1) Radioactive nuclei undergo spontaneous nuclear decay by emitting radiation such as alpha particles, beta particles, or gamma rays. This process is called nuclear transformation. 2) Different radioactive nuclides decay via different modes depending on their neutron to proton ratio and whether their nucleon numbers are odd or even. 3) Unstable nuclei are said to be radioactive because they emit radiation as they undergo spontaneous decay in order to become more stable nuclides. This radiation comes from either the nucleus or orbital electrons.

1. Lecture 8
Shahid Younas
NUCLEAR TRANSFORMATION

2. INTRODUCTION
Lecture 8
Why don't all the protons in the nucleus repel each other
and cause the nucleus to blow apart?
Nuclear Force

3. INTRODUCTION
Lecture 8
 Nuclei are composed of
combinations of nucleons.
 Certain combinations bear a high
degree of stability while others are
relatively unstable.

4. INTRODUCTION
Lecture 8
 One radioactive nuclide may have a high N/P ratio while for
another the ratio may be low.
 A radionuclide may have an odd number of protons and an even
number of neutrons, while for another the reverse may be true.

5. INTRODUCTION
Lecture 8
Do the radioactive nuclides different from each other?
Yes, of course

6. INTRODUCTION
Lecture 8
It is not surprising, then, that various modes of decay are possible,
depending upon the nature of the nuclide and the type of instability.

7. INTRODUCTION
Lecture 8
Unstable nuclei are said to be radioactive
because they emit radiation as they undergo
spontaneous decay.

8. INTRODUCTION
Lecture 8
 This radiation is emitted either from the nucleus or orbital electrons.
 The nature of this radiation is a function of the mode of decay of a
particular nuclear species.

9. INTRODUCTION
Lecture 8
Transformation literally means going
beyond your form.

10. Nuclear Stability Tests
Lecture 8
Magic Numbers:
Number of nuclear particles in a completed shell of protons or
neutrons.
 Magic Numbers for P+ → 2, 8, 20, 28, 50, 82, (114)
 Magic Numbers for No → 2, 8, 20, 28, 50, 82, 126
 If a nucleus has two magic numbers, it is very stable.

11. Nuclear Stability Tests
Lecture 8
 Magic Numbers
 Example:
 4He2
 p+ → 2
 no → 2
 Both are magic numbers, very
stable.
Which is more stable?
 102Sn51 or 101Sn51
 102Sn51 → p+ = 51, no = 51
 101Sn51 → p+ = 51, no = 50
 101Sn51 has a magic number and
102Sn51 doesn't.

12. Nuclear Stability Tests
Lecture 8
 The Even-Odd Rules
 1. There is instability when there is an odd number of neutrons
or protons in the nucleus
 2. Nuclei with an even number of protons and an even number
of neutrons are very likely to be stable.

13. Nuclear Stability Tests
Lecture 8
 Which is more likely to be stable, 62Ga31 or 64Ge32?
 64Ge32 because it has both an even number of protons and an even
number of neutrons.

14. Nuclear Stability Tests
Lecture 8
Band of Stability
The region in which stable
nuclides lie in a plot of number
of protons against number of
neutrons.

15. Nuclear Stability Tests
Lecture 8
 “Band of Stability”
 Any nuclide falling in the band
of stability will be stable and
therefore not radioactive.
 its edges are not as smooth as
in the diagram.

16. DECAY BY α- PARTICLE EMISSION
Lecture 8
 The α-particle consists of 2 protons and 2 neutrons and is a
relatively large particle
 For a nucleus to be capable of releasing so large a particle, the
nucleus must be relatively large itself.
 Nuclei which decay by α emission have a Z >83 and A > 150.

17. DECAY BY α- PARTICLE EMISSION
Lecture 8
Which is the origin of alpha particles?
Nucleus or Orbit

18. DECAY BY α- PARTICLE EMISSION
Lecture 8
 α decay is followed by gamma and characteristic x-ray emission.
 Alpha particles are emitted with discrete energy ranges from 2 to
10 MeV.
 These are not used in Medical imaging however potential source
of hazard in radiation protection.

