1. Radioactivity
Prepared by: Timothy John D. Matoy

2. RADIOACTIVITY Process of loosing energy to reach a stable state.
-This excited state can last for a few moments to billion of years and is measured in terms of half-lives.
-This lose of energy can be in form of pure energy, particles, or both.
-To maintain nuclear stability as the atomic number of an atom goes up to the number of neutrons must rise faster than the number of neutrons.
-radiocnuclide
-The highest stable atomic number is bismuth at 83, all higher elements are radioactive (any element with more than 83 protons will be radioactive.)

3. Radioactivity and Radioactive Decay
The nuclei of some nuclides are not stable
They disintegrate or undergo nuclear transformation spontaneously and in random process called radioactivity
Radioactivity is the emission of particles and energy in order to become stable.
Radioactivity decay results in emission of Alpha particles, beta particles and gamma rays.
Radioisotopes. – beta and alpha emission are important
Half-life – the time required for a quantity of radioactivity to be reduced to one-half its original value.
1Bq – 1 per second – the number of decaying nuclei per second
1 Cu = 3.7 x 10 10
process of losing energy to reach a stable state
This excited state can last for a few moments to billion of years and is measured in terms of half-lives

4. Henri Becquerel (1852-1908) Discover the radioactivity in 1896
He noted that a piece of mineral containing uranium when placed over an exposed photographic plate just as if it has been exposed to light.
- The blackening of the photographic plate was due not to light but to a radiation being emitted by the uranium mineral.

5. Marie Curie ( )
Pierre and Marie Curie discovered that polonium and radium also emit radiation.

6. Artificial Radioactivity
Radioactivity produced by man
Irene Curie-Joliot produce the first radioactive product when they bombarded aluminum with alpha particles from polonium source to study the emitted neutrons and positrons.

7. Radioactive elements emitted into 3 types of radiation
Alpha Particles
Beta Particles
Gamma Rays

8. Alpha Particles
Fast moving helium nuclei; positive electrical charge

9. Beta Particles
Negative electrical charged electrons.

10. Electrons, Positrons
Very light; in tissue do not travel in straight lines but are deflected by coulombic repulsions from atomic orbital electrons
Lose an average 50% of their energy in interaction

11. Gamma Rays
Electromagnetic waves of very short wavelength and travelling within the speed of light.
No charge at all.

12. Protons Generated by cyclotron beams
Because they are heavier than electrons, travel mainly in straight line by boring a path through atomic clouds
Medium Z materials used for shielding
10 MV produce neutrons
4 MV – 23 MV therapeutic
Slow electrons-
High Z materials must be avoided because they produce secondary radiation

13. Half-Life(t½)
the time in which a radioactive substance will lose half of its activity through disintegration.
Physical Half-life
Biological Half-life
Effective Half-Life
The amount of time that is required to reduce the radioactivity to ½ of its present value.
Radon gas – 3.83 days
Associated dose rate is also reduce to ½
Gold days

14. Physical Half-Life
the average time required for the decay of half the atoms in a given amount of a radioactive substance.

15. Biologic Half-Life
the time in which a living tissue, organ, or individual eliminates, through biologic processes, half of a given amount of a substance that has been introduced into it.

16. Effective Half-Life
the half-life of a radioactive isotope in a biologic organism, resulting from the combination of radioactive decay and biologic elimination.

17. Types of Decay Alpha Decay Beta Negative Decay Beta Positive Decay
Gamma Ray Emission
Electron Capture

18. ALPHA DECAY Americium 241 – smoke detectors
If substances emitting alpha particles are ingested, inhaled, injected or introduced through the skin, then it could result in a measurable dose.
accompanied by gamma photon emission.
Russian dissident Alexander Litvinenko's 2006 murder by radiation poisoning is thought to have been carried out with polonium-210, an alpha emitter.

19. ALPHA DECAY

20. BETA DECAY

21. Beta minus Beta plus BETA DECAY Electron antineutrino
Interacts with neutron
Beta plus
Electron Neutrino
Interacts with protons

22. GAMMA RAY EMISSION

23. ELECTRON CAPTURE

24. ELECTRON CAPTURE
Electron capture is a process in which a proton-rich nuclide absorbs an inner atomic electron (changing a nuclear proton to a neutron) and simultaneously emits a neutrino.
Emission of neutrino

25. Radioactive Decay Law
Elster and Geitel observed that the strength of a pure radioactive substance decrease exponentially.
Radioactivity was found to be a property of the individual atoms, not of a substance as a whole.
Statistical nature of disintegration was established.

26. Unit of Radioactivity Curie (Ci) Becquerel (Bq)
1 Bq = 1 disintegration per second
1 Ci = 3.7x1010 Bq

27. Exponential decay law expressed in the following equation:
N = N0e-λt or A = A0e-λt
Where:
A = present activity
A0 = original activity
λ = disintegration constant/ decay constant
t = elapsed time

28. Sample Problem
The half life for radioactive radon gas is 3.83 days, what will be the present activity of the radon gas after 5 days if the initial activity is 30 mCi?
N = mCi

29. Practice Problem
A Cesium-138 radioactive source has a half life of 30 years. If the initial activity is Ci. What will be the present activity after 30 years?
2.877 Ci

30. Practice Problem
A certain radioactive source has a present activity of mCi after days. If the initial activity is 15 mCi. Find the decay constant?
0.04

31. Where n = time/ half life
Activity Fraction
the fraction of the activity that is remaining after a given amount of time.
AF = 2 –n
Where n = time/ half life

32. Sample Problem
The half life for radioactive radon gas is 3.83 days, what will be the its activity fraction after 5 day?
N = mCi

33. Practice Problem
A Cesium-138 radioactive source has a half life of 30 years. If the initial activity is Ci. What will be its activity fraction after 55 years?
2.877 Ci

34. Nf = (AF) Ni Where Nf = final activity, Ni = initial activity
With the activity fraction, we can write a single equation to solve for the final activity if we are given the initial activity
Nf = (AF) Ni
Where Nf = final activity,
Ni = initial activity

35. Sample Problem
The half life for radioactive radon gas is 3.83 days, what will be the present activity of the radon gas after 5 days if the initial activity is 30 mCi?
N = mCi

36. Practice Problem
A Cesium-138 radioactive source has a half life of 30 years. If the initial activity is Ci. What will be the present activity?
2.877 Ci

37. Radioactive Decay Law Activity Remaining = original activity (0.5)n
Where n – number of half-lives

38. Sample Problem
The half life for radioactive radon gas is 3.83 days, what will be the present activity of the radon gas after 5 days if the initial activity is 30 mCi?
N = mCi

39. Practice Problem
A Cesium-138 radioactive source has a half life of 30 years. If the initial activity is Ci. What will be the activity after 30 years?
2.877 Ci

40. PRACTICE PROBLEM
A certain radioactive source has an initial activity of Ci. After 30 years only Ci of activity remains. What is its half-life?

41. Practice problem
Technetium 99m with a half-life of 6 hours was left in the laboratory at 6 o’clock in the morning. If the original activity is 100 mCi, when do the radioactive substance will have a 6.25% of its original value? What will be its activity at that time?