Chapter 6 Radiation Physics

What level does this chapter cover in the anode target interactions

Micro level

Use of ______ and _______ to manipulate the flow of electricity for the purpose of X-ray production

electricity, electrical devices

What directly determines the nature and makeup of the X-ray beam

Radiographers actions at the control panel

Inside the x-ray tube steps

Exposure factors selected, electricity has traveled to the anode, cathode, and filament, and electrons have been boiled off of the filament and are streaming across to the anode at tremendous speeds

Filament electrons penetrates the face of the target at a depth of

0.5mm

Filament electrons interact with the ________ target atoms in their path

Tungsten

2 ways filament electrons interact with target atoms to produce x-rays

characteristic and bremsstrahlung interactions

99% of all interactions do not result in X-ray but they

Produce heat

There are ____________ of interactions taking place inside the target at once

Thousands

Excitation

Raise atom to a higher energy level

How does heat get produced

Filament electrons interact with outer shell electrons but do not transfer enough of their kinetic energy to ionize the atom and the excess energy is immediately given off as infrared radiation (heat) as the outer shell electrons return back to normal.

Characteristic interactions involve

filament electron and orbital electron

In general during characteristic interaction=

A filament electron enters a target atom and strikes an orbital electron

Vacancy in a shell makes an atom

Unstable

How do electrons correct the vacancy

Outer shell electrons drop to fill inner shell vacancies

how do outer-shell electrons drop to fill inner-shell vacancies?

They expend some of its potential energy

What does the potential energy that the outer shell electrons drop turn into

Characteristic xray photon

Characteristic cascade

The process of outer-shell electrons filling inner-shell vacancies, creating a cascading effect during a characteristic interaction.

Each time an orbital electron moves to a lower orbit, a ___ is produced

characteristic photon

Can any outer shell electron fill an inner shell vacancy?

Yes

But most likely by proximity

Name of characteristic interaction derives from

Depends on the difference in binding energy between the shells involved

Do electron shells of each element have the same or different binding energies

Different

Tungsten has ____ electrons orbiting its nucleus in ____ shells

74, 6

Medical imaging focuses on what shell most

K shell

Why does medical imaging focus on K shell the most

They are the highest energy and most useful for imaging purposes

Tungsten binding energy k shell energy

69.5 keV

Must have _______ to remove from k shell in tungsten

Equal or greater than 69.5keV

If a radiographer selects a kvp less than ____ than no photons produced from k shell interactions

70

How do radiographers find energy of a characteristic photo

Must know target element and shells involved then subtract binding energy of the farther shell (shell providing) from the closer shell (shell w vacancy)

To remove, filament must have ______ energy equal or greater than binding energy of the electron of which interacts with

Kinetic

If not enough kinetic energy it turns into

Heat

If filament electron looses all its kinetic energy, then...

Drifts away to fill vacancy in another atom or become part of the current through the tube if removed orbital electron then be deflected in a new direction and excess keV energy would interact w another atom

Brems=

German word for braking or slowing down

Bremsstrahlung radiation

Filament electron misses all orbital electrons and interacts with the nucleus of the target atom

Strength of this attraction between the 2 depend

on how close the filament electron comes to the nucleus

The stronger the attraction in brems interaction the _______ the resultant brems photon

Stronger

The brems photon can vary from

The maximum kvp selected (filament electron passes very close and looses all its energy) to near zero (filament electron passes at a distance and loses almost no energy)

Attraction in brems interaction the kinetic energy looses or gains

Lose

The average energy of a brems photon is _______ of the kvp selected at the control panel

One third

In a tungsten target most of the photons are

Brems

In characteristic interactions only those involving the ___ shell are of sufficient energy to be useful

K

Why is the filament electron more likely to miss the orbital electrons of the target atom

they are in constant motion and the atom is mostly empty space

Average energy of an xray beam is to be how much of the kvp selected

1/3

Characterized xray beam is based on

How it was produced and how it behaves in its interactions with matter

Fiiltration

Use of a material to absorb xray photons for the xray beam

Forms of filtration

Inherent added or compensating

inherent filtration

Takes place when the primary beam passes through the glass window of the x-ray tube, the insulating oil, and the tubehead seal.

