Intro Lecture – X-Ray Physics

Q&A flashcards covering X-ray basics, wave properties, tube factors, attenuation, and exponential attenuation.

What type of radiation are x-rays?

Electromagnetic radiation.

Do photons have mass or charge?

No, photons have no mass and no electric charge.

What is the wavelength of diagnostic x-rays?

About 1e-11 m.

What equation relates wavelength, frequency, and speed of light?

c = fλ.

How does photon energy change with wavelength?

Shorter wavelength → higher frequency → higher energy.

How are x-rays produced in the tube?

Electrons from the filament are accelerated by kV and strike the anode target.

What does kV control in x-ray production?

The energy of electrons, and thus the energy of x-ray photons.

What does mAs control?

The quantity of electrons and the number of x-rays produced.

What is mAs in terms of current and time?

mAs = (mA)(seconds), equal to total charge crossing the tube.

What are the three possible x-ray interactions with matter?

Transmission, scatter, absorption.

Define attenuation.

The reduction in x-ray beam intensity due to scatter and absorption.

In the attenuation equation, what does mu represent?

The linear attenuation coefficient: probability of attenuation per cm.

Write the attenuation equation.

I = I0 e^(-mu*x) (ASCII: I = I0 e^(-mu x)).

Do transmitted x-rays lose energy?

No, transmitted photons have the same energy as incident photons.

What factors increase the attenuation coefficient mu?

Lower x-ray energy, higher material density, higher atomic number.

More 40 keV or 80 keV photons will transmit through tissue? Why?

80 keV photons transmit more; higher energy yields lower attenuation (mu).

What fraction of 80 keV x-rays transmit through 1 mm of copper? Through 2 mm?

About 50% through 1 mm; about 25% through 2 mm.