HTI5205 Diagnostic Radiology Physics
The Complete Exam Bible · Semester 1, 2026/27HTI5205 Overview
- The Hong Kong Polytechnic University
- Semester 1, 2026/27
- Postgraduate physics subject
- Written examinations
- Canvas learning materials
What this subject asks you to do
Diagnostic radiology physics connects fundamental physical models to imaging equipment, radiation measurement and protection. The subject expects both conceptual explanation and analytical problem solving.
- Assessed by Assignments, in-class quizzes and written examinations.
- Core calculation habit Name the quantity and target unit before substitution.
- Hardest distinction Separate energy transferred to charged particles from energy deposited locally.
- Where to confirm Check Canvas for current test timing, scope and permitted materials.
How HTI5205 is assessed
| Component | Weight | Format |
|---|---|---|
| Assignments | 20% | Four assignments, one for each published module |
| In-class quizzes | 10% | Quizzes after lectures also used for attendance; no make-up quiz will normally be arranged for absence |
| Written examinations | 70% | Two written tests using structures such as multiple-choice, short and long questions across the intended learning outcomes |
The published syllabus assigns 20% to assignments, 10% to in-class quizzes and 70% to written examinations, totalling 100%. It describes two written tests with structures such as multiple-choice, short and long questions. The available source does not publish the split between the tests, duration, permitted materials or a hurdle threshold; check the current Canvas instructions for those details.
Assessment structure
Segment widths reproduce the published weights and total 100%.
Current HTI5205 dates
| Date | Item | Control |
|---|---|---|
| 26 September 2026 | Assignment 1 | Basic Radiation Physics |
| 24 October 2026 | Assignment 2 | Atomic Structure and X-ray Production |
| 6 November 2026 | Assignment 3 | Interaction of Photons with Matter |
| 27 November 2026 | Assignment 4 | Radioactivity and Nuclear Physics |
Dates are as published in the subject syllabus calendar for this offering. Confirm exact deadlines and submission settings in the live LMS.
What HTI5205 covers
The chapters move from radiation quantities and wave physics through atomic structure, detection, X-ray production, photon interactions, radioactivity and electrical principles.
Radiation Quantities and Inverse-Square Reasoning
activity, intensity, exposure, absorbed dose and risk-adjusted dose with point-source geometryRadiation calculations become reliable when activity, intensity, exposure, absorbed dose and equivalent dose remain separate.
- Activity and source strength
- Intensity as power per area
- Point-source inverse-square geometry
- Exposure in air
- Absorbed and equivalent dose
- Unit and direction checks
Electromagnetic Waves and Modern Physics
wavelength, frequency, photon energy, momentum, relativity and wave-particle dualityX-rays require both wave and photon descriptions. This chapter links wavelength and frequency through wave speed, then adds photon energy and momentum.
- Wave speed, frequency and wavelength
- Photon energy
- Photon momentum
- Mass-energy equivalence
- Lorentz-factor boundary
- De Broglie Matter Waves
Radiation Classification, Fluence and Flux
direct and indirect ionisation, particle fluence, energy fluence and ionisation chambersThis chapter classifies radiation by the route through which it ionises matter and then separates cumulative field quantities from rates. Charged particles can ionise directly along their tracks.
- Direct and indirect ionisation
- Particle fluence
- Particle flux density
- Energy fluence
- Energy flux density
- Ionisation chamber response
Kerma, Absorbed Dose and Biological Effect
energy transfer, energy deposition, LET, RBE and radiation weightingKerma is energy transferred from uncharged radiation to charged particles per mass, while absorbed dose is energy retained in matter per mass. They share the gray but describe different stages.
- Initial energy transfer
- Local energy deposition
- Charged-particle escape
- Linear energy transfer
- Relative biological effectiveness
- Radiation weighting factor
Atomic and Nuclear Structure
atomic models, nuclide notation, binding energy, fission and fusionAtomic models are organised here by the evidence that forced each revision. Rutherford scattering replaced diffuse positive charge with a small dense nucleus, and Bohr's discrete stationary states addressed atomic spectra.
- Thomson and Rutherford models
- Bohr stationary states
- Atomic and neutron numbers
- Isotopes and isomers
- Mass defect and binding energy
- Fission and fusion
Quantum Numbers and Electron Transitions
allowed states, shell and subshell labels, selection rules and characteristic transitionsQuantum numbers form nested constraints: n limits the allowed subshell values, the chosen subshell limits orbital orientation, and spin has two permitted projections. Invalid states should be rejected before electron filling begins.
