Plutonium-244 dating VI. Initial ratios of plutonium to uranium in achondrites

Re-examination of all known xenon isotopic data for achondrites reveals that²⁴⁴Pu fission xenon can be resolved in about three-fourths of the meteorites of this class. The amounts of²⁴⁴Pu fission xenon found in these meteorites range from ca. 1–2 up to 20–40·10^–12 ccSTP/g. These meteorites started to retain their xenon some 200–500 million years later than did the carbonaceous chondrites Allende, Groznaya, Mokoia, Murchison, Murray, and Renazzo, which began to retain their xenon over 4800 million years ago.     

Plutonium-244 dating

Re-examination of all known xenon isotopic data for ordinary chondrites reveals that²⁴⁴Pu fission xenon can be resolved in about one-fourth of the meteorites of this class. The amounts of²⁴⁴Pu fission xenon found in these meteorites range from ca. 1–2 up to 6–8·10^?12 ccSTP/g. These meteorites started to retain their xenon some 200–500 million years later than did the carbonaceous chondrites Allende, Groznaya, Mokoia, Murchison, Murray, and Renazzo which began to retain their xenon over 4800 million years ago.     

Strange xenon in Jupiter

Jupiter's helium-rich atmosphere contains xenon with excess¹³⁶Xe and the ratio of r-products more closely resembles “strange” xenon (Xe-X, alias Xe-HL) seen in carbonaceous chondrites than xenon seen in the solar wind (SW-Xe). The linkage of primordial helium with Xe-X, as seen on a microscopic scale in meteorites, apparently extended across planetary distances in the solar nebula, This is expected if the solar system acquired its present chemical and isotopic diversity directly from debris of the star that produced our elements.     

Plutonium-244 dating I. Initial ratio of plutonium to uranium in the allende meteorite

Re-examination of all known xenon isotope data for the carbonaceous chondrite Allende reveals that this meteorite contains as much as (22±1)·10^{–1 2} csSTP per gram of fissogenic¹³⁶Xe (^136fXe) from the extinct nuclide²⁴⁴Pu and it appears to have started to retain its xenon more than 4800 million years ago, when the²⁴⁴Pu to²³⁸U ratio in the solar system was 0.113±0.006 (atom/atom).     

Plutonium-244 and strange xenon components in the solar system

A number of strange xenon components have been reported in the literature during the past three decades; for example, AVCC (average carbonaceous chondrite), CCF (carbonaceous chondrite fission) xenon, xenon-X, xenon-H, xenon-L, xenon-S, xenon-U, SUCOR (surface correlated xenon), BEOC (Bern Oberflächen-Correliert) xenon, and so on. It is often assumed that they reprsent the isotopic compositions of more or less pure or primordial components of xenon. If one attempts to interpret the existing xenon isotope data for meteorites and lunar samples, assuming that they are pure or primordial, however, one encounters all sorts of problems and no coherent theory concerning the variation of the isotopic composition of xenon in the solar system emerges. We have therefore re-examined over 4,000 sets of existing xenon isotope data for meteorites and lunar samples. The results indicate that these strange xenon components are mixtures of²⁴⁴Pu fission xenon and atmospheric xenon, whose isotopic compositions have been altered by the processes of a) mass-fractionation, b) spallation and c) neutron-capture reactions.     

Stable isotope dilution analyses of molybdenum in meteorites

Isotope dilution mass spectrometry is an ideal analytical technique to measure the elemental abundance of Mo in C1 carbonaceous chondrites and the metallic and troilite phases of iron meteorites. The mean abundance of Mo in two C1 meteorites is 0.909 ± 0.040 μg/g which corresponds to a value of 2.55 atoms Mo with respect to Si equal to 10⁶ atoms, which is identical to the currently accepted solar system abundance. The partitioning of Mo between the metallic and sulfide phases in the Mundrabilla iron meteorite was found to be 6.0 ± 0.2 μg/g and 8.6 ± 0.3 μg/g, respectively. A new, precise Mo concentration of 1.54 ± 0.04 μg/g for the Geochemical Reference Standard BCR-1 is also reported. Received: 15 December 1999 / Revised: 13 March 2000 / Accepted: 16 March 2000     

