Search results
Results from the WOW.Com Content Network
The scattering length in quantum mechanics describes low-energy scattering. For potentials that decay faster than 1 / r 3 {\displaystyle 1/r^{3}} as r → ∞ {\displaystyle r\to \infty } , it is defined as the following low-energy limit :
This scattering length varies by isotope (and by element as the weighted arithmetic mean over the constituent isotopes) in a way that appears random, whereas the X-ray scattering length is just the product of atomic number and Thomson scattering length, thus monotonically increasing with atomic number. [1] [2]
In physics, the atomic form factor, or atomic scattering factor, is a measure of the scattering amplitude of a wave by an isolated atom. The atomic form factor depends on the type of scattering , which in turn depends on the nature of the incident radiation, typically X-ray , electron or neutron .
The units of the structure-factor amplitude depend on the incident radiation. For X-ray crystallography they are multiples of the unit of scattering by a single electron (2.82 m); for neutron scattering by atomic nuclei the unit of scattering length of m is commonly used.
This allows the total spin of the unpaired electrons and neutron to be probed. The magnetic scattering length from one electron is b m = 𝛾r 0 = 1.348 fm which is on the same order of magnitude as the nuclear scattering length. Because of the dipole-dipole character of the interaction, the scattering is considered to be anisotropic. [7]
Rayleigh scattering causes the blue color of the daytime sky and the reddening of the Sun at sunset. Rayleigh scattering (/ ˈ r eɪ l i / RAY-lee) is the scattering or deflection of light, or other electromagnetic radiation, by particles with a size much smaller than the wavelength of the radiation.
The scattering of X-rays can also be described in terms of scattering cross sections, in which case the square ångström is a convenient unit: 1 Å 2 = 10 −20 m 2 = 10 000 pm 2 = 10 8 b. The sum of the scattering, photoelectric, and pair-production cross-sections (in barns) is charted as the "atomic attenuation coefficient" (narrow-beam), in ...
The Bragg condition is correct for very large crystals. Because the scattering of X-rays and neutrons is relatively weak, in many cases quite large crystals with sizes of 100 nm or more are used. While there can be additional effects due to crystal defects, these are often quite small.