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 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.     

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 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 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.     

Application of plutonium radiochronometry to the analysis of plutonium age dating reference materials

Journal of Radioanalytical and Nuclear Chemistry - Radiochronometry is an important tool for nuclear forensic analysis. Plutonium has a wide array of parent/progeny pairs that can be measured to...     

A ratio derivative spectrophotometric method for the simultaneous determination of uranium and plutonium

A ratio derivative spectrophotometric method has been developed for the simultaneous determination of uranium and plutonium at mg levels in 1M HNO₃ medium. In this method the overlapping spectra of uranium and plutonium are well resolved by making use of the first derivative of the ratios of their direct absorption spectra. The derivative ratio absorbances of uranium and plutonium are measured at 411.2 and 473.8 nm, respectively for their quantification. The method is simple, fast and does not require separation of uranium and plutonium. Another salient feature of the method is that it does not lead to generation of analytical waste thereby minimising the efforts required for the recovery of plutonium. Uranium in the conc. range of 10–25 mg/g and plutonium in the conc. range of 0.5 to 2 mg/g (U/Pu ratio varying from about 10 to 25) were determined in the same aliquot with a precision and accuracy of about 0.5% and 1%, respectively.     

A mobile mass spectrometry laboratory for isotopic ratio measurements of uranium and plutonium

A modified quadrupole mass spectrometer is housed in a van that serves as a mobile laboratory to provide on-site determinations of isotopic ratios and concentrations of uranium and plutonium. Each element can be determined at 1–3 ng levels with precisions of 1–2%.     

Determination of uranium and plutonium in shielding concrete

The formation of plutonium radionuclides (^239+240Pu) from uranium was determined in dismounted shielding concrete from accelerator components. Plutonium and uranium fractions were separated by radioanalytical techniques and measured by -spectroscopy. The measurements are consistent with yield calculations based on transport and single particle codes. The yield of ^239+240Pu did not exceed the two-fold exemption limit given in the Swiss Radiation Protection Law, thus the plutonium content in shielding concrete should not cause problem for the environment.This revised version was published online in November 2005 with corrections to the Cover Date.     

Determination of plutonium in the presence of uranium by alpha-spectrometry

The plutonium determination by alpha-particle spectrometry with semiconductor detectors in the presence of uranium has been described. It has been found that plutonium as well as uranium can be electrodeposited quantitatively on nickel or stainless steel discs from solutions in isopropanol. The time of deposition does not exceed 35–40 min. The determination of plutonium is possible within the uranium to plutonium weight ratio of 4000 with the accuracy better than 2%.     

Determination of uranium and plutonium in plutonium based fuels by sequential amperometric titration

A method is described for the sequential determination of uranium and plutonium in plutonium bearing fuel materials. Uranium and plutonium are reduced to U(IV) and Pu(III) with titanous chloride and then titrated with dichromate to two end points which are detected amperometrically using two polarized platinum electrodes. Uranium-plutonium solutions of known concentrations containing plutonium in the proportions of 4, 30, 50, and 70% were analyzed with precisions better than 0.3%, maintaining the amounts of plutonium per aliquot in the range of 2–10 mg. No significant bias could be detected. Several samples of (U, Pu)O₂ and (U, Pu)C were analyzed by this procedure. The effects of iron, fluoride, oxalic acid and mellitic acid on the method were also studied.     

Effect of plutonium on the potentiometric determination of uranium

Effect of the presence of plutonium on the determination of uranium by potentiometric method has been studied. The presence of large quantities of plutonium does not appear to affect the determination of uranium present at 5 mg as well as 250 mg levels.     

Thorium,uranium and plutonium isotopes in the Arkansas River

Radiochemical measurements of the concentrations of thorium, uranium and plutonium isotopes were carried out for the samples of Arkansas River collected at six locations in the states of Colorado and Oklahoma. The uranium to thorium ratios in the river samples were found to be highly variable and generally much greater than the ratios found in soils and in rainwater. An attempt has been made to determine the apparent²³⁰Th ages (or the times which elapsed since the last major disruption of the radioactive equilibria) from the observed²³⁰Th/²³²Th and²³⁴U/²³²Th ratios in the water samples.     

Luminescent kinetic determination of uranium mass fraction in plutonium

Measurement of lifetime along with measurement of intensity allow to determine both uranium and plutonium concentrations. If exciting light absorption is taken into account and temperature correction is introduced the intensity of uranyl limunescence extrapolated to zero time is a function of uranium and the ratior ₀/r-a function of plutonium concentration. Stadi of characteristics of uranyl luminescence was performed using a spectrometer interfased with a microcomputer. Luminescence was excited by nitrogen laser.     

On atomization of uranium in plutonium matrix using ETA-AAS

Atomization processes for uranium in aqueous media and in the presence of a plutonium matrix have been studied and a chemical mechanism is proposed. These studies have been utilized for the determination of uranium in plutonium by Electrothermal Atomization- Atomic Absorption Spectrometry (ETA-AAS) within the constraints of its stable carbide forming tendency and complexity caused by formation of plutonium suboxide at high temperatures. In spite of these limitations the analytical range obtained for determination of uranium is 2.5–100 ng with a sample aliquot of 5 μL containing 5 mg/mL plutonium concentration. The precision of the method is evaluated as 9% RSD. Received: 9 September 1997 / Revised: 29 December 1997 / Accepted: 31 December 1997     

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).     

