A brief presentation on radioactivity and nuclear decay process. The presentation is not too technical. The intention is only to give a brief idea about radioactivity

1. Radioactivity and Nuclear decay
Madhava B Mallia
Radiopharmaceuticals Division
Radiochemistry and Isotope Group
BHABHA ATOMIC RESEARCH CENTRE
Trombay, Mumbai - 400 085, INDIA

2. • Atom!!!
• Radioactivity and nuclear decay process
• Kinetics of radioactive decay
• Decay constant and half-life
• Units of radioactivity
Overview
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3. Atom: “Smallest indivisible particle of matter…”
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ATOM Mass No. A = Number of protons + number of neutrons
Atomic No. Z = Number of protons

4. Radioactivity
Radioactivity is a phenomenon of spontaneous emission of
radiation by unstable nuclei
Henri Becquerel
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Radioactivity: Story of unstable nucleus

5. 5
Florescence: Atomic phenomenon Radioactivity: Nuclear phenomenon

6. 6
Radioactive decay  Loose energy  Attain stability
Particles Electromagnetic
radiation

7. Types of radioactive decay
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Alpha α Helium nucleus
Beta β-/β+ Electron/Positron
Gamma  Electromagnetic
Radiation
Auger Electron

8. 223
88Ra  219
86Rn + 4
2He 223
88Ra87Fr219
86Rn
α Decay
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9. β- Decay
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131
53I  131
54Xe + β- 131
54Xe131
53I

10. 10
18
9F  18
8O + β+ 18
9F18
8O
β+ Decay

11.  Emission
• Transition of nucleus from excited state to ground state
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99mTc  99Tc + gamma

12. N/P ratio and nuclear stability in layman’s terms
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N/P ratio = Neutron/Proton ratio
Carbon-11 Carbon-12 Carbon-13 Carbon-14
N 5 6 7 8
P 6 6 6 6
N/P 0.83 1 1.16 1.33
Status Radioactive Stable Stable Radioactive
Mode of decay Positron (β+) - - Beta (β-)

13. 13
Carbon-11
N 5
P 6
N/P 0.83
Status Radioactive
Boron-11
N 6
P 5
N/P 1.2
Status Stable
Carbon-14
N 8
P 6
N/P 1.33
Status Radioactive
Nitrogen-14
N 7
P 7
N/P 1
Status Stable
Attaining stability through radioactive decay

14. Characteristics of radioisotopes
• Half-life
• Type of radiation
• Energy of radiation
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Actenium-225 (half-life – 10 days)
Alpha - 5.79 MeV (8.6%); 5.73 MeV (10.0%); 5.79 MeV (18.1%); 5.83 MeV (51.6%)
Gamma – 12 keV (21.3%)
Lutetium-177 (half-life – 6.9 days)
Beta (max) - 0.18 MeV (12.3%); 0.49 (78.7%)
Gamma - 112.95 keV (6.4%); 208.36 keV (11.0%)
Technetium-99m (half-life – 6 hours)
Gamma – 140 keV

15. Kinetics of radioactive decay
Radioactive decay follows first order kinetics
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A B
-dN/dt = N
‘N’

N = N0 e-t
-dN/dt  N
Where ‘’ is called decay constant

16. Decoding Decay Constant
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N = N0 e-t
Number Number Unit less quantity
Unit of ‘’ = inverse of unit of time
Unit of ‘’ = S-1 (Second inverse)
Decay constant  Probability of nuclear decay per second

17. 17
Activity
N = N0 e-t
Activity, A = N
 x x 
N = N0 e-t
A = A0 e-t
Activity = Number of disintegrations happening per second

18. Radioactivity and its units
• SI unit – Bq (Bequerels)
• 1 Bq = 1 dps (disintegrations per second)
• 1 Curie – 3.7 x 1010 dps (Bq) – Disintegrations in 1 gram of 226Ra
• 1 millicurie – 37 MBq
• 1 microcurie – 37 kBq
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19. Plot of A Vs time
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20. Half-life of a radioisotope
Half-life (t1/2) – Time taken to reduce the activity of a radioactive sample to half the
initial value
A = A0 e-t
At t = t1/2 , A = A0/2 x e-t1/2
t1/2 = 0.693/λ
Half-life is a constant for a given radioisotope
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21. Determination of half-life graphical method
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22. Can you alter half-life?
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23. When will a single nucleus of a radioactive atom
decay?
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One half life One half life
Finally
What is my fate?

24. THANK YOU...24