Chapter 7, 8, 9 Flashcards
Why is positioning crucial?
ionization chambers must be located
target tissue anatomy must be accurately positioned over selected detectors
What does automatic exposure control do?
it eliminates the need for radiographer to select exposure time and resultant mAs
What is the minimum response time?
exposure time required for detector to sense radiation and terminate exposure
typically 0.001 second
What is back up time?
150% expected time
X-rays vs gamma rays
X-rays are a man made process. They originate from electron cloud of atoms
Gamma rays are a natural process. They originate from atomic nucleus through radioactive decay
What is the velocity of accelerated electrons?
nearly 1/2 speed of light
when x-rays are created, what percentage of the electron kinetic energy is converted to heat and how much is actually x-rays?
98.9 percent heat and 1 percent x-ray
Target materials
Tungsten and rhenium
High Z#’s
High melting points
Similar electron binding energies
What target materials are used for mammography?
molybdenum
Lower Z#
Ideal for soft tissues of breast
Bremsstrahlung interactions
bremsstrahlung interactions is the word for breaking rays
What happens to electrons during a bremsstrahlung interaction?
Characteristic cascade
What electron contributes to an x-ray beam
only the electron that drops into the k-shell will contribute to the beam
biological effects of ionizing radiation are classified as what?
somatic or genetic
Somatic biological effects of radiation
cataracts, erythema, cancer formation