Plutonium-244 fission xenon and primordial xenon in the Allende meteorite

The carbonaceous chondrite Allende contains (22±1)·10⁻¹² cm³STP/g of²⁴⁴Pu fission xenon and two kinds of primordial xenon: Type I and Type II. The former represents the isotopic composition of a primordial xenon, which resided in the vicinity of a supernova shortly before it exploded, while the latter represents that of the xenon, which resided in the supernova. The isotopic composition of xenon found in the pink inclusion of the Allende meteorite, corrected for the presence of very large excesses of²⁴⁴Pu fission xenon,¹²⁹Xe from the decay of¹²⁹I, and of¹²⁸Xe from the neutron-capture reactions on¹²⁷I, resembles that of Type-I primordial xenon. The isotopic composition of xenon found in the diamond inclusions of the Allende meteorite, on the other hand, represents that of Type-II primordial xenon and it resembles that of a mixture of Type-I primordial xenon whose isotopic composition is severely altered by a combined effect of (a) mass-fractionation, (b) spallation, (c) stellar-temperature neutron-capture reactions, and (d) the presence of a large excess of²⁴⁴Pu fission xenon.     

Determination of the spallogenic radionuclides26Al and53Mn in Antarctic meteorites with respect to cosmic ray exposure and terrestrial ages

The spallogenic radionuclides²⁶Al (T=7.18·10⁵ a) and⁵³Mn (T=3.8·10⁶ a) were determined in 11 ordinary chondrites and 7 achondrites from Antarctica by nondestructive coincidence counting techniques and radiochemical neutron activation analysis, respectively. The results are discussed with respect to exposure ages, terrestrial residence times and possible genetic relationships of the meteorites investigated. The high terrestrial ages of some specimens (up to 800 000 years) are of importance for the study of the ice flow in Antarctica.     

Plutonium-244 dating

Re-examination of a vast amount of xenon isotope data which have been accumulated since the 1960s reveals that the so-called CCF (carbonaceous chondrite fission) xenon is a mixture of²⁴⁴Pu fission xenon and a severely mass-fractionated primordial xenon, whose isotopic composition has been further altered by neutron-capture and spallation reactions, which occurred in the vicinity of a supernova that most likely exploded sometime more than 4.8 billion years ago. The integrated flux of 10 KeV (stellar temperature) neutrons to which the xenon was exposed appears to have been in excess of 10²³ n/cm².     

Plutonium-244 fission xenon and primordial xenon in lunar samples and meteorites

Xenon found in lunar samples is a binary mixture of²⁴⁴Pu fission xenon and a trapped xenon, whose isotopic composition often shows a striking resemblance to that ofTakaoka's¹ primitive xenon. The decay product of¹²⁹I is conspicuously absent in lunar samples and this may be attributed to the facts that (a) the half-life of¹²⁹I is much shorter than that of²⁴⁴Pu, and (b) the separation of xenon from plutonium may take place easily, since the former is a gaseous element, while the latter is a refractory element. The separation of xenon from iodine may not take place easily, however, since the former is a gaseous element, while the latter is a volatile element. The isotopic compositions of the trapped xenon released from ordinary chondrites and achondrites resemble that ofTakaoka's primitive xenon, which has been mass-fractionated in such a manner that the heavier isotopes are systematically enriched relative to the lighter isotopes.     

Conformational and Structural Studies of 1-Fluoropropane from Temperature Dependant FT-IR Spectra of Rare Gas Solutions and Ab Initio Calculations

Variable temperature (–55 to –150°C) studies of the infrared spectra (3500 to 400 cm^–1) of 1-fluoropropane, CH₃CH₂CH₂F, dissolved in liquid krypton and xenon have been recorded. Utilizing three conformer pairs in the krypton solution and four conformer pairs in the xenon solution, enthalpy differences of 104±6 cm^–1 (1.24±0.07 kJ/mol) and 99±5 cm^–1 (1.16±0.06 kJ/mol) were obtained from the krypton and xenon solutions, respectively, with the gauche form the more stable conformer. From these data it is estimated that 24% of the trans forms is present at ambient temperature. The conformational stabilities, harmonic force constants, fundamental frequencies, infrared intensities and Raman activities have been obtained from RHF/6-31G(d) and/or MP2/6-31G(d) ab initio calculations and these quantities have been compared to the experimental values when appropriate. The optimized geometries have also been obtained with several different ab initio basis sets up to MP2/6-311+G(2d,2p). The r₀ structural parameters have been obtained by combining the ab initio data with the previously reported rotational constants for both conformers. The results are compared to the corresponding results for some similar molecules.     

