Detection efficiency of the Solar Neutron Telescopes located at high altitudes

Four solar neutron telescopes (SNTs) are installed at high altitude in China (Tibet, 4300 m a.s.l.), (Japan, Mt Norikura, 2770 m a.s.l), Mexico (Mt. Sierra Negra, 4850 m a.s.l) and Bolivia (Mt. Chacaltaya, 5250 m a.s.l). The SNT are composed by plastic scintillators (PS), photomultipliers tubes (PMT) are set on top of the PS. Proportional counters (PRC) surround the detector to discriminate between charged and neutral particles by anti-coincidence signal. Underneath the PS of the SNT an array of PRC is set to determine the arrival direction. The energy discriminator thresholds of the PMT are set at different energy levels in function of the PS thickness. The thickness of the PS is 40 cm (Tibet), 20cm (Norikura), 30cm (Sierra Negra) and 40cm (Chacaltaya). Incoming particles produce recoil protons by nuclear interactions with the PS. The PMT measure the ionization energy loss of the protons. In this way, the SNT can discriminate between incident charged and neutral particles, measure the energy, and determine the direction of the incoming particles. In this work, we present the experimental, GEANT3 and GEANT4 simulation results of the detection efficiency of the SNT to solar neutrons impinging the top of the detectors.