= X-ray tube
{c}
{wiki}
An <X-ray tube> accelerates <Electrons> from a negative <cathode> to a positive target <anode>. A heated <cathode> supplies <Electrons> by <thermionic emission>; the evacuated envelope limits collisions before the target. This differs from the <gas-discharge tube> in the <Röntgen X-ray discovery experiment>.<Diagnostic Radiology Physics: A Handbook for Teachers and Students/Chapter 5: X-Ray Production (teaching slides) by K. P. Maher>[Diagnostic Radiology Physics: A Handbook for Teachers and Students; IAEA, Chapter 5: X-Ray Production, §§5.2–5.3.2; authored teaching slides, inspected transcription]{ref}
\Image[/x-ray-tube-transmission-detection.png]
{title=From accelerated <Electrons> to a measured <X-ray> transmission signal}
{id=image-x-ray-tube-transmission-detection}
{description=Original schematic of a modern heated-cathode <X-ray tube> and a narrow-beam measurement, not Röntgen's apparatus. <Electrons> stop in the target; emerging <X-rays> continue toward the detector. Apertures of a <collimator> select a small angular range and reject much scattered radiation. The two reference readings use identical geometry. Arrow widths and component sizes are schematic.}
In <bremsstrahlung>, an <Electron> changes <velocity> in the target's <electric fields>, emitting a <photon> while losing <kinetic energy>. Different encounters allow a continuous range of transferred <energies>. This is distinct from the discrete <electronic transitions> producing <Characteristic X-rays>.
Changing the accelerating <voltage> changes the available <kinetic energy> per <Electron> and the <X-ray tube cutoff>. Changing the number of arriving <Electrons> changes the number of opportunities for <photon emission>. These are distinct controls: a larger <electric current> does not by itself give each <Electron> more <energy>. For an original idealized budget, $V=50\,\mathrm{kV}$ and tube <electric current> $i=0.20\,\mathrm{mA}$ give electrical <power> $Vi=10\,\mathrm W$ and arrival rate $i/e\simeq1.25\times10^{15}\,\mathrm{s^{-1}}$, where $e$ is the <elementary charge>. This is input <power>, not emitted <X-ray> <power>; obtaining the latter requires a conversion efficiency.
Back to article page
