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La periode du232Th est deduite de l’activite du228Th mesuree par les etoiles de desintegrations successives dans les emulsions nucleaires. On trouveT= 1.39.1010 ans avec une dispersion relative de ±2 %, en parfait accord avec la valeur de Kovarik et Adams.

The rate of snow accumulation has been measured at the U.S.S.R. station situated at the Pole of Relative Inaccessibility (eastern Antarctic plateau). Five independent methods were used. The results, expressed in g cm−2 year−1, are as follows: (1)Accumulation-stake measurements show an accumulation of 3·1±0·5 in 1965. A maximum value of 3·6 for the 6–year interval 1959–65 is derived from snow-thickness measurements.(2)Firn stratigraphy was found difficult to interpret in terms of annual layers. An upper limit of 12 g cm−2 year−1 is suggested.(3)18O/16O ratios were measured along the upper 235 cm. Assuming that each maximum in the isotope profile corresponds to a summer season, the accumulation would be 8·6±0·9.(4)Gross β radioactivity as a function of depth was measured on three firn sections. The 1955 radioactive fall-out horizon is clearly marked, enabling the derivation of an average accumulation of 3·0±0·3.(5)The average accumulation over the last 80 years, derived from the 210Pb distribution with depth, is 3·1±0·3.A multi-annual average accumulation rate of (3·0±0·3) is thus firmly established, as well as the validity of both the 210Pb method and the 1955 radioactive fall-out horizon method. Stratigraphie studies lead to uncertain results. Oxygen isotope variations give accumulation values which are too high by a factor of two at least.Accumulation values of the same order of magnitude (2·8±0·2) were derived from radioactive fall-out measurements at the U.S. “Plateau” station.

A drilling operation and core investigations at Base Roi. Baudouin (lat. 70° 25′ 5″ S., long. 24° 18′ 38″ E.) in January 1961 are discussed. The drilling, undertaken with light equipment, attained a depth of 115.72 m. From the start serious difficulties were encountered so that it was decided to use a SIPRE auger driven by the mechanism of the drilling machine. Core recovery was close to 100 per cent. Below a depth of 43.70 m., since the drill had reached the zone of high ice density (0.85 g./cm.3), a 3 m. double core barrel was used with air circulation. A depth of 79.33 m. was reached with a core yield close to 100 per cent. From this level downwards to the final depth of 115.72 in. the core yield was only 55 per cent. Preliminary observations were made at the site. A stratigraphie profile of the first 43 m. showed an al terna-ion of coarse-grained summer layers with ice formation and fine-grained winter deposits. From the seasonal alternations of the last six years, an average annual accumulation of 38.3 cm. of water was calculated. No coloured or dust layers were observed. Between 9 and 16 m. and between 41 and 44 m. an intense formation of ice was noticed. The depth-density curve is similar to those found by the. Norwegian-British-Swedish Antarctic Expedition at Maudheim and by the Americans at Little America V. If an average annual accumulation of 38 cm. of water is assumed, the whole depth drilled corresponds to approximately 240 yr. Temperature measurements could not he carried out b;rcause of the limited time available. Detailed stratigraphie and morphological studies of the cores, which are stored at −15°C. in Brussels, are planned, as well as chemical and isotopic investigations.

Sr90 and gross β activities were measured on firn sections collected around Base Roi Baudouin, Scott Base, and South Pole Station. The firn layers were dated by stratigraphy and by oxygen isotope variations. The depth distribution of Sr90 and gross β activities revealed three radioactive horizons of potential glaciological application. The deepest horizon occurred at the end of 1953 as a result of the fallout of fission products from the Ivy test series, the second and most important one was formed in early 1955 by the debris of the Castle test series, and a third horizon, defined by a sudden increase in the gross β activity but not in the Sr90 content, was formed at the end of 1962. The rate of Sr90 deposition over Antarctica has been nearly constant since 1956, amounting to 0.2 and 0.1 mc/km2 yr at Base Roi Baudouin and at the South Pole, respectively. The cumulative Sr90 deposition up to January 1963 in the 70–90°S latitude belt is found to lie between 1 and 3 mc/km2.

The concentration of Na, Mg, K, Ca, Cl, and Ni has been measured in firn samples collected in the vicinity of King Baudouin Base (70°S, 24°E) and Amundsen-Scott Station (90°S). The Ni content is of the order of a few ppb at both stations. About 35% of the Ni was probably present in the firn as soluble salts. Arguments are presented in support of an extraterrestrial origin for nearly all the Ni found in the south pole samples. The rate of Ni deposition at the south pole is of the order of 10−8 g/cm²/yr. Under the assumption of a Ni abundance of 1.3% (chondrite average), the influx rate of extraterrestrial matter over the entire earth's surface should lie between 3 and 10 million tons per year depending on the assumption made in the extrapolation.

