01 Nov 1954-Il Nuovo Cimento (Società Italiana di Fisica)-Vol. 12, Iss: 5, pp 733-742
Abstract: On compte les couples de desintegrations successives\(Tn\mathop \to \limits^\alpha ThA\mathop \to \limits^\alpha \). Le detecteur utilise est un compteur proportionnel. Un circuit special selectionne les intervalles inferieurs a un temps donne. Le choix du temps optimum est discute. La plus petite quantite de RdTh mesurable par la methode decrite est celle en equilibre avec environ 3·10−9 g de Thorium. Le rapport admissible entre les activites en α et en couples\(Tn\mathop \to \limits^\alpha ThA\mathop \to \limits^\alpha \) est examine.
Abstract: In order to study the geochemistry of thorium isotopes in the hydrosphere, particularly in the ocean, a method has been worked out by which Th-232 (thorium)λ, Th-230 (ionium), Th-228 (radiothorium), and Th-227 (radioactinium) can be determined separately. Eight samples of 20 to 40 litres of sea-water, from 23·0% to 34·97%, salinity, were collected in November 1953, in the Skagerak and the Gullmarfjord (Sweden).
Thorium was isolated by the following procedure: just after collection, the samples were brought to pH 2 and a given amount of Th-234 (UX1) was added as tracer. Thorium was first precipitated with Fe(OH)3 as carrier. Further purification was obtained by ion-exchange column chromatography followed by solvent extraction; the final fraction was obtained as the citric complex, a form suitable to incorporation in the photographic emulsion. The total yield varied from 8 to 23% according to the sample, as determined by the β-activity of the tracer.
The various thorium isotopes were measured through their α-activity, using nuclear photographic emulsions, more precisely the double-emulsion technique. RdTh and RdAc both generate five-branched stars; more than 90% of these originated from RdTh, as indicated by the length of the tracks: while Io and Th only yield single tracks of range 18·8 μ and 15 μ respectively in the emulsion. Most samples showed a much lower activity than expected; this did not make it possible to discriminate between Io and Th through the range distribution of their tracks, thus we could only ascertain upper limits of Io and Th concentrations.
Average concentrations corresponding to a total volume of 140 litres of water are as follows (in grams per ml): RdTh = (4.0 ± 1.4). 10−21 Th < 2.10−11 RdAc < 7.10−23 Io < 6.10−16
In one of these samples (salinity: 33·7%) we have found an Io concentration of 26.10−16 g/ml. This high value is attributed to a nonhomogeneous distribution of Io in the sea.
Before the conclusions are drawn, we must point out the following restriction:
(1) Our water samples, including those in the oceanic range of salinity, were not collected in an oceanic environment, as all were taken in coastal waters.
(2) Our experimental results should correspond to the total thorium content of the samples. It must be pointed out, however, that a thorium fraction which both would not exchange with UX1 at pH 2 and would not coprecipitate with Fe(OH)3 would remain undetected with our procedure.
We assume the following concentration for the other radioactive elements: U = 1·5. 10−9g/ml, Ra = 0·8.10−16 g/ml, Th < 6.10−12 g/ml.
The state of radioactive equilibrium between two nuclides A and B shall be denned by their activity ratio: RA/B = λA. NA/λB. NB
The following conclusions can be drawn from the above data:
(1)RIo/U-238 < 0.02. More than 98% of the Io resulting from U-238 disintegration in the oceann cannot be accounted for. This lack of Io in the sea-water must be correlated with the presence of unsupported Io in the deep-sea sediments. These two corroborating facts definitely prove the hypothesis of ionium precipitation with the sediments.
(2) RIo/Ra < 0.15. Ra is in excess by a factor of 6 with respect to its equilibruim with Io. This could possibly result from the redissolution of part of the Ra originating from this Io of the sediments.
