click below
click below
Normal Size Small Size show me how
X Ray Production
Radiation Physics
Term | Definition |
---|---|
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 |