Production and Properites Flashcards
Atomic no and atomic mass no
Atomic no Z = protons in nucleus
Atomic mass no A = protons and nucleus
Z electrons in orbit around nucleus (determines chemical properties)
Atom electrically neutral
Electron shells
Each shell has fixed energy for particular element - dependent on Z
K2 L8 M18 N..
Excitation
Normally atom electrically neutral. When E jumps from low energy to high energy shell. (Inner to outer)
Binding energy
Negative E attracted to positive nucleus
Work needed to overcome attraction remove electron - binding energy
Greatest for K she’ll as closest to nucleus
Ionisation
X-ray photon removes E from atom to give a positive ion.
Ion pair - positive ion and electron
What are X-rays?
Wave packets of energy
Each packet = photon. Quantum of energy.
X-ray beam has millions of photons
Form of EM radiation
X-ray properties
Invisible and weightless Travel in straight lines Travel at the speed of light Range of wavelengths 0.01-0.05nm Different wavelengths/frequencies give diff properties (40-150V) In free space- obey inverse square law
Production of X-rays
Produce lots of E
Accelerate to high energy
Smash them into target
Must be in vacuum - otherwise gas/air in way
X-ray process production
Electrons produced by filament heating, thermionic emission (CATHODE/mA) Tube current (flow between anode and cathode) fixed 7-10mA. Controlled by heat.
Electrons accelerated to anode by high potential difference (KV)
Variable 60-70kV, higher kV lower dose to patient.
Rapid deceleration by electrons by target, interaction of electrons with targets. (ANODE)
Heat producing collisions
E bombard tungsten target - suddenly brought to rest
Each incoming E can have many heat producing collisions
Energy lost by E - xrays (1%) heat (99%) wasteful, dissipated by copper block and oils.
Tungsten
High melting point, last a long time
High atomic number, lots of atomic E for filament to interact with, lots of Xrays produced.
X-ray set variables
kV- QUALITY OF X-RAY BEAM
Determines penetrating power of photons
Affects film contrast
mA and time - QUANTITY OF PHOTONS
Affects degree of blackening of film (optical density)
What happens in Bremsstrahlung radiation?
E penetrates outer shells and passes close to nucleus
E is slowed down and loses energy in the form of Xrays
Low E P are not useful and discarded in filtration.
If E stopped max potential energy produced as high energy photons
In continuous spectrum…?
E slowed down and deflected to various degrees
Produces complete range/continuous spectrum of X-ray photon energies
Lower kV = lower emax = less Xrays produced
Characteristic radiation
E collides with inner shell tungsten E displacing to outer shell/from atom
Large energy loss = X-ray production
Characteristic radiation binding energy
Only K shells are of diagnostic importance
Bombarding high speed E needs at least 69.5kV to displace K shell E to produce characteristic line on spectrum.
Energy to incoming E directly related to kV across X-ray tube
Binding energy process
After ionisation tungsten E rearrange themselves to return atom to neutral state
Involves E jumping from one energy level to another
Jump results in X-ray photon with a specific energy
X-ray producing collision
M to K K beta radiation
L to K K alpha radiation
Only X-ray photons of specific energies emitted following repositioning of orbiting electrons
These energy emissions are CHARACTERISTIC of tungsten
Combined spectra
X-ray equipment operating above 69.5kV of the final total spectrum will be addition of continuous and characteristic spectra
Atom structure
Nucleus in centre (protons and neutrons)
Electrons orbit nucleus
P positive mass =1amu
N neutral 1amu
E negative 1/1840amu
Amu = 1/12th mass 12C atom
