physics ch9

Coherent

Also called: classical, unmodified, elastic

Types of coherent

Thomson, Rayleigh

Coherent

No ionization

THOMSON

X-ray photon interacts with free electron

Rayleigh

X-ray photon interacts with whole electron cloud

Coherent

for x-rays with energies below 10 kev

Coherent

incoming photon changes

direction without loss of

energy

Compton electron

Ionized electron

Compton

Incident x-rays ionize outershell electrons and redirect x-rays as scatter

Linear energy transfer

If it has enough energy, the Compton electron can

continue ionizing other atoms, otherwise it will dissipate its energy as heat in tissue. This process is can be measured by

Linear energy transfer

Measure of rate if energy transfer from photon to soft tissue

Inversely related

Probability of Compton decreases with increasing kVp

100+ kev

(Compton) Predominant in soft tissue at

Increases

Although the absolute probability of Compton decreases

with increasing kVp, its relative number ___ compared to PE

Backscattered radiation

Compton - if these scatter back to the original direction

Cassette hinge image

backscattered radiation is responsible for the ____ where the x-rays pass through the IR and reach the hinge on the backside of the cassette

180 degrees

⅓ energy is transferred to compton electron, scatter retains ⅔ of its incident energy

maximum of ⅓ its energy

incident photons undergoing compton interaction can only transfer a ____ to the compton electron

Albert Einstein

Photoelectric was first described by

Photoelectric

incident photon gives up all its energy to a tightly bound inner-shell electron and

ionizes it

Photoelectron

Ejected electron is called

Pure absorption

Increases patient dose

Characteristic x-rays

In photoelectric, it has a byproduct of

Decreases

How does photoelectric effect probability change as kVp increases?

The 3rd power (1/E³)

PE probability is inversely proportional to what power of X-ray energy?

Directly proportional

What is the relationship between PE probability and atomic number (Z)?

Increase

If atomic number increases, does PE probability increase or decrease?

The 3rd power (Z³).

PE probability is directly proportional to what power of Z?

Decreases

Although the absolute probability of PE decreases with

increasing kVp, its relative number ___ further

compared to Compton.

40 kev below

Photoelectric, predominant bone and soft tissues at

Bremsstrahlung

Pair production is associated with what other X-ray interaction/process?

Energy

What does the positron convert into during annihilation?

Diagnostic photons do not have the required 1.022 MeV energy

Why does pair production not occur in diagnostic X-ray imaging?

Positive

What is the charge of a positron?

It unites with a free electron and undergoes annihilation

Pair production, What happens to the positron?

It loses energy through ionization and excitation

What happens to the negatron after pair production?

X-ray photon interacting with the nuclear field of an atom

What does pair production involve?

1.022 MeV (1,022 keV)

What is the minimum photon energy required for pair production?

photon disappears and produces two particles

What happens to the incident photon during pair production?

Each receives 0.51 MeV of energy

How is the incident photon’s energy divided between the particles?

no

Does photodisintegration occur in the diagnostic X-ray range?

At least 10 MeV

What is the minimum energy required for photodisintegration?

Electrons or the nuclear field

What does the incident photon NOT interact with during photodisintegration?

A nuclear fragment is emitted

What happens when the photon is directly absorbed by the nucleus?

Nuclear composition

What does photodisintegration alter?