The enthalpies of formation of XeF6(c), XeF4(c), XeF2(c), and PF3(g)

The energies of reaction of XeF₆(c), XeF₄(c), and XeF₂(c) with PF₃(g) were measured in a bomb calorimeter. These results were combined with the enthalpy of fluorination of PF₃(g), which was redetermined to be −(151.98 ± 0.07) kcal_th mol⁻¹, to derive (at 298.15 K) ΔH_f^o(XeF₆, c, I) = −(80.82 ± 0.53) kcal_th mol⁻¹, ΔH_f^o(XeF₄, c) = −(63.84 ± 0.21) kcal_th mol⁻¹, and ΔH_f^o(XeF₂, c) = −(38.90 ± 0.21) kcal_th mol⁻¹. The enthalpies of formation of the solid xenon fluorides were combined with reported enthalpies of sublimation to derive (at 298.15 K) ΔH_f^o(XeF₆, g) = −(66.69 ± 0.61) kcal_th mol⁻¹, ΔH_f^o(XeF₄, g) = −(49.28 ± 0.22) kcal_th mol⁻¹, and ΔH_f^o(XeF₂, g) = −(25.58 ± 0.21) kcal_th mol⁻¹. The average bond dissociation enthalpies,〈D^o〉(XeF, 298.15 K), are (29.94 ± 0.16), (31.15 ± 0.13), and (31.62 ± 0.16) kcal_th mol⁻¹ in XeF₆(g), XeF₄(g), and XeF₂(g), respectively. The enthalpy of formation of PF₃(g) was determined to be −(228.8 ± 0.3) kcal_th mol⁻¹.     

Conformational Studies of Methyl Vinyl Silane from Temperature-Dependent FT–IR Spectra of Xenon and Krypton Solutions

Variable-temperature (–55 to –155°C) studies of the infrared spectra (3500–400 cm^–1) of methyl vinyl silane, CH₂CHSiH₂CH₃, dissolved in liquid xenon and krypton have been recorded. Utilizing three sets of conformer doublets due to the cis and gauche rotamers, the enthalpy difference has been determined to be 133 ± 11 cm^–1 (1.59 ± 0.13 kJ/mol) with the gauche conformer the more stable form in the krypton solution. In the xenon solution, the enthalpy difference could not be determined because the infrared bands become so broad and the overlap was so extensive that meaningful areas could not be determined. Ab initio calculations have been carried out with several different basis sets up to MP2/6-311+G(2d,2p) from which structural parameters and conformational stabilities have been determined. With the largest basis set, the cis conformer is predicted to be the more stable conformer, which is inconsistent with the experimental results. Utilizing previously reported microwave rotational constants for both conformers along with the ab initio predicted distances and angles, r ₀ parameters have been obtained for both the cis and gauche conformers. The spectroscopic and theoretical results are compared to the corresponding quantities for some similar molecules.     

Determination of carbon and nitrogen in meteorites using gamma-ray activation analysis

The volume concentration of carbon and nitrogen in different meteorites was determined by gamma-ray activation analysis on a microtron. The ¹¹C and ¹³N radionuclides forming in photoneutron reactions were isolated by high-temperature extraction; their positron activity was then deactivated by the method of gamma–gamma coincidence of annihilation gamma quanta. A clear correlation was found between the sample darkness and the carbon concentration; the latter was at a level of 10^–2 wt %. No correlations was observed for nitrogen; its concentration was one order of magnitude lower than that of carbon and varied over the range (2–6) × 10^–3 wt %. The results obtained suggest that carbon entered different structural defects in chondrites as a result of its redistribution upon gaseous activity on parent bodies.Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 1, 2005, pp. 52–55.Original Russian Text Copyright © 2005 by Chapyzhnikov, Badyukov, Tsipenyuk.     

Pulse radiolysis studies of the quenching processes of Xe* excited atoms

The time resolved fluorescence of Xe ₂ ^* excimers in pure xenon and Xe-M (M=H₂,N₂,N₂O,CO₂) mixtures has been observed. The formation rate constant of Xe ₂ ^* , k₂=(1.1±0.1)·10^–30 cm⁶/s and the lifetime of the excimer precursors, ₀(100 ± 40) ns were evaluated. The quenching rate coefficients of Xe(6p) states by M have been found to be in the range of (0.5–1.3)·10^–9 cm³/s. The basic parameters and operating characteristics of the newly constructed pulse radiolysis set up based on SINUS-5 electron accelerator are also presented.     

