No abstract

High-energy particles were recorded by the near-Earth spacecraft and groundbased neutron monitors (NMs) on 2012 May 17. This event was the first Ground Level Enhancement (GLE) of the solar cycle 24. In present study, we try to identify the acceleration source(s) of solar energetic particles (SEPs) by combining in-situ particle measurements from W IND/3DP, GOES 13, and solar cosmic rays (SCRs) registered by several NMs, as well as the remote-sensing solar observations from SDO/AIA, SOHO/LASCO, and RHESSI. We derive the interplanetary magnetic field (IMF) path length (1.25 ± 0.05 AU) and solar particle release (SPR) time (01:29 ± 00:01 UT) of the first arriving electrons by using their velocity dispersion and taking into account the contamination effects. It is found that the electron impulsive injection phase, indicated by the dramatic change of spectral index, is consistent with the flare non-thermal emission and type III radio bursts. Based on the potential field source surface (PFSS) concept, a modeling of the open-field lines rooted in the active region (AR) has been performed to provide escaping channels for flare-accelerated electrons. Meanwhile, relativistic protons are found to be released ∼10 min later than the electrons, assuming their scatter-free travel along the same IMF path length. Combining multi-wavelength imaging data on the prominence eruption and coronal mass ejection (CME), we obtain some evidence of that GLE protons, with estimated kinetic energy of ∼1.12 GeV, are probably accelerated by the CME-driven shock when it travels to ∼3.07 solar radii. The time-of-maximum (TOM) spectrum of protons is typical for the shock wave acceleration.

Sulfur-ion tracks from an Apollo test heImet. Replicas (x 800) of the tracks of sulfur-32 ions were used to calibrate the heImets for cosmic ray detection. Statistical effects of slowing down appear in the form of the varying length of different tracks.