Fission track dating ppt

Part 1 - The method Induced tracks on dosimeter mica (rd): each irradiated sample package has at least two dosimeters (top, bottom)  estimation of irradiation gradient Spontaneous tracks on mineral grain (rs) Induced tracks on mica print of the mineral grain (ri) Part 1 - The method The FT age equation - 1 d NP/dt = -l NP NP = number of parent atoms NP = (NP )0e-lt l = decay constant ND = Np (e-lt -1) ND = number of daughter atoms ld= la lf where ld ≈ la Ns = lf / la238N(e-lat -1) Ns = number of spont.tracks t= 1/ la238ln[(la/ lf)(Ns/238N) 1] Part 1 - The method The FT age equation - 2 Ni = 235N s f s = neutron cross section f = neutron fluence Ni = 238N I s f I = 235U / 238U general age equation t= 1/ laln[(la/ lf)(Ns/Ni) I s f 1] G= geometry factor = 0.5 (2p/4p geometry) Q = revelation factor = 1 practical age equation t= 1/ laln[(la/ lf)(rs/ri) Q G I s f 1] Part 1 - The method The zeta (z) age approach Problem: Many of the factors in the age equation are loosely constrained or not accurately known.Less suitable: sandstones, greywackes, paragneisses, andesites, basalts Not suitable: very pure qtz or cal sandstones, limestones, silt- and claystones, ultramafics Part 1 - The method It dates a fast to very fast cooling event (with complete crossing of the partial annealing zone) It dates a moment during cooling across the partial annealing zone It forms a mixed age between an old and a young age component It provides an age information about the detrital origin the single grains in a sample Part 1 - The method if the time-temperature history is very complex (e.g.contains short-term hydrothermal events) if the sample has been heat treated after cooling (e.g.The number of tracks increases over time at a rate that depends on the uranium content.

Volcanic rocks – such as tuff and basalt – can be used in dating because they are formed at a particular moment in time, during an eruption.This damage is in the form of tiny marks called fission tracks.When volcanic rocks and minerals are formed, they do not contain fission tracks.Knowing when a dinosaur or other animal lived is important because it helps us place them on the evolutionary family tree.Accurate dates also allow us to create sequences of evolutionary change and work out when species appeared or became extinct. These are: Where possible, several different methods are used and each method is repeated to confirm the results obtained and improve accuracy.

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