The granodiorite from Adamello (Italy) shows a distribution of the α-radioactivity similar to that found in granitic rocks. This distribution is characterized by its heterogeneity. More than 95% of the activity is concentrated in accessories which amount to 0.1% of the volume of the rock. The most active accessories are 100,000 times more active than the essential minerals. In some cases, more than 90% of the α-radioactivity, apparently connected to the essential minerals is in fact due to microscopic inclusions of accessories. The apparent enrichment in uranium and thorium of the ferro-magnesian minerals, pointed out by several authors, is due to the abundance of radioactive inclusions in those minerals and not to the substitution by uranium and thorium of certain elements of their crystalline lattice. Very radioactive inclusions have been found. Their uranium and thorium content exceeds 10%. Their exact identification is not possible, but there are good reasons to believe that the most active are uraninite and torbernite. Allanite, the most active among the usual accessories, emits 0·47Tα/cm2/sec. corresponding to an uranium content of 0·16%. Following order of decreasing activity, then come: titanite, zircon, epidote, apatite. The "real activity" of the essential minerals, quartz, feldspar, biotite, is of the order of 3. 10-3 α/cm2/sec which would correspond to an uranium concentration of the order of 10-7 gr/gr. In contradiction to what has been observed in other granitic rocks, Adamello's granodiorite does not show any concentration of radioactivity into boundaries between crystals. Relationships between the intensity of the pleoehroic haloes and the activity of the inclusions-which produce them are discussed. © 1957., SCOPUS: ar.j, info:eu-repo/semantics/published

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After a short discussion on the Pb210 dating method, the results of Pb210 measurements on snow and firn samples from four Antarctic stations are reported as well as the experimental procedure used. Pb210 was also measured in the air at ground level, at Base Roi Baudouin, the average Pb210 activity of aerosols in 1958 being 1.3 × 10−3 dpm/kg of air. In samples of surface snow accumulated during the last two to five years, the average Pb210 activity is of the order of 100 dph/kg of snow. This activity seems to be independent of the local rate of accumulation. The variations of Pb210 activity as a function of depth were studied on two vertical firn profiles spanning an interval of more than 200 years, at Base Roi Baudouin (70°S, 24°E) and at Amundsen Scott Station (South Pole). Within experimental errors, the Pb210 activity was found to decrease exponentially with depth at both stations. The most plausible interpretation is that the rate of water accumulation and the initial Pb210 concentration in the snow have remained constant at both places over the last 100 years. The annual rates of water accumulation calculated from the decay curves are 6±1 cm at the South Pole and 45±3 cm at Base Roi Baudouin, in good agreement (to better than 10 percent) with accumulation rates so far obtained by other methods.

On examine la possibilite de localiser les mineraux de terres rares en lame mince par absorption des neutrons thermiques et de mesurer la concentration en Sm+Gd. Des plaques photographiques nucleaires chargees au bore sont utilisees comme detecteur.

The RaD method suggested by F. G. Houtermans for the determination of the “chemical” age of uranium minerals consists in the measurement of Pb/U, from the ratio RaD/Pb. Since RaD is an isotope of lead, this ratio can be determined on any quantity of lead from the mineral. In this way the quantitative analyses of uranium and lead are avoided. The determination can be carried out on an extremely small quantity of matter. The conditions under which the method is applicable, and the ways of measuring RaD, are discussed. A confirmation has been obtained with two samples of pitchblende from Shinkolobwe: the ratio Pb/U was determined on the one hand by chemical analysis, and on the other by the RaD method. All the measurements of the two methods were carried out independently at the second Physical Institute of the University of Gottingen, and at the Centre de Physique Nucleaire de l'Universite Libre de Bruxelles. One method of lead determination by dithizone extraction and polarography is described in detail. The technique of measuring the RaD by counting the beta particles of RaE was perfected. The ratios Pb/U determined by the two methods agree within the experimental errors. The advantages of the RaD method are summarized in the conclusion.

