The ⁴¹Ca bomb pulse and atmospheric transport of radionuclides

For the first time, the ⁴¹Ca signal from the nuclear weapon tests has been measured. Calcium 41 concentrations have been determined in alpine ice of the Fiescherhorn glacier (Switzerland) with accelerator mass spectrometry. The peak concentrations have been observed to be about 3×10⁶ atoms of ⁴¹Ca per per kilogram of ice in the 1950s. It has been found that ⁴¹Ca is produced essentially by the atoll bombs. A universal box model, able to describe atmospheric transport of radionuclides that are in gaseous form or attached to aerosols, has been developed. The model has been applied to calculate the bomb pulses of ¹⁴C, ³⁶Cl, ⁴¹Ca, ⁹⁰Sr, and ¹³⁷Cs. For the transport of radionuclides that are attached to aerosols such as ⁴¹Ca, ⁹⁰Sr, and ¹³⁷Cs, sedimentation (gravitational settling) in the upper stratosphere has been taken into account. It has been found that the deposition of bomb-produced ³⁶Cl on the Earth's surface is delayed compared to that of ⁹⁰Sr by about 1 year because ³⁶Cl stays gaseous in the stratosphere. The model can also be used to calculate the deposition of cosmogenic radionuclides, e.g.,³⁶Cl and ¹⁰Be, in their natural archives, such as polar ice sheets.