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We report results of a consortium study of a large interplanetary dust particle known as cluster L2008#5. This cluster is composed of fifty-three fragments (>5 pm in diameter) and several hundred fines ( Several methods were used to estimate the degree of heating that this cluster experienced. Variations in the inferred peak temperatures experienced by different fragments suggest that a thermal gradient was maintained. The cluster as a whole was not strongly heated; it is estimated to have a low earth-encounter velocity which is consistent with origin from an object in an asteroidal orbit rather than from a comet, which would most likely have a high entry velocity. Our conclusions show that cluster L2008#5 consists of a chemically and mineralogically diverse mixture of fragments. We believe that cluster L2008#5 represents a heterogeneous breccia and that it was most likely derived from an object in an asteroidal orbit. We also present an important cautionary note for attempts to interpret individual, small-sized 10–15 μm IDPs as representative of parent bodies. It is not unique that individual building blocks of IDPs, such as discrete olivine, pyroxene, sulfide grains, regions of carbonaceous material, and other noncrystalline material, are found in several fragments; however, it is unique that these building blocks are combined in various proportions in related IDPs from one large cluster particle.

Helium and neon were extracted from individual lunar ilmenite grains, approximately 100 micrometers in diameter, using a pulsed step-heating technique. Grains from lunar samples 71501 and 79035, believed to have been exposed to solar corpuscular radiation at greatly different times, were studied. The results found were consistent with the hypothesis that in addition to solar-wind-implanted gas, a second more deeply implanted component was present in both species of grains. Average isotopic ratios were determined giving equal weight to each of the particles. As found in depth studies employing chemical etching, both the He-3/He-4 and Ne-20/Ne-22 ratios were lower in the more deeply implanted gas than in the solar wind component. The He-3/He-4 ratio in the solar wind component of the more ancient grains was lower than that in the more recently exposed ones, whereas no difference was found for the more deeply embedded He. In the deeply embedded component of the ancient grains, the He-4/Ne-20 ratio was approx. 2x that found in the more recently exposed grains. In the shallowly implanted component, the ratio varied greatly from grain to grain, preventing comparison with the solar wind elemental composition.

Fragments of 24 individual interplanetary dust particles (IDPs) collected in the Earth's stratosphere were obtained from NASA's Johnson Space Center collection and subjected to pulse-heating sequences to extract He and Ne and to learn about the thermal history of the particles. A motivation for the investigation was to see if the procedure would help distinguish between IDPs of asteroidal and cometary origin. The use of a sequence of short-duration heat pulses to perform the extractions is an improvement over the employment of a step-heating sequence, as was used in a previous investigation. The particles studied were fragments of larger parent IDPs, other fragments of which, in coordinated experiments, are undergoing studies of elemental and mineralogical composition in other laboratories. While the present investigation will provide useful temperature history data for the particles, the relatively large size of the parent IDPs (approximately 40 micrometers in diameter) resulted in high entry deceleration temperatures. This limited the usefulness of the study for distinguishing between particles of asteroidal and cometary origin.

Fragments from 20 individual particles, collected in the earth's stratosphere and believed to be interplanetary dust particles (IDPs), were subjected to step-heating to see if differences in the release pattern for He-4 could be observed which might provide clues to the origin of the particles. Comparisons were made to the release pattern for 18 individual lunar surface grains heated in the same manner. Twelve of the IDP fragments contained an appreciable amount of He-4, 50 percent of which was released by the time the particles were heated to approximately 630 C. For the 18 individual lunar grains, the corresponding average temperature was 660 C. The He-3/He-4 ratios found for these fragments agreed well with those found for deep Pacific magnetic fines believed to be of extraterrestrial origin, and were comparable to those which have been observed for the solar wind and lunar surface soil grains. Four of the IDP fragments contained appreciably less He-4, and this was released at a higher temperature. The remaining four fragments had too little He-4 to permit a determination. From Flynn's analyses of the problem of the heating of IDPs in their descent in the atmosphere, the present results suggest that the parent IDPs of the 12 particles which contained an appreciable amount of He-4 suffered very little heating in their descent and are likely of asteroidal origin, although one cannot rule out the possibility that at least some of them had a cometary origin and entered the earth's atmosphere at a grazing angle.

