Explorer 12 observations of charged particles in the inner radiation zone

Observations of energetic charged particle intensities in the inner radiation zone with two shielded, omnidirectional Geiger‐Müller tubes flown on Explorer 12 have been used to construct B‐L contours of the GM tube responses for the period August 16 to September 19, 1961, prior to the Starfish high‐altitude nuclear burst on July 9, 1962. The energy thresholds for penetrating particles are E p = 21 Mev and E e ≃ 1.6 Mev for the 302 GM tube and E p = 65 Mev and E e ≃ 20 Mev for SPB, a heavily shielded background GM tube of an electron spectrometer. The character of these measurements does not allow a unique identification of the GM tube responses as attributable to penetrating protons or electrons, but comparison with other inner‐zone proton observations strongly indicates that their responses are predominantly due to penetrating protons. These B‐L contours are important in providing preStarfish responses of these GM tubes over a large region of the inner radiation zone for subsequent studies of the decay of the artifically injected radiation. Upper limits for the omnidirectional intensities of electrons E e ≳ 1.6 Mev at the geomagnetic equator before the Starfish test are J 0 ≤ 10 4 (cm² sec) −1 at L = 1.2, ≤ 4 × 10 4 (cm² sec) −1 at L = 1.25, ≤ 2.5 × 10 5 (cm² sec) −1 at L = 1.5, ≤ 8 × 10 4 (cm² sec) −1 at L = 1.8, and ≤ 1.5 × 10 4 (cm² sec) −1 at L = 2.4.