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Sydoriak, Crilly and Hammel1 have reported the preparation and separation of the pure helium isotope of mass 3. They have succeeded in condensing it and have determined its vapour pressure in the temperature range 1·21°–3·34° K. (the critical temperature) and its boiling point at 3·20° K. These vapour pressure measurements appear to have interesting consequences with regard to the possibility of a phase transition in the pure helium isotope of mass 3. They provide evidence for such a transition at 1·9° K. In this communication, the possibility of this transition is first examined, the vapour pressure equations in the two ranges 1·2–1·9° K. and 1·9–3·20° K. are given, and a few remarks are made about the theoretical implications of the existence of a phase transition in the pure helium isotope of mass 3.

When tritiated 2-aminopurine was eluted from an anion exchange column the tritiated molecules moved slightly faster than the non-tritiated ones. This effect is apparently caused by a charge difference between the molecular species since their steric difference is extremely small and since the column used mainly distinguishes molecules of different average charge. Results are reported from a detailed examination of the isotope effect with purified aminopurine. (C.H.)

IN preparing the tables for Prof. L. Rosenfeld's book1 I noticed that an error was made in the mass-defects of the heavy isotopes as given in the "Isotopenbericht 1942" of Flu gge and Mattauch2. The difference of the mass-defects Δ e in every β -decay was taken equal to the maximum energies of the β -particles, eventually increased by the γ -energies. No correction was made for the fact that a neutron changes into a lighter proton, so that the mass-defect difference is

NATURAL oxygen, which forms about 50 per cent of the earth's crust, contains one heavy atom (O18) in almost exactly 500 atoms of the light isotope (O16). There exists, however, an appreciable isotopic differentiation which may be as high as some 4 per cent of the natural ratio and which has been studied extensively by Dole1, Urey2 and many others3. Nevertheless, we know very little about the distribution of the oxygen isotopes in the lithosphere. Only a few of the more abundant rocks such as limestones and iron ores have been investigated; but nothing is known about silicate rocks, which form about 99 per cent of the outer shell of the earth. It is obvious that the study of the oxygen isotope abundances in silicate rocks may yield valuable geological information.

IN both clinical practice and, experimental research, isotope dilution methods1–7 are being used routinely for the determination of total blood volume. The isotopes most commonly used are chromium.-51 (labelled red blood cells) and iodine-131 (serum albumin), both γ-emitting isotopes. Chromium-51-labelled red blood cells are used to obtain the total red blood cell circulating mass, which, in conjunction with the haematocrit, allows for an indirect determination of the total blood volume. Conversely, radioactive iodinated serum albumin gives a measure of total plasma volume and, with the haematocrit, an indirect measurement of the total blood volume. The use of either of these methods alone is subject to criticism, since the final calculations for total blood volume are based on the assumption that the peripheral haematocrit is the same as, or represents, a constant percentage of the total body haematocrit. It has been demonstrated that these assumptions are not valid5–14. The ideal method for excluding haematocrit error would be to measure the red cell portion and the plasma portion of the vascular compartment separately, the total blood volume then being the sum of these two independent measurements. Several methods3,9,15,16 have appeared utilizing chromium-51-tagged red cells and radioactive iodinated serum albumin in the same subject for measurements of total circulating red cell mass and total plasma volume, respectively. Some methods5,19 have combined repetitive injections of the respective isotopes; whereas others, the simultaneous injection of both. In those methods19 where the isotopes are injected separately, it is necessary to obtain repeated samplings of the subject's blood, which in clinical practice may be only a slight inconvenience to the patient, but is, with small animals, a significant handicap. Repeated bleeding and intravenous injecting of small laboratory animals are not only difficult but also may create stress in the animals which could influence the results in the final determinations.

RADIOACTIVE isotopes are, at the present time, being used in a wide variety of scientific investigations. Thus the development of accurate methods for the assay of these substances is of considerable importance. The three methods in common use involve the Geiger counter, the ionization chamber and the micro-calorimeter; and, although simple in principle, they are quite complicated in practice. It therefore seemed worth while to investigate the possibilities of a new method based on the fact that a flow of β-particles is equivalent to a current. In the case of a pure β-emitting isotope, 3.7 × 107 β-particles are emitted per second per millicurie (by definition), and this is equivalent to a current of 5.93 × 10−12 amp. If the isotope is deposited on a thin foil, mounted in a vacuum to eliminate gas ionization, and an electric field is applied to prevent slow secondary electrons from escaping, then the current flowing from the foil should be a direct measure of the total activity. The accurate measurement of a current in the region of 10−12 amp. is quite feasible, so that in principle it should be possible to measure radioactivity in this way. A preliminary investigation of the method has been completed, and the present communication gives a brief account of the results so far obtained, with particular reference to the effects caused by secondary emission and by ionization of the residual gas.

