A Program of Solar Neutron Observation with NM-64 Counters at Yangbajing in Tibet

We started the Japan-China international solar neutron observation program at Yangbajing (30.11N 90.53E, 4300m), Tibet. 28 NM-64 counters were installed and the single counts and multiplicities from one to eight for every two adjacent counters are recorded for every second. The mean atmospheric pressure is about 602 hPa and the cosmic ray vertical cut off rigidity is about 14.1 GV. The stable continuous data taking has started on mid October 1998. We got the tentative atmospheric pressure coefficient and obtained counting rate were -0.70 %/hPa and 1.07×107 counts/hour. In the current available data of only 5 months' duration, we cannot find apparent 'solar neutron event' yet.