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.     

Plutonium-244 fission xenon in carbonaceous inclusions of primitive meteorites

A total of 13 samples of diamond separates studied so far, all contain excess ²⁴⁴Pu fission xenon. On the other hand, none of the SiC separates contains excess ²⁴⁴Pu fission xenon, while 5 out of 10 samples of graphite separates studied so far contain excess ²⁴⁴Pu fission xenon.     

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.     

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 dating VII. Initial abundances of uranium-235 and plutonium-244 in lunar samples

Re-examination of a vast amount of lead and xenon isotope data that have been accumulated since the Apollo 11 landing on the moon in July 1969 reveals that some of the lunar fines and breccia started to retain their radiogenic lead and fissiogenic xenon isotopes about 5 billion years ago when the ratios of²³⁵U and²⁴⁴Pu to²³⁸U in the early solar system were approximately 4 and 2 atoms per 10 atoms of²³⁸U, respectively.     

Further attempts to isolate superheavy elements in the meteorite Allende

The search for superheavy elements /SHE/ in the carbonaceous chondrite Allende was continued. This time we carried out a thermochromatographic separation at 1050 °C in O₂-, resp., H₂-gas flow. The volatile fraction /mostly Pb/ was collected on a Pt-foil or trapped in KOH-solution. The heavy element probes were investigated for spontaneous fission activities. We observed zero spontaneous fission decays during 421 days. This yielded an upper limit of 2.9 fission x kg^–1 x year^–1 /95% confidence limit/. We were unable to confirm the existence of a spontaneous fission activity in the meteorite Allende.     

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.     

Direct search for primordial 244Pu in Bayan Obo bastnaesite

The abundances of heavy elements produced in r-process nucleosynthesis in the early solar system need experimental verification. ²⁴⁴Pu could be the heaviest primordial nuclide produced before the formation of the Earth still being detectable today. As recent attempts failed to confirm the discovery of ²⁴⁴Pu signals at a concentration of 1.0 × 10^?18 g/g in bastnaesite reported by Hoffman et al. in this study, the total primordial ²⁴⁴Pu in 450 g bastnaesite sample from Bayan Obo ore (China) was measured using ultra-sensitive compact accelerator mass spectrometry (AMS). As no ²⁴⁴Pu signal was detected, an upper limit for the ²⁴⁴Pu in our bastnaesite sample was estimated to be 2.1 × 10^?20 g/g at 99% confidence level.     

Cumulative yields of short-lived xenon isotopes in the spontaneous fission of252Cf

Cumulative yields of short-lived xenon isotopes^137,138,139Xe have been determined in the spontaneous fission of²⁵²Cf, using a fast radiochemical separation method followed by gamma spectrometry. Xenon-137 yield is reported for the first time. The measured cumulative yields are converted to chain yields assuming normal charge distribution systematics for comparision with the literature data.     

Retention of fission xenon in air by activated carbon at 2 °C

Xenon retention in air by activated carbon for two sizes of grain and two flows of gas is described. ¹³³Xe obtained from the residual gases existent in the decay tanks of the ⁹⁹Mo Production Plant of Ezeiza Atomic Center, was mixed with natural xenon as carrier and air as the major component. The gas stream was passed through a drier, two columns filled with activated carbon at 2 °C and one filled with small wires of porous copper at -196 °C. On the basis of the results obtained, the conditions of an equipment could be extrapolated with the conditions of operation to the routine treatment of fission gases. Recommendations with respect to the movement of gases in a hot cell are also formulated.     

Quantitative and isotopic analysis of released and retained krypton and xenon fission gases from irradiated metallic fuels

We quantitatively measured the amounts and isotopic distributions of the released and retained fission gases (Kr and Xe) from two irradiated metallic fuels (U–10Zr and U–10Zr–5Ce) at approximately 2.9 at.% burnup, using a gas chromatography and a quadrupole mass spectrometer. The obtained Xe/Kr ratios indicate that the released and retained fission gases from the irradiated metallic fuels came primarily from the fission of ²³⁵U, instead of that of heavy isotopes such as ²³⁹Pu and ²⁴¹Pu. The calculated (⁸³Kr + ⁸⁴Kr)/⁸⁶Kr and (¹³¹Xe + ¹³²Xe)/¹³⁴Xe ratios suggest that no fuel rods became defective during the irradiation process.     