19. DECAY BY α- PARTICLE EMISSION
Lecture 8
 Generic Reaction equations,

20. DECAY BY α- PARTICLE EMISSION
Lecture 04
 α-EMISSION: DECAY OF (Rn222)

21. DECAY BY α- PARTICLE EMISSION
Lecture 8
 In Route 1, the decay is
directly to the ground
state. There is no excited
or metastable state
formed and no gamma
rays are released.

22. DECAY BY α- PARTICLE EMISSION
Lecture 8
 In Route 2, there is decay
by alpha to a metastable
state of the daughter,
followed by emission of a
gamma ray and transition
to the ground state.

23. DECAY BY α- PARTICLE EMISSION
Lecture 8
There is alpha decay to a highly
excited state of the daughter,
followed by gamma ray emission
either directly to the ground state
or indirectly to the ground state
through sequential emission of
two separate gamma rays.

24. DECAY BY α- PARTICLE EMISSION
Lecture 8
Do you know about Recoil / Transition Energy?
What happens to your shoulder when you fire a bullet.
The emitting particle transfers a small part of the energy to the
parent or daughter element. This gives an recoil to that element.

25. DECAY BY α- PARTICLE EMISSION
Lecture 8

26. BETA MINUS (β-) NEGATRON DECAY
Lecture 8
 N/Z ratio is too large i.e. neutron-rich region.
 The neutron is converted into a proton, which remains in the
nucleus.

27. BETA MINUS (β-) NEGATRON DECAY
Lecture 8
 Generic decay equation is,

28. BETA MINUS (β-) NEGATRON DECAY
Lecture 8
Do you know about isobaric transitions?
Decay in which mass number remains constant is called as isobaric
transition.

29. BETA MINUS (β-) NEGATRON DECAY
Lecture 8
 Beta-minus decay decreases the N/Z ratio, bringing the daughter
closer to the line of stability;

30. BETA MINUS (β-) NEGATRON DECAY
Lecture 8
 Emitted β particles are poly-energetic with Emax = Eβ- + Ev

31. BETA MINUS (β-) NEGATRON DECAY
Lecture 8
 DECAY SCHEME OF Au198:
 Three steps are involved same
as alpha decay.

32. BETA MINUS (β-) NEGATRON DECAY
Lecture 8
COMPARISON OF ALPHA- AND BETA- DECAY SCHEMES
 Alpha decay schemes and Beta decay schemes are mirror images of
each other.

33. BETA PLUS (β+) POSITRON DECAY
Lecture 8
 Neutron poor i.e. low N/Z ratio.
 Increases the neutron number by one.

34. BETA PLUS (β+) POSITRON DECAY
Lecture 8
 Decreases the atomic number by 1
 Isobaric transition.

35. BETA PLUS (β+) POSITRON DECAY
Lecture 8
 Accelerator produced radionuclides often decay by β+ mode.

36. BETA PLUS (β+) POSITRON DECAY
Lecture 8
 Accelerator produced radionuclides often decay by β+ mode.
18F9 β+ 18O8
95Tc 43 → 95Mo42 + 0
1e

37. BETA PLUS (β+) POSITRON DECAY
Lecture 8
 Energy distribution between the positron and neutrino is similar to
that between the negatron and the anti-neutrino in B minus decay.
 Positron decay is also poly-energetic.
 Negatron are physically identical to electron.
 Opposite magnetic moment than electron.

38. BETA PLUS (β+) POSITRON DECAY
Lecture 8
Do you know the difference between neutrino and anti-neutrino?
Both are neutral particles but different magnetic moment.

39. BETA PLUS (β+) POSITRON DECAY
Lecture 8
FATE OF POSITRONS IN
MATTER
 When they come to rest
they react violently with
their electrons.
 Two 511 keV energy
photons emitted.

40. BETA PLUS (β+) POSITRON DECAY
Lecture 8
FATE OF POSITRONS IN
MATTER
 According to E= mc2 is the
energy equivalent of the
rest mass of both particles.

41. RADIOACTIVITY & NUCLEAR TRANSFORMATION
Lecture 8
Be less curious about people and more
curious about ideas.