Semi Conductor Flashcards
What are semi conductor diodes
They are sensitive to ionising radiation.
They are useful for QA and dosimtery for electrons and photons
How are P N type conductors formed
We need to create extra elections so he crate these holes by adding impurities. This creates extra elections in the crystal structure.
Then a P and N type semi conductor is formed.
What are P type semi conductors
The impurity could be boron
It has 3 electrons so it has a hole and therefore gets a + charge
What are N type semi conductors
The impurity is phosphorus
And has 5 electrons so it creates a spare electron leaving a negative charge
Explain the combining the P and N materials
When P-N junction is formed and fre electrons and holes are formed to create a DEPLETION ZONE
How is dose measured in a semi conductor diode
When irradiates the ion pairs are creates.
The N type electrons are attracted to the positive side and the positive electrons diffuse to the negative side. This creates an ionisation current that is proportional to the dose rate which can be calculated by an electro meter
Explain the advantages of a semi conductor diode
Very sensitive to dose.
Stability
Immediate read out
Small size
What are the disadvantages of the semi conductor diode
Temperature affects sensitivity.
Non linear response to dose rate
Difficult to manage and easily damaged.
What is a TLD
passive radiation detection device
Good for patient dose measuring
How does the TLD work
The detector gives light when heated.
TLD is phosphor.
When ionising radiation hits TLD electrons are free from atoms and move to another part and leaves holes of positive charge.
The electrons get trapped and locked in the crystal structure.
How to read a TLD
electrons need energy to escape those traps
Heat is applied to TLD SO THE electrons CAN MOVE
As the electrons calls back into valance band the lost energy is emitted as light.
The light intensity is proportional to amount of radiation incident on TLD
Disadvantage and advantage of TLD
advantage- linear to dose and energy independent and reusable
Dis- no permanent record,
No immediate read out
