1. Oral Radiology
Radiation Physics

2. Ionization
When the number of electrons in an atom is equal to the number of protons in its nucleus ,the atom is electrically neutral.
If such atom loses an electron ,the nucleus a becomes positive ion & the free electron a negative ion.
This process of forming an ion pair is termed ionization.

3. Ionization

4. To ionize an atom requires sufficient energy to overcome electrostatic force binding the electrons to nucleus.
The binding energy of an electron is related to the atomic number of the atom & the orbital type.

5. Electron in in the inner orbitals are more tightly bound than the more distant outer orbitals.
Tightly bound electrons requires the energy of x- rays or high energy particles to remove them, whereas loosely bound electrons can be displaced by ultraviolet radiation.

6. However non ionizing radiation, such as visible light, infrared, & microwave radiation , & radio waves do not have sufficient energy to remove bound electrons from their orbitals.

7. Radiation is the transmission of energy through space & matter.
Nature of Radiation
Radiation is the transmission of energy through space & matter.
Radiation occur in 2 forms:
I-particulate .
II-electromagnetic.

8. RADIOACTIVITY
Small atoms have roughly equal numbers of protons & neutrons.
Larger atoms tend to have more neutrons than protons. This makes them unstable & they may brake up, releasing α or β or γ rays. This process called radioacvtivity.

9. PRTICULATE RADIATION
Alpha particles α are helium nuclei consisting of 2 protons & 2 neutrons. They result from the radioactive decay of many large atomic numbers like uranium, thorium, actinium, and radium. 

10. Because of their double positive charge & heavy mass , α particles densely ionize matter through which they pass.
These particles quickly give up their energy & penetrate only a few micrometers of body tissue (an ordinary sheet of paper absorbs them).
After stopping α particles acquire 2 electrons & become neutral helium atom.

11. Beta particles β
When a neutron in a radioactive nucleus decay, it produces a proton, β particle. These β particles are identical to electrons.
Feynman diagram

12. High-speed β particles are not densely ionizing : thus, they are able to penetrate matter to a greater depth than α particles can , up to a maximum of 1.5 cm in tissue.
This deeper penetration occurs because β particles are smaller & lighter & carry a single negative charge.
β particles are used in radiation therapy for treatment of some skin cancers.

14. ELECTROMAGNETIC RADIATION
Is the movement of energy through space as a combination of electric & magnetic fields.
It is generated when the velocity of an electrically charged particle is altered.
Gamma ( γ ) rays , x rays , ultraviolet rays, visible light, infrared radiations (heat), microwaves, radio waves are all examples of electromagnetic radiation.

15. ELECTROMAGNETIC SPECTRUM

16. Gamma rays originate in the nuclei of radioactive atoms
Gamma rays originate in the nuclei of radioactive atoms. They typically have greater energy than do x rays.
X rays are produced extranuclearly from the interaction of electrons with large atomic nuclei in x ray machines.
Quantum theory considers electromagnetic radiation as a small bundles of energy called photons. Each photon travels at the speed of light & contains a specific amount of energy.

17. The unite of photon energy is the electron volt ( eV ).
High energy photons such as γ rays & x rays are typically characterized by their energy ( electron volts).
Medium energy photons ( e.g., visible light & ultraviolet waves ) characterized by their wave length ( nanometers ).
Low energy photons ( e.g., AM & FM radio waves ) characterized by their frequency (KHz & MHz)

18. X-RAY MACHINE
The primary components of x-ray machine are x-ray tube & its power supply.

19. Tube head

20. X-RAY TUBE
An x-ray tube is composed of a cathode & an anode situated within an evacuated glass envelope or tube.
Power supply is required to :1-heat the cathode filament to generate electrons.
2-establish a high-voltage potential between the anode & cathode to accelerate the electrons toward the anode.

21. Cathode Cathode consists of a filament & a focusing cup.
The filament lies in a focusing cup & it is the source of electrons within x-ray tube
The parabolic shape of the focusing cup electrostatically focuses the electrons into a narrow beam directed at a small rectangular area on anode called focal spot.

22. X-ray tube

23. X-ray tube

24. Anode The anode consists of tungsten target embedded in a cupper stem.
The purpose of the target is to convert the kinetic energy of colliding electrons to x-ray photons. .

25. The target material is made of tungsten, an elements that has several characteristics of an ideal target material . It has :
High atomic number (74).
High melting point .
High thermal conductivity.
Low vapor pressure at working temperatures of x-ray tube .

