X-ray Production

Question 1

Coulomb scattering

Answer 1

general term used to describe elastic Coulomb interaction
between two charged particles: an energetic projectile and a stationary
target.

Question 2

An atom with an electronic vacancy in its inner shell is in a highly excited state
and returns to its ground state through one or several electronic transitions. In
each of these transitions an electron from a higher atomic shell fills the shell
vacancy and the energy difference in binding energy between the initial and
final shell or sub-shell is emitted from the atom in one of two ways:

Answer 2

either
(1) in the form of characteristic (fluorescence) radiation or (2) radiation-less
in the form of Auger electrons, Coster–Kronig electrons, or super Coster–
Kronig electrons.

Question 3

Define an atomic shell vacancy, list the two types of shell vacancy, and
briefly describe the ultimate fate of a shell vacancy.

Answer 3

(a) A shell vacancy is defined as an electron missing from the normal complement
of electrons in a given atomic shell. Two types of vacancy are known: (1) primary
and (2) secondary.
(1) Primary shell vacancy occurs when an atomic electron is displaced from the
atomic cloud through one of 8 known processes that fall into 5 categories: incident
photon–atom interactions; nuclear effects; incident charged particle–atom Coulomb
interactions, Auger effect, and positron annihilation. Primary vacancy can occur in
any one of the electronic shells of an atom, making a positive ion (anion) out of the
neutral atom.
(2) Secondary shell vacancy occurs when an electron makes a transition from a
higher-level electronic shell to a lower-level electronic shell in an atom, meaning
that the vacancy moves in the opposite direction. The transition energy is emitted
in the form of characteristic (fluorescence) radiation or is transferred to an electron
in a higher-level shell that is ejected as Auger electron leaving behind a primary
vacancy.

Question 4

List at least 4 processes resulting in production of a primary atomic
shell vacancy and briefly describe each process.

Answer 4

Eight processes that result in production of a primary shell vacancy are as
follows:
(1) Photoelectric effect. A photon-atom interaction whereby the photon is completely
absorbed by the atom and its energy is given to an orbital shell electron. The
orbital electron is ejected from the atom as a photoelectron leaving behind a shell
vacancy.
(2) Compton scattering. A photon-orbital electron interaction whereby the photon
is scattered with a lower energy by a loosely bound orbital electron and energy
difference between the incident and scattered photon is absorbed by an orbital
electron. The orbital electron is consequently ejected from the atom as a Compton
(recoil) electron leaving behind a shell vacancy.
(3) Triplet production. A photon-orbital electron interaction whereby the photon
interacts with the Coulomb field of an orbital electron of the absorber atom. The
photon disappears and an electron-positron pair is created (materialization). To conserve
momentum, the orbital electron absorbs part of the incident photon energy and
is consequently ejected from the atom leaving behind a shell vacancy.
(4) Charged particle Coulomb interaction with atom. A charged particle as it
traverses absorbing medium interacts through Coulomb force with orbital electrons
and nuclei of atoms in the absorber. The orbital electrons absorb part of the charged
particle energy and are either ejected from the atom or excited to higher energy
levels leaving behind shell vacancies in the absorber atoms.

Question 5

Define the fluorescence yield ω

Answer 5

Fluorescence yield of a given shell (K, L, or M) is defined as the number of
fluorescence (characteristic) photons emitted per vacancy in the shell. It can also be
regarded as the probability, after creation of an electronic shell vacancy, of fluorescence
photon emission as opposed to Auger electron emission

Question 6

Cˇ erenkov radiation

Answer 6

Energetic charged particles moving through an optically transparent dielectric
absorber with uniform velocity υi that exceeds the phase velocity of light cn
in the particular absorber give rise to emission of photons called