Nous avons donne dans ce travail les doses d’α necessairesa la formation des halos pleochroiques dans des biotites de differentsgranites. Nous avons etudie seulement les halos resultant de l’action des a de la famille de l’Uranium et du Thorium en equilibre, emis en couche epaisse a partir d’inclusions grandes par rapport au parcours des a. Le debut d’apparition du halo a lieu pour 1014 α emis par cm2 de l’inclusion, la saturation pour environ 5–1016 α/cm2, le debut d’inversion pour 5–1017 a/cm2. Les biotites des memes granites ont ete irradiees, experimentalement par une source de Rn+RaA+RaC’, les a etant completement absorbes dans la biotite. Les diverses biotites presentent des. sensibilites tres differentes aux irradiations des α, l’accroissement de densite pour une meme dose pouvant varier d’un facteur 5. L’evolution de la coloration suit approximativement une loi de la forme Δdmax=Δd(1−exp[−ϱα]), ϱ, Δdmax etant deux parametres specifiques et a la dose d’α par cm2. Le debut de la coloration apparait pour une dose de 2–1013 a/cm2 en accord, avec les anciens resultats de Joly et Rutherford sur des biotites de pegmatites. La saturation necessite des doses de 7 a 10 · 1014 α5cm2 et l’inversion de la coloration n’apparait pas encore pour des doses de 1.5 · 1015 a/cm2. Ces doses semblent plus faibles que celles qui sont necessaires pour produire les memes effets dans les halos. Il n’est cependant pas possible de comparer directement ces doses a celles donnees pour les halos, a cause des differences dans le spectre d’energie des a et dans les conditions geometriques d’irradiation. Si au lieu de comparer les doses en nombre d’α, on les compare ennombre d’ions formes, l’accroissement de la coloration reste plus rapide dans l’irradiation experimentale que dans les halos. Les accroissements maxima de densite optique correspondant a la saturation de la coloration sont a peu pres les memes dans les halos et dans les biotites irradiees experimentalement. La comparaison des halos et des Motites irradiees montre qu’il existe une correspondance au moins qualitative entre les sensibilites d’une biotite aux irradiations experimentales et naturelles. Au point de vue des mesures d’âge, il n’est pas encore possible d’utiliser ces experiences de coloration artificielle pour une determination d’âge absolue par les halos. Pour les determinations relatives, il faut tenir compte des differences de sensibilite. Une methode proposee consiste a comparer entre elles des biotites presentant la meme sensibilite a l’irradiation experimentale en supposant que cette similitude de sensibilite est valable aussi pour la formation des halos.

210Pb and 90Sr measurements were carried out on firn and ice samples from the Kesselwandferner (Austrian Alps). 90Sr seems to be selectively lost in the firn with respect to the other fission products and to 210Pb. The distribution of the 210Pb 'ages' of the ice samples follows a consistent pattern and is in general agreement with surface velocity measurements. © 1967., SCOPUS: ar.j, info:eu-repo/semantics/published

On montre que des erreurs importantes peuvent être faites dans les mesures d'activité α naturelle par suite de la diffusion du Radon. Ces erreurs peuvent être évitées en mesurant l'activité de l'échantillon refroidi à - 180 °C, à l'aide d'un compteur à scintillation. © 1956 Società Italiana di Fisica., SCOPUS: ar.j, info:eu-repo/semantics/published

On a etudie par la methode des emulsions photographiques nucleaires la radioactivite alpha de deux echantillons de meteorites metalliques: Toluca (Hambourg) et Carbo. On decrit la procedure utilisee pour la preparation des echantillons, l'exposition et le developpement photographique, le controle du fading et du background et l'observation microscopique. Les meteorites ont ete exposees 140 jours a des plaques Ilford C-2. Deux mille particules alpha reparties sur 36 cm2 des plaques temoins et des plaques exposees aux meteorites ont ete comptees et localisees, leurs vraies longueurs ont ete mesurees. L'analyse de la distribution des parcours des alpha montre que plus de 85% des alpha emis par les meteorites doivent etre attribues a une contamination de la surface de l'echantillon par du polonium, malgre les precautions prises. II faut noter que cette contamination correspond a la presence de 100 atomes seulement de polonium par cm2. Pour minimiser la contribution de la contamination de la surface des plaques et des echantillons, on a calcule les concentrations en uranium et thorium en se basant seulement sur les traces d'alpha ayant un parcours residuel dans l'emulsion inferieur a 15 microns (parcours de l'alpha du Th-232). Vu l'importance relative du background, on peut seulement donner des limites superieures des concentrations, qui sont pour les deux echantillons: U < 0,6 · 10−8 g/g (Th = 0) Th < 2 · 10−8 g/g (U = 0). Ces limites sont tres proches des valeurs trouvees par le groupe de Paneth sur d'autres echantillons de ces memes meteorites. On a aussi determine une valeur maximum de 10−7 g/g pour la concentration en uranium dans la troilite de Toluca. Dans l'etat actuel de la technique, les limites de detection correspondent a des concentrations en uranium et thorium de l'ordre de 5 · 10−8 g/g. La distribution des parcours des alpha sur les plaques temoins montre que 90% du background de surface des plaques provient du radon de l'air. Il serait done possible dans les meilleures conditions d'exposition d'abaisser le background d'un facteur 10 et de detecter des concentrations en uranium et thorium de 5 · 10−9 g/g.

