Robert W. Lawson

Radioactivity and the Heat of the Earth

IN his presidential address to the Geological Society, abridged in NATURE of Jan. 1, Dr. J. W. Evans refers (page 15) to the above topic in the following words: “although the whole of the energy given out by radioactive elements”, when isolated, is converted into heat, it is probable that a considerable proportion of the energy liberated by such elements, when they occur as rock-constituents, is used up in effecting physical, chemical, or atomic changes in the surrounding minerals.

Temperature Inversion by Convective Cooling

MOST physicists are familiar with Prof. R. W. Woods beautiful experiment1 on the anomalous dispersion of sodium vapour. In the form in which the experiment is carried out by students in this Department, the sodium pellets are distributed evenly over about five inches in the middle part of a steel tube roughly twenty inches long and of diameter one inch, with a wall thickness slightly less than one-sixteenth of an inch. The tube is fitted with a side tube connected to a pump and a manometer, its ends being sealed off by a pair of spectacle lenses of suitable focal length. The horizontal slit is situated at the focus of the lens at the incidence end of the tube, and the vertical slit of the spectrometer is placed at the focus of the lens at the emergence end of the tube. It is best to work with a horizontal slit 1–2 mm. wide. Heating is carried out by means of six jets uniformly spaced 1 in. apart and about 0.1 in. in diameter, drilled along one side of a piece of brass tubing fed by gas and closed at the other end. The heater ia arranged about 2 in. below the middle of the steel tube, and the gas supply is adjustable to give flame jets up to 3 in. high.

Residual lonisation in Closed Vessels

EXPERIMENTS have frequently been carried out to determine the residual ionisation in closed vessels, and to reveal the conditions under which this is a minimum. One of the lowest values hitherto measured is that of McLennan and Murray, who made their measurements over Lake Ontario, using an ionisation chamber of ice. They obtained the value q = 2.6 pairs of ions per c.c. per second.

Mitteilungen aus dem Institut für Radiumforschung

ZusammenfassungEs wurde eine Reihe von radioaktiven Mineralien auf den Gehalt von Uran, Thorium und Blei untersucht und das Mengenverhältnis, unter dem diese drei Substanzen vorkommen, bestimmt. Unter der Voraussetzung, daß die Zerfallsprodukte von RadiumF und ThoriumD beide isotop mit Blei sind, ergibt sich aus diesen Verhältnissen mit einiger Wahrscheinlichkeit, daß Thoriumblei nicht stabil sein kann.Weitere Überlegungen führen zu dem Resultat, daß es eine Halbwertszeit von zirka 106 Jahren besitzt, woraus man weiter folgern kann, daß es ein β-Strahler ist und sich in ein stabiles dem Wismut isotopisches Element verwandeln dürfte.