2: radiation physics

Orbits

7 shells named K (close to nucleus) to Q (farthest)

Binding energy

the energy that holds a nucleus orbits together

Is binding energy different or the same for each shell?

Different - depending on the distance from nucleus

Ionization

removal of an electron

Radiation

Energy that is radiated or transmitted in the form of rays or waves or particles.

What are the characteristics of electromagnetic radiation?

- no mass or weight
- speed of light
- no charge

What kind of radiation are x-rays?

ionizing radiation

Radioactivity

unstable atoms or elements undergo spontaneous
disintegration or decay in an effort to attain a more balanced nuclear state

Cathode

negatively charged - focuses electrons into a narrow beam accelerating them towards anode

Anode

positively charged to attract electrons- made up of tungsten focal spot in copper stem

What are the 7 parts of the x-ray tube head?

1. metal housing
2. insulating oil
3. transformers
4. tube head seal
5. aluminum disk
6. collimator
7. position indicating device

Filtration

low energy photons can not reach image receptors and are removed by a filter

Inherent filtration

X-ray tube housing, glass envelope & oil

Collimation

used to restrict the size and shape of the x-ray beam and to reduce patient exposure

Tube current

flow of electrons from cathode to anode

Tube voltage

high voltage is required to generate x-rays

What is the function of the step down transformer?

reduces the voltage to 4-5V

What is the function of the step up transformer?

generate high voltage when exposure is activated

What happens too the heat produced during x-ray production?

1. carried away from copper stem
2. absorbed by insulating oil

Bremsstrahlung Radiation

"Braking radiation." The sudden deceleration of electrons as they interact with highly positively charged nuclei.

Characteristic Radiation

a form of radiation that occurs when a high speed electron dislodges an inner shell electron from an atom, causing excitation, or ionization of the atom

Photoelectron interaction

interaction with matter in which a photon strikes an inner shell electron, causing its ejection from orbit with the complete absorption of the photon's energy

Compton scattering

Interaction of an x-ray photon with a loosely bound outer shell electron of an atom

Coherent Scattering

An interaction that occurs with low energy x-rays, typically below the diagnostic range. The incoming photon interacts with the atom, causing it to become excited. The x-ray does not lose energy but changes direction.

Shorter wavelength x-ray

more energy - more penetrating

longer wavelength x-ray

low energy - less penetrating

What does exposure time determine?

quantity of impulses

milliamperes x exposure time

mAs

If the milliamperage is increased, the exposure time is

decreased

What is the formula for intensity?

(# of photons x energy of photon) / (area x exposure rate)

What is the source of electrons?

filament

What two aspects control quantity of electrons?

mA + exposure time