5 important Radio physics question for para medical student for DRD

5 important Radio physics  question for para medical student of DRD.

1st - what is the X-ray ?

X-rays are a type of radiation that known as a electromagnetic waves. X-ray imaging makes pictures of the inside of our body. The images show the parts of our body in different shades of black and white. Calcium in bones absorbs x-rays the most, so bones look white. Fat and other soft tissues absorb less and look gray. Air absorbs the least, so lungs look black.

           The inside bone of human body .
The most familiar use of x-rays is checking for fractures (broken bones), but x-rays are also used in other ways. For example, chest x-rays can spot pneumonia. Mammograms use x-rays to look for breast cancer, barium meal used for to look appendix and other pictures of abdomen etc.

2nd - How X-ray is produced?
Overview ?.

A high voltage current is passed through the tungsten filament and heats it up.

The tungsten filament become excited, As it is heated up the increased energy enables electrons to be released from the filament through thermionic emission.

The electrons are attracted to the positive charged anode and hit the tungsten target with a maximum energy difinite by the tube potential (voltage).

As the electrons like as a bombard the target they interact via Bremsstrahlung and characteristic interactions which result in the fictional of energy into heat (99%) and x-ray photons (1%).

The x-ray photons are released in a beam with a range of energies (x-ray spectrum) out of the window of the tube and form the basis for x-ray image formation.

                     X-ray production.


3rd- What type of interaction between X-ray with matter?

There are normally five types of interactions X-ray with matter, that's are -


Comphoton.
 
    A Compton interaction is one in which only a portion of the energy is absorbed and a photon is produced with reduced energy. This photon leaves the site of the interaction in a direction different from that of the original photon, as shown in the previous figure. This is significant in some situations because the material within the primary x-ray beam becomes a secondary radiation source. The most significant object producing scattered radiation in an x-ray procedure is the patient's body. The portion of the patient's body that is within the primary x-ray beam becomes the actual source of scattered radiation.
   

Coherent :

There are actually two types of interactions that produce scattered radiation. One type, is referred to by a variety of names, including coherent, Thompson, classical, and elastic, is a pure scattering interaction and deposits no energy in the material. Although this type of interaction is possible at low photon energies, it is generally not significant in most diagnostic procedures.

Photoelectric

This is the interaction photon with electron.In the photoelectric (photon-electron) interaction, as shown above, a photon transfers all its energy to an electron located in one of the atomic shells. The electron is scatter from the atom by this energy and begins to pass through the surrounding matter. The electron speedily loses its energy and moves only a relatively short distance from its original location. The photon's energy is, therefore, deposited in the matter close to the site of the photoelectric interaction.

Pair production.

                     Pair production .
Pair production is a photon-matter interaction that is not encountered in diagnostic procedures because it can occur only with photons with energies in excess of 1.02 MeV. In a pair-production interaction, the photon interacts with the nucleus in such a manner that its energy is converted into matter. The interaction produces a pair of particles, an electron and a positively charged positron. These two particles have the same mass, each equivalent to a rest mass energy of 0.51 MeV.

Electronic transaction :

The interaction and transfer of energy from photons to tissue has two phases. The first is the "one-shot" interaction between the photon and an electron in which all or a significant part of the photon energy is transferred; the second is the transfer of energy from the energized electron as it moves through the tissue. This occurs as a series of interactions, each of which transfers a relatively small amount of energy.

4th - Describe the diagram of X-ray film.?

X-ray film:

THE STRUCTURE OF THE X – RAY  FILM

If an undeveloped X-ray film is examined in daylight it will be found to consists of a flexible base of either cellulose acetate or polyester plastic coated on both sides with thin layers of apple-green photographic emulsion.X-ray film displays the radiographic image and consists of emulsion (single or double) of silver halide (silver bromide (AgBr) is most common) which active when exposed to light, produces a silver ion (Ag+) and an electron. The electrons get attached to the sensitivity specks and attract the silver ion. After, the silver ions attach and clumps of metallic silver (black) are formed 1,2.

The silver can be reclaimed from old x-ray film, in a process known as silver recovery.

Layers: there are three main layer and one or two protective layer in the X-ray film.

1st, base: cellulose triacetate or polyester

2nd, substratum: an adhesive layer containing gelatin and solvents that bind emulsion and base

3rd, emulsion: Emulsion is composed of a homogeneous mixture, of silver halide and gelatin, with some hardening agents

protective layer: gelatin.

The total thickness of a X-ray film is about 0.25 mm.

Types:-

1,screen type films: faster when used with intensifying screen

2,conventional

3,orthochromatic (green sensitive)

4,direct exposure type: used for dental     exposures.

5th - what is the film contrast , and what do you mean by the speed of film?

Contrast :

 Contrast is perhaps the most significant characteristic of an image recorded on film. Contrast is the alternative in film density (shades of gray) that actually forms the image. Without contrast there is no image. The volume of contrast in an image depends on a number of factors, including the ability of the particular film to record contrast. 

   Film can be envisaged as a contrast converter. One of its functions is to change differences in exposure (subject contrast) into film contrast (differences in density), as shown below. The volume of film contrast resulting from a specific exposure difference can vary considerably.


*Speed of the film?.

The film typically used for the intraoral bitewing exam falls into three film speed classes - D (slowest), E (medium) and F-speed (fastest). Like as photographic film, the faster the film, the less exposure it needs. Film speed can be an important aspect in realizing the amount of radiation exposure received by a patient. The greater the film speed, became the lesser the exposure received by the patient. The types of film used by dental practices in this survey varied, with D-speed film comprising approximately 70% of the film used, E-speed film about 21%, and F-speed film about 9%.

So friends this is the 5 important question for para medical. 

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