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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.
Chemical etching of polished internal surfaces of these minerals reveals spontaneous fission tracks, and the track density can be determined.
Because etched tracks are relatively large (in the range 1 to 15 micrometres), counting can be done by optical microscopy, although other imaging techniques are used.
Urge and urge and urge, Always the procreant urge of the world.