Dating Fundamentals
Most techniques
Depend on radioisotope decay (unstable nuclides)
Element Stability
Stable N/Z = 1.5
Unstable NZ > 1.5
= f ( mass / atomic number ) ∴ position on periodic table
Radioactive decay
Elements w atomic no. > 89
decay via mass loss instantly
stick around a long time
Unstable nuclides with high energy
Decay via emission of heavy particles e.g. α-particles
∴ reducing nuclide mass & release energy
Nature of particle emitted
= f ( location of unstable nuclide wrt 'valley' )
Decay types
Isobaric decay
mass of nuclide does not change
Heavy particle emission
isobars = nuclides of equal mass
α - decay
mass of nuclide does change
Unstable isotopes
U & Th important
= Highly unstable in periodic table
Decay by spontaneous fission
--> to release mass & energy
Significance radioactive decay
One parent isotope
--> Decays to 2 fission fragments/daughters
similar size & different mass
Mass loss & energy emission
Energy emission distorts lattice
Produces damage tracks
238 U & 235 U
Undergo natural fission
But insignif track contribution
Why?
Less abundant isotopes
Longer fission half lives
Spontaneous decay / fission occurs
Decay by mass loss
occurs in nuclides that are unstable
(have atomic number > 89)
as lose mass & emit energy
Energy emitted by fission
Distorts lattice structure
within a finite distance
of location of spontaneous fission event
Fission track is produced by this distortion
i.e. damage track of fission reaction
i.e. surrounding decaying atom
Fission track
Defines areal extent around atom damaged/distorted by energy emission
Fission may be induced
by bombarding mineral with nuclear radiation
With time
Radioactive decay increase
Damage increase
Tracks = increasingly abundant