A purely physical model for the simulation of cosmic ray particle interactions with the Earth's atmosphere and subsequent production and transport of secondary particles is presented. Neutron and proton spectra as a function of the coordinate in the atmosphere were calculated using a GEANT / MCNP-based code system. The calculated neutron fluxes are in good agreement with experimental data based on neutron monitor measurements. These fluxes, together with experimental or evaluated cross sections, were used to calculate the production rates of 3 H, 7 Be, 10 Be 14 C, and 36 Cl. The dependencies of these production rates on solar activity and geomagnetic field intensity were investigated in detail. The obtained production rates agree well with most published experimental and theoretical values. Possible reasons for some differences are discussed.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1998JD200091

Simulation of particle fluxes and cosmogenic nuclide production in the Earth's atmosphere

Independent records of relative magnetic palaeointensity from sediment cores in different areas of the world can be stacked together to extract the evolution of the geomagnetic dipole moment1,2 and thus provide information regarding the processes governing the geodynamo. So far, this procedure has been limited to the past 800,000 years (800 kyr; ref. 3), which does not include any geomagnetic reversals. Here we present a composite curve that shows the evolution of the dipole moment during the past two million years. This reconstruction is in good agreement with the absolute dipole moments derived from volcanic lavas, which were used for calibration. We show that, at least during this period, the time-averaged field was higher during periods without reversals but the amplitude of the short-term oscillations remained the same. As a consequence, few intervals of very low intensity, and thus fewer instabilities, are expected during periods with a strong average dipole moment, whereas more excursions and reversals are expected during periods of weak field intensity. We also observe that the axial dipole begins to decay 60–80 kyr before reversals, but rebuilds itself in the opposite direction in only a few thousand years.

Geomagnetic dipole strength and reversal rate over the past two million years

Radiocarbon dating the appearance of modern humans and timing of cultural innovations in Europe: new results and new challenges.

Six relative palaeointensity records from the north Atlantic Ocean were stacked together to produce a new record for the last 75 kyr (NAPIS75). Five of these records have been previously correlated...

North Atlantic palaeointensity stack since 75ka (NAPIS–75) and the duration of the Laschamp event

Geochemical and geophysical implications of the radiocarbon calibration

Geomagnetic field strength is expected to affect the production rate of cosmogenic isotopes such as beryllium-10, carbon-14, or chlorine-36. Chlorine-36 data from the Greenland Ice Core Project (GRIP) ice core agree well with a production rate calculation based on a paleomagnetic reconstruction for the past 100,000 years over both long- and short-term variations. A chlorine-36 peak at 38,000 years ago previously found in the beryllium-10 record from the Vostok ice core can be explained by a period of low geomagnetic field intensity.

L. Meynadier

Papers

Geomagnetic modulation of the 36Cl flux in the GRIP Ice Core, Greenland