Physics Flashcards
Define an Element? 2
elements cannot be broken down into simpler forms. I.e Hydrogen or carbon
Element is a substance whos atoms have the same atomic number.
Define a compound?
two or more elements linked together chemically i.e water or oxygen
Describe and define an Atom? 3
Smallest part of an element, which retains the chemical properties of the element.
Positively charges nucleus contains proton and neutrons.
Electrons - negative charge
Define the Atomic Number? 2
Defines Chemical behaviour of the atom
Number of Protons in the nucleus which is the same as the number of electrons.
Carbon (Z) = 6
Define a molecule? 2
smallest part of a compound which retains the chemical properties of that
compound
molecule comprises a number of atoms linked together e.g water is H2O.
State the charge of a proton and electron
Proton = +1.602 x 10^-19 coulombs Electron = -1.602 x 10^-19 coulombs.
State the mass of a proton and electron?
Proton = 1.66 x 10-27kg
Electron = 9.11 x 10-31kg
Define the mass/nucleon Number? 1
provide formula to calculate neutron number 1
Total number of protons and neutrons in an atom
N=A-Z}
Define an isotope 2
Atoms with the same number of proton and electrons but different number of Neutrons.. same chemical properties. Different atomic mass. In part a radioactive variation of the element.
State the number of e in each shell
k
L
M
N
k2
L8
M18
N32
Define an electron volt
1 eV = 1.6 x 10-19 J
Describe what happens when an electron is in an excited state 1
absorb energy via collision or em radiation
electrons may be shifted to a higher energy level
atom is unstable and described as being in an ‘excited state
electron will
soon (less than one microsecond) fall back to its original shell, at the same time releasing in the
form of EM radiation the energy that was originally absorbed
Increase in atomic number can have what effect on Binding energy?1
Increase
state two types of Attenuation = 1
scattering and absorption
Define absorption 1
photon interacts with the atom and loses all of its energy to the atom
Define scattering 1
photon interacts with the atom and is deflected, which may or may be accompanied
with a loss of energy
Define Total linear attenuation coefficient 1
fraction of x-rays removed from a parallel beam of monochromatic radiation per unit
thickness of a homogeneous attenuator
what two factors can effect total linear coefficient? 2
1 The area and material presented to the incoming x-ray photons i.e. high atomic number
materials have high number of electrons.
2 spacing between the atoms in the medium. A dense medium provides a higher
probability of attenuation then a less dense medium, even if the atomic number is the
same.
Define HVT/L 1
thickness of a substance which will transmit exactly one-half of the intensity of
radiation incident upon it
what HVT materials are used in radiography and radiotherapy? 2
we use aluminium to measure the HVTs, whereas in
therapy we use copper.
What can Linear attenuation coefficient figures be used for? 1
radiation protection purposes
Draw a graph showing the relationship between intensity and material thickness. 2
y- intensity
x - attenuator thickness
what is the HVT of water 1
30 mm
What is the HVT of lead 1
0.1 mm
define the total mass attenuation coefficient and where is it used? 2
Total mass attenuation =
μ/p
linear attenuation coefficient/ density
radiotherapy
With increasing energy the linear attenuation coefficient decreases. What happens to the HVT? 1
Increases
define attenuation 1
gradual decrease in intensity as a beam passes through an absorbing material
Define intensity
Intensity WM-2 = watts/area m-2
What has a higher absorption coefficient bone or fat?
Bone
State the unit of the attenuation coefficient
M-1 or per meter
Define total mass absorption coefficient
Total mass absorption coefficient
This is defined as the fraction of the energy contained in the x-ray beam which is absorbed per
unit mass of the irradiated medium.