Application of Nuclear Chemistry in the Study of the Universe

Isotopic compositions of the strange Xenon components-HL and the s-type xenon can be explained in a straightforward manner as due to the alteration of the isotopic composition of xenon caused by a combined effect of (a) mass-fractionation, (b) spallation and (c) stellar-temperature neutron-capture reactions. As much as 42.49% of total ¹³⁶Xe ( ¹³⁶Xe) found in the Allende diamond inclusions is ²⁴⁴Pu fission xenon (^136fXe) and the trapped xenon is severely mass-fractionated in such a manner that the lighter xenon isotopes are systematically depleted relative to the heavier isotopes. The relative abundances of ¹³⁰Xe and ¹³²Xe in the trapped xenon component are both markedly enhanced indicating that it was irradiated with a total flux of 1.2·10²³ n·cm^-2 of stellar-temperature (10 keV) neutrons. The xenon found in the s-type xenon, on the other hand, resemble that of the atmospheric xenon irradiated with a total flux of about 6.0·10²³ n·cm^-2 of 10 keV neutrons. These results indicate that we are seeing here the effects of nuclear processes occurring inside of a star, such as the exploding supernova.     

Some noble metals and copper content of italian meteorites as determined by destructive neutron activation analysis

Copper, iridium, platinum and gold content was determined in 15 italian chondritic meteorites by destructive neutron activation analysis. The chemical procedure involves few steps: sample dissolution, group separation of noble metals on inorganic adsorbers and gamma-ray spectrometry. Element content and atomic abundances (Si=10⁶ atoms) are presented and discussed. Precision and accuracy of the analytical method are given as well. Copper, platinum and gold content is within the reported ranges for ordinary chondrites, whereas the iridium content is located on the low side of reported values.     

Analyses of radionuclides in the Oued Awlitis 001 and Galb Inal lunar meteorites by HPGe gamma-ray spectrometry

Highly sensitive nondestructive HPGe gamma-ray spectrometry was used for the analysis of the cosmogenic (²⁶Al) and primordial (⁴⁰K, ²³⁸U, and ²³²Th) radionuclides in the Oued Awlitis 001 and Galb Inal lunar meteorites. The measured ²⁶Al activities were very different (84.0?±?4.8 dpm/kg vs. 8.4?±?1.2 dpm/kg, respectively), mainly because of different cosmic-ray exposure ages of the investigated meteorites. The pre-atmospheric radii were 5?±?1 cm and 11?±?2 cm, respectively, which would result in total pre-atmospheric masses in the range of 0.7–2.5 kg and 7–23 kg, respectively.

     

Stable isotope dilution analyses of molybdenum in meteorites

Isotope dilution mass spectrometry is an ideal analytical technique to measure the elemental abundance of Mo in C1 carbonaceous chondrites and the metallic and troilite phases of iron meteorites. The mean abundance of Mo in two C1 meteorites is 0.909+/-0.040 microg/g which corresponds to a value of 2.55 atoms Mo with respect to Si equal to 10(6) atoms, which is identical to the currently accepted solar system abundance. The partitioning of Mo between the metallic and sulfide phases in the Mundrabilla iron meteorite was found to be 6.0+/-0.2 microg/g and 8.6+/-0.3 microg/g, respectively. A new, precise Mo concentration of 1.54+/-0.04 microg/g for the Geochemical Reference Standard BCR-1 is also reported.     

One‐dimensional TOCSY 1H NMR experiments on adducts of amino acid esters with cobalt(III) tetramethylchiroporphyrin. Prospects for the analysis of amino acid mixtures

Cobalt(III) tetramethylchiroporphyrin, CoCl(TMCP), is a useful chiral shift reagent for structure attribution, absolute configuration assignment and enantiomeric excess determination of amino acid methyl esters by ¹H NMR spectroscopy. However, it has two axial sites available for amine coordination, a structural feature which generates n(n + 1)/2 diastereomeric species and n² distinct spin systems from a mixture of n amino ester enantiomers, making the analysis of complex amino acid samples exceedingly difficult by classical 1‐D or 2‐D NMR methods when n > 3. The 1‐D TOCSY experiment is shown to be a powerful tool for the selective excitation and detection of every single component of a mixture of four amino acid methyl esters bound to CoCl(TMCP): those of(S)‐Leu, (S)‐Asp, (R)‐Asp and (S)‐Glu, for example. The potential utility of this methodology for the determination of amino acid enantiomers in carbonaceous meteorites or other extraterrestrial samples is suggested. Copyright © 2002 John Wiley & Sons, Ltd.