New Precision Technique for Removing Radioactive Emanations From Matter, and for Measuring Minute Quantities of Radon and Thoron [thesis]

Robley Dunglison Evans
2009
I. INTRODUCTION: The accurate determination of the radium content of ordinary matter has many applications in cosmology and geophysics, but is a difficult analysis to carry out. Two problems are involved, first the removal of radon from the material being tested, then the accurate measurement of this radon by means of its alpha ray ionization. The radon removed and measured is about 10-18 gm. II. REMOVAL OF RADON FROM MATTER: The principles used heretofore for removing radon from liquids are
more » ... ified somewhat, and the apparatus given a simplified and entirely new form. The estimated uncertainty of measurement is now less than 1%. A new principle for removing radon from rocks, involving an entirely different and much simpler type of apparatus is presented. Powdered rock specimens are boiled without flux by direct heating to 1800°C in a vacuum, graphite resistance furnace. The gases are led to the ionization chamber through a simple electrostatic ion-trap which removes all the ionized molecules coming from the boiling granite. All moisture absorbents and reservoirs are eliminated from the gas line, a small insulation drying device in the ionization chamber protecting the amber insulation from deleterious vapors. A systematic study of the percentage of the total radon removed as a function of (a) temperature, (b) time of heating, and (c) fineness of sample grains, showed that temperature is the only important factor and that 1800° effects complete radon removal. The duration of heating is 2 1/2 min., which is to be compared with one hour for the quickest of former methods. III. MEASUREMENT OF SMALL QUANTITIES OF RADON: In the measurement of small quantities of radon, emphasis is laid on accurate knowledge of the background ionization due to cosmic and local radiation. The statistical variations in the background are shown to impose the natural observation limit in these measurements, and twenty possible sources of background are discussed with a view to minimizing these variations. A new bifilar, vacuum, rem [...]
doi:10.7907/c3t8-0515 fatcat:3srlcfwcxrd5vlmix3qfl6scny