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In X-ray tubes, the heel effect or, more precisely, the anode heel effect is a variation of the intensity of X-rays emitted by the anode depending on the direction of emission along the anode-cathode axis. X-rays emitted toward the anode are less intense than those emitted perpendicular to the cathode–anode axis or toward the cathode.
The intensity of the beam from the positive anode side is lower than the intensity from the negative cathode side because the photons created when the electrons strike the target have a longer way to travel through the rotating target on the anode side. This effect is called the anode heel effect and is why thicker body parts should be placed ...
This is a fixed-anode, reflection-type x-ray tube, whose name is composed of three parts: "SR" meaning self-rectified, "T" meaning therapeutic, and "1" indicating a 1-mm diameter nominal focal spot size. Its beryllium window produces a beam with very low inherent filtration but it is subject to beam non-uniformity due to heel effect.
Reflection type targets exhibit the heel effect and can use a rotating anode to aid in heat dissipation. Compton scattering is the dominant interaction between a megavoltage beam and the patient, while the photoelectric effect dominates at keV energies.
Solid-anode microfocus X-ray tubes are in principle very similar to the Coolidge tube, but with the important distinction that care has been taken to be able to focus the electron beam into a very small spot on the anode. Many microfocus X-ray sources operate with focus spots in the range 5-20 μm, but in the extreme cases spots smaller than 1 ...
A plate, usually called anode in Britain, is a type of electrode that forms part of a vacuum tube. [1] It is usually made of sheet metal, connected to a wire which passes through the glass envelope of the tube to a terminal in the base of the tube, where it is connected to the external circuit.
Crookes X-ray tube from around 1910 Another Crookes x-ray tube. The device attached to the neck of the tube (right) is an "osmotic softener". When the voltage applied to a Crookes tube is high enough, around 5,000 volts or greater, [16] it can accelerate the electrons to a high enough velocity to create X-rays when they hit the anode or the glass wall of the tube.
The terms anode and cathode are not defined by the voltage polarity of electrodes, but are usually defined by the direction of current through the electrode. An anode usually is the electrode of a device through which conventional current (positive charge) flows into the device from an external circuit, while a cathode usually is the electrode through which conventional current flows out of ...