ENERGETIC NEUTRONS, PROTONS, AND GAMMA-RAYS DURING THE 1990 MAY 24 SOLAR COSMIC-RAY EVENT

The solar cosmic-ray event on 1990 May 24 can be divided into three ph ases: a first impulsive production of gamma-rays and greater than 200 MeV neutrons; a second; slower phase during which there were high-ener gy protons at the Sun for similar to 20 minutes producing pions and hi gh-energy neutrons; and a third phase when the protons observed by the IMP 8 and GOES spacecraft and by neutron monitors were injected into interplanetary space. This third phase started after the onset of the event but before the second phase had ceased. We found that high-energ y neutron production occurred during the last 60 s of the impulsive ph ase and at least the first 19 minutes of the second phase. During the second phase the high energy-neutron and gamma-ray emissions decayed m ore slowly than either the 2.2 MeV or 4-7 MeV gamma-ray line emissions . A two-component neutron energy spectrum that changes between the fir st and second phases gives a reasonable fit to the count rate increase recorded by the Climax neutron monitor. From the st we infer that the integrated neutron emissivity at the Sun was similar to 3.5 x 10(30) sr(-1) for E > 100 MeV. The maximum intensity of P > 1.5 GV solar prot ons near the Earth was 4.5 x 10(3) (m(2) sr s)(-1). The differential s olar proton energy flux (dJ/dE) as a function of rigidity at the Sun c an be described by an evolving power-law spectrum. We estimate that th e number of escaping protons with E > 30 MeV in the third phase was 7% -14% of the number of protons required to produce the solar neutron in crease at the Earth. Although it is attractive to assume that the inte rplanetary solar protons simply leaked out from the trapping region at the Sun, the data suggest that the interplanetary solar protons were not from the population of energetic particles that produced the neutr on and gamma-ray emissions but were freshly accelerated during the thi rd phase of the solar flare.