Sodium, magnesium, potassium, calcium, iron, manganese and nickel were measured in firn samples from Base Roi Baudouin (BRB, 70°S, 24°E), Amundsen-Scott Station (ASS, 90°S) and Plateau Station (PLA, 79°S, 40°E). The rates of snow accumulation at the three stations are respectively, in g.cm-2.yr-1 :40, 6 and 2.8. The analyses were carried out by neutron activation, atomic absorption and isotope dilution. In most cases, Fe, Mn, Ni were measured simultaneously by two or three methods on aliquots of the same sample. The corrections for contamination never exceeded 10%. Average concentrations found at BRB (5 samples, 14 kg total) and at PLA (4 samples, 32 kg) respectively are as follows, in p.p.b. Na 250-30; Mg 29-5; K 29-5; Ca 17-8; Mn 0.1-0.35; Fe 6-7; Ni 0.36-0.08. At AAS (2 samples, 3 kg) :Na 9; Mn 0.2; Ni 0.1. On account of the everpresent possibility of contamination, these values must be considered as upper limits. The following conclusions are drawn from the results: 1. 1), SCOPUS: ar.j, info:eu-repo/semantics/published

O18/O16 ratios have been measured along a firn profile extending from the surface to a depth of 16 meters in the shelf ice of King Baudouin station (East Antarctica, 70°26′S, 24°19′E). Periodical variations are found which are believed to reflect the seasonal variations in the O18/O10 ratio of precipitations. They allow the identification of annual layers following the method suggested by Epstein and Sharp. The oxygen isotope variations are compared with the stratigraphic features of the same profile. The notion ‘winter’ or ‘summer’ layers is shown to be meaningless when the layers are derived from stratigraphie criteria only. Very often the fine-grained unmetamorphosed layers (generally called ‘winter’ layers) are made up of snow with high O18 content which must represent summer precipitation. On the other hand, the coarse-grained recrystallized layers (‘summer’ layers) often display a minimum O18 content and are composed of snow that fell in the winter. Identification of annual layers involves a similar degree of uncertainty from personal interpretation in the stratigraphic method as well as in the isotope ratio method, but the two methods are complementary, being affected differently by natural circumstances. A good agreement is found between the average accumulation rates deduced from both methods.

In this preliminary work, the possibility of dating crystalline rocks by pleochroic haloes has been studied. Halo-microphotometry has been combined with measurement of the alpha-activity of the inclusions by the photographic method. Standard thin sections of well dated granites have been used for calibration purposes. The reciprocity law is shown to be valid within the limit of error. The resolving power of this method depends essentially on the age ratio. Tertiary and primary rocks are easily separated.

Climatological records from the Amundsen-Scott Station, South Pole, show the summer 1957-1958 to be characterized by periods of exceptionally warm air temperature and above normal snow accumulation. The firn layer deposited during this summer displays an exceptionally high oxygen-18 content, as revealed by 18O/16O ratio profiles obtained by Epstein et al. [6,7] and by us in five pits dug along-side accumulation stakes. © 1966., SCOPUS: ar.j, info:eu-repo/semantics/published

The reasons why 53Mn (a cosmogenic radionuclide with a half-life of 3.7 × 106 y) appears as one of the best indicators of the presence of interplanetary dust are summarized. This paper reports the detection of 53Mn in pre-1952 snow samples collected on the Eastern Antarctic Plateau in the vicinity of Plateau Station. The measurements were carried out by neutron activation and X-ray spectrometry on three samples weighing a few hundred kg and covering each the time interval 1935-1950. The specific activity of 53Mn was found to be (0.82 ± 0.17) disint.min-1/103 tons of snow, corresponding to a deposition rate at Plateau Station of (2.2 ± 0.5) × 10-5 disint. min-1 m-2 y-1. The mean global deposition rate would be three times higher if 53Mn were assumed to behave in the same way as stratospheric 90Sr. By comparing this figure with existing data on the meteorite flux reaching the earth and with the galactic and solar production rates of 53Mn, it is concluded that the bulk of the 53Mn found at Plateau Station is associated with interplanetary dust in which it had been produced by the action of solar protons on iron. The deposition rate of extra-terrestrial dust-borne iron must be between 1.3 × 10-5 and 1.3 × 10-4 g m-2 y-1 at Plateau Station. These results support jointly with other studies the concept of an interplanetary zodiacal cloud of dust with a chemical composition and density not essentially different from chondritic meteorites, with a relatively 'flat' grain size distribution and a mass influx to the earth of the order of 105 tons/y. © 1974., SCOPUS: ar.j, info:eu-repo/semantics/published