THE reactions of nitrogen atoms with oxygen and with nitric oxide are of considerable interest, since whereas both processes (1) and (2) are exothermic : the former reaction is very slow at room temperature, while the latter is extremely rapid. Kistiakowsky and Volpi1 obtained a value of 2 × 1012 exp(−6200/ R.T.) cm.3 mole−1sec.−1 for k1 from a mass spectrometric investigation of the reaction between nitrogen atoms and oxygen molecules in a stirred reactor between 390° and 520° K. while a value of 1.7 × 1013 exp(−7,500/R.T.) can be obtained from Kaufman's2 work on the oxygen-sensitized decomposition of nitric oxide between 1,500° and 1,700° K. No direct determination of k2 appears to have been reported, although values of 2 × 1011 (ref. 3) and a lower limit of 5 × 1013 cm.3 mole−1sec.−1 (ref. 1) have been recorded.

Data are tabulated on the incidence of pathological findings in the lungs of mice following the intratracheal administration of ruthenium-106 oxide and plutonium239 oxide. Results are presented from gross and microscopic examinations, and estimates of the total dose to lung tissue are included. The mice were killed either 100 or 500 days after treatment. Pneumonitis and pulmonary papillary cystadenomas were observed, with a marked increase in histological effects observed after 350 to 500 days. Several malignant tumors were observed. (C.H.)

AMONG the reactions commonly used in volumetric work, only two are suitable for radiometric titrations: (a) reactions which result in combinations which are only very slightly soluble1,2; (b) reactions which result in complexes3.

AUTORADIOGRAPHY has developed quickly during the past year or two, mainly following two different lines. These may be termed ‘track autoradiography’ and ‘contrast autoradiography’. In the latter the exposed grains add to a picture with varying photographic density, which may be estimated or measured quantitatively in different ways. With short exposure it may be possible to count the individual grains as shown by Doniac and Pelc1; but the normal background fog in the emulsion disturbs the process seriously.

THE purpose of the present note is to suggest that the discrepancy between the measurements of helium-like spectra made by F. Tyren and by H. Flemberg1, on one hand, and the theoretical calculations made by E. Hylleraas (non-relativistic) and by me2(relativistic corrections) on the other hand, may possibly be due to the same reason which causes the discrepancy between theory (Dirac‘s fine-structure formula) and experiment (Lamb and Retherford3) in the hydrogenium spectrum.

ABOUT ten years ago Keston and co-workers developed an isotope dilution method for the estimation of amino-acids1. This method, by which the amino-group of amino-acids is labelled with radio-active ‘pipsyl chloride’ (p-iodophenylsulphonyl chloride, labelled with iodine-131), was not found applicable for other types of compounds until recently. Last year, however, this method was also used for the detection and estimation of histamine2, pyrimidines3 and 17-hydroxycorticosterone4. In the last method the labelling agent was ‘pipsan’ (p-iodophenylsulphonylic acid anhydride).

ARGON targets can be prepared by bombarding silver disks with the separated beams of the argon isotopes in a mass-spectrograph. This technique has already been used in a study of the resonance capture of protons in the isotopes of neon1. The possibility of collecting argon atoms in a metal surface has previously been demonstrated2, and has recently been used as a method of producing samples of separated argon isotopes3.

THE trypanosomes can be cultured in media containing nucleic acids or purines. Crithidia fasciculata grows in a synthetic medium with folic acid, guanine or guanosine1,2. Trypanosoma cruzi has been cultured by Citri and Grossowicz3 in a defined medium enriched with ribonucleic acid, and its growth is stimulated by guanosine. T. rhodesiense seems to need adenine and adenosine as growth factors4.

Photonuclear (γ, n) and (γ, p) reactions produced by 23 MeV. X-rays from a synchrotron have been used to prepare new radioactive isotopes, the method being particularly advantageous for neutron-excess isotopes in the region Z=63 to 79. Whenever possible the isotopes were chemically identified. The following Table summarizes the results Element Irradiated Element Chemically Identified Half-Life Assignment Se As 9 minutes 79As Sm Sm 8 minutes 143Sm or 146Sm Eu Eu 15 hours 150Eu Gd - 20 minutes 159Eu or Gdm Dy - 14 minutes 162Tb or 163Tb Er - 96 minutes 163Er, 167Ho or 169Ho Yb - 19 minutes 172Tm, 173Tm or 175Tm Hf Lu 22 minutes 178Lu or 179Lu W Ta 48 minutes 185Ta W Ta 116 hours 183Ta Os Re 17 minutes 189Re or 191Re Pt Ir 66 minutes 195Ir or 197Ir Hg Au 27 minutes 201Au or 203Au Definite mass assignments, hitherto uncertain, have been made for 18-hour 159Gd and 48-minute 200Au.

