Contribution To Statistics In Fission Track Counting

In order to test the new statistical model proposed in two papers by McGee, Johnson and Naeser for calculating the standard error in fission track dating, spontaneous and induced track counts from external detector method-EDM-or similar were simulated by random numbers, assuming that, for a given uranium content, fission tracks were spatially distributed according to Poisson distributions. By the results of such a simulation it can be concluded that: 1. (1) In EDM, (1/nS + 1/nI)1 2 represents a reliable evaluation of the relative standard error of ρS/ ρI - ratio of spontaneous to induced track densities in a sample in which nS spontaneous and nI induced tracks were counted. 2. (2) The new model confirms the validity of the above conclusion, by applying it to the spontaneous and induced track counts whose relative standard deviations of the means were evaluated by normal sampling statistics. Population method-PM-data were also simulated; (σ'2 S + σ'2 I)1 2, where σ' S and σ'I are the above relative standard deviations of the mean, offers a reliable evaluation of the uncertainty of ρS/ρI ratio for the simple cases analyzed in the present work. © 1986.113123136Arias, Bigazzi, Bonadonna, Size corrections and plateau age in glass shards (1981) Nucl. Tracks, 5, pp. 129-136Bardsley, Random errors in fission-track dating (1982) Math. Geol., 14, p. 545Beyer, (1980) Handbook of Mathematical SciencesBigazzi, Bonadonna, Ferrara, Datazione degli zirconi: confronto delle età ottenute con il metodo delle tracce di fissione e con il metodo 206Pb/238U (1976) Rend. Soc. Ital. Min. Petrol., 32, pp. 617-623Bigazzi, Bonadonna, Ferrara, Innocenti, Fission track ages of zircons and apatites from Northern Apennines ophiolites (1973) Fortschr. Miner., 50, pp. 51-53Bigazzi, Bonadonna, Radi, Fission track dating of obsidians and prehistory (1982) Fifth International Conference on Geochronology, Cosmochronology and Isotope Geology, pp. 1-4. , Nikko (Japan), Proc. Workshop on Fission-Track DatingBigazzi, Ferrara, Determinazione dell'età di zirconi con il metodo delle tracce di fissione (1971) Rend. Soc. Ital. Miner. Petrol., 27, pp. 295-304Evans, (1955) The Atomic Nucleus, , Tata McGraw-Hill, Bombay, New DelhiGalbraith, On statistical models for fission track counts (1981) Math. Geol., 13, pp. 471-478Galbraith, On statistical models for fission track counts: reply (1981) Math. Geol., 13, pp. 485-488Gold, Armani, Roberts, Absolute fission rate measurements with solid-state track recorders (1968) Nucl. Sci. Engng., 34, pp. 13-32Green, A new look at statistics in fission track dating (1981) Nucl. Tracks, 5, pp. 77-80Green, A criticism of the paper entitled “A practical method of estimating standard error of age in the fission track dating method” by Johnson, McGee and Naeser (1981) Nucl. Tracks, 5, pp. 317-323Green, In reply to Johnson, McGee and Naeser (1982) Nucl. Tracks, 6, pp. 56-57Johnson, McGee, Naeser, A practical method of estimating standard error of age in the fission track dating method (1979) Nucl. Tracks, 3, pp. 93-99Johnson, McGee, Naeser, Reply to P. F. Green's criticism of “A practical method of estimating standard error of age in the fission track dating method” (1982) Nucl. Tracks, 6, pp. 53-57Kendall, Stuart, (1963) The Advanced Theory of Statistics, 1. , Griffin, LondonMcGee, Johnson, Statistical treatment of experimental errors in the fission track dating method (1979) Math. Geol., 11, pp. 255-268McGee, Johnson, On statistical models for fission track counts: comment (1981) Math. Geol., 13, pp. 479-484Swinehart, Boellstorff, Age of Bishop tuff of Eastern California as determined by the fission-track method (1977) Comment. Geol., 5, pp. 648-65

Effects Of Etching On Zircon Grains And Its Implications For The Fission Track Method

Studies of zircon grains using optical microscopy, micro-Raman spectroscopy, and scanning electron microscopy (SEM) have been carried out to characterize the surface of natural zircon as a function of etching time. According to the surface characteristics observed using an optical microscope after etching, the zircon grains were classified as: (i) homogeneous; (ii) anomalous, and (iii) hybrid. Micro-Raman results showed that, as etching time increases, the crystal lattice is slightly altered for homogeneous grains, it is completely damaged for anomalous grains, and it is altered in some areas for hybrid grains. The SEM (energy dispersive X-ray spectroscopy, EDS) results indicated that, independent of the grain types, where the crystallinity remains after etching, the chemical composition of zircon is approximately 33% SiO 2:65% ZrO 2 (standard natural zircon), and for areas where the grain does not have a crystalline structure, there are variations of ZrO 2 and, mainly, SiO 2. In addition, it is possible to observe a uniform surface density of fission tracks in grain areas where the determined crystal lattice and chemical composition are those of zircon. Regarding hybrid grains, we discuss whether the areas slightly altered by the chemical etching can be analyzed by the fission track method (FTM) or not. Results of zircon fission track and U-Pb dating show that hybrid and homogeneous grains can be used for dating, and not only homogeneous grains. 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