Computer Science
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30q.493b&link_type=abstract
Meteoritics, vol. 30, no. 5, page 493
Computer Science
Scientific paper
The noble gas study in meteorites is often carried out using step-wise heating technique, that allows to separate gas components and calculate activation energies. The relative gas yield during step-wise heating is usually plotted as gas abundances released at each step from the step temperature. It is impossible to compare correctly the data of different runs using that plot if step temperatures are not equal in the runs. Changing of the temperature step dimension during heating can result in spurious peak or masking the true peak. As the presence of few peaks is caused by different mechanisms of gas release it is important to determine the real number of peaks. The data plotted in the Arrhenius diagram allow to determine correctly the number of gas release mechanisms [1] and to calculate activation energies if there is no peaks overlap. Some russian authors (for example [2]) have represented the step-wise heating data like described below. 1. Experimental points have been plotted as the sum abundances of released gas from the step temperature and connected by a smooth line, as shown in Fig. 1a. 2. The cumulative curve such obtained has been manually differentiated and differential points have been plotted and connected by a smooth line also. We have constructed a computer code to plot curves accordingly the above algorithm. Cumulative curve plotting is performed by means of the cubic spline technique. This curve is continious and monotonous, therefore the first derivative is continious too. The differential curve is constructed by data of the first derivative. During curves construction the error of measuring may be taken into account by means of Monte Carlo algorithm. To compare the data of different runs the plot of differential gas release curves is easy. It allows to split the complex differential curve on the single peaks and to determine activation energies for each peak [3] as well as to speculate different mechanisms of gas migration. We have studied radiogenic and spallogenic He, Ne and Ar in bulk sample of Pomozdino eucrite as well as in pyroxene and plagioklase of Chervony Kut eucrite. These data have been used to calculate cumulative (Fig. 1a) and differential (Fig. 1b) curves of gas release. One and the same gas component can have some release peaks with different activation energies so there are different mechanisms of gas migration and release. Main gas release peaks seem to correspond to two independent migration mechanisms: gas diffusion from mineral lattise (low temperature peaks) and melting of minerals at high temperatures. The diffusion mechanism corresponds to gas escaping in natural conditions. The calculated diffusion parameters can be used to estimate gas losses in eucrites in natural conditions. References: [1] Zashu S. and Hiyagon H. (1995) GCA, 59, 1321-1328. [2] Ashkinadze G. Sh. (1980) Migration of the Radiogenic Isotopes in Minerals, Nauka, Moscow, in Russian. [3] Krylov D. P. and Shukolyukov Yu. A. (1994) Petrology, 2, 259-265, in Russian.
Assonov Sergey S.
Bulgakhova L. M.
Shukolyukov Yu. A.
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