Alpha Particle Pressure Gauge for High Altitude Constant Level Balloon Flights

Abstract

This paper describes an alpha particle pressure gauge designed for use on very high altitude constant level balloon flights. The instrument gives continuous readings from sea level to pressures less than 1 millibar with an accuracy in the 1–10 millibar range of a few tenths of a millibar. The instrument utilizes a sensitive electrometer measuring the ionization current due to a very weak polonium alpha particle source of less than 1 μCi in the form of nonreactive ceramic microspheres. The pressure is read out by the time interval between resets of the drifting electrometer in a form convenient for transmitting by radio telemetry. Temperature compensation in the electronic circuitry corrects for the gas law so that the instrument measures pressure independent of temperature to suitable accuracy between −25 and +25°C. The instrument has been tested on more than 50 balloon flights and gives reproducible and accurate results. The paper describes the complete physical and electronic operating principles and shows detailed drawings and photographs of the improved version sufficient to enable the experimenter to construct a copy. The instrument uses all solid state components and the size, weight, and power requirements are very small.