How X-rays are generated? What is the process?

Question

Also, what are the functions of electrons and neutrons in an X-ray?

Answer 1

X rays are generated inside a vacuum tube when the electrons hit the plate fast. Let's look at the process in some detail

Inside a vacuum tube are several electrodes, connected to wires sealed in the glass and leading outside. The x-ray tube is a diode (meaning it has two elements.) One is the cathode. This is usually a coil of wire coated with the rare element thorium, which gives off electrons easily. That coil is wrapped around a smaller coil called the filament, similar to the filament in a light bulb.

(Technically, the outer coil is an 'indirectly heated cathode'. In some vacuum tubes used for electronics, they just use the filament alone as the cathode, but not in x-ray tubes.)

The purpose of the cathode is to give off electrons. The other electrode, called the plate, or, anode, has a positive voltage connected to it, to attract the electrons. (Remember, opposite charges attract and like charges repel. It's a law of nature!)

Without a positive charge on the plate, the electrons would just form a cloud around the cathode. But, when they are attracted to the positively-charged plate, they go flying toward the plate.

They don't have a very long distance in which to accelerate, so they don't actually get near the speed of light. But they go well over 10,000 MPH. They form a stream, a 'particle beam'. (This is the same thing that your picture tube uses to write on the phosphor inside the screen.)

When the electron beam hits the plate (or, anode, to give it its technical name), the plate gets hot. So, the plate is made hollow and has water flowing through it to cool it off. This is how x-ray machines can run for more than a few instants at a time without destroying themselves. (Otherwise the plate would melt. The electron beam is THAT powerful!)

Now, let's look at what happens when the electrons hit the plate. We are talking about electrons hitting a metal surface, a flat array of metal atoms in rows and columns. The metal atoms are bound together into a solid material by sharing their electrons.

(Think of basketball players doing a passing drill, where they stand in one place and pass the balls around to each other. That is how the metal atoms bond to one another by sharing electrons.)

The electons of the metal atoms are in their orbits around the nuclei (inner parts) of the metal atoms. The protons and neutrons are in the nucleus of each atom and don't take part in the x-ray process.

So, what happens when one of the beam electrons hits an electron in orbit around one of the metal atoms...? It knocks it out of orbit.

The thing about atoms, is that they want to have an electron (negative charge) in orbit for each proton (positive charge) they have in the nucleus. So, the electron that was knocked loose comes flying back to where it belongs, because the opposite charges attract. (It might not be the exact same atom, but all the electrons are identical and are interchangeable.)

Because of the collision, some of the momentum (energy) was transferred from the electron in the beam to the electron that was knocked loose. The one from the beam goes bouncing off (and eventually returns to the positively-charged plate, but it is the first and most energetic collision that we are concerned with.)

The electron that was knocked loose now has extra energy to get rid of, from the collision. When it returns to its proper place in orbit around the atom, it has to radiate that energy away.

Because all the electrons in the beam were accelerated to the same speed (by the same voltage on the plate attracting them) the amount of energy transferred to the electrons that are knocked off is the same for each one.

When each electron drops back in place where it belongs, it radiates (emits, gives off) a photon. We can SEE light photons, if there are enough of them for our eyes to detect, and we can FEEL heat photons if there are enough of them for our skin to detect. But these photons are so energetic that they will go right through a lot of materials, and mostly only stop in hard, dense materials like teeth and bones! And we don't feel a thing!

(The higher the voltage that accelerates them, the denser materials they will go through. Some x-ray machines used in industry can check a car's engine block for cracks!)

The plate is shaped so that the x-rays get reflected and focused off to the side, and your doctor or dentist aims the tube so that they go through you and into the x-ray film. Once the film is developed (or if they are using a phosphor screen, like on a tv) they can see if you have cavities or broken bones. Film is usually used, so that a permanent medical record can be kept.

So, the filament heats the cathode, the electrons boil off the cathode, the high voltage attracts the electrons to the plate (anode) they slam into the plate at the proper angle (by the design of the tube) and x-rays are generated when the electrons that are knocked loose return to their proper orbits.

Effectively, it takes some of the momentum (energy of movement) from the accelerated electrons and uses that to generate photons.

The electrons are matter; the x-ray photons are energy without any matter. But we did not convert matter to energy! We just converted momentum (one kind of energy) into another kind of energy.

I hope this answers your question. If it didn't, ask another and I'll keep my eyes open on science and mathematics!

Answer 2

The basic production of X-rays is by accelerating electrons in order to collide with a metal target (usually tungsten, but sometimes molybdenum). Here the electrons suddenly decelerate upon colliding with the metal target and if enough energy is contained within the electron it is able to knock out an electron from the inner shell of the metal atom and as a result electrons from higher energy levels then fill up the vacancy and X-ray photons are emitted. This causes the spectral line part of the wavelength distribution. There is also a continuum bremsstrahlung component given off by the electrons as they are scattered by the strong electric field near the high Z (proton number) nuclei.

Nowadays, for many (non medical) applications, X-ray production is achieved by synchrotrons (see synchrotron light).