A machine is forming permanent images
from a brightly lit original, but is using the transfer of static
electrical charges rather than photographic film, hence the term
electrophotography. Image by George Watson.
Are a form of electromagnetic radiation
with a wavelength approximately in the range of 5 pm – 10 nanometers
(corresponding to frequencies in the range 30 PHz – 60 EHz). X-rays
were first observed and documented in 1895 by Wilhelm Conrad Röntgen.
X-rays are highly penetrating of many materials, and are used
in medicine to take pictures of bones and teeth. This is because
bones absorb the radiation more than the less-dense soft tissue.
X-rays from a source are passed through the body and onto a photographic
plate; areas where radiation is absorbed show up as white and
can be used to show broken or fractured bones.
A technique in crystallography in which
the pattern produced by the diffraction of x-rays through the
closely spaced lattice of atoms in a crystal are recorded and
then analyzed to reveal the nature of that lattice. The material
and molecular structure of a substance can often be inferred from
the quantitative study of this pattern. It is widely used in chemistry
and biochemistry to determine the structure of molecules.
Energetic X-rays (E > 30 keV) can penetrate
the air at least for distances of a few meters (they would never
have been detected and medical X-ray machines would not work if
this was not the case) the Earth’s atmosphere is thick enough
that virtually none are able to penetrate from outer space all
the way to the Earth’s surface. X-rays in the 0.5 – 5 keV range,
where most celestial sources give off the bulk of their energy,
can be stopped by a few sheets of paper; ninety percent of the
photons in a beam of 3 keV X-rays are absorbed by traveling through
just 10 cm of air! [more]