JOURNAL OF GEOFHYSICAL RESEARCH VOL. 68. No. 13 JVLY 1. 1963

Measurements of the Tritium and Deuterium Concentration in Atmospheric Hydrogen

B. GONSIOR Institut fur Kernphysik der Universitiit Koln, Cologne, Germany

I. FRIEDMAN U. S. Geological Survey, Washington, D. C.

D. EHHALT II. Physikalisches Institut der Universitiit Heidelberg

Heidelberg, Germany

Abstract. Tritium and deuterium measurements were made on closely spaced samples of atmospheric hydrogen collected from August 1957 through January 1958. Some of the variations in tritium concentration were also shown by the deuterium variations. These variations in concentration of tritium and deuterium can be explained by admixture of industrial hydrogen, as suggested by Begemann and Friedman. However, there were also large rapid variations in tritium concentration that did not correlate with changes in deuterium, and these tritium peaks appear in samples collected in Germany several days after known Soviet H-bomb explo­sions . To study tritium peaks whose rise and decay times are fairly rapid it is necessary to have samples spaced out but a few days apart. It is also necessary to analyze these samples for deuterium as well as for tritium in order to assess the role of industrial contamination..

Since about 1954 the T content of atmos­pheric H has risen because of A-bomb explo� sions . Falting8 and Harteck [1950] discovered T in atmospheric H at a concentration of 3.8 X 10· TU; in 1960 a T concentration of about 5 X 10' TU was measured. As usual, 1 TU equals a T concentration relative to H of 10-18. Several further investigations of T and D concentrations were conducted by Grosse et al. [1954], Gonsior [1959], Begemann and Fried­

man [1959] , Bishop and Taylor [1960], Bain­

bridge et al. [1961], Israel (private communica­tion), and Ehhalt (private communication).

This report deals with measurements made on a continuous series of samples collected during the years 1957 and 1958. In most cases the samples were taken successively every two or three days; therefore, we believe that we have achieved a sufficiently accurate representation of the time dependence of the T concentration. Such short time intervals were indeed a condi­tion of our measurements, since the T concen­tration shows relatively strong and fast varia­tions, which might have been overlooked if the samples had been taken at larger intervals. The results are shown in Figure 1.

In the upper part of the figure the T concen­trations are given in TU and in the lower part the corresponding D values are given in per cent deviation from a standard Lake Michigan water. Some of the D measurements were made in Heidelberg, and these should be lowered by 2.4 per cent because a different standard was used. The points which are connected indicate that the samples were taken within no more than two or three days.

The T variations are relatively fast compared with the time constants known in atmospheric exchange processes. We can now look for a cor­relation with the D measurements and check the model proposed by Begemann and Friedman [1959] as a possible explanation of the varia­

tions in T concentration. These authors assumed that 'the samples are not representative of the atmosphere as a whole, but only of its lowermost layer near the surface of the earth,' because up to n')w samples could be supplied only by large liquefaction plants. Moreover they said that atmospheric H consists of a fraction of 'mean atmospheric hydrogen and a fraction of locally produced hydrogen.' These two parts vary and would therefore result in varying T concentra-

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INTERNATIONAL SYMPOSIUM ON TRACE GASES AND RADIOACTIVITY 3755 tions. The locally produced H comes mainly from industrial production; it is relatively low in T and D. It is desirable to consider the corre­lation separat.ely for different parts of the curve, as the variations are apparently caused by differ­ent influences. The measurements from January 1958 show a typical correlation between T and D values. The extrapolated D content of the admixed industrial H, containing practically no T, amounts to -30 per cent, again on the basis of Lake Michigan water. This shows good agreement with the value found by Begemann and Fried­man for their samples taken at Buffalo. Sup­posing our highest D value to be undisturbed, that is, without admixture of industrial H, we find a D value of + 10 per cent as compared "ith Lake Michigan water, and for our samples a maximum degree of admi::\.iure of 'industrial' H of 45 per cent. Regarding the samples from Buffalo of Begemann and Friedman we would get 75 per cent 'industrial' H. Thus it appears that the samples from Buffalo are more con­taminated by industrial H than our samples are, although they were taken at the same time. In the summer of 1958 T as well as D values were comparatively low , perhaps because of an in­creased contamination. Measurements on sam­ples collected in 1959 and 1960, made by G. Israel in Heidelberg, indeed seem to confirm that the T content in atmospheric H has not de­creased, even after intermittent nuclear tests stopped. On the contrary, it increased.

