X-ray Production

xrays

discovered x-rays in 11/8/1895 by Wilhelm Conrad Roentgen

prodcued by e- interacting with matter

properties of xray

no mass

unaffected by electromagnetic fields

travel in straight lines

exponentially attenuated by matter

cannot be focused

electron shells

max. #: 7

names: K, L, M, N, O, P, Q

e- per shell formula: 2n^2

ionization

removal of an orbital e- from an atom

resulting ion pair

electron binding energy

strength of attachment an e- has to the nucleus

excitation

electron is moved to a higher electron shell

types of radiation

characteristic

bremmstrahlung

characteristic radiation

produced when a high-speed e- dislodges an inner-shell e- from the target and causes ionization of that atom

x-ray is emitted when an outer shell e- fills an inner shell void

x-rays emitted from shells termed from their origin

only K characteristic xrays of Tungsten useful in making diagnostic radiograph

bremsstrahlung radiation

braking radiation

projectile e- slowed by the electric field of target atom nucleus resulting in loss of kinetic energy

electrostatic force increases with increasing Z#, closer to nucleus

no threshold of 70 kVp

most common in diagnostic range

ways of losing kinetic energy

heat

characteristic

bremsstrahlung

xray emission spectrum

characteristic: discrete, specific values, based on target material

bremsstrahlung: continuous, 0 max energy possible, peak = 1/3E

filters

absorb undesirable low energy xrays

harden the beam

Genz rays

5-15 keV

filter: plastic

superficial

50-150 kVp

filter: Al, Cu

orthovoltage

150-400 kVp

filter: Thoraceus (Sn, Cu, Al from beam to pt)

megavoltage

filter: transmission target, beam flattening

beam direction

high energy: more forward, narrower, more intense in the forward direction

KE coming in, EM coming out

beam direction dependency

target design affects xray direction

high atomic Z#

diagnostic, superficial, and orthovoltage: no bending magnet

therapeutic: transmission target

megavoltage xrays

4 MV: 10% xrays produced

25 MV: 65% xrays produced

water used to dissipate heat