(3)The average RdTh concentration of 4.10−21g/ml should correspond to an equilibrium concentration of 2.6.10−11 g/ml of the Th-232. We have, however, shown that, in at least two samples, RdTh is far over its equilibrium value with Th. Indeed, if we assume Th 4. We can only account for this surprising result by supposing that the excess RdTh results from an excess of its parent MsTh, (Ra-228) brought in by rivers or redissolved from the sediments. Owing to the short half-life of both these nuclides, such a RdTh excess should be found only in the vicinity of the shore or the bottom.
(4)RRdAc/U-235 < 0·1. More than 90% of the RdAc from U-235 in the ocean cannot be accounted for. Considering the short half-life of RdAc, this suggests that actinium or protactinium are precipitated with the sediments together with the Io.
(5)In both U-238 and Th-232 families, a radium isotope (Ra and MsTh) appears to be in excess over its parent thorium-isotope (Io and Th). The presence in the ocean of unsupported Ra(T = 1600 years) and MsTh (T = 6·7 years) is of great interest. A study of the distribution of these isotopes should yield valuable data on their diffusion rates and on deep currents.
As far as radioactive geochemistry is concerned, the ocean is characterized by extremely low concentrations of nuclides of all three radioactive families and by the total disruption of the radioactive equilibrium in these families. A calculation of the geochemical balance of radioactive elements in the hydrosphere from the above data is given in the last part of the paper.
Abstract: A solution of Th-234 from Uranyle nitrate was prepared for the use as tracer of its α emitting isotopes Th-230, 228, 232.
The aim of the work was to obtain Th-234 containing as little as possible α emitting elements.
U was separated from Th by ether extraction.
The impurities present in the solution of Th-234 are:
— U due to incomplete separation.
— Th-230 growing from U-234 and chemically inseparable frm U-234
— U-234 formed by desintegration of Th-230
The most favourable conditions for obtaining a solution of Th-234 with high radioactive purity are discussed.
The preparation of a Th-234 solution with a ratio αβ < 1,8 10−6 is described in detail. This solution can be used as radiotracer in measuring quantities of Th-230 (Ionium) as low as 10−11 g.
Abstract: MEASUREMENTS carried out in the Oceanographical Institute, Goteborg, on the radium content in deep-sea cores by H. Pettersson, Traude Bernert, V. Kroll1 et al. showed the vertical distribution of radium to be highly complicated. We were therefore asked to develop a method for direct measurement of the ionium content in samples of sediment from the Swedish Deep-Sea Expedition.
Abstract: THE surprisingly high content of radium in certain deep-sea sediments discovered nearly fifty years ago by J. Joly1 remained unexplained until 1937, when H. Pettersson2 suggested an ocean-wide precipitation of ionium from sea water on to the ocean bottom as its origin. Extensive radium measurements on deep-sea cores raised by the Swedish Deep-Sea Expedition carried out in this institute by Pettersson3, T. Bernert4 and me did not confirm the regular vertical distribution of radium reported by other workers5. An expected rise in radium content from moderate values in the uppermost surface layers to a maximum corresponding to a radioactive equilibrium between precipitated ionium and ionium-supported radium generally occurred; but the maximum was not followed by the theoretical exponential decline downwards governed by the rate of decay of ionium, to 50 per cent in 83,000 years, to 25 per cent in 166,000 years, etc. Instead, a number of secondary maxima of radium content separated by equally pronounced minima were observed (see graph), which could not well be explained as due to intervening changes in the rate of total sedimentation. Another explanation offered was that ionium and radium are not in radioactive equilibrium; that is, the assumption underlying the use of measurements of radium as indicating the concentration in the same layer of its mother element is unjustified.
Abstract: Methods are described for the isolation of uranium and thorium, and some of their radioactive disintegration products, from 10 to 100 g samples of iron meteorites. The concentrations of these elements were of the order of 10 −8 g per g of meteorite. The methods used were liberation of radon and thoron, and classical co-precipitations and solvent extractions for isolation of uranium, ThB and ThC. Estimations of uranium by two methods are described, counting of radon in equilibrium with the uranium series in a gas counter, and fluorimetry. Thorium estimations were accomplished either by thoron gas counting or by α-particle scintillation counting of equilibrium amounts of ThC in a counter of extremely low background.