26. More than 99% of the kinetic energy of the electrons converted to heat & only 1% of this energy converted to x-ray.
A target made of high atomic number material is most efficient in producing x-rays.
Because heat is generated at the anode, there is a requirement for a target of a high melting point is clear.

27. X-ray tube

28. Focal spot
Is the area on target to which the focusing cup directs the electrons & from which x-rays are produced.
The sharpness of a radiographic image increases as the size of focal spot decreases .
The target is inclined about 20 degrees to the central ray of the x-ray beam, this causes the effective focal spot to approximately 1 x 1 mm.

29. POWER SUPPLY The primary function of power supply :
1-provide a low voltage current to heat the x-ray tube filament.
2-generate a high potential difference between the anode & cathode.

30. Tube current
Is the follow of electrons through the tube, from the cathode filament, across the tube to the anode & then back to the filament.
The mA setting on the filament current control actually refers to the tube current, typically 10 mA, which is measured by the milliammeter .
The tube current is dependant on the tube voltage : as the voltage increases between the anode & cathode , so does the current flow.

31. Tube voltage
A high voltage is required between the anode & cathode to give electrons sufficient energy to produce x-ray.
The actual voltage is adjusted with the autotransformer.
The best tube voltage is as high as 60 to 100 kVp to boost the peak energy of electrons & provides them sufficient energy to produce x- ray.

32. By using the kilovolt peak ( kVp ) selector, the operator adjusts the autotransformer & converts the primary voltage from input source into desired secondary voltage.

33. Timer
A timer is built into the high voltage circuit to control the duration of x-ray exposure.
The electronic timer controls the length of time that high voltage is applied to the tube & therefore the during which the tube current flows & x-rays are produced.

35. CHAPTER 2
RADIOBIOLOGY Radiobiology : is the study of the effects of ionizing radiation on living systems.

36. Radiation Causes Ionizations of:
ATOMS
which may affect
MOLECULES
CELLS
TISSUES
ORGANS
THE WHOLE BODY

37. The initial interaction between ionizing radiation and matter occurs at the level of the electron within the first second after exposure.
These changes result in modification of biologic molecules within the ensuing seconds to hours.
In turn, the molecular changes may lead to alterations in cells and organisms that persist for hours, decades, and possibly even generations.
These changes may result in injury or death.

38. Radiation Chemistry
Radiation acts on living systems through direct and indirect effects.
When the energy of a photon or secondary electron ionizes biologic macromolecules, the effect is termed direct effect.

39. Alternatively, a photon may be absorbed by water in an organism, ionizing some of its water molecules.
The resulting ions form free radicals (radiolysis of water) that in turn interacts and produce changes in biologic molecules.
Because intermediate changes involving water molecules are required to alter the biologic molecules, this series of events is termed indirect effect.

41. DIRECT EFFECT
If radiation interacts with the atoms of the DNA molecule, or some other cellular component critical to the survival of the cell, it is referred to as a direct effect.
Such an interaction may affect the ability of the cell to reproduce and, thus, survive.
If enough atoms are affected such that the chromosomes do not replicate properly, or if there is significant alteration in the information carried by the DNA molecule,

42. then the cell may be destroyed by “direct” interference with its life-sustaining system.
Approximately one third of the biologic effects of x-ray exposure result from direct effects.
However, direct effects are the most common outcome for particulate radiation such as neutrons and α particles.

44. INDIRECT EFFECTS
If a cell is exposed to radiation, the probability of the radiation interacting with the DNA molecule is very small since these critical components make up such a small part of the cell.
However, each cell, just as is the case for the human body, is mostly water(about 70% by weight).
Therefore, there is a much higher probability of radiation interacting with the water that makes up most of the cell’s volume.
About two thirds of radiation-induced biologic damage results from indirect effects.

45. When radiation interacts with water, it may break the bonds that hold the water molecule together, producing fragments such as hydrogen (H) and hydroxyls (OH).
These fragments may recombine or may interact with other fragments or ions to form compounds, such as water, which would not harm the cell.
However, they could combine to form toxic substances, such as hydrogen peroxide (H2O2), which can contribute to the destruction of the cell.

46. CHANGES IN DEOXYRIBONUCLEIC ACID
Damage to a cell ’ s deoxyribonucleic acid (DNA) is the primary cause of (1) radiation-induced cell death, (2) heritable (genetic) mutations, and (3) cancer formation (carcinogenesis).
Radiation produces a number of different types of alterations in DNA, including the following:
1-Breakage of one or both DNA strands
2-Cross-linking of DNA strands within the helix to other DNA strands or to proteins
3-Change or loss of a base
4- Disruption of hydrogen bonds between DNA strands

48. Radiosensitivity of various cells
Not all living cells are equally sensitive to radiation.
Those cells which are actively reproducing are more sensitive than those which are not.
This is because dividing cells require correct DNA information in order for the cell’s offspring to survive.