- Principal quantum number
- Orbital and magnetic numbers
- Spin projection
- Shell and subshell notation
- Transition selection rules
- Characteristic line counting
Band Structure and Luminescence
valence and conduction bands, forbidden gaps, trapping and optical emissionDiscrete atomic states broaden into bands when many atoms form a solid. The valence band contains outer occupied states, the conduction band supports mobile carriers, and the forbidden gap controls how readily electrons enter conduction.
- From atomic levels to bands
- Valence band
- Conduction band
- Forbidden energy gap
- Fluorescence and phosphorescence
- Trapping and thermal release
X-Ray Tube Physics and Spectra
cathode and anode physics, bremsstrahlung, characteristic lines, kVp, mA and heatAn X-ray tube heats a cathode filament, focuses released electrons and accelerates them through a potential difference toward a heavy target.
- Cathode emission and focusing
- Electron acceleration
- Anode target and heat
- Bremsstrahlung continuum
- Characteristic lines
- kVp, mA and mAs controls
Photon Interactions with Matter
attenuation, photoelectric absorption, Compton scatter, transmission and dose trade-offsPhoton interaction is classified by the products that leave the site. Photoelectric absorption removes the incident photon and ejects a bound electron. Compton scattering leaves a recoil electron and a lower-energy photon travelling in a new direction.
- Photoelectric absorption
- Compton scattering
- Transmission
- Linear attenuation coefficient
- Exponential beam reduction
- Half-value layer and contrast
Radioactivity and Electrical Physics
nuclear decay, half-life, activity, capacitors, alternating current and transformersRadioactive decay changes an unstable nucleus through alpha, beta or gamma processes, while activity and population decrease exponentially. Half-life describes equal fractional reductions over equal times rather than equal absolute losses.
- Alpha, beta and gamma change
- Activity and decay constant
- Half-life calculations
- Capacitance and dielectric response
- Alternating-current labels
- Ideal transformer ratios
A successful answer therefore does more than reproduce a formula: it identifies the radiation quantity, states the mechanism, shows the unit conversion, checks the physical direction and explains the imaging or dose consequence.
This guide follows that sequence throughout, using newly authored problems grounded in the question types and methods visible in the subject materials.
How the chapters fit together
The opening chapters build the measurement language: activity, intensity, fluence, flux, exposure, kerma, absorbed dose and equivalent dose. Wave and photon relations then connect wavelength, frequency, energy and momentum.
Atomic models, quantum numbers and electron transitions explain why characteristic radiation has discrete energies, while band theory and luminescence show how deposited energy can become an optical detector signal. X-ray tube physics joins electrical input to electron acceleration, spectrum formation and heat. Photon interactions explain attenuation, contrast and scatter.
Radioactivity and electrical physics close the route with decay, capacitance, alternating current and transformation of voltage.
Why the subject feels difficult
The difficulty is rarely one equation. Several quantities share dimensions while describing different stages, and several mechanisms can occur in the same apparatus.
Gray and sievert can carry the same numerical value for X-rays while answering different questions. Kerma and absorbed dose can be close at lower photon energy while separating when secondary electrons escape. Raising tube voltage and raising mAs can both increase output while changing different properties of the spectrum.
The remedy is to draw the pathway before calculating and label every arrow with the mechanism it represents.
How to revise efficiently
Build a two-column formula sheet. Put the equation and units on the left, and the model boundary on the right. Beside inverse square, write point source and unchanged output. Beside exponential attenuation, write uniform material and primary-beam model.
Beside equivalent dose, write radiation weighting. Beside transformer ratios, write ideal power conservation. Then work one fresh numerical example and one verbal contrast for each row. This method prepares simultaneously for multiple-choice discrimination, short explanations and long calculations without assuming an unpublished paper structure.
Worked example · free
Separate geometry from dose interpretation
- 3Apply the squared distance ratio to the rate.
- 2Convert the exposure duration to minutes.
- 3State the quantity and model limitations.
Key terms
- Activity
- The expected rate of nuclear transformations, measured in becquerels or decays per second.
- Particle Fluence
- The number of particles crossing a unit area over a stated interval.
- Particle Flux
- The rate at which particle fluence accumulates per unit time.
- Kerma
- The initial kinetic energy transferred by uncharged radiation to charged particles per unit mass.
- Absorbed Dose
- The energy imparted to matter per unit mass, measured in gray.
