X-ray production

Unit 20 strand 1 (P2)Describe the production of x-rays and ultrasound

X-rays were first discovered in 1895 by the German physicist William Roentgen, when using a Crookes tube

He called them ‘x’ rays, ‘x’ for ‘unknown’.

The first x-ray photograph: Roentgen’s wife Bertha’s hand

X-rays are electromagnetic radiation of high frequencies (1017-1020 Hz). They penetrate soft tissue but are blocked by bone etc.

X-rays are produced when high-speed electrons hit a metal target. In medical x-rays this is usually tungsten.

x-rays

Electrons

Tungsten target(anode)

Electrons are produced by thermionic emission.

They are accelerated across the vacuum tube towards the positive (anode) target.

The electrons strike the target and lose about 99% of their energy in low-energy collisions with the target atoms – this heats up the target. The remainder of the energy reappears as x-ray radiation.

Overheating is prevented by using a rotating anode and circulating oil. Copper is used for the anode mountings.

Overheating is prevented by using a rotating anode and circulating oil. Copper is used for the anode mountings.

The energy exchange in x-ray production