What is the purpose of vacuum in x ray tube?

Answer 1

Section II. PRODUCTION OF X-RAYS

1-6. PARTS AND COMPONENTS OF THE DENTAL X-RAY MACHINE

1. General. The standard structural parts of the dental x-ray machine include a control panel (usually mounted behind a protective shield); a tube head, which houses the dental x-ray tube; and a flexible extension arm from which the tube head is suspended (see figure 1-1).
2. The Control Panel. The components of the control panel are switches, dials, gauges, and lights. Basically, each control panel has the same function, the arrangement and location of these components will differ, depending upon the make, model, and year of construction of the dental x-ray unit. An operator's manual is issued with each unit. The operator should study it until he is familiar with its operational capability.
3. The Extension Arm. The tube head is attached to the metal extension arm by means of a yoke that can revolve 360 degrees horizontally where it is connected. The construction of the yoke also provides vertical movement as well.
4. The Tube Head. Inside the metal tube housing is the x-ray tube. The diagram in figure 1-2 represents a dental x-ray tube head and a dental x-ray tube. This tube emits radiation in the form of photons (photons will be discussed in Lesson 2) or x-rays. X-ray photons expose the film. In addition to exposing the film, it also exposes the patient to radiation. Unless certain protective measures are taken, the x-ray technician may also be exposed.

Figure 1-1. A representation of a control panel, x-ray tube head, and extension arm.

Figure 1-2. Dental x-ray tube head and dental x-ray tube.

1-7. THREE STEP PROCESS OF X-RAY PRODUCTION

1. The First Step. The first step in x-ray production is to turn on the machine. (If there is doubt on the part of the x-ray technician concerning the operation of the unit, reference should be made to the operator's manual.) When the unit is turned on, the filament of the cathode is heated by electrical current, causing it to emit electrons (see figure 1-3).
2. The Second Step. For the second step of this three-step process, high voltage is passed across the x-ray tube. When this is done, the electrons or electron cloud from the filament are drawn across the opening toward the anode. The anode is made of tungsten and is sometimes called the tungsten target. Figure 1-4 depicts the electrons speeding toward the anode (tungsten target).
3. The Third Step. The third and final step in this three-step process is the collision of electrons with the anode (tungsten target). This rapid deceleration of electrons produces x-rays, also referred to as photons. Figure 1-5 represents electrons striking the anode (tungsten target) and producing x-ray photons.

Figure 1-3. Tube head with the filament of the cathode emitting electrons.

Figure 1-4. Electrons speeding toward the anode (tungsten target).

Figure 1-5. Electrons striking the anode (tungsten target) producing x-ray photons.

Answer 2

Vacuum in the X-ray tube is needed to let the electrons "flow" from cathode to anode.