[sup 187]Os-[sup 186]Os and [sup 187]Os-[sup 188]Os method of dating: An introduction

Journal Article · Sun Aug 01 00:00:00 EDT 1993 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(93)90358-4· OSTI ID:5577395

Yin, Q Z; Jagoutz, E; Waenke, H ^[1]; Verkhovskiy, A B ^[2]

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1. Max-Planck-Institut fuer Chemie, Mainz (Germany)
2. The Open Univ., Milton Keynes (United Kingdom)

A Re-containing sample is irradiated with thermal neutrons in a nuclear reactor. The following reactions occur with high cross sections: [sup 185]Re(n, [gamma])[sup 186]Re and [sup 187]Re(n, [gamma])[sup 188]Re. Both [sup 186]Re (half-life 90.6 h) and [sup 188]Re (16.7 h) [beta]-decay to the stable isotopes [sup 186]Os and [sup 188]Os. Thus [sup 186]Os and [sup 188]Os are enriched in proportion to the neutron fluence and R/Os ratio of the sample being irradiated. Analyzing merely the isotopic composition of the sample, the authors get two ages that should be consistent. In one irradiated molybdenite sample from Kingsgate molybdenum mine in New South Wales, Australia, the measured [sup 186]Os/[sup 192]Os and [sup 188]Os/[sup 192]Os are 0.3284 and 0.6299, whereas in an unirradiated sample they are assumed to be 0.0390 and 0.3248. These ratios are measurable with negative thermal ionization mass spectrometry (N-TIMS) to a precision of 1[per thousand]. The derived ages for this sample are t[sub 186] = 220.5 [+-] 8.6 Ma and t[sub 188] = 214.9 [+-] 8.9 Ma, respectively (or [+-] 1.4 Ma and [+-] 1.7 Ma, respectively, when excluding the uncertainty of [sup 187]Re half-life). These values are in close agreement with the 221--238 Ma K-Ar ages of the leucogranites emplacement that causes the Mo mineralization at Kingsgate. The major limiting factor on the precision of this age determination is the uncertainty in the half-life of [sup 187]Re. The errors associated with the irradiation parameters are greatly reduced by choosing an appropriate neutron flux monitor. The advantage of this method is that the Re/Os ratio is determined on the same sample and that only one measurement of the isotope composition of osmium is required, thus overcoming some of the experimental difficulties of the conventional Re-Os analysis. The problem of sample inhomogeneity and the need to measure the absolute concentrations of rhenium and osmium are thus eliminated. 30 refs., 3 figs., 1 tab.

• OSTI ID: 5577395
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Vol. 57:16; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
MINERALS
IRRADIATION
ISOTOPE DATING
OSMIUM 186
ISOTOPE RATIO
PRODUCTION
OSMIUM 187
OSMIUM 188
BETA DECAY
MOLYBDENUM
REACTORS
RHENIUM 185
RHENIUM 186
RHENIUM 187
RHENIUM 188
THERMAL NEUTRONS
AGE ESTIMATION
ALPHA DECAY RADIOISOTOPES
BARYONS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
DAYS LIVING RADIOISOTOPES
DECAY
ELECTRON CAPTURE RADIOISOTOPES
ELEMENTARY PARTICLES
ELEMENTS
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
FERMIONS
HADRONS
HEAVY NUCLEI
HOURS LIVING RADIOISOTOPES
INTERNAL CONVERSION RADIOISOTOPES
ISOMERIC TRANSITION ISOTOPES
ISOTOPES
METALS
MINUTES LIVING RADIOISOTOPES
NEUTRONS
NUCLEAR DECAY
NUCLEI
NUCLEONS
ODD-EVEN NUCLEI
ODD-ODD NUCLEI
OSMIUM ISOTOPES
RADIOISOTOPES
RHENIUM ISOTOPES
STABLE ISOTOPES
TRANSITION ELEMENTS
YEARS LIVING RADIOISOTOPES
400101* - Activation
Nuclear Reaction
Radiometric & Radiochemical Procedures