AN automatic scanning technique employing a Geiger–Muller tube for the location and estimation of radioactive substances separated on unidimensional paper chromatograms has been described1. The application of this technique to two-dimensional chromatograms is tedious because a large sheet of paper has first to be cut up into the equivalent number of unidimensional strips and each strip scanned separately. To obviate this difficulty, an alternative technique to the conventional form of two-dimensional paper chromatography has been successfully developed for the application of two or more solvent systems to the same labelled mixture.

The Rare Isotope of Helium, He3 ; A Key to the Strange Properties of Ordinary Liquid Helium, He 4

Several observations of electron magnetic resonance in human teeth in vitro are reported. An initial search in the unirradiated material at room temperature disclosed no paramagnetic resonances in the region 3300-- 10200 gauss. Immediately following the 2.5 days after irradiation electron magnetic resonances spectra were observed at room temperature. The spectra exhibit three salient features: a broad line centered at g = 2.003 and approximately 20 gauss wide between the inflexion points; a Pake shape line the absorption curve maximum of which lies at g = 2.0004; and a weak doublet centered at g = 2.0029 plus or minus 0.0003, corrected for second-order effects, and a splitting of 498 plus or minus 2 gauss. Several conclusive arguments are made for the identification of a doublet in one spectrum as hydrogen atoms. (P.C.H.)

By re-investigating the Raman spectrum of C2N2 we have obtained, in addition to the frequencies already known1, four more frequencies: 521.4 cm.−1, 561.4 cm.−1, 841 cm.−1 and 2298.4 cm.−1. The last one, which appears as a weak satellite to the very strong 2328.5 cm.−1, is most probably an isotope line due to C12C13N214, and enables us to calculate the complete harmonic potential function using some infra-red frequencies also2. In order to get an interpretation of the physical nature of the potential function, it is helpful to calculate the forces called into action on different atoms i by special atomic displacements. Considering only displacements, Δx, along the axis of the linear molecule, these forces are given by

THE Atomic Energy Act 1948 of the Union of South Africa gave the Atomic Energy Board the sole right to import into the Union artificially made radioactive elements. The Board has designated the South African Council for Scientific and Industrial Research as its agent in this matter, and as a result its subordinate organisation, the National Physical Laboratory, has had to consider the problem of bringing into the Union, over a distance of six thousand miles, considerable quantities of radioactive elements the lives of which are so short that air transport is the only possible method.

STUDIES of the distribution of intravenously injected potassium-42 in rats have shown that the kidney takes up this cation from the plasma at considerably higher rates than does any other organ1,2. In the first few minutes after the injection, the specific activity in the renal tissues exceeds that of the plasma2,3. At 2 min., approximately 15 per cent1 and 10 per cent4 of the injected dose were found in rabbit kidneys and about 12 per cent (unpublished observations) in rat kidneys. These fractions are far greater than the expected equilibrium value. Analysis of these findings indicated that all the potassium arriving in the plasma in the kidney is exchanged with potassium from cells. Morel and Guinnebault have recently presented evidence that the renal cortex is the main site of this very rapid exchange3. From their experiments it appears that in the rabbit as much as 15 per cent of the total potassium present in the cortex is exchanged per minute. This was corroborated macroscopically by autoradiography in which X-ray films were exposed to 2-mm. thick frozen kidney slices. The resulting autoradiograms indicated that in the 5 min. following an intravenous injection, the intense activity emanated from a region roughly corresponding to the cortex.

IN a recent study of the transmutation of a number of elements by deuterons1, the emission of three groups of protons from magnesium under deuteron bombardment was reported. These groups were assigned to particular isotopes by arguments based chiefly on the value of the energy released in similar reactions with other elements and on differences between the excitation functions of the groups. We have now been able to bombard separated isotopes, and the accompanying graph shows the proton groups observed from targets of magnesium-24, -25 and -26 deposited on stainless steel. The deuteron energy was 930 keV. as in the earlier experiments, and the protons were observed at right-angles to the incident beam. The three targets for which the results are shown in the figure were cut from larger areas on which the magnesium was deposited; but since the deposits were not uniform, the target thicknesses could not be accurately estimated. In the case of the magnesium-24 target, observation of the width of a (ργ) resonance-level suggested an equivalent thickness of about 10 keV. ; the thickness of the magnesium-25 and -26 targets was unknown, and the relative intensities of the groups shown in the graph are therefore unlikely to be those which would be obtained from targets in the normal isotopic ratio of thickness.

