Physics Exam 5

Xrays are electromagnetic waves carrying much __ energies than visible light

Higher

Formula for kinetic energy of a moving object

KE = ½ mv²

Energy is __ proportional to mass, but changes by the square of the velocity

Directly

Energy is __ proportional to speed

Exponentially 

Which has a bigger impact on energy? Mass or velocity

Velocity

What are the 2 possibilities for a projectile electron to interact with atoms in the anode

Interact with an orbital electron

Interact with the nucleus

Where are xrays actually produced

Anode at the actual focal spot

“Braking” radiation is called

Bremsstrahlung 

Positive attraction from the nucleus pulls the electron toward it as the electron passes, which does what

Slows and deflects it

What type of radiation is an interaction with the nucleus

Bremsstrahlung

Energy lost from deceleration is emitted as

Xray

What type of radiation accounts for the vast majority of the xrays in the beam 

Bremsstrahlung 

Bremsstrahlung radiation is responsible for the __ nature of the xray beam

Heterogenous or poly-energetic nature

A silhouette image such as this would result from what beam

Mono-energetic

The closer a projectile electron passes to the nucleus, the more it will be decelerated, so the __ energy it will lose

More

The amount of energy lost goes into 

Xray produced

The closer the electron passes to the nucleus, the __ the energy of the xray produced

Higher

Which is more likely? A projectile electron will pass closer to the nucleus or a projectile electron will pass further from the nucleus

It will pass further from the nucleus

Are more xrays produced at lower or higher energies

Lower

The higher the kV, the (more or less) xrays produced

Less

What type of beam will provide adequate subject contrast

Poly-energetic 

What interactions happen in the anode

Bremsstrahlung and characteristic

What interactions happen within matter (the patient)

Photoelectric, Compton, scatter

Xray are ___ waves with energies much __ than light and most other forms of electromagnetic radiation

Electromagnetic, higher

In order to generate such energetic waves, electrons emitted from the xray tube filament must acquire extreme amounts of __ energy by the time they strike the anode

Kinetic

What is the formula for the total kinetic energy that a moving object will be carrying

KE=1/2 mv²

The energy changes __ to the mass

Proportionately 

Energy increases by the __ of the velocity

Square

With the large voltages supplied by the step-up transformer of an xray machine, the electrons reach speeds of up to __ the speed of light

50-80%

Mass of a single electron

9.1 × 10^-31

Einsteins theory of relativity states that as a particle approaches the speed of light, it (gains or loses) mass

Gains

What are the 2 possibilities of the electron

It may interact with an orbital electron or it may interact with the atom’s nucleus

An electron passes near the atomic nucleus and the positive attraction will cause it to brake or slow down. What is this called?

Bremsstrahlung

During brem, the deceleration in the speed of the electron represents a loss of __ energy and that energy which is loss is emitted as an xray __

Kinetic, photon

What does Bremsstrahlung mean in German 

Braking radiation 

Which type of radiation accounts for the vast majority of the overall xray beam

Brems

The closer an electron passes to the nucleus, the __ will be the deceleration of the electron

Greater

The attractive force of the nucleus also causes the electron to __ in its path of travel toward the nucleus

Bend

The greater the deceleration of the electron, the (more or less) it deviates from its original direction and the more __ energy is lost

More, kinetic 

The closer the electron passes by the nucleus, the __ the energy of the emitted xray

Higher

Brems occurring at various distances from the nucleus, provides a wide range of xray energies and is responsible for the __ or __ nature of the xray beam

Heterogenous or poly-energetic

Heterogeneity contributes to what within the patient’s body

Differential absorption

Differential absorption provides __ in the remnant beam and makes the radiographic image possible 

Subject contrast

If all of the xrays were of the same energy, the info reaching the IR would result in a

Silhouette image

Computers can modify the image in many ways, but they cannot

Create information that was not present in the first place

The full range of information from different tissues in the body must be represented within the __ beam that reaches the detectors

Remnant

The distance at which a projectile electron will pass by the atomic nucleus is a function of 

Statistical probability

At a greater distance from the nucleus, a larger __ is contained within the sphere of that radius surrounding the nucleus 

Volume 

The volume of a sphere will increase by the __ of the radius distance

Cube

As we get further from the nucleus, the volume of space (Increases or decreases) exponentially

