum in production rate is similar in age to that which would be produced by variations in geomagnetic field strength, as indicated by archeomagnetic data.However, the production rate variations (a factor of 2.3 ??0.8) are poorly determined due to the large uncertainties in the youngest samples and questions of surface preservation for the older samples.Calculations using the atmospheric production model of O'Brien (1979) , and the method of Lal and Peters (1967) , predict smaller production rate variations for similar variation in dipole moment (a factor of 1.15-1.65).