Electromagnetic Radiation & Electricity

RTEC 111

Objectives

Properties of photons

Visible light, radiofrequency & ionizing

radiation

Wave-particle duality of EM radiation

Inverse square law

Electricity

X-ray photons

X-rays and light are examples of electromagnetic photons or energy

EM energy exists over a wide range called an “energy continuum”

The only section of the EM continuum apparent to us is the visible light segment

Visible light

Photon

Is the smallest quantity of an type of EM radiation. (atom is the smallest element)

A photon may be pictured as a small bundle of energy or quantum, traveling through space at the speed of light

Properties of photons include frequency, wavelength, velocity, and amplitude

AMPLITUDE, WAVELENGTH, SPEED, VELOCITY, FREQUENCY

Photons

All EM photons are energy disturbances moving through space at the speed of light

Photons have no mass or identifiable form

They do have electric and magnetic fields that are continuously changing

Photons – variations of amplitude over time Photons travel in a wave-like fashion called a

sine wave

Amplitude is one

half the range from

crest to valley

over which the sine

wave varies

Velocity

When dealing with EM radiation all such radiation travels with the same velocity

X-rays are created at the speed of light and either exist with the same velocity or do not exist at all

Frequency

The rate of the rise and fall of the photon is frequency

Oscillations per second or cycles per sec

Photon energy is directly proportional to its frequency

Measured in hertz (Hz) 1 Hz = 1 cycle per second

Frequency

the # of

crests

or the # of

valleys that

pass a point

of observation

per second.

Wavelength

The distance

from one crest to

another, from

one valley to

another

Describing EM Radiation

Three wave parameters; velocity, frequency, and wavelength are needed to describe EM radiation

A change in one affects the value of the other

Which value remains constant for x-rays?

WavelengthEquation

Just to keep it simple

For EM radiation, frequency and wavelength are inversely proportional

Electromagnetic Spectrum

Frequency ranges from 102 to 1024

Wavelengths range from 107 to 10-16

Important for Rad Techs: visible light, x-radiation, gamma radiation & radiofrequency

Visible light: Important for processing, intensifying screens, viewing images and fluoroscopy image

Smallest segment of the EM spectrum The only segment we can sense directly White light is composed of photons that vary

in wavelengths, 400 nm to 700nm

Sunlight

Also contains two types of invisible light: infrared and ultraviolet

RadiofrequencyMRI uses RF & Magnets RF waves have very low energy and very

long wavelengths

Ionizing Radiation

Contain considerably more energy than visible light photons or an RF photon

Frequency of x-radiation is much higher and the wavelength is much shorter

When we set a 80 kVp, the x-rays produced contain energies varying from 0 to 80 keV.

X-ray vs Gamma rays

What is the difference?

Wave – particle duality

A photon of x-radiation and a photon of visible light are fundamentally the same

X-rays have much higher frequency, and hence a shorter wavelength than visible light

Visible light vs X-ray

Visible light vs X-ray

Visible light photons tend to behave more like waves than particles

X-ray photons behave more like particles than waves.

Wave-particle duality - Photons

Both types of photons exhibit both types of behavior

EM energy displays particle-like behavior, and sometimes it acts like a wave; it all depends on what sort of experiment you're doing. This is known as wave/particle duality, and, like it or not, physicists have just been forced to accept it.

Characteristics of RadiationVisible light

Light interacting with matterReflectedTransmittedAttenuatedAbsorbed

Characteristics of RadiationX-rays

X-rays interacting with matterScatterTransmittedAttenuatedAbsorbed

RadiopaqueRadiolucent

Energy interaction with matter

Classical physics, matter can be neither created nor destroyedLaw of conservation of matter

Energy can be neither created nor destroyedLaw of conservation of energy

Inverse Square Law

When radiation is emitted from a source the intensity decreases rapidly with distance from the source

The decrease in intensity is inversely proportional to the square of the distance of the object from the source

Inverse Square Law Formula

Inverse Square Law

Applies basic rules of geometry

The intensity of radiation at a given distance from the point source is inversely proportional to the square of the distance.

Doubling the distance decreases intensity by a factor of four.

Inverse Square Law Formula

Intensity #1

Intensity #2

Distance #2 - Squared

Distance #1 - Squared

Inverse Square Law

Intensity Is Spread OutIntensity Is Spread Out

Questions?Questions?

Electricity

RTEC 111

Bushong Ch. 5

X-ray imaging system

Convert electric energy to electromagnet energy.

A well controlled electrical current is applied and converted to mostly heat and a few x-rays.

Atom construction

Because of electron binding energy, valence e- often are free to travel from the outermost shell of one atom to another.

What do we know about e- binding energy of an atom?

Electrostatic Laws

Electrostatic force Unlike charges attract; like charges repel

Electrostatic force is very strong when objects are close but decrease rapidly as objects separate. Electrostatic force has an inverse square

relationship. Where else do we apply the inverse square relationship with intensity?

Electric Potential

Electric charges have potential energy. When positioned close to each other. E- bunched up at the end of a wire have electric potential energy.

Electric potential is sometimes called voltage, the higher the voltage, the greater potential.

Electric Circuit

X-ray systems require complicated electric circuits for operation.

Circuit symbols and functions. Pg. 80

Electric current

Electricity = the flow of electrons along a conductor.

E- travel along a conductor in two ways. Alternating current (AC) - sine wave Direct current (DC)

X-ray imaging systems require 20 to 150 kW of electric power.

More on x-ray circuitry to come later…

• What questions

do you have?

• No excuses

especially for x-ray

students!