— Helium and neon isotope ratios were determined for 16 interplanetary dust particles (IDPs) collected in the stratosphere. The concentration of helium observed varied greatly from particle to particle, with the highest values approaching those found for lunar surface fines and some gas-rich meteorites. With the exception of one particle, for which the 3He/4He was (1.45 ± 0.05) × 10−3, the remainder of the particles had ratios falling between 1.4 and 3.1 × 10−4, with an average of (2.4 ± 0.3) × 10−4, substantially less than is associated with the solar wind or observed in average lunar fines or in lunar fines having sizes comparable to those of the IDPs studied. The average 20Ne/22Ne found was 12.0 ± 0.5. Only three reasonably reliable 21Ne/22Ne ratios could be determined, and for these the average was 0.035 ± 0.006. The isotopic ratios appear to preclude the presence of any appreciable amount of cosmic ray-produced spallogenic products. The high 4He concentrations observed for some of the particles, approaching those observed for lunar surface grains, suggest they were not heated to high temperatures and degassed as they descended in the earth's atmosphere. From Flynn's study of the dynamics of IDPs entering the earth's atmosphere this could mean they entered the atmosphere at relatively low velocities, and hence may be primarily of asteroidal rather than cometary origin.

A discussion is given of the electron impact ionizing system introduced by Bleakney in 1929 and how it influenced mass spectrometer development in the next decade. The transformation from an instrument mounted in a solenoid whose magnetic field both collimated the ionizing beam of electrons and performed the mass analysis to an instrument in which an electromagnet replaced the solenoid is traced. The further transition to an arrangement in which a sector magnetic field is employed for performing the mass analysis, and the ion source and collector systems are outside the sector magnet, is described.

Helium and neon concentration measurements, along with isotope ratio determinations, have been made for particles collected in the deep Pacific with a magnetic sled, and they are believed to be of extraterrestrial origin. Analyses were made for samples consisting of composites of many extremely fine particles and for several individual particles large enough to contain sufficient gas for analysis but small enough to escape melting in their passage through the atmosphere. Step-heating was employed to extract the gas. Cosmic-ray spallation products or solar-wind helium and neon, if present, were not abundant enough to account for the isotopic compositions measured. In the case of the samples of magnetic fines, the low temperature extractions provided elemental and isotopic ratios in the general range found for the primordial gas in carbonaceous chondrites and gas-rich meteorites. The isotopic ratios found in the high temperature extractions suggest the presence of solar-flare helium and neon.

A recent study of the isotopic ratio of helium (3He/4He) in the terrestrial atmosphere led the individuals who made the investigation to suggest that this ratio is decreasing with time, probably due to anthropogenic release of low isotopic ratio crustal helium from oil and gas wells. The measurements made over an 11 year period from 1977 to 1988 led to the prediction that the rate of decrease was of the order of 1 × 10−9/yr. Several absolute isotopic ratio measurements made between 1969 and the present time also have been reported. These show a slight decrease in the helium isotopic ratio (much less than the 11 year data set shows). In the present paper, we report an unpublished, absolute helium isotopic ratio measurement the authors made in 1956. This value, when combined with the previously reported results, extends the time over which such measurements were made to a 32 year period and does not confirm that there is any decrease in the helium isotopic ratio in the atmosphere over this time.

A summary is given of experiments performed to determine the amounts and isotopic composition of the helium and neon found in individual interplanetary dust particles collected in the Earth’s stratosphere. The role of step‐heating and pulse‐heating techniques for performing the extractions is discussed together with the application of the techniques to determination of the thermal history of the particles. The practicality of using these methods for distinguishing between particles of cometary and asteroidal origin is considered.

Simultaneous measurements of ambient O2 and N2 concentrations and temperature were made near winter solstice 1975 by the open source neutral mass spectrometer on Atmosphere Explorer-D. The data, taken at midmorning and all latitudes, are analyzed using scatter plots and correlation coefficients. Results indicate that O2 concentrations at about 200 km is controlled both by temperature variations and wind-induced diffusion. Since the winds are most effective in controlling O2 at lower altitudes, it is reasonable to expect that temperature effects will dominate over wind effects at higher altitudes.