Redox determination of uranium in presence of plutonium in low phosphoric acid medium and the recovery of plutonium

Quantitative determination of uranium in (U, Pu)O₂ fuels is usually done by the DAVIES-GRAY method. High concentrations of phosphoric acid in the analytical waste generated by this method make the revocery of plutonium rather complex. Studies on the recovery of plutonium from nitric acid medium containing different concentrations of H₃PO₄ by conventional anion-exchange procedure reveal that more than 90% of the plutonium can be easily recovered when the phosphoric acid concentration is less than 0.5 M in the solution. A method was developed for the determination of uranium in the presence of plutonium, which involves the reduction of U(VI) to U(IV) by Fe(II) in a medium of 3.5M H₃PO₄ +4.5M H₂SO₄ instead of 10–11M H₃PO₄ so as to have the H₃PO₄ concentration 0.6M in the waste. A number of determinations of uranium in UO₂(NO₃)₂ working standard solutions and (U, Pu) synthetic solutions with uranium at the 3–7 mg level were carried out by this method. The precision obtained was better than ±0.2% and the accuracy was also within the precision limits. The resulting analytical waste generated was directly subjected to anion exchange separation for the recovery of plutonium which was found to be more than 90%.     

Contamination of the earth's surface by plutonium and uranium fallout

The^239,240Pu/²³⁸U ratios in nature determined by previous and present workers have been used to evaluate the extent of plutonium and uranium fallout contamination on the earth's surface. The contamination of the earth's surface due to radioactive fallout of plutonium and uranium varies between 0.01 and 24%. The overall results show that the whole globe is affected by the fallout, thus explaining the high^239,240Pu/²³⁸U ratios found in our environment today.     

Determination of uranium in presence of plutonium using differential spectrophotometry

The use of beams of heavy ions such as carbon, neon and argon for radiation therapy has the advantage that they have a very sharp Bragg maximum. When the Bragg peak coincide with the tumour location, it is possible to deposit the bulk of the energy of the ion in the region occupied by the malignancy. However, the concentration of ions and free radicals will be very high in the Bragg peak region which has not received the attention it deserves. So mutual recombination of these species will be very high. It is therefore necessary to assess the extent of these radical-radical recombinations at very high LET values. Spur diffusion model calculations have been made for high energy argon ions using water as a medium. For comparison, calculations have been done for proton tracks. It has been shown that in the Bragg peak region of argon ions even very high concentrations of scavengers have very little effect on radical-radical interactions. The implication is that when LET values are very high, practically all the radicals undegro recombination with each other. In order to explain the observed lethality of high LET radiation, it is suggested that the hydrogen peroxide formed also contribute to the killing of cells. In addition, the decomposition of H₂O₂ will contribute oxygen. This may be one of the reasons why high LET radiation shows strong lethality to hypoxic cells.     

Precise coulometric determination of uranium,plutonium and americium-application to small samples

Summary Isotopic dilution followed by mass spectrometry is currently used for the determination of microquantities of actinides, but for this method it is necessary to prepare certified solutions of isotopic diluents. The isotopes used are very expensive and often available only in small quantities. New methods have been developed for the accurate and precise determination of small amounts of uranium, plutonium and americium. By using controlled-potential coulometry 0.5eq of uranium and plutonium can be determined with a precision of 0.1% (coefficient of variation). For americium a constant-current coulometric titration allows the determination of 1eq with a precision of 0.3%. The equipment, coulometric cells and procedures are described. The results obtained for standard materials and comparisons with results from other analytical methods are given.

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Genaue coulometrische Bestimmung von Uran, Plutonium and Americium; Anwendung auf kleine Proben

Zusammenfassung Isotopenverdünnung und nachfolgende Massenspektrometrie werden laufend für die Bestimmung kleiner Mengen von Actiniden verwendet; dazu ist es aber notwendig, genaue Lösungen von Isotopen zur Verdünnung herzustellen. Die dazu verwendeten Isotopen sind sehr teuer und oft nur in sehr kleinen Mengen zu haben. Für die genaue Bestimmung kleiner Mengen Uran, Plutonium und Americium wurden neue Methoden ausgearbeitet. Unter Verwendung der potential-kontrollierten Coulometrie lassen sich 0,5eq Uran und Plutonium mit einer Genauigkeit von 0,1% (Variations-Koeffizient) bestimmen. Gleichstromcoulometrische Titration ermöglicht die Bestimmung von 1eq Americium mit einer Genauigkeit von 0,3%. Einrichtung samt coulometrischer Zellen und Arbeitsweise wurden beschrieben. Die mit Standardproben erzielten Resultate wurden mit den Ergebnissen anderer Verfahren verglichen.

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Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.