Isochronal measurements

In Figure 1 in addition to isochronal measurements plateau values of a small step armealing treatment (order-order relaxations) are given for a comparison (o). These points reflect a variation of equilibrium state of LRO-parameter with temperature. 

Three to four years and continued during use of CRM very rehable approach isochronous measurements ... 

Fig. 2-5 Typical storage design for isochronous measurements — long term study (Lamberty et al. 1998)...

Lambeety a, Schimmel H, Pauwels J (1998) The study of the stability of reference materials by isochronous measurements. Fresenius J Anal Chem 360 359-361. 

Fig. 10.1. Rb-Sr isochrone measured from separated components of the stony meteorite Guarena. The initial 87Sr/86Sr ratio is slightly higher than that inferred in basaltic achondrites (BABI) because of a period of metamorphism. After Wasserburg, Papanastassiou and Sanz (1969), with permission. Courtesy G.J. Wasserburg.

Fig. 4.14. The road-map for the isochronous measurement of stability shows when the bottles have to be taken out from the initial storage temperature of -20 to be set at the increased destabilisation temperature. At the end of the production, 100 bottles are set aside at -20 °C (could be lower e.g. -80 C). After the homogeneity study (month 0), 5 bottles are stored at each of the studied temperatures. Here a very extensive temperature study is performed (+4, +20, +40, +80 °C), usually materials are tested at room temperature and +40 °C unless feasibility studies have revealed risk of instability. After 6,9 and 11 months each time 5 more bottles are added at each storage temperature. All bottles (100 in total) are analysed together. Such a study can be planned over three years instead of 12 months. When the analyses do not reveal instability a new study can be started in the same conditions taking as time 0 the end of the measurements of the first study. The disadvantage of such an approach is that the study reveals a possible instability only at the end. Therefore, it is hardly usable for the development and first production of a CRM. It is an advantageous approach for the monitoring of stability by the suppliers as it allows an easy planning of the laboratory work if several materials have to be followed [49].

In isochronal measurements where the temperature is varied, the two transition zones are clearly distinguished, as illustrated in Fig. 12-19 for a styrene-butadiene triblock copolymer." ... 

The loss tangent for the /(3 mechanism in poly(methyl methacrylate) can now be compared with those of other homologs, the ethyl, tertiary butyl, and cyclohexyl methacrylates, in Fig. 15-7, cited by Heijboer. The maximum for ethyl occurs at about the same frequency, but with greater magnitude. From other (isochronal) measurements by Heijboer, it is evident that the magnitude of tan S ax increases in the order methyl, ethyl, n-propyl, and n-butyl, while the frequency remains about the same. This is also evident in the maximum in the retardation spectrum as derived from shear creep measurements by Hideshima" when the methyl, -propyl, and... 

In many studies, isochronal measurements have been made at two or more different frequencies and the loci of maxima in the loss tangent mapped against temperature and frequency, often supplemented by dielectric and nuclear magnetic resonance data, as illustrated for polystyrene in Fig. 15-11. Here, five mechanisms... 

That the first stage of ordering (resistivity decrease) is correlated with excess vacancies not being in thermal equilibrium can be seen from measurement during isochronally lowering the temperature from the disordered state (0), which shows that atomic mobility is frozen below 280°C. 

Figure 7. Resistivity change during isochronal anneaUng of Ni76Al24+0.19at%B ( pure ordering ) after separating non-ordering effects of defect recovery from as-measured curves (broken line) For more details see . S1(G) 8% reduction, S2(0) 14% reduction, S3(i) slow-cooling, S4( ) quenched from 973K.

Data on mineral s arates in present day volcanic rocks. Since every dating method (including the K-Ar or C systems) can be affected by several geochemical perturbations which may lead to erroneous ages, the best test for the °Th- U mineral isochrons consists in the analysis of presently erupted lavas or historic lavas of well known eruption dates. Rather surprisingly the data obtained on such samples are not so numerous (some examples are illustrated in Fig. 10). Early data showed that, in some cases, there were interlaboratory analytical discrepancies, especially in Th isotope ratios measured on mineral separates extracted from the same lava flows (this was the case for the 1971 lava from Mt. Etna and 1944 lava from Mt. Vesuvius Capaldi and Pece 1981 Hemond and Condomines 1985 Capaldi et al. 1985). This emphasizes the fact that °Th- U mineral analyses... 

Figure 23. Measured ( °Th/ Th) ratios in basalts from Piton de la Fournaise (Reunion Island) as a function of their eraption ages deduced from mineral isochrons. These ratios decrease with increasing emption ages as a result of post-eraptive radioactive decay. The curve shows the theoretical evolution by radioactive decay for a rock with a Th/U ratio of 3.95 and a ( °Th/ Th) ratio of 0.93, similar to the values measured in presently erapted lavas. An approximate age can thus be obtained from the measured ( °Th/ Th) ratio of an old sample. Part of the dispersion around the theoretical curve are due to small source heterogeneities (slightly variable ( °Th/ rh) and Th/U ratios), also evidenced by Sr/ Sr ratios (Condomines et al. 1988, and unpublished results).

Figure 24. Measured 6 Tla) vs. Th diagram used to infer the ages of lava flows from Mt. Etna in the age range 0 to 8 ka. The eurves labeled 0, 0.5, 1... ka correspond to isochron curves. The isochron 0 is defined by the 6 Tla)o-Th correlation observed in historical lava flows of the last two millennia (Condomines et al. 1995). Five samples of previously unknown ages are reported in this diagram (Condomines et al. 1995, and unpublished results).

Bischoff JL, Fitzpatrick JA (1991) U-series dating of impure carbonates An isochron technique using total-sample dissolution. Geochim Cosmochim Acta 55 543-554 Broecker WS, Olson EA, Orr PC (1960) Radiocarbon measurements and annual rings in cave formations. Nature 185 93-94... 

These drawbacks of the Rosholt isochron largely disappear when used for igneous systems, where Th, being the most-abundant actinide, is measured with approximately equal or better precision than the other U-Th isotopes, thus minimizing error correlations. In fact, for data where all analyses have relatively high Osmond diagrams can... 

For TIMS or ICP-MS analyses, error correlations in the measured isotope ratios are almost always negligible, as the ion beam is always much larger that of and the Th ion-beam is almost always much larger than that of °Th (if the latter is not the case, recourse to isochrons is uimecessaiy). 

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