The Atmosphere Explorer (AE) satellites have acquired a large data base of aeronomic parameters measured over a wide range of geophysical conditions over the past 3 years. These data have already been used in a straightforward way to determine rate coefficients for many thermospheric reactions. In this paper we report the use of the AE data in a new way to simulate laboratory-type control of variables to determine the rate coefficient for the reaction . By appropriate selection of data we succeed in eliminating the effects of three uncertain rate coefficients on our determination; these are recombination of N2+ and electron and N2 quenching of O+(²D). We find that k < 3 × 10−11 cm³ s−1. This upper limit is a factor of 3 smaller than an earlier estimate of the rate coefficient made from AE data. The difference in results is attributed to a large uncertainty in the dependence of N2+ recombination on vibrational excitation which affected the earlier work. Our technique demonstrates how the atmosphere can be used successfully as a laboratory to study atomic and molecular processes.

The open source neutral mass spectrometer on the Atmosphere Explorer satellites used for direct in situ measurements of the neutral gas temperature by means of the 'fly-through' mode of operation is evaluated. The derived neutral temperature (Tn) is compared with ion temperatures (T1) obtained simultaneously from the on-board retarding potential analyzer for altitudes and conditions where the two temperatures should be equal. A statistical analysis showed consistency between concurrently observed values of Tn and T1, also shown through profiles depicting their altitude distributions between 150 and 225 km. The overall magnitude of temperatures calculated from the Jacchia (1971) model results in a better representation of the observations than the higher temperatures predicted for this region by the MSIS model (Hedin, 1977), and agreement is also found between observed temperatures and neutral temperatures derived from altitude distributions of N2 particle densities.

The Atmosphere Explorer satellites (AE-C, -D, and -E) were initially placed into highly elliptical orbits with perigees around 140 km and apogees of 4000 km. As a result of such an orbital geometry, measurements of neutral constituents at high altitudes represent mainly vertical changes in densities. The influence of horizontal density gradients on measurements above 400 km is small. Under geomagnetically quiet conditions, the density profiles can be used to derive scale-height temperatures of the exosphere. The open-source neutral mass spectrometer (OSS) flown on all three AE-satellites measured neutral constituents such as N2, O, and N well above 400 km. The temperatures derived from scale heights show a good agreement among the constituents and the expected close correlation with the F10.7-cm solar flux. Satellites with highly elliptical orbits provide the opportunity to measure simultaneously both densities and temperatures.

Atomic nitrogen number densities in the upper thermosphere measured by the open source neutral mass spectrometer (OSS) on Atmosphere Explorer-C during 1974 and part of 1975 have been used to construct a global empirical model at an altitude of 375 km based on a spherical harmonic expansion. The most evident features of the model are large diurnal and seasonal variations of atomic nitrogen and only a moderate and latitude-dependent density increase during periods of geomagnetic activity. The model also suggests the presence of a substantial semiannual variation and of nighttime minima at mid-latitudes. Maximum and minimum N number densities at 375 km for periods of low solar activity are 3.6 × 106 cm−3 at 1500 LST (local solar time) and low latitude in the summer hemisphere and 1.5 × 105 cm−3 at 0200 LST at mid-latitudes in the winter hemisphere. The amplitude of the diurnal variation at equatorial latitudes is about a factor of 8.

Number-density data obtained at orbital 'crossover' points with the neutral-gas mass spectrometers aboard the Esro 4, Aeros A, AE-C, and Aeros B satellites are intercompared. All the mass spectrometers were designed to measure the ambient number densities of atomic oxygen, molecular nitrogen, helium, and argon. It is found that the agreement for N2 and O is satisfactory within the experimental errors and that the He measurements exhibit unexpectedly large discrepancies far outside the error range. Calibration and instrument sources of error are considered.

An apparatus which produces neutral gas beams in the velocity range from thermal to 6 km/s makes possible studies simulating the motion of instruments through tenuous atmospheres. Use of the apparatus in studying the response of an open-source mass spectrometer is examined. Experiments performed include responses when the instrument is in a normal mode of operation, when the ion source potentials are adjusted to reject striking gas particles, when the beam is restricted so that portions of the ion source are struck, and when the beam strikes at angles other than normal incidence. Results indicate specular radiation of particles out of the source and stagnation ratios close to unity for normal operation. Retarding potential studies dropped the sensitivity by a factor of about 10, and as angles of attack are varied, the effect was found to depend upon beam velocity and the way the ions are initially accelerated.