Cumulative and independent yields of krypton and xenon isotopes from reactor neutron induced fission of 232Th

The fractional cumulative and independent yields of ¹³⁹Xe, ¹⁴⁰Xe, ⁹⁰Kr and ⁹¹Kr from the fission of ²³²Th induced by reactor neutrons were measured. The fission produced gases xenon and krypton were separated from the other elements by fast sweeping with a stream of helium. The γ-ray spectra of the noble gases and their daughters were followed and from these γ-ray activities and the known absolute γ-ray abundances, the corresponding yields were calculated. The procedure was verified by remeasuring the yields of the noble gases from the thermal fission of ²³⁵U and an excellent fit with the published values was obtained.The fractional independent yields of the cesium and rubidium isotopes were derived from the measured yields of the corresponding isobaric members, krypton and xenon. The comparison of the measured yields with the “normal” yields reveals an enhancement or diminishing of products with an even or odd number, respectively, of ∼30%.     

Xenon 5d emission in pure xenon and xenon doped argon

The radiative of Xe 5d ($\text{3}\text{2}$)₁ states in photoexcited Xe and Xe doped Ar is investigated. The Xe 5d fluorescence contains new information about the deactivation of highly excited states of Xe and about the energy transfer from Ar to Xe.     

Trace elements and cosmogenic radioactivity in the meteorite Hohenlangenbeck

Trace elements have been determined by instrumental and radiochemical NAA and the cosmogenic radioactivity of²²Na and²⁶Al using gamma spectrometry in the smallsize L-chondrite Hohenlangenbeck. A low condensation temperature is indicated by relatively high contents of Rb and Cs. The low activity ratio of²²Na/²⁶Al is due to a relatively low particle flux in the orbit during the last four years.     

Cosmic induced radioactivity in the meteorite Trebbin

7 days after the fall of a stony meteorite its -spectrum has been measured on a Ge/Li/-detector installed in an underground laboratory. The activity of²²Na,²⁶Al,⁴⁰K,⁴⁸V, and⁵⁴Mn has been determined.     

On the behaviour of solutions of xenon in liquid cycloalkanes: Solubility of xenon in cyclopentane

The solubility of xenon in liquid cyclopentane has been studied experimentally and theoretically. Measurements of the solubility of xenon in liquid cyclopentane are reported as a function of temperature from 254.60 K to 313.66 K. The imprecision of the experimental data is less than 0.3%. The thermodynamic functions of solvation of xenon in cyclopentane, such as the standard Gibbs energy, enthalpy, entropy and heat capacity of solvation, have been calculated from the temperature dependence of Henry's law coefficients. The results provide further information about the differences between the xenon + cycloalkanes and the xenon + n-alkane interactions. In particular, interaction enthalpies between xenon and CH₂ groups in n-alkanes and cycloalkanes have been estimated and compared. Using a version of the soft-SAFT approach developed to model cyclic molecules, we were able to reproduce the experimental solubility for xenon in cyclopentane using simple Lorentz-Berthelot rules to describe the unlike interaction.     

Absolute yields of the fission products in the neutron induced fission of 232Th and 233U

Absolute yields of 10 fission products in the reactor neutron induced fission of ²³²Th and 17 fission products in the thermal neutron induced fission of ²³³U have been determined using track etch-cum γ-ray spectrometric technique. The number of fissions occurring in the target is obtained by recording the fission events in a mica track detector. The fission product atoms are determined by the direct counting of the irradiated target on a 60 cm³ Ge(Li) detector coupled to a 4096 channel analyser. A one step radiochemical separation was done, before gamma ray counting, for few fission products in the reactor neutron induced fission of ²³²Th. The measured yield values are compared with the available literature data and an analysis of the possible errors are done. The overall uncertainty in the measurements is estimated to be 4–5%.     

Yields of rare earth fission products in the spontaneous fission of californium-252

Cumulative fission yields of rare earth isotopes have been determined in the spontaneous fission of²⁵²Cf by fast radiochemical separation and gamma-ray spectrometry. The determined yield values are compared with the available literature data. The yield values for¹⁴⁷Nd,¹⁵¹Nd and¹⁵¹Pm differ from the reported values. The yield for¹⁴⁵Ce is determined for the first time.     

Synthesis of the missing oxide of xenon, XeO2, and its implications for Earth's missing xenon

The missing Xe(IV) oxide, XeO(2), has been synthesized at 0 °C by hydrolysis of XeF(4) in water and 2.00 M H(2)SO(4(aq)). Raman spectroscopy and (16/18)O isotopic enrichment studies indicate that XeO(2) possesses an extended structure in which Xe(IV) is oxygen bridged to four neighboring oxygen atoms to give a local square-planar XeO(4) geometry based on an AX(4)E(2) valence shell electron pair repulsion (VSEPR) arrangement. The vibrational spectra of Xe(16)O(2) and Xe(18)O(2) amend prior vibrational assignments of xenon doped SiO(2) and are in accordance with prior speculation that xenon depletion from the Earth's atmosphere may occur by xenon insertion at high temperatures and high pressures into SiO(2) in the Earth's crust.