Gamma-ray astronomy with a digitized spark chamber

Abstract

A series of high-altitude balloon flights designed to look at possible point sources of cosmic gamma radiation have been made beginning in September 1966. The heart of the detector system used in these investigations consists of a 32-level magnetic-core digitized spark chamber, with 256 wires per level and thin (0.02 radiation length) high-Z pair-producing plates between each level. This spark chamber is surrounded by a bell-shaped plastic scintillator dome and is triggered by a coincidence between a thin central scintillator and a Cerenkov counter in anticoincidence with the dome. This device is flown in an oriented balloon gondola. Results related to several potential γ-ray sources have been obtained in a series of three flights. Upper limits for the flux of γ rays above 30 MeV of (2–4) × 10−5 (cm2 s)−1 have been established for Sco X-1, Sgr SR-1, Sgr SR-2, Sgr SR-3, the Kepler Supernovae (Oph XR-1), the galactic center, the moon, and the quiet sun. Somewhat less severe limits have been set for Centaurus A and Taurus A.