The availability of rockets and space probes has made possible in situ investigations of the earth's upper atmosphere and the atmospheres of other planets and comets. Mass spectrometers are able to make both gas and isotopic analyses. They have played a major role in the study of the earth's upper atmosphere and in the investigation of the atmospheres of Mars and Venus. The results obtained have important consequences in furthering our understanding of the evolution of the solar system. Application to the exploration of the outer planets and comets promises to provide important results no one can foresee.

The open source neutral mass spectrometer (OSS) on the Atmosphere Explorer-C satellite (AE-C) measures the neutral constituents of the upper atmosphere. It has been found that atomic nitrogen densities can be determined at altitudes above 380 km. Most of the nitrogen atoms combine with oxygen adsorbed on the walls of the ion source to form NO. The measured net peaks at 14 amu and 30 amu show the scale height expected for atomic nitrogen; both peaks have a pronounced diurnal variation. We computed absolute number densities at 400 km for a time period between February and April 1974 when measurements were taken in the northern hemisphere. Minimum and maximum densities of atomic nitrogen occur between 4 and 6 hr LST in the morning and around 16 hr LST in the afternoon, respectively. At 400 km the minimum particle density is 1.0 × 105 cm−3 and the maximum density 1.5 × 106 cm−3. In contrast to the response of N2 to geomagnetic activity, atomic N shows no appreciable effect.

Densities for carbon dioxide measured by the upper atmospheric mass spectrometers on Viking 1 and Viking 2 are analyzed to yield height profiles for the temperature of the martian atmosphere between 120 and 200 kilometers. Densities for nitrogen and argon are used to derive vertical profiles for the eddy diffusion coefficient over the same height range. The upper atmosphere of Mars is surprisingly cold with average temperatures for both Viking 1 and Viking 2 of less than 200 degrees K, and there is significant vertical structure. Model calculations are presented and shown to be in good agreement with measured concentrations of carbon monoxide, oxygen, and nitric oxide.

Results are presented of measurements obtained with an open-source mass spectrometer both in earth orbit and in a laboratory molecular beam facility. The mass spectrometer/ion source combination was developed in the laboratory to be operable in either of two modes by altering ion extraction potential on ground command, i.e., as a stagnation cavity or to respond only to the incoming molecules of the unperturbed atmosphere. Results indicate that the use of this open-source configuration and dual-mode capability, allied with both standard static calibration and dynamic calibration using high-speed molecular beam techniques in the laboratory, allows collection of useful data on aeronomy of the upper atmosphere of planets and comet tails.

The Atmosphere Explorer-C satellite carries a large number of experiments including an open source neutral mass spectrometer. Among the measurements obtained with this instrument were ones of particle densities of N2, O, and He at northern latitudes in early February and late June 1974. The orbital geometry of the satellite was such that comparisons could be made between the winter and summer values at the same altitudes and latitudes and at similar local solar times. The helium density shows in midmorning a winter to summer enhancement of a factor of 29 at 400 km. The enhancement at other altitudes, both higher and lower, is less. At 250 km the winter/summer oxygen ratio is 1.7, whereas the winter/summer nitrogen ratio is 0.6. Both ratios decrease with increasing altitudes. The analysis identifies an oxygen enhancement at low altitudes in winter and at high altitudes in summer.

The Atmospheric Explorer-C satellite used a neutral mass spectrometer containing a quasi-open ion source operating either in normal mode or in one that utilizes the satellite velocity to distinguish between incoming ambient particles and ambient particles which have struck instrument surfaces and become accommodated. An analysis was made of data from the mass spectrometer for those orbits when the open ion source operated either partially or entirely in the fly-through mode. A comparison of N2 density, total O density and O2/N2 density values at 200 km was made. The average N2 and O2 density values agree well with previous rocket soundings and other studies. It is believed that the individual absolute number densities obtained in the normal mode of operation are accurate to within 20% while those deduced from fly-through data may be accurate to only 30%.

