Radioisotope Dating.pdf

Radioisotope Dating

1. Radioisotope Dating
Presentedby:
Ms.PriyankaShandilya
AssistantProfessor
Govt.CollegeNarnaul

3. Exponential Decay

4. Exponential Decay

5. Half-Life

6. Basic Equations
•Basic Equation
•Rearrange and integrate:
•Half-life:dN
dt
=-lN dN
N
N
0
N
ò
=-ldt
0
t
ò ln
N
N
0
=lt N=N
0e
-lt t
1/2=
ln2
l ln
1
2
=lt
1/2

7. Determining Half Life
•Decay Constant λ= Fraction of isotope that
decays/unit time
•N= Number of remaining atoms of parent
•dN/dt= -λN
•dN/N = -λdt
•ln N = -λt + C
•N = N
0e
-λt
where
•N
0= original number of Parent Atoms

8. Determining Half Life
•N = N
0e
-λt
•Solve for N = N
0/2
•N
0/2 = N
0e
-λt
•½ = e
-λt
•-ln(2) = -λt
•Half life t = ln(2)/λ= 0.693/λ

9. Ideal Radiometric Dating
•A (parent) →B (Daughter)
–A decays only one way
–No other sources of B
–Both A and B stay in place
•Unfortunately there are no such isotopes in
rocks
–Branching Decay
–Inherited Daughter Product
–Diffusion, alteration, metamorphism

10. The no. of radiogenic daughter atoms
formed (D*) is equal to the no.of
parent atoms consumedNND −=
0*

11. General geochronological equation)1(
)1(*
*
0 −+=
−=
−=
t
t
t
eNDD
eND
NNeD




12. Decay curve of a radionuclide and growth curve of its stable
daughter in linear coordinates.
Decay curve of parentt
eNN
−
=
0 ( )
t
eND
−
−=1
0
*
Growth curve of daughter

13. Contact details:
Ms. Priyanka Shandilya
[email protected]