Radioisotope Dating

1. Radioisotope Dating
Presented by:
Ms. Priyanka Shandilya
Assistant Professor
Govt. College Narnaul

3. Exponential Decay

4. Exponential Decay

5. Half-Life

6. Basic Equations
• Basic Equation
• Rearrange and integrate:
• Half-life:
dN
dt
= -lN
dN
N
N0
N
ò = -l dt
0
t
ò
ln
N
N0
= lt
N = N0e-lt
t1/2 =
ln2
l
ln
1
2
= lt1/2

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 = N0 e-λt where
• N0 = original number of Parent Atoms

8. Determining Half Life
• N = N0 e-λt
• Solve for N = N0/2
• N0/2 = N0 e-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 consumed
N
N
D −
= 0
*

11. General geochronological equation
)
1
(
)
1
(
*
*
0 −
+
=
−
=
−
=
t
t
t
e
N
D
D
e
N
D
N
Ne
D




12. Decay curve of a radionuclide and growth curve of its stable
daughter in linear coordinates.
Decay curve of parent
t
e
N
N 
−
= 0
( )
t
e
N
D 
−
−
= 1
0
*
Growth curve of daughter

13. Contact details:
Ms. Priyanka Shandilya
pshandilya1210@gmail.com