DR.S.KARTHIGA KANNAN PROFESSOR ORAL MEDICINE & RADIOLOGY

SPECIFIC LEARNING OBJECTIVES  To know about atomic structure and subatomic particles  To know about types of radiation  To know about production of x-rays

Format  Introduction  Atomic Structure  Types of radiation  Parts of X ray Machine  Production of X-rays  Properties of X-rays

 Matter may be described in to Elements or Compounds  Elemental matter is made-up of accumulation of single type atoms  Compounds are composed of more than one type of atoms  Atoms are the fundamental unit of any particular element  Subatomic Particles  More than 100 sub atomic particles have been described  Electron caries an electrical change designated as -1, Proton a charge of +1 and neutron no charge at all  Mass of an electron is about 9.10 x grams  The mass of proton is x grams  The mass of a neutron is 1.68 x 10 – 24 grams

 Atomic Structure  In 1913 NIELS BOHR described the structure of an atom like a miniature solar system - Quantum Mechanical Model  Nucleus at the centre is analogous to a sun and the electrons orbits around the nucleus are analogous to the planets  The nucleus has a +VE charge, the magnitude of which is equal to the number of protons.  The number of protons in the nucleus and similarly the number and arrangement of the orbital electrons determines the identity of an atom  The distinguishing number of protons (+VE) in the nucleus of an atom is referred to as its atomic number and is designated by the symbol Z  The total number of protons and neutrons in an atom is called as atomic mass and designated by the symbol A  The orbits or shells are spaced at defined distances from the nucleus and designated by K, L, M, N, O, P and Q (or) 1, 2, 3, 4, 5, 6 and 7.

Atom (electrically neutral) K-shell L-shell protons neutrons electrons M-shell

Binding energy - Attraction between protons in the nucleus and electrons in the orbit Electrostatic Force Centrifugal Force Pulls electrons away from nucleus EFCF  Balance between electrostatic force and centrifugal force keeps electrons in orbit around nucleus

 The inner most shell is K or shell 1, L -2, M-3, N-4, O-5, P-6 and Q-7  These are the principal quantum numbers and represented by letter n  Only two electrons may occupy the “K: shell with increasingly large number in the outer shells These includes  L-8  M-18  N-32  O-52  P-72  Q-98 Pauli’s principle  According to Pauli’s principle, the maximum number of electrons in a given shell is 2n 2

Ionization  The process of converting atoms to ions is known as IONIZATION  It may be produced by the addition of electron to neutral atom or by removing electrons by heating or collision with high energy radiation. Nature of Radiation  Definition- Radiation is the transmission of energy through space and matter  It is of 2 types 1)Particulate radiation 2)Electro magnetic radiation

Particulate Radiation  Definition- Atomic nuclei / sub atomic particles moving at very high velocity.  Alpha, Beta and cathode rays are examples of particulate radiation  Alpha rays consists of a high speed stream of doubly ionized helium atom.  Beta and cathode rays are streams of high speed electrons  When the electrons are emitted by a radioactive materials they are called beta rays  When the electrons are originate in a device such as X-Ray tube they are called cathode rays

The movement of energy through space as a combination of electric and magnetic fields Electromagnetic Radiation 3 x 10 8 meters/second 186,000 miles/second Travel at the speed of light

Electromagnetic Radiation R – RADIO WAVES T – TELEVISION WAVES M– MICROWAVES R – RADAR WAVVES I – INFRARED WAVES RadioTVVisible light X-raysGamma rays Cosmic rays V–VISIBLE LIGHT U – ULTRAVIOLET RAYS X – X RAYS G – GAMMA RAYS C – COSMIC RAYS RT MRI VUX GC

A B C Highest energy? Highest energy Shortest wavelength Highest frequency More penetrating More ionizing More harmful to living tissue

X-ray Tube

X-Ray tube consists of (1)Cathode or filaments and (2)Anode or target They are engaged in an evacuated glass or tube and x-rays are produced when the electrons strikes the target. Cathode consists of 2 parts 1)T ungsten filament 2)Focusing cup Tungsten filament is about 0.2cm in diameter and 1 cm or less in length The filament is located in a molybdenum focusing cup and it focuses the electrons emitted by the filament in to a narrow beam directed at a small rectangular area on the anode is called focal spot.

(molybdenum) (tungsten) Cathode Focusing cup Filament

x-section of filament hot filament The hotter the filament gets, the greater the number of electrons that are released electrons Release of electrons from hot filament when current flows after depressing exposure switch Thermionic Emission Low voltage current - mA

Anode Dental x-ray machines have stationary anode Copper stem Target side viewfront view Target

Tungsten High atomic number (Z=74) Low vapour pressure Transfers heat readily High melting point (3370º C) Can be drawn into fine wire (Filament and Target)

exposure button oil filter filament X-ray Machine Components X-ray Production

mA 70Kvp

Bremsstrahlung X-ray Production + High-speed electron from filament enters tungsten atom Electron slowed down by positive charge of nucleus; energy released in form of x-ray Electron continues on to other atoms until all of its energy is lost

Bremsstrahlung X-ray Production Maximum energy High-speed electron from filament enters tungsten atom and strikes nucleus, losing all its energy and disappearing The x-ray produced has energy equal to the energy of the high- speed electron; this is the maximum energy possible +

Characteristic X-ray Production L K M High-speed electron with at least 70 keV of energy (must be more than the binding energy of k-shell Tungsten atom) strikes electron in the K shell Ejected electron leaves atom Recoil electron (with very little energy) exits atom vacancy

Characteristic X-ray Production K L M Outer-shell electron drops into vacant spot X-ray with 59 keV of energy produced. 70 (binding energy of K-shell electron) minus 11 (binding energy of L-shell electron) = 59.

Properties of X-rays Travel in straight line Cannot be focused to a point Differentially absorbed Cause fluorescence Harmful to living tissue

X-ray Characteristics High energy waves No mass No charge (neutral) Travel at speed of light Invisible