![]() The X-ray housing prevents X-rays from being released in all directions, provide suitable high voltage insulation and allow cooling of the tube/system. Housing cracks/ Oil Leaks – The x-ray tube lies within a metal protective housing called the tube housing.Excessive vibration in the rotor is the primary cause of anode stem cracks as an anode disc imbalance. Anode damage can be due to bearing damage, repeated overload and exceeding maximum heat storage capacity. Also, this may often lead to increased X-ray production and excessive vibrations of the rotor. These melted particles can interfere with the vacuum integrity within the X-ray tube, leading to its failure. Extreme heat within the housing of an X-ray tube leads to the melting of the tungsten material of the anode disc. This can occur due to excessive heating during the X-ray generation without adequate cooling. Tube failure could result from maintaining the anode at elevated temperatures over long exposure times. The most frequent mode of failure of an x-ray tube is the failure to adequately dissipate the heat generated during normal operation. Anode failure – In the production of X-Rays less than 1% of the energy produces useful X-rays while the remaining 99% is transformed into heat.Other than insulator surface flashover, other common causes of arcing are – vacuum flashover due to particulate impurities or high residual gas within the tube, insulator degradation or breakdown and spurious electron emissions. This results in a temporary loss of x-ray output, a localized artefact and/or possible damage to the glass envelope. When the tungsten deposit is sufficiently thick, arcing may occur at high temperatures, when electrical current flashes from the cathode to the tungsten deposit on the glass envelope/ insulator, and then to the target, essentially causing a short-circuit. This slowly causes darkening of the surface of the glass tube. However, because of the immense heat load, over time, tungsten gradually vaporizes and instead of the target, deposits onto the surface of the glass envelope. Melting point of Tungsten used in Cathode or Anode is 3422 0C and hence does not vaporize easily. Tube Arcing – Tungsten vaporization and deposition on the inside of the glass enclosure is the most common cause of tube failure.Due to high temperatures, Tungsten may start evaporating from the filament surface in a non-uniform, spotty or patchy way – soon leading to filament breakage and failure. If the filament is subjected to higher than necessary or longer than necessary tube current, the filament may start burning-out. Higher the tube current, higher the filament temperature. The tube current, tube voltage, anode to cathode spacing, target angle and the focal spot size are some of the main factors affecting X-Ray tube characteristics. Excessive and/or prolonged heating of the filament may cause breakage or vaporization of filament leading to cathode failure. Cathode Filament failure – One of the significant factors that can cause the failure of an X-ray tube is extremely high voltage.Common causes of X-Ray tube failureĬathode filament failure, tube arcing, anode failure, Glass housing cracks/oil leak, aging of the x-ray tube components, Rotor bearing failure and x-ray filament transformer/high tension transformer failure in self-contained x-ray tube( stationary anode) are some of the common causes of x-ray tube failure. This helps re-establish vacuum inside the tube and increase the strength of the insulation as well as the dielectric. If your x-ray tube has sustained some damage, the first thought that may occur is – Is it repairable? The most common x-ray tube repair involves replacing the oil inside the tube housing and removing any air, gases, particles that could cause arcing. ![]() In some tubes, thin beryllium windows are used to reduce inherent filtration of the x-ray beam.Replacing an x-ray tube can be expensive. The x-ray beam emerges through a thin glass window in the tube envelope. The physics of x-ray production will be discussed later, in section 3.4. The x-rays are produced by the sudden deflection or acceleration of the electron caused by the attractive force of the tungsten nucleus. When a high voltage is applied between the anode and the cathode, the electrons emitted from the filament are accelerated toward the anode and achieve high velocities before striking the target. The anode consists of a thick copper rod at the end of which is placed a small piece of tungsten target. ![]() The cathode is a tungsten filament that when heated emits electrons, a phenomenon known as thermionic emission. At one end is a cathode (negative electrode) and at the other an anode (positive electrode), both hermetically sealed in the tube. The tube consists of a glass envelope that has been evacuated to high vacuum. Figure 3.1 is a schematic representation of a conventional x-ray tube. ![]()
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