49. A direct interaction of radiation with an active cell could result in the death or mutation of the cell,
As a result, living cells can be classified according to their rate of reproduction, which also indicates their relative sensitivity to radiation.
This means that different cell systems have different sensitivities.

50. Lymphocytes (white blood cells) and cells which produce blood are constantly regenerating, and are, therefore, the most sensitive.
Reproductive and gastrointestinal cells are not regenerating as quickly and are less sensitive.
The nerve and muscle cells are the slowest to regenerate and are the least sensitive cells.

51. Cellular effects of radiation
Cells, like the human body, have a tremendous ability to repair damage.
As a result, not all radiation effects are irreversible.
In many instances, the cells are able to completely repair any damage and function normally.

52. If the damage is severe enough, the affected cell dies.
In some instances, the cell is damaged but is still able to reproduce.
The daughter cells, however, may be lacking in some critical life-sustaining component, and they die.

53. The other possible result of radiation exposure is that the cell is affected in such a way that it does not die but is simply mutated.
The mutated cell reproduces and thus remains the mutation. This could be the beginning of a malignant tumor

54. Cellular effects of radiation

55. Radiosensitivity of organs
The sensitivity of the various organs of the human body correlate with the relative sensitivity of the cells from which they are composed.
For example, since the blood forming cells were one of the most sensitive cells due to their rapid regeneration rate, the blood forming organs are one of the most sensitive organs to radiation.
Muscle and nerve cells were relatively insensitive to radiation, and therefore, so are the muscles and the brain.

57. RADIATION EFFECTS ON EMBRYOS AND FETUSES
Embryos and fetuse are considerably more radiosensitive than adults because most embryonic cells are relatively undifferentiated and rapidly mitotic.
Exposures in the range of 2 to 3 Gy during the first few days after conception are thought to cause undetectable death of the embryo. .

58. The cells in the embryo are dividing rapidly and are highly sensitive to radiation.
Lethality is common and many of these embryos fail to implant in the uterine wall.
The first 15 weeks includes the period of organogenesis when the major organ systems form

59. The most common abnormalities among the Japanese children exposed early in gestation were:-
Reduced growth that persists through life and reduced head circumference (microcephaly), often associated with mental retardation.
Other abnormalities included small birth size, cataracts, genital and skeletal malformations, and microphthalmia.

60. The period of maximal sensitivity of the brain is 8 to 15 weeks after conception.
The frequency of severe mental retardation after exposure to 1 Gy during this period is about 43%.
These effects are believed to have a threshold of about 0.1 to 0.2 Gy.
This threshold dose is 400 to 800 times higher than the exposure from a dental examination (0.25 mGy from a full-mouth examination when a leaded apron
is used).

61. CARCINOGENESIS
Radiation causes cancer by modifying DNA. The most likely mechanism is radiation-induced gene mutation.
Most investigators think that radiation acts as an initiator, that is, it induces a change in the cell so that it no longer undergoes terminal differentiation.
Evidence also exists that radiation acts as a promoter, stimulating cells to multiply.
Finally, it may also convert premalignant cells into malignant ones, for instance, conversion of proto- oncogenes to oncogenes.

63. Balanced diet
Imagine that, every time you breath, free radicals are formed. This process of oxidation is similar to what you see when metal rusts or an apple slice turns brown from exposure to air. Once again, your body can defend against normal levels of free radicals, but if you exercise intensely, live in a polluted area, or have a stressful life, as most of you and your students do, then supplementing your diet with antioxidants may be of great value.
A well balanced diet with plenty of fruits and vegetables is important and will help, but alone it’s just not enough. Factory processing, additives and pesticides all work to destroy antioxidants within our foods and nutrient depleted soils no longer provide us with the nutrient rich foods that our grandparents enjoyed. 
The following list of antioxidants play an important role in free radical protection, especially for the active athlete: Vitamin C, Vitamin E, Vitamin A, selenium, coenzyme Q10 and glutathione.
Eating a well balanced diet and a taking strong Multi- Vitamin/Mineral/Antioxidant Supplement each day should be considered for adequate antioxidant protection and to promote optimum performance and long-term health