However, there are T variations that cannot be explained by merely assuming the admixture of locally produced tritium-free H. This became most evident around October 16, 1957. At about this time the T activity increased to ten times the normal values, with no corresponding change in D. We propose that this was due to an injec­tion of a large amount of man-made T, which probably indicates a connection with nuclear tests. From public announcements we learned that the first explosion of a new Soviet test series of October 7, 1957, was extraordinarily large. Five days later the T concentration showed a sudden increase, and it reached its maAimum after another four days. It is certain that the increase had a definite connection with a nuclear test.

We can therefore assume that man-made T also influences other variations of concentration, even though it might not always be so evident.

The assumption that unburnt T leaves the explo­sion center seems to be valid. According to Wolf­gang [1961] a reducing core exists at the center of the fireball. He suggests that the high T con­tent of atmospheric H is directly due to an injec­tion of H., primarily generated in the reducing core, and that the T content does not depend on a secondary exchange with tritiated water. A small unburnt fraction of the T produced is sufficient to change the T concentration greatly, because the absolute amount of H in the atmos­phere is small.

The activity peaks in central Europe are prob­ably caused by Soviet tests because the Soviet test areas are at a high latitude, whereas those of the United States and the United Kingdom lie at the equator. Thus, clouds of man-made radioactive isotopes arrive in central Europe along the lines of latitude before they dissipate in a meridional direction. All known Soviet nuclear tests are marked on the abscissa of Fig­ure 1. It is possible that a direct influence of atomic tests also exists at points other than those discussed. As an analytical comparison we can estimate the correlation, and we shall see the eAient to which the two series of T and D mea­surements vary concomitantly. If we take the deviations dT and dn of the T and D measure­ments from the average of their series, we get the coefficient of correlation, C, in the usual manner. If we choose to do so, we get an indi­cation for the percentage of elemental factors that contribute to both T and D variations. The additional elemental factors contribute in­dependently to one or the other of these varia­tions only. Taking all synchronous T and D measurements, except the sharp peak in Octo­ber 1957, we find a coefficient of correlation:

C = 0.73 ± 0.11

Following the same method for the Begemann and Friedman [1959] results, we arrive at a co­efficient of correlation:

C = 0.59 ± 0.15

For the Buffalo measurements alone, we get

C=0.85±0.1

It must be pointed out, however, that. the slope of the regression line increases with time, since the T content of atmospheric H increases and

3756 GONSIOR, FRIEDMAN, AND EHHALT

the D content of the tritium-free H will remain about the same. This holds for the same location only, since at other locations the production mechanism for H and therefore the fractiona­tion for D also may be different.

The coefficients of correlation are similar. This is to be expected when one takes the mean of the whole series, as was done for our estima­tion of the coefficients.

Considering different parts of the curve sepa­

rately would give correlation coefficients of limited significance owing to the small number of measurements. However, relations between the T and D curves are indicated by the char­acter of the curves.

In conclusion, we find T variations which are clearly related to the D variations, for example,

those of January 1958. This is also shown by the fact that this variation disappears almost com­

pletely if corrected by D. Such variations, as suggested by Begemann and Friedman, are caused by a local admixture of H which is with­out T and which is depleted in D; industrial H, for example. On the other hand we find T varia­tions, mainly in October 1957, which are not correlated in this sense to synchronous D varia­tions. These T variations will not disappear

when corrected by D. They are due to injections of man-made T. Some of these can cause a de­tectable rise of specific activity before being dissipated. It is obvious that D and T measure­

ments must be made on the same samples in order to assess the cause or causes of the T vari­ations in atmospheric H.

REFERENCES Bainbridge, A. E., H. F. Suess, I. Friedman, K. F,

Bishop, B. T. Taylor, and A. F. J. Eggleton, Iso. topic composition of atmospheric hydrogen and methane, Nature, 192, 648, 1961

Begemann, F., and 1. Friedman, Tritium and deu· terium content of atmospheric hydrogen, Z, Naturforsch., 14a, 1024, 1959.

Bishop, K. F., and B. T. Taylor, Growth of the tritium content of atmospheric molecular hy­drogen, Nature, 185, 26, 1960.

Fltltings, V., and P. Harteck, Der Tritiumgehalt der Atmosphiire, Z. Natw·forsch., 5a, 438, 1950.

Gonsior, B., Tritium-Anstieg im atmosphiirischen Wasserstoff, Naturwiss., 46,201,1959.

Grosse, A. V., A. D. Kirschenbaum, J. L. Kulp, and W. S. Broecker, The natural tri tium content of atmospheric hydrogen, Phys. Rev., 93, 250, 1954,

Wolfgang, R., On the origin of high tritium con­tent of atmospheric methane, hydrogen and stratospheric water, Nature, 192, 1279, 1961.

(Manuscript received January 25,1963.)