1. Introduction (Atomic and Nuclear Structure-Radioactivity)
Dr: Mohamed Bahaaeldin Afifi By
Lecturer of Radiological Science

2. Matter &The Atom
The term matter describes all of the physical substances around us
Matter is anything that has mass and takes up space
The Universe is made up of matter and energy

3. Matter is made up of atoms
Matter is made up of atoms. An atom is the smallest whole particle of matter.

4. Early Models of the Atom
Rutherford
Mostly empty space
Small, positive nucleus
Contained protons
Negative electrons scattered around the outside

5. Early Models of the Atom
Bohr
Electrons move in definite orbits around the nucleus

6. Modern Model of the Atom
The electron cloud
Sometimes called the wave model
Spherical cloud of varying density

7. Which force holds the electrons in orbit?
The Coulomb force

8. ATOMIC STRUCTURE

9. The nucleus of an atom is made up of tightly bound protons and neutrons, which are called nucleons.
The nucleus contains most of the atomic mass.

10. Protons Neutrons Much larger and heavier than electrons
Protons have a positive charge (+)
Located in the nucleus of the atom
Neutrons
Large and heavy like protons
Neutrons have no electrical charge
Located in the nucleus of the atom 

11. Electrons Tiny, very light particles
Have a negative electrical charge (-)
Move around the outside of the nucleus in shells Fig1.2.

13. Each shell is assigned a principal quantum number (n), beginning with one for the K-shell, two for the L-shell, and so on.
The number of electrons each shell can contain is 2n2.

14. Electrons are arranged in Energy Levels or Shells around the nucleus of an atom.
first shell K a maximum of 2 electrons
second shell L a maximum of 8 electrons
third shell M a maximum of 18 electrons

15. The Atom The atom consists of two parts:
1. The nucleus which contains:
protons
neutrons
2. Orbiting electrons.
Atoms in nature are electrically neutral so
The number of electrons orbiting the nucleus equals the number of protons in the nucleus.

16. X Z A Mass number = number of protons + number of neutrons
Element symbol Z
Atomic number
= number of protons

17. X A Z A = number of protons + number of neutrons Z = number of protons
N = A – Z = number of neutrons
Number of neutrons = Mass Number – Atomic Number

18. Electron binding energy
The work that is required to remove an electron from an atom is called the electron binding energy.
The binding energy of outer-shell electrons is smaller than the binding energy of the inner-shell.

19. Energetic particles can knock out inner-shell electrons only if their energy is equal to or greater than the electron binding energy.

20. A vacancy in the K-shell will be filled by an electron from a higher shell.
Electrons moving from an outer shell to an inner shell may emit excess energy as electromagnetic radiation.

21. Electromagnetic radiation
Radiation is the transport of energy through space.
Electromagnetic radiation represents a transverse wave, in which the electric and magnetic fields oscillate perpendicular to the direction of the wave motion.

23. Wavelength (λ) is the distance between successive crests of waves.
Amplitude is the intensity defined by the height of the wave.

25. Frequency (f) is the number of wave oscillations per unit of time expressed in cycles per second, or in hertz (Hz).
The period is the time required for one wavelength to pass (1/f).

26. X-rays are an example of electromagnetic radiation.
The product of the wavelength (λ) and frequency (f) of electromagnetic radiation is equal to the speed of light c
(c = f .λ ).

27. Fig. 1.3 shows the electromagnetic spectrum from radio waves (long wavelength) to x-rays and gamma rays (short wavelength).

29. Photons Photons may behave as waves or particles but have no mass.
Electromagnetic radiation is quantized, meaning that it exists in discrete quantities of energy called photons.
Photons may behave as waves or particles but have no mass.

30. U U 235 92 238 92 There are many types of uranium: A Z
Number of protons
Number of neutrons A Z
Number of protons
Number of neutrons

31. U
235 92 U
238 92 A
235 Z 92
Number of protons
Number of neutrons
143 A
238 Z 92
Number of protons
Number of neutrons
146
Isotopes of any particular element contain the same number of protons, but different numbers of neutrons.

32. Most of the isotopes which occur naturally are stable.
A few naturally occurring isotopes and all of the man-made isotopes are unstable.
Unstable isotopes can become stable by releasing different types of particles.
This process is called radioactive decay and the elements which undergo this process are called radioisotopes/radionuclides.

33. The word decay means to "break down."
Radioactive Decay
The word decay means to "break down."
Radioactive decay results in the emission of either:
an alpha particle (a),
a beta particle (b),
or a gamma ray(g).

34. Radiation
Radiation: Energy in the form of particles or electromagnetic waves.
Radiation is the transport of energy through space + -

35. Classification of radiation
Radiation is classified into two main categories, non-ionizing and ionizing, depending on its ability to ionize matter.
Ionizing Radiation:
energy to remove an electron from an atom or molecule Radiation with sufficient .
Non-ionizing radiation:
Is radiation without enough energy to separate molecules or remove electrons from atoms. Examples are visible light, radio and television waves, ultra violet (UV), and microwaves with a large spectrum of energies.

37. Radioactivity Units of Activity Curie (Ci) Bequerel (Bq)
The process by which unstable atoms spontaneously transform to new atoms* and in the process emit radiation.
Units of Activity
Curie (Ci)
Bequerel (Bq) $-

38. Half-Life
Half-life is the amount of time needed for the activity to reach one half of the original amount. f e l t l ln ( ) 2
T1/2 f 1 2 t
T1/2
Days

39. Common Types of Radiation

40. Common Types of Radiation

41. Alpha Particle
An alpha particle is identical to that of a helium nucleus.
It contains two protons and two neutrons.

42. Alpha Particle

43. X Y + He Alpha Decay A Z A - 4 Z - 2 4 2 unstable atom alpha particle
more stable atom

44. Alpha Decay Rn
222 86 He 4 2 Ra
226 88

45. Alpha Decay X A Z Y
A - 4
Z - 2 + He 4 2 Ra
226 88 Rn
222 86 + He 4 2

46. Beta Particle
A beta particle is a fast moving electron which is emitted from the nucleus of an atom undergoing radioactive decay.
Beta decay occurs when a neutron changes into a proton and an electron.

47. Beta Decay
As a result of beta decay, the nucleus has one less neutron, but one extra proton.
The atomic number, Z, increases by 1 and the mass number, A, stays the same.

48. Beta Decay
As a result of beta decay, the nucleus has one less neutron, but one extra proton.
The atomic number, Z, increases by 1 and the mass number, A, stays the same.

49. Beta Decay b -1 At
218 85 Po
218 84

50. Beta Decay X A Z Y
Z + 1 + b -1 Po
218 84 Rn 85 + b -1

51. Photons
A photon is an x or gamma ray
Has no weight
Has no charge

52. Gamma Rays
Gamma rays are not charged particles like a and b particles.
Gamma rays are electromagnetic radiation with high frequency.

53. Photon Decay 99mTc 99Tc Stable Nucleus Excited Nucleus Gamma ray
Gamma emissions occur during transitions such as fission, radioactive disintegration and electron-positron annihilation.
Gamma rays are monoenergetic electromagnetic radiations that are emitted from nuclei of excited atoms following radioactive transformation; they provide a mechanism for ridding excited nuclei of their excitation energy.
Source: Cember, H, Introduction to Health Physics, 1989
Stable Nucleus
Excited Nucleus

54. Photon Decay
When atoms decay by emitting a or b particles to form a new atom, the nuclei of the new atom formed may still have too much energy to be completely stable.
This excess energy is emitted as gamma rays (gamma ray photons have energies of ~ 1 x J).