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Fleming, Erika; Ghiorso, A.; Cunningham, B.B.

doi:10.1103/physrev.88.642

Cited by 90 publications

(8 citation statements)

References 10 publications

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“…In order to calculate the age accurately, accurate values for the decay constants must be known. Previous studies have used mean lives of 108,500 years for 23°Th and 357,800 years for 234U, based on the studies of Attree et al [56] and presumably Fleming et al [57], respectively. We have chosen to use the more recent determinations of 108,750 + 850 years (2o; [58]) for the mean life of 23°Th As T increases, ?`23o becomes a more important term and the uncertainty in T increases.…”

Section: The 238u-234u-23°th Age Equation and The Uncertainty In Agementioning

confidence: 99%

238U234U230Th232Th systematics and the precise measurement of time over the past 500,000 years

Edwards

Chen

Wasserburg

1987

Earth and Planetary Science Letters

1,088

100

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We have developed techniques to measure the 23°Th abundance in corals by isotope dilution mass spectrometry. This, coupled with our previous development of mass spectrometric techniques for 234U and 232Th measurement, has allowed us to reduce significantly the analytical errors in 23~U_ 234U-230Th dating and greatly reduce the sample size.We show that 6 × l0 s atoms of Z3°Th can be measured to ± 30%~ (2o) and 2 × 10 l° atoms of 23°Th to ± 2%e. The time over which useful age data on corals can be obtained ranges from a few years to -500 ky. The uncertainty in age, based on analytical errors, is ±5 y (20) for a 180 year old coral (3 g), ±44 y at 8294 years and +1.1 ky at 123.1 ky (250 mg of coral). We also report 232Th concentrations in corals (0.083-1.57 pmol/g) that are more than two orders of magnitude lower than previous values. Ages with high analytical precision were determined for several corals that grew during high sea level stands -120 ky ago. These ages lie specifically within or slightly postdate the Milankovitch insolation high at 128 ky and support the idea that the dominant cause of Pleistocene climate change is Milankovitch forcing.

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Section: The 238u-234u-23°th Age Equation and The Uncertainty In Agementioning

confidence: 99%

238U234U230Th232Th systematics and the precise measurement of time over the past 500,000 years

Edwards

Chen

Wasserburg

1987

Earth and Planetary Science Letters

1,088

100

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“…A summary of the various publishecl values of the U238/U235 ratio is given in Table 111. (3,6,7,8,12,14) as shown in Table IV. A best value is rather difficult to arrive a t , because several authors, claiming Thus, excluding the value of Chamberlain et al for the reason discussed above, the values obtained for the natural abundance of Uz4 fall into two groups, one giving 0.0055 atom %, and the other giving 0.0059 atom %.…”

Section: B Mass Spectrometrymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…Nier also discovered the very rare isotope U"', and determined its abundance to be 0.0059 atom yo. Further determinations of the abunclance have been made bj7 several authors (3,6,7, 8, 12) sing both mass spectrometric and specific activity methods.Subseq~ient mass spectron~etric determinations of the U238/U235 abundance ratio have been reported by Inghram ( l l ) , Fox and Rustad (7), and Chamberlain, Williams, and Yuster (3), all in 1946. Inghram's value of 137.8 was lower than the earlier determination by Nier by almost one per cent.…”

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The Natural Abundances of the Uranium Isotopes

Lounsbury¹

1956

Can. J. Chem.

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Using a surface-ionization rnass spectrometer, the natural U238/U235 abundance ratio in uranium obtained from Great Bear Lake Pitchblende has been measured t o be 137.80&0.14. From a survey of results reported in the literature 011 Uz3+ best value of 17,325&550 was estimated for the natural U238/U234 abundance ratio. The corresponding isotopic abundances are 0.7204&0.0007 atom yo and 0.00573&0.00018 atom yo for U235 and UZ3l, respectively. INTRODUCTIONThe first mass spectrographic analysis of ~~r a n i u m was made by Aston (1) in 1931. He observed only U?38, and estimated the abundance of other isotopes t o total not more than two or three per cent. In 1932, von Grosse (9), from studies of the actinium (4n + 3) series of natural radioactivity, predicted that U?35 existed in natural uranium to the extent of 0.4 atom yo. Dempster (5) in 1935 discovered U235 mass spectrographically and determined its abundance to be less than 1 atom yo. He also predicted the existence of US4 from studies of the uranium (4n + 2) series of natural radioactivity, and calculated that its abundance would be 0.008 atom yo, "and therefore too faint to be observed by the mass spectrograph".Nier (14) in 1939 made the first mass spectrometric analysis of natural uranium and obtained a value of 138.9f 1.4 for the U?38/U235 abundance ratio. Because it was a t one time thought that the ratio might be a function of the age of the mineral in which the uranium was found, he measured the ratio for three samples of widely different geologic age. He found that for Swedish Kolnl (4 X lo8 yr.), Wilberforce Uraninite (1.0 X 10"~r.), and Dakeite (1 X lo3 yr.), the ratio was constant to 0.07%, and therefore did not depend on the age of the mineral or its source. Nier also discovered the very rare isotope U"', and determined its abundance to be 0.0059 atom yo. Further determinations of the abunclance have been made bj7 several authors (3,6,7, 8, 12) sing both mass spectrometric and specific activity methods.Subseq~ient mass spectron~etric determinations of the U238/U235 abundance ratio have been reported by Inghram ( l l ) , Fox and Rustad (7), and Chamberlain, Williams, and Yuster (3), all in 1946. Inghram's value of 137.8 was lower than the earlier determination by Nier by almost one per cent. Fox and Rustad actuall~, obtained two values, 137.0f0.7 by electron bombardment ionization, and 1 3 8 . 0 f 0.3 by thermal ionization. Using the latter ion source they found, as did Kier, that the ratio was constant t o 0.03% for two African ores, one Canadian ore, and one Colorado carnotite. Chamberlain et al. obtained a value of 139 for the U238/U235 ratio, in agreement with the first determination blNier. ln/Ianuscript

