How are x-rays produced?

Where are x-rays produced and what is this made of?

• In an x-ray tube

• The tube consists of a negative CATHODE and a positive ANODE

How is an x-ray beam generated?

By ‘powering’ a beam of electrons which are attracted from the negative CATHODE to the positive ANODE

What happens when the electrons reach the anode?

They decelerate (break) rapidly which reduced heat (99%) and x-rays (1%)

The components of the x-ray tube are .. 

• Composed of a Pyrex tube surrounding the anode and cathode

• Contains a vacuum to prevent unwanted interaction during the production of x-rays 

• Both the anode and cathode have a high tension electoral supply which provides the direct current necessary to generate the x-rays  

• The Pyrex tube is surrounded by oil to prevent the build up of heat during the production of x-rays 

• The entire structure is surrounded by a lead case, within which there is a small window, directly under the anode which allows the primary beau to exit the tube 

What is the cathode and what is is made up of?

• The negative part of the x-ray tube 

• Made up of the filament and the focusing cup 

• Filament is a very small piece of wire made of tungsten which emits electrons when heated 

What does an increase in mA equal ..

An increase in the production of electrons

The cathode - what is the temperature of the filament controlled by?

Milliamperage (mA)

The cathode - what is the function of the focusing cup which surrounds the filament?

To stream the electrons in a narrow band towards the anode when an exposure is made

What is the anode and what may it be? 

• The positive part of the x-ray tube

• May be stationary or rotating 

Where are stationary anodes usually found?

In dental machines and in smaller portable machines

Where are rotating anodes found and why are they good?

• In general machines

• For the production of high quality x-rays in a very short period of time 

What does the process of producing x-rays result in?

99% heat production and only 1% actual x-rays

What is one role of the anode in the production of x-rays regarding heat?

Helps to remove excess heat from the tube

What is the target?

The area that the electrons strike in the anode

Why does the target (in the anode) rotate?

So that the area that the electrons strike changes which increases the area that the electrons can strike and increasing the life span of the tube

What is the target made up of?

Tungsten alloy embedded in a copper anode 

How is the target constructed and why?

• At an angle 

• So that the x-rays produced are directed downwards (towards the x-ray cassette) through a window in the housing of the x-ray tube 

What does the window have and why? (hint: the filter and what is this made up of) 

• The window has a small aluminum filter to remove any low energy x-rays from the primary beam which improves the quality 

• Aluminium helps to absorb low energy to improve the quality of the x-ray 

How many stages are in x-ray production?

Two

What happens in the first stage of x-ray production?

• ‘preps’ the machine by heating the cathode 

• Starting the rotation of the anode 

• The milliamperage (mA) selected determines the amount of heating the cathode will undergo

• Heating releases electrons from the surface of the filament wire and these collect in the focusing cup 

• When a charge is applied these electrons flow from the negative cathode to the positive anode

The milliamperage (mA) selected determines …

The amount of heating the cathode will undergo

The higher the mA …

The higher the heat meaning that more electrons will be produced

What happens to the electrons collected in the focusing cup (from the filament) when a charge is applied?

These electrons flow from the negative cathode to the positive anode

What happens to the second stage of x-ray production?

• A high kilovoltage (kV) is selected and applied

• The higher the chosen kV, the faster the electrons will move towards the anode (targer)

• This results in higher energy x-rays with more penetrating power 

• The applied kV causes the electrons to accelerate from the cathode to the anode and upon hitting the target they are stopped 

• This sudden ‘braking’ results in energy being released, some of which is in the form of x-rays which are then released through the x-ray tube through the window 

• The window contains an aluminum filter which helps to absorb low energy resulting in a better quality x-ray 

What does the kV applied cause the electrons to do? What do they do once they hit the target?

• The electrons accelerate from the cathode to the anode

• Upon hitting the target they are stopped 

What does the sudden ‘braking’ at the target cause? 

Results in energy being released - some of this energy is in the forms of x-rays which are then released through the x-ray tube through the window 

The ‘breaking’/’stopping’ of the electrons causes …

• Heat

• X-rays

• Some will be absorbed and some will go to the plate and result in a good contrast

The process of x-ray production

1 - Filament

2 - mA applied

3 - Electrons produced

4 - kV applied between cathode and anode

5 - Electrons accelerated across tube

6 - Electrons hit target

7 - Heat and x-rays produced