Report of Cosmic-Ray Neutron Observation in the 9th Japanese Antarctic Research Expedition 1968-1969 (Reports of the Japanese Antarctic Research Expedition)

Abstract

From February 1968 to January 1969, cosmic ray nucleonic component was observed at Syowa Station, Antarctica (69°00'S, 39°35'E), using a duplicate set of 5-NM-64 super neutron monitor with a multiplicity meter. Almost complete observations were achieved except the lack of 4 consecutive days for one monitor. The mean multiplicity of the monitor is 1.42 ± 0.03 and is in agreement with the value of the standard 6-NM-64 monitor obtained by HATTON, et al. The mean life time of neutrons in the pile is found to be 547 ± ^_μs which is a little longer than that in the 6-NM-64 monitor. These results come from the pile which was constructed as a single pile consisting of 10-NM-64 neutron counters. The annual change of neutron intensity covers 9.0% in range, showing the maximum in April and the minimum in November, with larger disturbance in the later half year than in the former half. The multiplicity dependence of the barometric pressure effect and Forbush decreases are surveyed briefly. Using the data from three large Forbush decreases, the relation between the multiplicity events and their corresponding primary rigidities is discussed by comparing the latitude dependence of the amount of decrease. Descriptions and data of the solar cosmic ray event of November 18, 1968 are also given.