Radiation Detection Lab #1
A Brief Introduction to Neutron Activation Analysis
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Why NAA?
Applications
Archaeology
Geology
Environmental Analysis
2
Advantages
Non-destructive
Time efficient
Semiconductor
Epidemiology
Forensics
Multi-element
Not limited by chemical form
Why NAA?
Applications
Archaeology
Geology
Environmental Analysis
3
Advantages
Non-destructive
Time efficient
Semiconductor
Epidemiology
Forensics
Multi-element
Not limited by chemical form
Why NAA?
Archaeology
Geology
Environmental Analysis
Semiconductor Industry
Epidemiology
Forensics
4
Why NAA?
Archaeology
Geology
Environmental Analysis
Semiconductor Industry
Epidemiology
Forensics
5
Iridium is a metal which has very low abundance on earth
Excess iridium in K-T band is attributed to an impact of a 10-kilometer diameter asteroid
Cretaceous
Tertiary
Why NAA?
Archaeology
Geology
Environmental Analysis
Semiconductor Industry
Epidemiology
Forensics
6
Structure of Atoms
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Structure of Atoms
8
Ernest Rutherford
1871-1937
”It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you.”
1911
1919
Hydrogen nucleus is present in other nuclei
Proton
Nucleus:
Proton
Electron
Structure of Atoms
9
Ernest Rutherford
1871-1937
”It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you.”
1911
1919
Proton
Nucleus:
Proton
Electron
Structure of Atoms
10
James Chadwick
Carries no charge - neutral
Similar mass as proton
Neutron
1932
Nuclear Engineering is the branch of engineering concerned with the application of the breakdown of atomic nuclei and/or other sub-atomic physics, based on the principles of nuclear physics.
Chemistry/Chemical Engineering – Atomic level
Nuclear Physics/Nuclear Engineering – Subatomic
Isotope vs. Element
12
N=Z-A
Z
Element 1
Element 2
Element Z
…
Isotope
Isotope
Isotope
Isotope
Isotope
Isotope
Isotope
Isotope
Isotope
Nucleus Energy Levels
13
Ground state
Excited states
Unique energy level structure
Unique energy
Unique ‘relaxation’ path
Well documented
Raise
$ 0
$ 100
$ 1000
$ 10,000
Energy
Nucleus Energy Levels
14
The GOALs of NAA??
Identification - What
Quantification – How much
Ground state
Excited states
Unique energy level structure
UNIQUE energy
Unique ‘relaxation’ path
Well documented
Energy of the Excited Levels
Nucleus Energy Levels
15
The GOALs of NAA??
Isotope Identification - What
Isotope Quantification – How much
Ground state
Excited states
Unique energy level structure
UNIQUE energy
Unique ‘relaxation’ path
Well documented
Energy of the Excited Levels
Origin of Gamma-rays
16
Ground state
Excited states
Unique energy level structure
UNIQUE energy
Unique ‘relaxation’ path
Well documented
Energy of the Excited Levels
Energy of the De-excitation Gamma rays
16
Isotope Identification
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Isotope Identification
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Isotope Identification
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Al Lab
20
27Al + n -> 28Al*
27Al* -> 28Al + γ
28Al -> 28Si* + β
28Si* -> 28Si + γ
What could be measured in the lab?
Al Lab
21
27Al + n -> 28Al*
27Al* -> 28Al + γ
28Al -> 28Si* + β
28Si* -> 28Si + γ
What could be measured in the lab?
Beta particle
Gamma ray
What is the half life of Al-28?
Al Lab
What is the activity of Al-28 after and irradiation period of t?
Balance equation of # of Al-28 nuclei
Increase rate:
ΦNpσ
Decrease:
λNd
Rate of change:
dNd/dt = ΦNpσ - λNd
Initial condition:
Nd(0) = 0
Activity
At = λNd(t) = ΦNpσ(1-e-λt)
22
Al Lab
What is the activity of Al-28 after and irradiation period of t?
At = λNd(t) = ΦNpσ(1-e-λt)
What is the activity after cooling time tc?
23
time
tc
t
Al Lab
24
Amplifier
SCA
Counter
Al Lab
25
Amplifier
SCA
Counter
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