Solar neutron and proton production during the 1990 May 24 cosmic-ray flare increases

A detailed analysis of the solar cosmic-ray event on 1990 May 24 has now led us to conclude that the first increase was due to direct solar neutrons and the second increase was produced by solar protons presumably accelerated by an extended coronal shock. The first increase due to solar neutrons lasted about 25 minutes, had an integrated neutron flux at the Earth of 2.5 x 10 exp 4 neutrons/sq cm for En equal to or greater than 100 MeV, and was produced by a time-extended neutron production mechanism at the sun which had approximately the amplitude-time profile of the 79.5-109.6 MeV gamma-ray emission. The second increase starting at about 2102.5 UT was observed by many neutron monitors around the world. It had a duration of about 6 hr and was caused by a highly anisotropic flux of solar protons with a rigidity spectrum proportional to P exp -5.5 at the time of maximum intensity (2115-2125 UT). We concluded that these solar protons were accelerated for about 60 minutes by a diffusive coronal shock, and the total integrated number of protons with P greater than 0.25 GV (Ep equal to or greater than 30 MeV) at the sun was estimated to be equal to or greater than 2 x 10 exp 34. This is less than 10 percent of the total number of protons required at the sun to produce the observed solar neutron fluence of 2.5 x 10 exp 4/sq cm at the Earth. These results are discussed in the context of recent calculations by Ryan & Lee (1991).