We describe the measurement of the 7320- to 7330-A emissions by O+(²P) in the evening twilight over Arecibo. We show how contamination by scattered sunlight and by OH airglow can be subtracted from the measured spectrum to achieve an unambiguous identification of both doublets. The measured ratio of the brightnesses of the two features is in agreement with theory. The measured wavelength of the doublet at 7320 A (7319.9 ± 0.1 A) is different from the value usually quoted (7319.0 A). We have assumed photoionization to be the major source, and we have compared our surface brightnesses measured as a function of solar depression angle with those derived theoretically from nearly coincident Atmosphere Explorer data on neutral composition and solar ultraviolet flux. Agreement is good. Since quenching of O+(²P) is negligible under the conditions of our experiment, it appears that ground-based airglow measurements of the kind we describe can be used to monitor the variation of atomic oxygen density in the F region.

The characteristics of an open-source mass spectrometer designed for use on the Atmosphere Explorer satellites C, D and E were determined in a high speed molecular beam simulating upper atmosphere flight. In its normal mode of operation it was found that for CO2 and Ar beams having speeds as great as 3.9 km sec−1 the performance closely matched that of an idealized closed source instrument. When operated in a “fly-through” mode, one in which no drawing out fields were applied to ions formed in the electron beam, the mass spectrometer rejected either residual gases or molecules which had reflected from the instrument's surfaces, and passed only incident beam molecules or ion fragments acquiring kinetic energy in the ionization process. The application as a gas analysis tool is discussed, as is the application to analyses of an ambient atmosphere by an instrument carried on a fast-moving spacecraft such as an earth satellite or planetary probe.

Measurements of O(++) concentrations made by the Atmosphere Explorer C satellite are analyzed for altitudes where photochemical equilibrium conditions prevail in order to determine the photochemical sources and sinks of the doubly charged ion. The major loss process is found to be through partial charge exchange with neutral atomic oxygen with a rate coefficient of 1 x 10 to the -11th cu cm/s with an uncertainty of 40%. Above 220 km the major source is photo-ionization of O(+). However, X ray ionization of O (at not greater than 23.3 A) producing O(++) directly through the Auger process provides a better fit to the observed profile at lower altitudes.

Simultaneous nighttime measurements of ion and neutral concentrations and temperatures made by the Atmosphere Explorer-C satellite were used to determine the recombination rate coefficient of NO(+) as a function of electron temperature. The results agree in shape and absolute magnitude to within one standard deviation with those of Walls and Dunn (1974), indicating that NO(+) ions in the ionosphere may be in the ground vibrational state.

A total of four Martian samples, one surface and one subsurface sample at each of the two Viking landing sites, Chryse Planitia and Utopia Planitia, have been analyzed for organic compounds by a gas chromatograph-mass spectrometer. In none of these experiments could organic material of Martian origin be detected at detection limits generally of the order of parts per billion and for a few substances closer to parts per million. The evolution of water and carbon dioxide, but not of other inorganic gases, was observed upon heating the sample to temperatures of up to 500 C. The absence of organic compounds seems to preclude their production on the planet at rates that exceed the rate of their destruction. It also makes it unlikely that living systems that behave in a manner similar to terrestrial biota exist, at least at the two Viking landing sites.

The quasi-open-source mass spectrometer carried on the Atmospheric Explorer-C satellite has a mode of operation which utilizes the velocity of the vehicle to distinguish between incoming ambient particles and ambient particles which have struck instrument surfaces and become accommodated. Utilization of this mode has made possible the simultaneous measurement of atomic and molecular ambient oxygen without the ambiguity which usually arises due to surface reactions in the instrument. The method appears promising as a means for analyzing planetary atmospheres or the gas surrounding comets.

The cosmogenic He 3 and He 4 distribution in a cross-section of the iron meteorite, Carbo, has been made with a mass spectrometer. The He 3 /He 4 ratio is approximately constant throughout most of the cross-section and has a value of 0·239. The amount of He 3 varies between the approximate limits of 3·2 and 4·6 × 10 −6 std. cm 3 /g of meteorite. Contours of constant He 3 and He 4 were plotted. These are open curves indicating the meteorite was either split in half late in its lifetime or eroded away on one side since its fall to earth.

