Isotope discrimination function

Diet and stable isotopes, western Mediterranean prehistory, 118-120 Dietary reconstruction from coprolites, human mtDNA extraction, Hinds Cave, Texas, 81 Dietary research through stable isotopes, principles and interpretation, 115-117 Dikgatlampi workings, Botswana, specularite sourcing, 465 Discriminant function analysis, INAA geochemical data, 466,469-477/... 

Flanagan, L. B., Brooks, J. R., and Ehleringer, J. R. (1997). Photosynthesis and carbon isotope discrimination in boreal forest ecosystems A comparison of functional characteristics in plants from three mature forest types. 7. Geophys. Res. 102, 28,861-28,869. 

Figure 5.4 Ratio of mass bias discrimination functions for seiected sets of mercury isotopes (Figure 5.3a,b). Adapted from [17].

This is the model equation for the calibration of isotope amount ratios based on the log-linear temporal isotope amount ratio regression. Note that a and b are perfectly correlated (p = +1) if Rtp < 1 (inRup < 0) and perfectly anti-correlated (p = —1) if Rk/i > 1 (InRfe/ > 0). It is important to stress that this calibration method is fundamentally different from the conventional mass bias correction la vs. Since the regression model does not invoke the principle of time-mass separation, it does not need either the discrimination exponent or the equality of the discrimination functions [17]. 

Note that even if we are to adopt a more fitting discrimination law for the double-spike calculus, we still have to accept the equality of the discrimination functions between the isotopes of the same element - an assumption that is now shown experimentally to be incorrect [17]. To date, this remains the breaking point in the chain of metrological traceability for double-spike calibration results. 

Mass discrimination with distillation effects. Let us assume that the isotope composition of an element is being measured by thermal ionization. This method consists in ionizing the sample atoms by evaporation on a metal filament. Statistical thermodynamics (e.g., Denbigh, 1968) tells us that, while vapor pressure is a function... 

Figure 12. Apparent growth temperatures for various Altiplano carbonates based on clumped isotope thermometry, plotted as a function of estimated maximum burial depth. Symbols discriminate among soil carbonates from sections near Callapa, Corque and Salla and lacustrine carbonates from near Tambo Tambillo, as indicated by the legend. The heavy solid line indicates an estimated burial geotherm, assuming a surface temperature of 20 °C and a gradient of 30 °C per km. The dashed lines define a 10° offset from this trend, which we consider a reasonable estimate of its uncertainty. Carbonates deposited within the last 28.5 Ma and buried to 5000 meters or less exhibit no systematic relationship between apparent temperature and burial depth, and show no evidence for pervasive resetting of deeply buried samples. Error bars are la (when not visible, these are approximately the size of the plotted symbol).

Plot the counts per minute observed in steps 3-15 and 3-18 as a function of the average of the upper and lower discriminator values. Why are the shapes of the plots so similar even though the maximum jS energy of these isotopes differs by a factor of more than 10 A plot from this type of experiment is shown in Figure 3-11. 

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