Plutonium-244 dating

Re-examination of all known xenon isotopic data for the carbonaceous chondrites Renazzo, Mokoia, and Groznaya reveals that these meteorites contain (26±7), (33±1), and (36±4)·10^–12 (ccSTP^136fXe/g) of²⁴⁴Pu fission xenon, respectively. These meteorites started to retain their xenon more than 4,800 million years ago at about the same time as did the carbonaceous chondrites Allende, Murray, and Murchison.     

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.     

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 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 dating

Re-calculation of the²⁴⁴Pu ages of lunar rocks 10057 and 12013 indicates that, while the former started to retain its xenon (4,189 _?74 ⁺⁴⁵ ) million years ago, the latter was formed at a much later time, after the extinct nuclide²⁴⁴Pu had essentially decayed away.     

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.     

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 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.     

Extraterrestrial radioactivity

Until recently, scientists believed that the chemical elements were synthesized only in stars. The discovery of the Oklo Phenomenon in 1972 has revealed, however, that a nuclear fire had existed in terrestrial uranium ore deposits about two billion years ago. The discovery of²⁴⁴Pu fission xenon in extraterrestrial samples, such as the Moon and the meteorites, on the other hand, has demonstrated that the transuranium elements were synthesized in exploding stars (supernovae).     

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.     

Variation of the isotopic composition of xenon in the solar system

Re-examination of a vast amount of existing xenon isotope data, which have been accumulated in the literature since the 1960's, reveals that the variation of the isotopic composition of xenon in the solar system can be attributed to a combined effect of (a) mass-fractionation, (b) spallation and (c) stellar-temperature neutron-capture reactions plus the addition of (d) the beta-decay product of ¹²⁹I and of (e) the spontaneous fission products of ²⁴⁴Pu. The effect of each of the above-mentioned processes can be extremely large, due, primarily to the fact that these processes occurred in the interior of a supernova, which exploded about 5.1 billion years ago.     

Reversed-phase partition chromatographic separation of minor actinides with bis(2-ethylhexyl) sulfoxide from acidic nitrate PUREX waste solutions

The uptake behavior of U(VI), Pu(IV), Am(III) and a few long-lived fission products from nitric acid media by bis(2-ethylhexyl) sulfoxide (BESO) adsorbed on Chromosorb has been studied U(VI), Pu(IV) and Zr(IV) are taken up appreciably as compared to trivalent actinides/lanthanides including some coexisting fission product contaminants which are weakly sorbed on the column. Chromosorb could be loaded with (1.12±0.03) g of BESO per g of the support. Maximum sorption is observed around 4–5 mol·dm^–3 HNO₃ for both U(VI) and Pu(IV), which are sorbed as their disolvates. The elution of (U(VI) and Pu(IV) from the metal loaded sorbent has also been optimized. Desorption of U(VI) is easily accomplished with dilute nitric acid (ca. 0.01 mol·dm^–3)while Pu(IV) is reductively stripped with 0.1 mol·dm^–3 NH₂OH·HCl. Effective sequential separation of U(VI), Pu(IV) and Am(III) from their several admixtures could be readily achieved from real medium and low level active acidic process raffinates.     

Non-destructive determination of spontaneously fissioning nuclides by neutron coincidence counting using multichannel time spectroscopy

A non-destructive method for determining the amount of actinoids has been developed. The method is based on thermal neutron coincidence counting and employs a selective detection of neutrons resulting from the spontaneous fission of actinoids. The detection system is described in detail and the measurement results of²⁴⁴Cm as an example are presented. The results show that the measured fission rate of²⁴⁴Cm is consistent with the fission rate calculated from ENDF/B-V data and that the amount of²⁴⁴Cm can be determined within about 5% accuracy even in the presence of a large amount of actinoids, for example, up to 2.6·10⁶, 3.6·10⁴, or 1.6·10³ times in the mass ratio of²³⁹Pu,²⁴¹Am, or²⁴⁰Pu to²⁴⁴Cm, respectively.     

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.     

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.     

The behaviour of plutonium in aqueous basic media

Behaviour of Pu(IV) and Pu(VI) in basic media has been investigated by studying their stabilities and quantitative determination by spectrophotometry. Beer's law was found to be obeyed in the range of 1·10^–3 to 5·10^–3 M Pu(IV) at 485 nm peak with a molar absorption coefficient of 95M^–1· cm^–1 in sodium carbonate medium. In case of Pu(VI), in the same medium Beer's law was obeyed in the concentration range of 2·10^–3 to 1·10^–2M at 550 nm with a molar absorption coefficient of 50M^–1·cm^–1. Distribution ratios of Pu(IV) and Pu(VI) for their sorption on Al₂O₃ and Amberlyst A-26 (MP) resin from bicarbonate and carbonate media have been determined. High distribution ratios obtained indicate the feasibility of decreasing the plutonium content of basic carbonate streams in reprocessing. 10% breakthrough capacities for Pu(IV) and Pu(VI) with these exchangers during column operations have also been determined.     

