APPLICATION OF SHORT-LIVED COSMOGENIC RADIONUCLIDES AS TRACERS OF IN-CLOUD SCAVENGING PROCESSES.

Measurements of the cosmogenic radionuclides 38Cl (37.3 min half-life), 39Cl (55 min), and 24Na (15 hours) in consecutive rain water samples during storms have provided a basis for studying precipitation formation processes. These radionuclides, which result from cosmic ray spallation of atmospheric argon, “label” the natural aerosols, and can thus serve as tracers of in-cloud scavenging. Rain collected on a 450-meter2 polyethylene sheet is continuously passed through ion exchange beds, which retain the radionuclides. Subsequent direct counting of the beds by selective coincidence counting techniques allows their direct measurement. Analysis of rain samples collected over consecutive periods as short as 10 min has established several basic relationships from which the rates and possible mechanisms of various in-cloud precipitation formation and scavenging process are determined.