Increases

Is it more likely that an electron will pass close to or further away from the nucleus

Further away

With brems, many more xrays will be produced at (higher or lower) energies 

Lower 

The higher the energy, the (more or fewer) brem xrays are produced up to the set kVp

Fewer

The anode itself acts as a

Filter

Filters absorb xrays with the __ energies

Lowest

Why are more xrays produced at low energies 

Filtration

Why are fewer xrays produced at high energies 

The statistical distribution of brem xrays produced

The electron interacts with one of the atoms orbital electrons. When it passes near an orbital electron, its repulsive charge can eject the orbital electron out of its orbit, leaving a vacancy in that atom. What type of radiation is this?

Characteristic

After the orbital electron is ejected out of its orbit, the atom, left with a positive charge will eventually pull in another electron from a __ orbit to return to a neutral state

Higher

What the atoms state with the least energy called 

Ground state

When an electron falls from an outer orbit down into an inner orbit, there is a loss of __ energy

Potential

After a loss of potential energy, it is emitted as a

Characteristic X-ray

What type of radiation makes up only a small portion of the overall beam

Characteristic

Why are characteristic xrays still important in producing a radiographic image if they only take up a small portion of the beam 

They possess higher energies that can penetrate through the patient to the IR

Characteristic x-rays depend entirely on what

The difference in energy levels between different orbital shells in the atoms

During characteristic radiation, xrays will be emitted at __ energies, rather than a range

Discrete

How many characteristic xrays can be produced from each shell

3-4

How to predict the energies from characteristic xrays

Subtract the binding energies for the higher shell from that of the vacant shell 

If the vacancy is in the L shell of a tungsten atom, and electron falls into the M shell, what is the energy of the emitted xrays

12-3= 9 Volts

K shell binding energy

69

L shell binding energy

12

M shell binding energy 

3

N shell binding energy

1

O shell binding energy

.01

What term refers to the movement of several electrons as they fall in sequence from higher energy levels to fill vacancies in lower energy shells

Characteristic cascade

What is initiated when a projectile electron knocks out an inner shell electron of a tungsten or rhenium atom 

Characteristic cascade

In tungsten atoms, characteristic xrays will be produced in the __ shell

Innermost or K

Characteristic xrays produced in the K shell produce how many kilovolts of enrgy

57,66,68,69

A vacancy in the L shell will produce xrays of __ kV

9,11, and 12

A vacancy in the M shell will produce xrays of __ kV

2 and 3

Shells further than the M shell will produce electromagnetic waves, but these will be of such low energy, less than 1 kV, that they would be classified as __ rather than xrays

Ultraviolet light

Inherent filtration will remove virtually all of the __ kV x-rays

2-3

The characteristic x-rays having __ kV largely escape the xray tube and are considered part of the useful xray beam

57,66,68,69 kV

The bell curve represents __ radiation 

Heterogenous (brem)

The spikes represent __ radiation

Homogenous (characteristic)

A total filtered xray beam is generally __ and has an average energy of __ of the set kVp

Heterogenous, 1/3

Only about __% of the energy deposited by projectile electrons into the anode in converted into xrays, the other 99.5% is lost as heat, infrared radiation, and light

0.5%

A process called __ momentarily raises orbital electrons to a higher energy level

Excitation 

In __, the repulsive negative charge of passing projectile electrons can slightly raise the energy of orbital electrons without knocking them out of their atoms

Excitation

Excited electrons immediately fall back into their normal energy level by emitting their excess energy in the form of __

Infrared radiation and light

After excited electrons fall back into their normal energy, __ radiation is absorbed by the anodes other molecules, causing increased molecular vibration

Infrared

Increased molecular vibration is __

Heating

What is responsible for most of the heat generated in xray tube anodes

Infrared radiation

Standard diagnostic xray tubes use an alloy of __ and __ for the target material, embedded in the circular focal track area of the anode disc

Tungsten and rhenium 

The higher the atomic number of the target material, the more __ it is and the (More or less) xrays are produced

Efficient, more

Atoms with higher atomic numbers improve the __ of the xray beam

Quality

Gold atomic number

79

Tungsten atomic number

74

Rhenium atomic number

75

Some specialty xray tubes use __ to achieve an increase in xray production and quality

Gold