- in all X-rays it's built in

added filtration

any filtration that occurs outside the tube and housing before the image receptor. Another 2.0mm AL placed

Can radiographers physically removed the added filtration

No

Compensating filter

Material inserted between an x-ray source & a patient to shape the intensity of the x-ray beam.

We adjust these and add them

Tube head assembly amount of inherent filtration

.5mm

Radiographer must always use ______ judgement founded in science when incorporating compensating filters

Sound

How is beam quantity effected

mAs kVp distance and filtration

If kVp doubles then mAs _____

Increases by a factor of 4

Small changes in kVp can have a profound impact on ___

mAs

Kvp incr by 15% then mAs _____

Doubles

Kvp gives ______ to filament electrons

Kinetic energy

Is it more desirable or less desirable to use kvp to change quantity

Less because it influences too many other factors and is less predictable in its imaging effect where quantity is concerned

Photons that reach the IR create ____ shades on the image

dark

Areas where no photons reach result in what color

light or clear areas of the image

Kvp increase ability to _______ matter

Penetrate

Xray beams with high energy=

High quality or hard beams

Filtration makes average energy

Higher

Beam quality measured by _______

Half value layer

-necessary to reduce energy of the beam to one half its original intensity

How to found HVL

Measuring intensity of the beam with rad detector then placing Al filters of known thickness between the tube and detector until the intensity reading is reduced to one half its original value

Normal HVL of general diagnostics beam is what length

3-5 mm Al

Characteristic photons have what spectrum

Discrete

Brem photons have what spectrum

Continuous

X axis

Xray energy

Y axis

# of each type of xray photon

Why is characteristic discrete

Because the photon energies are limited to just a few exact values

Continuous spectrum depends on

The strength of this attraction

Xray emission spectrum is used to

graphically represent the energies of the xray beam and to reflect the effects of different factors on the xray beam

5 factors that change appearance of xray emission spectrum

mA, kVp, tube filtration, generator type, and target material

mA does what to graph

Incr amplitude of both graphs

Does the quantity change the position of the quality factors

No

Changes in kvp effect what factors

Quantity and quality

Incr kvp does what to the graph

Incr amplitude and shifts to the right side

Kvp inc on control panel results in

Xray tube giving more electrons the kinetic energy to produce X-rays and kinetic energy overall within them

Discrete line is related specifically to

The target material

Changes in generator type results in

Change of xray production efficiency of machine

High frequency units =

More efficient producing X-rays than single phase units

Does the electricity in two types of units matter if one is high frequency or single phase when relating to producing X-rays

No

Does the radiographer have the ability to select the target material used (excluding mammography)

No

As atomic number goes up so does

Average energy quantity of photons and the position of the discrete line

Increase atomic number makes the atom

More complex and easier target for filament electrons to interact with

Energy of photons depend on

The shells binding energy

Does the discrete line move if increased binding energy of target material and if so what direction

Yes to the right

Does a high or low atomic number used for mammography

Low because lower energies

What element is never suitable

Gold because of low melting point and high cost

what describes the penetrating power of the x-ray beam?

beam quality

What describes the total number of x-ray photons in the x-ray beam?

beam quantity

what is the term used to describe the process of outer=shell electrons filling inner-shell vacancies

characteristic cascade

the continuous emission spectrum graphically demonstrates

bremsstrahlung interactions

the discrete emission spectrum graphically demonstrates

characteristic interations

what is used to measure beam quality?

half-value layer

which of the following terms describes the x-ray beam upon exiting the collimator and exposing the patient.

primary beam

which of the following describes the x-ray beam that remains after the interaction with a patient and exits the patient to expose the image receptor?

remnant beam

the term used to describe x-ray photons exiting the patient without interacting with anatomic structures

transmission

the term used to describe photons that have lost energy and have been redirected after interacting with anatomic structures:

scatter