An investigation of the ${\mathrm{He}}^{3}$/${\mathrm{He}}^{4}$ abundance ratio in helium extracted from the atmosphere, gas wells and a number of minerals has been made. Wide variations in this ratio are observed indicating that a more comprehensive program would be well worth while. ${\mathrm{He}}^{3}$ is observed in all sources of helium except radioactive minerals. This suggests the possibility of a primordial source as well as more recent sources for this isotope.

A mass spectrograph is described with which a study of the isotopic constitution of argon, potassium, rubidium, zinc and cadmium has been made. A calculation is carried out which indicates that the radioactivity of potassium and rubidium can best be explained by assuming that it is ${\mathrm{K}}^{40}$ in the case of potassium and ${\mathrm{Rb}}^{87}$ in the case of rubidium which is undergoing decay.

The open-source mass spectrometer will be used to obtain the number densities of the neutral atmospheric gases in the mass range 1 to 48 amu at the satellite location. The ion source has been designed to allow gas particles to enter the ionizing region with the minimum practicable number of prior collisions with surfaces. This design minimizes the loss of atomic oxygen and other reactive species due to reactions with the walls of the ion source. The principal features of the open-source spectrometer and the laboratory calibration system are discussed.

A mass spectrometer suitable for routine isotope analyses of the lighter elements is described. Complete electronic circuits are given. An all metal mass spectrometer tube is employed. A null method of determining relative abundances of the elements carbon, nitrogen, and oxygen is used. Although designed primarily for analyzing elements for which separated isotopes are available as tracers, the instrument may be modified for use over the entire atomic table or for making gas analyses.

Lower thermosphere composition over New Mexico, discussing rocket flight mass spectrometer measurements during summer 1967

A mass spectrometer suitable for routine isotope analyses of carbon, nitrogen, and other light elements which may be put in the gaseous or vapor form is described. Although a simple, relatively inexpensive magnet consuming little power is used, good resolution is obtained.

A six-inch double-focusing mass spectrometer employing the peak matching method of measurement has been used to measure 36 atomic masses in the region $130\ensuremath{\leqq}A\ensuremath{\leqq}154$ and $54\ensuremath{\leqq}Z\ensuremath{\leqq}63$. Atomic masses of 41 radioactive nuclei have then been calculated from mass differences derived from nuclear reaction and $\ensuremath{\beta}$-decay energies. Nucleon binding and pairing energies have been calculated from the resulting mass table. The effect of the shell closure at $N=82$ on the systematics of nuclear binding and pairing energies has been investigated in greater detail than has previously been possible. The discontinuity in neutron binding energy, observed in reaction measurements and $\ensuremath{\beta}$-decay systematics, is shown to be caused by a decrease in binding energy of neutrons beyond $N=82$ rather than a particular large binding energy at $N=82$. The systematic behavior of proton binding and pairing energies is also studied. The nucleon binding and pairing energy results show departures from uniformity in the region near $N=90$. Electric quadrupole systematics have also indicated a change in nuclear structure in this region. The present atomic masses are also employed in the isotopic identification of several reactions, in the study of several natural alpha decays, and in the interpretation of several $\ensuremath{\beta}$-decay disintegration schemes.

Measurement of the neutral atmospheric composition above Fort Churchill, Canada (59 N, 94 W), by mass spectrometers in two rocket flights at 0835 CST on Feb. 4 and 6, 1969. A quantitative measure for the extent of agreement with static diffusive equilibrium is introduced, and substantial agreement with profiles predicted when static diffusive equilibrium was assumed is found for all constituents including helium. A sensitive search for atomic nitrogen yielded upper limits of a few per cent for one flight and of 0.2% for the other.

The experimental investigation of the atomic oxygen response of an open-source mass spectrometer conducted in a high-velocity molecular-beam facility is described, and its results are evaluated. These preliminary results illustrate the value of studies of this type and tentatively support the thesis that in rocket flights of open-source mass spectrometers atomic oxygen loss is not a serious problem.

