X-ray class exam #2

Who discovered the X-ray?

German scientist Wilhelm Conrad Roentgen

When was x-ray discovered?

Nov 1895

When the number of electrons \= the number of protons, what is occuring?

Ionization

When the number of electrons \= the number of protons, is the atom stable or unstable?

stable

What energy type has the most energy and shortest wave length?

x-rays / gamma rays

What energy type has the least energy and the longest wavelength?

radiowaves

radiowaves are measured in what unit?

meters

Infrared, visible light, ultraviolet, and x-rays are measured in what unit?

nanometers

Electromagnetic radiation travels like a \___, travels at the speed of \____, and in a \____ line

wave

light

straight

Electromagnetic radiation has a charge or not?

does not have a charge

Electromagetic radiation interacts with

matter causing ionization

Electromagetic radiation has a specific range of

photon energy and corresponding wavelength

What is the speed of light?

3.00 x 10^8 m/s

Wave theory equation

E (energy) \= h (plank's constant) x C (velocity) / wavelength

What is Plank's constant?

6.626 x 10^-34 Js

Dental imaging wavelength

0.1 - 0.01 nm

Dental imaging energy (keV)

65 keV

Particle/quantum theory

energy unit of 1 eV \= amount of energy acquired by one electron accelerating through a potential difference of 1 volt

A photon is a

small massless discrete bundle of energy

Is electromagnetic radiation natural or man made?

both

X-rays are produced when highly electric \____ interact with matter and convert their \____ energy into \_______ \_______

electrons

kinetic

electromagnetic radiation

Requirements for X-rays

1. electron source

2. Evacuated path for electron acceleration

3. external energy source

4. target electrode

X ray tube contains the

electron source and target within an evacuated glass

Tube housing provides

shielding and coolant oil bath

Collimator

define xray field

Power supply/generator

energy source that supplies the voltage to accelerate the electrons

What are the two aspects of the cathode?

1. filament

2. focusing cup

Cathode filament

a coil of tungsten wire with 1% thorium

filament heated \-- emits electrons proportional to the

temperature of the filament

Focusing cup is a

negatively charges concave reflector made of molybdenum

the focusing cup focuses the

electrons into a narrow beam directed to a focal spot on the anode

Power supply is to heat the cathode \____ to generate \____ and establish a high voltage potential to accelerate the electrons toward the \____

filament

electrons

anode

Anode is a

tungsten target embedded in a copper stem

Why do we use tungsten?

1. high atomic number (74)

2. high melting temperature (3422 C)

3. high thermal conductivity

4. low vapor pressure at the working temperature of an xray tube

Anode copper stem is

a good thermal conductor and reduces the risk of the target melting

Focal spot is where

the xrays are made

the smaller the focal spot,

increased risk of melting

improved sharpness

Solution of Focal spot

1. target inclined 20 degrees to increase size of spot

2. rotating the anode (CBCT/MDCT)

Therm/Ionic emission

Heat --\> Ionization --\> Xray

Production of xrays come from the

tungsten target of the anode

high speed electrons will

release their energy as heat (99% heat - 1% xrays)

Electrons will convert their kinetic energy into xray photons by formation of

1. bremsstrahlung

2. characteristic radiation

bremsstrahlung means

braking radiation

bremsstrahlung is made by...

1. suddenly stopping (hitting the nuclei)

2. slowing of the high speed electrons by tungsten nuclei in the target

Suddenly stopping ex

all the kinetic energy of the electron is transformed into a single x-ray photon

the energy of the resultant photon \= energy of electron that is the voltage applied across the x-ray tube

Slowing of the high speed electrons by tungsten nuclei in the target ex

electrons are attracted to positive charge nuclei, resulting in change of path and deceleration

loss of kinetic energy is given off in the forms of photons

the closer the electron approaches the nuclei, the greater the braking effect and the energy of the resulting bremsstrahlung photons

the efficiency is proportional to the square atomic number of the target

bremsstrahlung radiation generates

photons with continuous spectrum of energy

Nucleus contains

protons and neutrons

Characteristic Radiation is an incident \____ ejecting an inner electron from the \____, then the outer orbit electron fills the void in the inner orbital

electron

tungsten

A photon with energy equivalent to the difference in the

binding energies of the two orbitals

Characteristic radiation will contribute to a

small fraction of the generated x-ray photons

Current is the

number of photons (through cathode tungsten)

Voltage is the

controls the speed of photons (from cathode to anode)

Current is measured in

amperes - A

miliamperes - mA