In the area around King Baudouin Station (70°S, 24°E), it is shown that a reference horizon, easy to identify, was formed by the stratospheric fallout of radioactive debris from thermonuclear bomb tests. Gross β activity and Sreo have been measured in snow and firn samples from 1935 to 1960. The samples were dated by stratigraphy and by oxygen isotope-ratio measurements. The contribution of natural radionuclides is negligible, and the gross β activity can be taken as a measure of the fission products concentration. The following average values were found: from 1955 to 1960, 14 dpm/kg of snow; beginning of 1955, 22 dpm/kg (Sr90 = 4.5); 1953 and 1954, 2 dpm/kg; and from 1935 to 1952: 0.5 dpm/kg (Sr90

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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. (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. (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. (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. (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. (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 < 6.10-12g/ml, this should lead to: RRdTh/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. (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. (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. © 1957., SCOPUS: ar.j, info:eu-repo/semantics/published

Total beta measurements have been made on melt water samples from a stratigraphically dated firn core profile from the inland Greenland ice sheet (77°10′N, 61°08′W). A marked increase in radioactivity is found in the 1953 firn layer which corresponds to the first important fallout from nuclear test bombs. The pre-1953 natural beta activity is 5 d.p.m./kg. The influx of artificial debris from the Ivy tests in 1953 is noted by a sharp rise in beta activity to 10 d.p.m./kg. Total 90Sr deposit to June 1964 is 9.3 ± 1.5 millicuries/km 2 (24 ± 4 mC/mi 2). Average 210Pb activity at time of deposit is 3.9 ± 0.4 d.p.m./kg. © 1966., SCOPUS: ar.j, info:eu-repo/semantics/published

THE work recorded here is a continuation of that reported in Nature 1,2 on the isotopic composition of Antarctic snows. © 1963 Nature Publishing Group., SCOPUS: ar.j, info:eu-repo/semantics/published

THE relative abundance of oxygen isotopes in atmospheric precipitation being closely related to temperature, it has been suggested that the variations of the ratio oxygen-18/oxygen-16 in snow should be used in glaciological studies of polar regions1,2. It has been recently announced that very promising results have been already obtained by analysing cores of old ice from deep bore holes in Greenland3. © 1959 Nature Publishing Group.

A nuclear emulsion study of the alpha activity of iron meteorites is reported. The four meteorites studied were Carbo, Toluca, Tamarugal, and Thunda. Results are tabulated. (L.T.W.)

Microscopic crystals of uraninite are found in the accessories of the Baveno granite by the nuclear photographic emulsion technique. The uraninite is believed to be a primary mineral of the granite, its concentration in the sample is less than 1 p.p.m. but it contributes about 10% of the total α activity.

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.

Es wird ein vorlaufiger Maximalwert (60 Millionen Jahre) fur das Alter der pleochroitischen Hofe des alpinmetamorphen Medelser-Granites (Gotthardmassiv) mitgeteilt. Das so bestimmte Alter durfte demjenigen der alpinen Metamorphose entsprechen, welche die Biotite (mit ihren pleochroitischen Hofen) des wohl herzynischen Granites rekristallisieren liess.

THIS communication is a report of the age measurement project carried out on rocks from the Sor-Rondane Mountains (Queen Maud Land, 23° E. to 28° E.). The rocks were sampled by Picciotto1,2 during the 1958 Belgian Antarctic Expedition led by Gaston de Gerlache1. A first set of results has already been published3. The biotite strontium/rubidium ages of various eruptive and metamorphic rocks ranged from 460 to 500 million years.

Das Alter der pleochroitischen Hofe in den Graniten von Baveno und Monte Orfano wurde durch Vergleich mit dem Elba-Granit zu ungefahr 75 Millionen Jahren (Kreide) bestimmt. Dies konnte dem Alter der Intrusion entsprechen; es ist aber auch moglich, dass diese alter, zum Beispiel herzynisch, ist (Schwachung der pleochroitischen Hofe wahrend der alpinen Orogenese).

IN the course of the summer field parties of the Expedition Antarctique Beige 1957-58, I carried out a geological reconnaissance in the Sör-Rondane ranges, unexplored up to then. © 1960 Nature Publishing Group., SCOPUS: ar.j, info:eu-repo/semantics/published