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X Ray Production

Radiation Physics

TermDefinition
When were X-Rays Discovered November 8, 1895
Who Discovered X-Rays? Roengten
Four basic requirements for the efficient production of x-rays A vacuum A source of electrons A target for the electrons A high potential difference (voltage) between the electron source and the target
Electrode an electrical terminal or conductor
Diode An electrical device with two electrodes
Triode An electrical device with three electrodes
An X-ray is a Diode
If an electron gives up all of its energy in a single event to produce one photon, then that photon will have the maximum possible energy and the minimum possible wavelength
The number of x-ray photons created in the target proportional to the number of electrons striking the target.
Twice the current will lead to twice the number of x-ray photons.
AC (alternating current) The electrical current supplied by the power company
kVp maximum or peak voltage across the tube
The kVp available may range from 20 to 300 kVp
maximum voltage across the tube is given by kVp
three classes of therapeutic x-ray beams superficial orthovoltage megavoltage
Diagnostic x-ray machines utilize a potential difference ranging from 20 kVp up to about 120 kVp
Superficial x-ray beams have tube potentials between 50 and 150 kVp and are used to treat skin conditions
Orthovoltage beams are produced by tube potentials between 150 and 300 kVp
Megavoltage beams are produced by linear accelerators,
Therapy X-Ray Tubes -Do not have a rotating anode -Have a larger spot size - 5mm is typical -instantaneous heating rate is lower
The copper of the hooded anode stops the secondary electrons and any x-rays produced by them
Grids Reduce scatter reaching image receptor
Grides are made of thin lead strips separated by radiolucent interspacing
Supplies proper voltage to anode and cathode X ray generator
To make a radiographic exposure, there are three fundamental quantities that must be set at the generator console tube voltage tube current time of exposure
tube voltage is measured in kVp
tube current is measured in milliamperes (mA)
time of exposure is measured in second(s)
Tube current is directly related to the number of electrons that strike the target
X-ray “output” is proportional to the number of x-ray photons produced by the use of a particular technique
The total number of electrons striking the target is directly proportional to the product of the tube current and the time of the exposure
The number of x-ray photons emitted by the target is affected by kVp
Heat May produce a pitting in the target
Overheating of the anode, tube, and tube housing can shorten tube life
Most tube failure occurs as the result of thermal wear on the internal component parts
Common types of tube failure include worn rotor bearings, a cracked or pitted anode, gassing of the tube, and filament breakage
ways to maximize x-ray tube life include Minimize filament boost (preparation) time Limit rotor/start/stop operations Use lower tube current (mA) Do not make a high mA exposure on a cold tube
The tube and the housing can overheat depending on the number of exposures, the time between exposures, and the technique
Transformers are principal components of generators
Transformer Law The ratio of the number of coil turns in the primary winding to the number of coil turns in the secondary winding is equal to the ratio of the primary voltage to the secondary voltage
Transformer does what to voltage increase or decrease, depending on the number of turns in the two coils
Ns > Np “step-up” transformer, increases secondary voltage
Ns < Np “step-down” transformer, decreases secondary voltage
Power is the energy of production or expenditure per unit time (1 Watt = 1 J/s)
Solid-state diode contains a crystal of a semiconductor material
Voltage ripple of a DC waveform is defined as the difference between the peak voltage and the minimum voltage, divided by the peak voltage and multiplied by 100
Created by: cgriesen