The cosmogenic Ar/sup 38/, Ar/sup 36/, Ne/sup 22/, Ne/sup 21/, Ne/sup 2/ s/sup 0/, He/sup 4/, and He/sup 3/ distribution in part of a cross section of the iron meteorite Grant was measured. The amounts were found to vary systematically with depth. The depth effect was analyzed in terms of a production mechanism, and numerical parameters were determined. Comparisons were made with the results of other investigations. Functional relationships correlating relative amounts of cosmogenic nuclides with position and size of a meteoritic body are demonstrated. In principle the determination of a sufficient number of cosmogenic nuclides in a single sample permits deductions about the radiation dosage and the size of the meteoroid as well as the location of the sample within the body. (auth)

A mass spectrographic measurement of the relative abundances of the isotopes in eight samples of radiogenic lead and thirteen samples of common lead has been made. As five of the radiogenic lead samples originated from minerals containing both uranium and thorium, three independent determinations of the age could be made. One of the samples was the oldest so far studied and appears to have an age close to two billion years. The common lead samples were found to have large variations in the relative abundances of the same sort as were reported in a previous investigation of twelve other samples.

A double-focusing mass spectrometer employing a 90\ifmmode^\circ\else\textdegree\fi{} electrostatic analyzer followed by a 60\ifmmode^\circ\else\textdegree\fi{} magnetic analyzer has been constructed having a resolution sufficiently great to permit mass difference measurements by the familiar doublet method. High stability is obtained by use of an auxiliary mass spectrometer tube which compensates for fluctuations in both the magnetic field and the source of potential for the deflecting and accelerating plates of the main spectrometer. Ion currents are measured electrically and data recorded automatically.The doublets determined and their values in ${10}^{\ensuremath{-}4}$ amu are as follows: ${\mathrm{D}}_{2}$${\mathrm{O}}^{16}$-${\mathrm{A}}^{40}$/2, 419.67\ifmmode\pm\else\textpm\fi{}0.18; ${\mathrm{D}}_{2}$${\mathrm{O}}^{16}$-${\mathrm{Ne}}^{20}$, 307.21\ifmmode\pm\else\textpm\fi{}0.39; ${\mathrm{Ne}}^{20}$-${\mathrm{A}}^{40}$/2, 112.80\ifmmode\pm\else\textpm\fi{}0.18; ${({\mathrm{C}}^{12})}_{2}$${\mathrm{H}}_{4}$-${\mathrm{C}}^{12}$${\mathrm{O}}^{16}$, 364.43\ifmmode\pm\else\textpm\fi{}0.22; ${({\mathrm{N}}^{14})}_{2}$-${\mathrm{C}}^{12}$${\mathrm{O}}^{16}$, 112.80\ifmmode\pm\else\textpm\fi{}0.13; ${({\mathrm{C}}^{12})}_{3}$${\mathrm{H}}_{8}$-${({\mathrm{N}}^{14})}_{2}$${\mathrm{O}}^{16}$, 617.6\ifmmode\pm\else\textpm\fi{}0.9; ${\mathrm{C}}^{12}$${\mathrm{H}}_{4}$-${\mathrm{O}}^{16}$, 364.78\ifmmode\pm\else\textpm\fi{}0.22; ${\mathrm{C}}^{12}$${\mathrm{H}}_{2}$-${\mathrm{N}}^{14}$, 125.86\ifmmode\pm\else\textpm\fi{}0.13; ${({\mathrm{C}}^{12})}_{3}$${\mathrm{H}}_{4}$-${\mathrm{A}}^{40}$, 688.77\ifmmode\pm\else\textpm\fi{}0.35; ${({\mathrm{C}}^{12})}_{3}$${\mathrm{H}}_{4}$-${\mathrm{Ca}}^{40}$, 685.39\ifmmode\pm\else\textpm\fi{}0.46; ${\mathrm{Ca}}^{40}$-${\mathrm{A}}^{40}$, 3.2\ifmmode\pm\else\textpm\fi{}0.8; ${\mathrm{D}}_{2}$-${\mathrm{He}}^{4}$, 256.12\ifmmode\pm\else\textpm\fi{}0.09; ${\mathrm{H}}_{2}$${\mathrm{O}}^{16}$-${\mathrm{A}}^{36}$/2, 267.02\ifmmode\pm\else\textpm\fi{}0.40.

Lower thermosphere neutral composition diurnal variations, noting molecular N and O, Ar, He and atomic O