THERE have been several attempts1–6 to identify the sources of lead in the air and vegetable or animal tissue by analysis of stable isotopes. Blood sampling is the easiest means of conducting a large scale investigation of lead in the human body. Here I report some measurements as part of an exploration of the feasibility of such a programme.

CHLOROBIPHENYLS with one to four chlorine atoms per molecule are metabolised by certain animals, plants and microorganisms but the more highly chlorinated biphenyls are rather resistant to metabolic change1.

THE gastro-intestinal absorption of many substances may be determined by faecal measurements following oral ingestion of a test dose containing a radioisotope. During the course of experiments of this type to determine the absorption of vitamin B12 in rats, it was noticed that residual radioactivity appeared in the excreta of control animals which had not been given the radioactive test dose. This radioactivity, which was first noticed in July 1956, has recently increased to an extent which makes it impossible to continue the experiments as originally designed.

EXPERIMENTS recently carried out in this Institute1 have shown that, by bombarding silver disks with beams of ions of neon isotopes obtained from a high-intensity mass-spectrograph2,3, it is possible to prepare targets, containing the separated neon isotopes, that are suitable for certain investigations in nuclear physics. Due to the high energy of 60 keV., the ions penetrate into the silver surface to a depth of about one hundred atomic diameters, and to this depth a high concentration of neon atoms can be obtained. The experimental results (loc. cit.) indicate that a maximum concentration is approached when the surface has been hit by about 6 × 1016 ions per cm.2, corresponding to the collection of 2 μ gm. of neon per cm.2, if all the neon atoms remain in the surface.

ON the occasion of the French atomic explosion of February 13, 1960, in the Sahara, a control system of radioactivity in the air was set up covering the whole of Italy. The controlling stations of the system were equipped to collect samples of atmospheric dust by means of suction through a filter. The β-activity of the samples was measured 120 hr. after they had been collected.

IN a former communication1 I calculated the energy and distribution of nucleon density of atomic nuclei by Ritz's method in the first approximation, assuming Yukawa forces between the nucleons. In the energy expression of the nucleus, in addition to the exchange energy and kinetic zero-point Fermi energy of the nucleons, we have also taken into account the kinetic energy correction of Weizsacker, the electrostatic Coulomb energy of protons and the Coulomb exchange energy of protons arising from the Coulomb interaction of protons. In the first approximation for the neutron density ρn and the proton density ρp, functions of Gaussian type have been set up in the following form: where r is the distance from the centre of the nucleus, r0 is the Compton wave-length of the π-mesons divided by 2π, and are normalizing factors and a denotes a variational parameter to be determined from the minimization of the energy.

THE potential hazard of genetic changes induced by radioactive substances and of mutagenic and radiomimetic action of non-radioactive compounds is of current interest. Information, however, as to the intimacy of contact of these substances, when introduced into the human body, with the reproductive cells, particularly the ovum, is scant.

A search for tungsten radio-isotopes was made using a 5-mil tantalum foil which had received 80 micro-ampere-hours bombardment with approximately 20 MeV. deuterons from the 60-in. Crocker Laboratory cyclotron. The foil was dissolved in nitric acid containing five per cent of hydrofluoric acid. A few milligrams of tungsten carrier was added, and after removal of hydrofluoric acid by fuming with sulphuric acid, the tantalum was precipitated by sodium hydroxide and the precipitate digested with hot alkali. Tungsten was precipitated from the alkaline solution by boiling with excess nitric acid. The procedure was repeated until the tantalum-scavenging carrier precipitates were inactive.

THE mechanism of elemental sulphur transport from the medium into the cells of sulphur-utilizing micro-organisms was investigated by Umbreit, Vogel and Vogler1, They concluded that for Thiobacillus thiooxidans, the sulphur, on contact with the cells, dissolves in globules of highly unsaturated fat located at the poles of the cells. Knaysi2 was unable to confirm the existence of polar fat globules and pointed out the difficulties involved in postulating contact between an extracellular particle and an intraprotoplasmic structure. Vishniac and Santer3 suggested a sulphur-transport mechanism involving reduced glutathione (GSH) or a similar molecule reacting as follows: the sulphide formed enters the cell in free or bound form and the GSSG is reduced by subsequent intracellular sulphide oxidation. No experimental evidence was presented to support this mechanism. It is apparent that the problem is not yet solved.