CH08 - X Ray Spectroscopy Flashcards
XRF, XRA, XRE
Every day life
Security, Medicine, Astronomy, Chemistry
The emission maxima depends on…
the element (exclusively)
Emission spectrum results from transitions of internal electrons. Therefore it does not depend on ionization state (unlike AES) or bonding.
Incoming radiation hits which electron?
the lowest energy electron (K)
what happens to this electron?
it gets kicked out
formula for change in E
change in E= E-E0
E0 is
K orbital (lowest energy)
E in E-E0 is
the incoming radiation
What happens to E0 when it is kicked out?
Another electron from a higher energy will take its place
formula for K alpha line energy
change in E= E1-E0 = K alpha line energy
The first xray emission line is from
Relaxation of whichever electron is taking the place of the electron being kicked out
The second E in E-E0 is…
Whichever orbital the electron being kicked off is located
Remembering E formula
Where it’s currently at - where its going ,= letter orbital where its going
Moseley’s law
The square root of the frequency of the x-ray emitted by an atom is proportional to its atomic number
Xray Absorption formula
I=I0e ^ -umpx
“Beer’s law” for XRA
Meaning of I in absorption formula?
transmitted power
Meaning of I0 in absorption intensity formula?
incident power
um=
mass absorption coefficient (units: (cm2)/gr)
- Characteristic value depends on element and absorbed wavelength.
- Does not depend on chemical or physical state of element.
p=
(It’s actually “rho”)
sample density (units: gr/cm)
“rho”
x=
sample thickness (units:cm)
Fluorescence
sample placed in a beam of Xrays. Some absorbed.
qualitative analysis with XRF?
xrays of characteristic wavelengths emiited
quantiative analysis with XRF?
Emission intensity proportional to element concentration
Bragg Equation
nλ=2dsinθ
n - differaction order
lamba - x ray wavelength
d - interplanar spacing
theta - x-ray angle of incidence
unit cell
smallest volume element thats completely represenative of the whole crystal