Intercomparison study of inductively coupled plasma mass spectrometry, thermal ionization mass spectrometry and fission track analysis of µBq quantities of 239Pu in synthetic urine

Even today, some Marshall Islanders are looking forward to permanentlyresettling their islands after five decades. The U.S. Department of Energyand the resettled residents require reasonable but cost-prudent assurancethat the doses to residents from residual ²³⁹Pu will not exceedrecognized international standards or recommendations, as estimated from theexcretion of ²³⁹Pu in urine. The goal of this study was to evaluatethe bias, uncertainty and sensitivity of analytical techniques that measure3–56 µBq ²³⁹Pu in synthetic urine. The analytical techniquesstudied in this work included inductively coupled plasma mass spectrometry,thermal ionization mass spectrometry and fission track analysis. The resultsof the intercomparison demonstrated that all three techniques were capableof making the measurements, although not with equal degree of bias and uncertainty.The estimated minimum detectable activity was 1 µBq of ²³⁹Puper synthetic urine sample. This exercise is also the first effort to certifytest materials of plutonium in the nBq . g –1 range.     

Environmental applications of stable xenon and radioxenon monitoring

Characterization of transuranic waste is needed for decisions about waste site remediation. Soil-gas sampling for xenon isotopes can be used to define the locations of spent fuel and transuranic waste. Radioxenon in the subsurface is characteristic of transuranic waste and can be measured with extreme sensitivity using large-volume soil-gas samples. Measurements at the Hanford Site showed ¹³³Xe and ¹³⁵Xe levels indicative of ²⁴⁰Pu spontaneous fission. Stable xenon isotopic ratios from fission are distinct from atmospheric xenon background. Neutron capture by ¹³⁵Xe produces an excess of ¹³⁶Xe in reactor-produced xenon, providing a means of distinguishing spent fuel from separated transuranic material.     

Fallout of transuranium elements following the Chernobyl accident

The deposition of transuranium elements in Sweden following the Chernobyl accident was investigated through the analysis of carpets of lichen-and moss-samples and also air-filters and precipitation. The impact of transuranium elements was small compared to that of radiocesium. The deposition of^239+240Pu was, as for other actinides, inhomogeneously distributed and ranged from 0.1% to 100% of the inventory in 1986 from nuclear detonation tests. The activity ratio of^239+240Pu/¹³⁷Cs was between 10^–3 and 10^–6 in comparison to 10^–2 for nuclear test fallout. The activity ratios of²⁴¹Pu,²⁴²Cm,²³⁸Pu,^243+244Am and^239+240Pu were about 86, 14, 0.47, 0.14, and 0.13 respectively, but large variations were observed. The results from Sweden were compared with those found in South Finland, Denmark and Southern Europe. The deposition over Scandinavia originated from the initial explosion at Chernobyl, which contained relatively higher amounts of actinide elements than the second emission, which occurred a few days later and was a result of actions taken to bring the fire under control.     

Voltamperometric determination of uranium and plutonium in alkaline solutions

The simultaneous determination of U(VI), Pu(VI), Pu(V) in 0.5–4.0 M NaOH has been elaborated by means of classical and differential pulse voltamperometry. U(VI) is determined with a dropping mercury electrode (DME) at the half-wave potential of E_1/2=–0.89 V vs. Ag/AgCl reference electrode due to reduction to U(V). The limiting current or peak heights are proportional to uranium(VI) concentration in the range of 1.3.10^–7–3·10^–4 M U(VI). Deviation from proportionality is observed for higher concentrations due to polymerization of uranates. Pu(VI) and Pu(V) are determined with a platinum rotating electrode at E_1/2=–0.02 V due to the reaction Pu(VI)+e^–»Pu(V) and with DME at E_1/2=–1.1 V due to the reduction to Pu(III). The limiting currents of both Pu(VI) and Pu(V) are proportional to their concentrations in the range of 4·10^–6–1.2·10^–3 M Pu. The determination of U(VI), Pu(VI), Pu(V) is not interfered by the presence of the following salts: 2M NaNO₃, 2M NaNO₂, 1.5M NaAlO₂, 0.5M NaF and ions of Mo(VI), W(VI), V(V), Cu(II). The presence of CrO ₄ ^2– and FeO ₂ ^– ions disturbs the determination of U(VI) in 1–4M NaOH, however, contribution of the reaction Fe(III)+e^–»Fe(II) to uranium reduction peak can be calculated from the height of the second peak Fe(II)+2 e^–»Fe(0).