B. Dayton

Large Area Double Scattering Telescope for Balloon-Borne Studies of Neutrons and Gamma Rays

A large area (1 m × 1 m) double scattering telescope1 for balloon-borne research will be described here. It measures the flux, energy and direction of 2-100 MeV neutrons and 0.5-30 MeV gamma rays. These measurements are made using time-of-flight and pulse height analysis techniques with two large tanks of mineral oil liquid scintillator. Results from Monte Carlo calculations of the efficiency, energy resolution and angular resolution are presented and the electronics implementation for the processing of 80 photomultiplier tubes signals will be discussed. The detector weighs 800 kg with a large part of this weight being the liquid scintillator (320 kg). It will be flown at 3 mbars for flight durations up to 40 hours. The first flight is planned for Spring, 1975.

Double Scatter Telescope for Medium Energy Gamma Ray Astronomy from a Satellite

A large area (1 m2) medium energy (1-30 MeV) telescope for gamma ray astronomy is discussed. This telescope utilizes the double scattering of gamma rays between two scintillator arrays with directionial discrimination by means of time-of-flight. The first and second arrays consist of a series of plastic and NaI(Tl) scintillators, respectively, in the shape of long (1 m) linear elements viewed by photomultiplier tubes at both ends. The lateral position of the interaction in the plastic is determined by timing and in the NaI(Tl) by pulse height. Neutron-induced background is eliminated by using a pulse shape discrimination plastic scintillator. At 6 MeV, the telescope has an area-efficiency factor of 300 cm2, an energy resolution of 8% (FWHM), an angular resolution of 3° (HWHM) and a sensitivity of 5 × 10-6 ¿/cm2sec for line emission. Discrete sources can be located to 0.5°.

Gamma Ray Detection with Long NaI(Tl) Scintillator Bars

Extensive position, energy and timing resolution measurements have been made for a l00×5×5 cm3 NaI(Tl) scintillator bar. The arrival times and the pulse heights of signals from two photomultiplier tubes, one at each end of the bar, are used to provide the energy loss, linear position and time-of-flight for gamma ray interactions in the bar over the energy range from 0.5 to 20 MeV. The scintillator bar has an approximately exponential roll-off with a mean attenuation coefficient of 0.015 cm-1. At 0.662 MeV, resolutions (FWHM) of 5 cm, 9.4% and 10 ns were obtained for position, energy and timing, respectively. The timing resolution is 6 ns at 1.25 MeV. At 6.13 MeV, a spatial resolution of 2.2 cm was obtained. This bar is a prototype element of a Compton scatter telescope that uses both plastic and NaI(TI) scintillator bars. The technique is being used for medium energy gamma ray astronomy from a balloon platform. The telescope will have 3.5° (FWHM) angle and 6% energy resolutions at 6 MeV.