Module 3 Flashcards
What is the atomic number Z
is the number of protons
in the nucleus
What charge do protons have?
Positive charge
What charge do electrons have
negative charge
What charge do neutrons have?
None
Isotope
protons and neutrons in the nucleus are not of equal number
Radioisotopes
isotope with unstable nuclei which undergoes radioactive disintegration
(radioactive)
What do eletrons do?
They orbit the nucleus in shells, each shell has
a different energy level
K shell electron
has the least energy and is the nearest to nucleus
How do electrons travel?
Electrons can jump from one shell to another
but cannot exist between shells (forbidden
zone)
What is the forbidden zone
Between shells electrons cannot exist
What is the electron binding energy?
Electrons are bound to the nucleus by
electromagnetic force
Positive Ion is?
If an electron is removed the atom becomes
positively charged and becomes a positive ion
Ionisation
The process of removing the electron from shell
Excitation
If an electron is moved from an inner shell to an
outer shell the atom remains neutral this is called
Excitation
electron volt (eV)
The unit of energy in the atomic system is called
the electron volt (eV)
Heat Producing Collisions
The incoming electron is deflected by the cloud of
outer shell tungsten electrons with a small loss of
energy
Heat Producing Collisions alternative
The incoming electron collides with an outer shell
tungsten electron displacing it to a peripheral
shell (excitation) or displaces it completely from
the atom (ionisation)
X-Ray Producing Collisions
The incoming electron penetrate the outer electron
shell and passes close to the nucleus of the tungsten
atom. The incoming electron is dramatically slowed
down and deflected by the nucleus with a large loss of
energy which is emitted in the form of X-rays
X-Ray Producing Collisions alternative
The incoming electron collides with an inner shell
tungsten electron displacing it to an outer shell
(excitation) or displaces it completely from the atom
(ionisation) with a large loss of energy and emission
of X-rays
The two different types of x-ray collisions result
in different x-ray spectra
Characteristic spectrum
Continuous/ Bremsstrahlung spectrum
Intensity peaks appear when
In the characteristic spectrum
Kilovoltage (Kv)
Voltage across the tube determines the
quality of the beam
increase the Kv the contrast is decreased
longer
grey scale and the dose is reduced
Milliamperage (mA)
- Electrical current flowing through
the tube- determines the quantity of the beam
What happens if you increase the mA
the image will be darker and the
higher the dose
Time (s)
The duration of the exposure time
increase the time the image will be darker and the dose
will be higher
Xray interactions with matter. What are the Four outcomes
Scattered Absorbed Attenuated The electrons do not interact and so are transmitted unchanged
xray interactions with matter depends on
the amount of energy the photons possess
Scattered
The electrons are deflected from their
original path and carry on travelling in a different
direction with no loss of energy.
Absorbed
The electrons are absorbed with a total
loss of energy
Attenuated
A combination of absorption and
scattering which will reduce the intensity of the
beam
‘Photoelectric
effect’
Absorption – pure absorption
‘Compton effect’
Attenuation – scatter and absorption
The incoming photon and inner shell electron collide
The energy of the incoming x-ray photon needs to be
equal to or greater than that of the binding energy for
ejection to take place 69.5Kv
The inner shell electron is ejected with considerable
energy into the tissues
this ejected electron is now
called a photoelectrons (further interactions will take
place with the photoelectrons)
X-ray photon has deposited all its energy
pure
absorption – x-ray photon no longer exists
Vacancy within the electron shell has to be filled
outer shell electrons fall in to replace ejected
photoelectron.
The atom has to return to neutral state
it captures a free electron to achieve stability
Soft tissue has an atomic number of
7
Bone has an atomic number of
12
Aluminium Z is
13
Copper Z is
29
Lead is used in radiation protection as Z is
82
Low Energy Scattered Photons produce?
back scatter
which may be absorbed by patient and may not leave
body – lead provides no protection or can possibly trap
them in the body
High Energy Scattered Photons will produce
forward
scatter, if it reaches film it will degrade the image but
normally it is removed by an anti scatter grid
The interaction of the photon hitting an electron is not
dependent on the Z number
very little diagnostic
information as there is very little contrast produced on
the radiograph
