RADIOACTIVITY OF THE ATMOSPHERE* 
By H. ISRAEL 
Buchau Observatory and University of Tubingen 
Introduction 
The conductivity of the air is a characteristic of the 
entire atmosphere at all times. It is the result of the 
most varied ionizing radiation of a corpuscular and 
electromagnetic nature. In the lower layers of the at- 
mosphere the radiation of the radioactive substances 
that are contained in the air and in the uppermost 
strata of the earth’s crust is the principal source of this 
ion formation. 
Table I gives a summary of the three decay series of 
radioactive substances and the physical qualities of the 
respective types of atoms. As far as the atmosphere is 
concerned, our interest begins only with the gaseous 
intermediate transformation products (7.e., the emana- 
The discovery of radioactive substances in the atmos- 
phere was made by Elster and Geitel [19], who thus 
gave a physical explanation for the weak conductivity 
of the air, already known to Coulomb in 1785. 
Methods of Measurement 
There are two possible methods of measuring the 
radioactive elements of the atmosphere. One method 
consists of removing the emanations from the air by 
adsorption or condensation and measuring them in an 
ionization chamber (emanometry). In the second 
method, the property of so-called ‘inductions’ is uti- 
lized, that is, the property of some radioactive decay 
products of carrying a positive electrical charge; these 
Tasie I. RADIOACTIVE SUBSTANCES IN THE ATMOSPHERE 
Element Symbol Rays Half-life Disinieeravou constant 
TRACOM 0054.66 60 0d ERODE eae Rn a 3.825 day 2.097 X 10-° 
TRerchiuias AN.) bale n oe ane eee eee RaA a 3.05 min 3.78 xX 10-8 
TRehitten 18). dis on Bet enne & eee ee eee: RaB Boy 26.8 min 4.31 X 104 
TReclinisn (C, 6 do ose Oe eae meee eens RaC at+Bt+y 19.7 min 5.86 Xx 1074 
IReGhinai 1D). eae ee eee eee RaD Boy 22 yr CO S< 10-8 
PVEUCUUTINWE Secs yoke gle cs ayspigeoe ee bese be eens Rak B+y 5.0 day 1.61 X 10-6 
TReyoliqiinn 1B"? ac acletee Oe ae Ine RaF a(+6)t 140 day 5.73 X 10% 
“ING TRG cio.6 ci oes Renae Tn a 54.5 sec Wail 3< Or 
piToniumeAUy ye whee. cca sees cess ThA a 0.14 sec 4.95 
MINIVOTINM Bake cccaes ches cs aee ees ThB Boy 10.6 hr 1.82 xX 10-5 
TNovareribinay (Chis aie estes see ce ee ThC a+p+y 60.5 min WCHL LO 
ACHING tgce8 eee RO oR nee An a 3.92 sec 0.177 
AGU TAVTUINGY 7A ine ee AcA a 2 X 107-3 sec 347 
PANE IMAM eRe teccsccutccdale dees geaeoo cane AcB B+y 36.0 min Hoel S< Wore 
PNG UUMUUITI Os. oc. oisocts 6 svags sieeve ee bos AcC atp+y 2.16 min 5.8) S< Ilr’ 
* Polonium (Po) t uncertain 
tions) and therefore a consideration of all preceding 
elements has been omitted. 
The gaseous emanations radon (Rn), thoron (Zn), 
and actinon (An) are emitted from the rocks and the 
soil into the air entrapped in the ground capillaries or 
directly into the air at the earth’s surface and are 
transported to higher levels by the apparent diffusion 
of the vertical atmospheric mass exchange (austausch). 
Because of the interaction between this exchange and 
the disintegration rate of the emanations and their by- 
products, a certain characteristic vertical distribution 
for each element can be expected which, in the mean, 
can be proven experimentally (see below). The contri- 
bution made by these radioactive elements to the for- 
mation of ions in the atmosphere decreases rapidly with 
altitude and ceases approximately at the height of the 
tropopause. 
* Translated from the original German. 
products are deposited on negatively charged collectors 
where their ionizing effect can be examined. This tech- 
nique is termed the “induction method.” The experi- 
mental technique of the induction method is simpler 
than that of emanometry, but quantitatively less relia- 
ble. Therefore, emanometry is to be preferred for analy- 
sis of the relatively long-lived Rn. However, direct 
emanometry does not work for Th- and Ac-products 
because of the short life of 7m and An, and only the 
indirect induction method is possible. 
Emanometry. The international unit of Rn is the 
curte (C). The curie is the quantity of radon which is 
in radioactive equilibrium with one gram of radium 
and thus emits as many alpha particles per unit time 
as does one gram of radium. The current which 1 C 
can maintain at saturation and with complete utiliza- 
tion of its radiation is 9.22 X 10-* amp. In the course 
of approximately 3 hr, equilibrium is reached between 
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