Module 2.1 – Electromagnetic Energy

SPEED OF LIGHT (C) =

3 x 10⁸ m/s

Cycle

One complete wave form or repetition

Crest

top of wave

Trough

bottom of wave

Amplitude

Max. displacement from equilibrium

Wavelength λ

Distance traveled by wave in a single cycle

Wavelength Units

cm, mm, m (meters)

Frequency (F)

Number of cycles per unit time

Frequency (F) unit

hertz (Hz)

Attenuation

Reduction in the number of x-ray photons to the image receptor (IR)

Refraction

o   Deviation in the line of travel of a light photon

o   X-rays cannot be refracted, but scattered

Radiolucent

o   X-rays easily penetrate

o   EX: Air and tissue - Very dark on x-ray scans since x-rays passes through

Radiopaque

o   X-rays are absorbed

o   EX: bone and metal -  Very white on x-ray scans since x-rays are absorbed on bones

Beta Particles

Like electrons except originate in nucleus of radioactive isotopes

Gamma Rays

Like x-rays except originate in nucleus of radioactive isotopes

Frequency vs. Wavelength Relationship

INVERSE RELATIONSHIP

Frequency vs. Wavelength Formula

WL = C / F

C =

3 x 10⁸ m/s

Frequency vs. Energy Relationship

DIRECT RELATIONSHIP!

Frequency vs. Energy Formula

E (ev) = h (f)                         

Wavelength vs. Energy Relationship

INVERSE RELATIONSHIP!

Wavelength vs. Energy Formula

WL(Å) = 12.4 / E (keV)

Inverse Square Law Formula

I/i = d²/ D²

Radiation intensity is ___________ ____________ to the square of the distance

INVERSELY PROPORTIONAL

General Characteristics of EMS

·         No mass or physical form

·         Travels at SPEED OF LIGHT (C) in a vacuum or air

• C = 3 x 10⁸ m/s – MEMORIZE THIS NUMBER!

·        Travel in a linear path (until interaction occurs)

·         Transverse or Shear Wave (up and down movements)

·         Unaffected by: Electric or magnetic fields and Gravity

The example has how many cycles?

2

V of EM radiation always =

c

Solve: A photon of red light has a frequency of 3.15 X 10¹⁵ Hz, what is the wavelength?

Wl = 9.5 X 10^-8 m 

Solve: A photon of blue light has a frequency of 6 X 10¹⁵ Hz, what is the wavelength?

Wl = 5 X 10^-8 m 

When frequency (F) _____, wavelength (WL) _______!

Increases, Decreases

When Energy (eV) _____, Frequency (F) ______!

Deceases, Decreases

When Energy (eV) _____, Wavelength (WL) _____!

Increases, Decreases

Solve: What is the wavelength of a photon that has a frequency of 1.5 X 10²⁰ Hz?

2 x 10^-12 m                 

Solve: What is the frequency of a 40 keV x-ray photon? (Planck’s Constant: 4.15 X 10^-15 eVs)

9.64 x 10¹⁸

Solve: What is the wavelength of a 60 keV photon?

0.21 Å                    

Solve: The exposure from an x-ray tube is 200 mR at 72". What is the exposure at 56"?

331 mR

Solve: Radiation intensity from an x-ray tube is 40 mR/min. at a distance of 1 foot. What is the intensity at 3 feet?

4.44 mR/ min

Change to proper form: 16.87 X 10¹⁸  Hz

1.687 X 10¹⁹ Hz

Change to proper form: 13.25 X 10¹⁸  Hz

1.325 X 10¹⁹ Hz

Change to proper form: .05 X 10^-7 m 

5 X 10^-8 m 

Change to proper form: .95 X 10^-7 m 

9.5 X 10^-8 m 

Velocity of EMS

Speed each cycle travel