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“…The figures in the last columns of Tables II, III, and IV have been corrected for carrier activity by subtracting 0.75 counts/min/~g of carrier from the observed counts/min (11).…”

Section: Quantitative Studies On Electrodeposition Of ['Ranium At ~{mentioning

confidence: 99%

Electrodeposition of Uranium at the Microgram Level

Rulfs¹,

De²,

Elving³

1957

J. Electrochem. Soc.

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The recovery of microgram and submicrogram quantities of U by electroplating has been studied, using radioactive U-233 as a tracer with and without the presence of microgram quantities of natural U as carrier. Optimum results were obtained in an ammonium oxalate medium with electrolysis at 80~176 being performed first in acidic solution and then in alkalinesolution. A small Pt disk which fitted into a flow counter was used as cathode, and a Pt spiral served as anode. With 20 t~g of U carrier present and a volume of 25 ml, an average recovery, based on alpha counting, of 94 • 3% was obtained for amounts of U-233 ranging from 0.03 to 0.13 ~g. Several methods have been described for the analytical electrodeposition of milligram quantities of U (1-6). In acetate medium, up to 4 mg U were deposited (2); results were not accurate due to variation in composition of the plates. Use of an oxalate medium at 80~176 gave satisfactory results with about 3 mg U (2). Up to 0.5 mg U was plated quantitatively from fluoride medium at room temperature (3-5). Micro quantities of U were deposited from oxalate medium containing potassium hydrogen phthalate buffer by electrolyzing at 80~176 in two stages: first on the acid side, then on the alkaline side (6). In all these cases a Pt disk was used as cathode, and the plated fihns were ignited to U308.The use of an A1-Zn disk as cathode in oxalate medium at pH 8.0-8.5 and 80~176 has been reported (7). Two German patents (8) describe the deposition of metallic U onto Pt and other surfaces from an organic solvent like acetone which exerts no oxidizing action.Recovery of microgram quantities of U from human urine by electroplating for the determination of alpha activity has been examined (9). One microgram of enriched Us08 (130 a counts/min/t~g) was added to 100-ml urine samples. After evaporation to dryness and ignition to destroy organic matter, the residues were dissolved; Ca was removed by double precipitation as the oxalate; and U was then electroplated at 80~ onto a Ni disk from the resulting ammonium oxalate medium of pH 9.6, using a current of 3 amp for 60 min. The recovery of U from 18 samples was 85 • 4% with a precision of • on a single sample.Previous studies on the electrodeposition of U such as those cited above have generally been applicable only to the recovery of milligram amounts of U. Attempts to plate microgram quantities of U, usually present in rather small volumes of solution, resulted in U recoveries which were both low and variable. Apparently no reliable results have been reported for electrodeposition of submicrogram amounts of U. Consequently, the present study was initiated in an attempt to define conditions for more nearly quantitative recovery by electrodeposition of microgram amounts of U. In addition, an attempt was made to investigate the feasibility of electrodeposition of submicrogram amounts of U and to define the reproducibility of the procedure for microgram levels of U. 80Initially, quMitative observations were made on the plates obtained from solutio...

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The Specific Alpha-Activities and Half-Lives ofU234,U235, and

Cited by 90 publications

References 10 publications

238U234U230Th232Th systematics and the precise measurement of time over the past 500,000 years

238U234U230Th232Th systematics and the precise measurement of time over the past 500,000 years

The Natural Abundances of the Uranium Isotopes

Electrodeposition of Uranium at the Microgram Level

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