Search for solar neutrons associated with proton flares in solar cycle 23

Solar neutrons associated with solar proton events have been searched for in solar cycle 23 by using data obtained by the worldwide network of solar neutron telescopes, which are dedicated to observe solar neutrons. No clear evidence of solar neutron events in association with proton events has been found so far, although a systematic analysis for all the proton events in solar cycle 23 is still in progress. The analysis result for the proton event on April 18th 2001, when the ground level enhancement has also been detected, is presented. The solar neutron telescopes at Mt. Norikura and in Tibet also showed similar enhancements of counting rates at the same time, when both detectors are at good positions to observe solar neutrons. These enhancements were also compared with counting rates obtained by other solar neutron telescopes, and it is concluded that they are due to high energy protons of the order 10 GeV. This analysis shows the probability of detecting not only solar neutrons but also very high energy protons by the network of solar neutron telescopes.