A - Radiation Flashcards
What is the definition of radiation?
“Radiation is the emission of transmission of energy in the form of waves or particles through space or through a material medium”
Main concept: Movement of energy
What types of waves are EM and how can you calculate their energy?
Transverse waves
Visible light: 400-700nm
E = hc/lamda = hf = hv
What is the significance of the de broglie wavelength equation and it’s used in physics?
Lambda = h / p (momentum)
•Suggest particles with a mass exhibit wave like properties and thus have a wavelength
• helps determine how these particles behave within a quantum system (interactions with potential barriers)
• Explains how electrons diffract through crystals and other small openings
Break down the different types of radiation and approximate their range and energies
Alpha: 2-9MeV | bremsstrahlung | paper / mm air
Beta: coulombic collisions | 0.154MeV max range 0.29mm & 1.71MeV max range 8mm (in tissue) | thin plates of wood/metal
Gamma rays: lead/iron/thick metal plates | photoelectric effect or Compton scattering | 0.035MeV max range 33mm & 1.33MeV max range 164mm
Neutrons: indirect ionisation (collide with proton which then cause’s ionisation damage) | water/concrete (travels much further)
Briefly describe what READ stands for
Radioactivity - amount of ionising radiation released by a material (Ci & Bq)
Exposure - amount of radiation travelling through air (Röntgen C/kg)
Absorbed dose - amount of energy that radioactive sources deposit in materials through which they pass (rad and gray Gy)
Dose equivalent (effective dose) - combines amount of radiation absorbed and medical effects of that type of of radiation (rem and Sievert Sv)
What is the concept of LET and which radiation is in which bracket?
Linear Energy Transfer - a measure of energy transferred by ionising particle to traverse material.
Low-LET - x rays and gamma rays are sparsely ionising radiation, energy is distributed homogeneously (widely)
High-LET - alpha, beta and neutrons are densely ionising radiations, energy is distributed inhomogeneously (specific)
What are two main mechanisms by which x- rays are produced?
Characteristic X rays and Bremsstrahlung X-rays
Both involve accelerating electrons through an excitation voltage into a metal target.
What is Bremsstrahlung X-rays?
High-speed electrons from an x-ray tube are decelerated or deflected by the +ve charge nuclei of the target material (typically tungsten).
As the electrons slow down or change direction they emit EM radiation as X-rays
The energy spectrum is continuous as the energy levels depend on the range of KE of the incident electrons. The X-rays originate from the incoming electrons decelerating.
What is characteristic X-rays and where do they come from?
High speed electrons knock inner-shell electrons out of their orbits in the target material.
Outer-shell electrons drop down to fill the vacancy, emitting X-ray photons with **specific energies corresponding to the difference in energy levels.
Each element has its unique set of characteristic x ray energies corresponding to energy transitions between the shells
What are the different labels and orbital shells for electrons orbiting around a nucleus?
n - principle quantum number (1,2,3,4,5)
l - orbital AM (0,1,2…n-1)
m - projection of l (-l, -l+1,…,0,…, l-1, l)
s - spin (+1/2 or -1/2)
S orbitals: l = 0 (X-rays most interested in lowest energy state)
P orbitals: l = 1 | m = -1, 0, +1
d orbitals: l = 2 | m = ….
f orbitals: l = 3 | m = …
What is the electron configuration for Argon-18?
1s2
2s2, 2p6
3s2, 3p6
What are typical effective dose ratings Sv for dental, chest x ray, CT scan (head) full body CT scan, etc
All measurements in mSv
Dental X-ray 0.005
Chest X-ray 0.1
CT Scan Head 2
Background radiation per year 2
CT Scan Full Body 10
EDF annual limit 10
UK ONR annual limit 20
Lowest annual dose at which any increase in cancer is clearly evident 100
Chernobyl residents who were relocated after the blast 350
Single does which would kill half of those exposed to it within a month 5000
Typical dosage of Chernobyl worker who died within weeks 6000
What is the Rydberg formula and why is it important?
1/lambda = R_H(1/n_1^2 - 1/n_2^2)
Calculates the wavelengths of light emitted or absorbed by an electron transitioning between energy levels in a hydrogen atom — allows us to calculate wavelength of light and hence energy levels within atoms
Electron is knocked out of the core (n1) then replaced by an electron at higher energy, as long as electric dipole selection rules are obeyed.
What do the symbols represent in a characteristic X-Ray Lines graph?
K L M N etc - tells you which energy state the electron is travelling to.
• K is n=1, L is n=2 etc
Alpha, beta, gamma etc tells you what energy state the electron was coming from
• alpha = n+1, beta = n+2 etc
What is Mosley’s law and what’s its significance?
Discovered that the square root of the frequency emitted X-rays (v) is linearly proportional to the atomic number (Z) of the element.
SQRT(v) = a(Z-b)
Where a and b are constants
Scientists used this to predict and verify the existence of undiscovered elements and rectify positions of certain elements within the periodic table.