- Equivalent Dose
- Absorbed dose adjusted by a radiation weighting factor and expressed in sievert.
- Linear Energy Transfer
- The energy deposited by radiation per unit length of its track.
- Half-Value Layer
- The material thickness that reduces the uncollided primary beam to one half.
- Bremsstrahlung
- Continuous radiation produced when a charged particle is decelerated by an electric field near a nucleus.
- Characteristic Radiation
- Discrete photons emitted when an outer electron fills an inner-shell vacancy.
- Band Gap
- The forbidden energy interval between valence and conduction bands in a solid.
- Luminescence
- Light emission following excitation that is not generated solely by high temperature.
- Half-Life
- The time required for activity or the undecayed population to fall to half its earlier value.
- Selection Rule
- A quantum condition that determines whether a proposed transition is allowed under the model.
HTI5205 FAQ
How is the subject assessed?
The published split is assignments worth twenty per cent, in-class quizzes worth ten per cent and written examinations worth seventy per cent. The syllabus describes four module assignments, quizzes immediately after lectures and two written tests. It does not publish the individual test split in the available material, so use Canvas for current operational details.
What question formats can appear in the written examinations?
The syllabus says the two written tests use different structures such as multiple-choice, short questions and long questions and are designed across the intended learning outcomes. It does not give a section-by-section blueprint, duration or exact question count in the available files. Prepare both rapid discrimination and complete worked reasoning.
Why are activity, kerma and absorbed dose not interchangeable?
They occupy different stages. Activity counts nuclear transformations per second. Kerma describes initial energy transferred from uncharged radiation to charged particles per mass. Absorbed dose describes energy retained in matter per mass. A physical model must connect those stages, so a number in becquerels cannot simply be relabelled gray.
Should I memorise every formula on the formula sheet?
Memorise less and annotate more. For each relation, know its target quantity, units, limiting direction and assumptions. Inverse square needs point-source geometry; attenuation needs a beam and material model; equivalent dose needs a radiation weighting factor. Those conditions tell you when the equation is valid and often earn the explanatory part of an answer.
Are the weekly question banks past examination papers?
No file in the available material is labelled a past examination, sample final or practice final. The Week 1 to Week 3 question and solution banks are valuable because they show recurring calculation types and explicit working, but they should be used as method practice rather than as evidence of the exact written-test paper.
How do kVp and mAs differ?
Peak voltage governs electron energy and therefore the X-ray spectrum endpoint and threshold for characteristic production. The current-time product governs the total electron loading and mainly changes photon quantity and heat. Holding kVp fixed while doubling mAs does not double maximum photon energy; it increases how many electrons strike the target.
How can I distinguish photoelectric absorption from Compton scatter?
Look at the products. Photoelectric absorption removes the incident photon and ejects a bound electron, leaving a vacancy. Compton interaction produces a recoil electron and a lower-energy scattered photon. That scattered photon can reach the detector from the wrong direction and reduce image contrast.
What is the fastest way to catch a numerical mistake?
Check units and limiting direction before trusting the calculator. Greater point-source distance should reduce intensity, positive attenuation thickness should leave transmission between zero and one, additional half-lives should reduce activity, and shorter wavelength should mean higher photon energy. A result that violates one of those directions usually contains a ratio, sign or conversion error.
Questions students ask in each HTI5205 chapter
- When does inverse square apply?
- It applies to an ideal point source radiating uniformly with unchanged output through free space. A broad source, attenuation, shielding or strong scatter can break the simple relationship, so state the geometry before using the squared distance ratio. Chapter 01 · Radiation Quantities and Inverse-Square Reasoning
- Does higher frequency make light travel faster?
- Not in vacuum. The speed remains c, so increasing frequency shortens wavelength. The photon energy rises because E equals h times frequency, but the propagation speed does not rise with energy. Chapter 02 · Electromagnetic Waves and Modern Physics
- Why are photons indirectly ionising?
- A photon is uncharged. It first interacts to release or accelerate a charged particle, and that secondary charged particle produces ionisation along its path. The intermediate transfer is why photon fields lead naturally to kerma. Chapter 03 · Radiation Classification, Fluence and Flux
- When are kerma and absorbed dose close?
- The teaching material states that for lower-energy photons they may be numerically approximately equal under suitable conditions. At higher energy, secondary electrons can transport energy out of the region or radiate it elsewhere, causing separation. Chapter 04 · Kerma, Absorbed Dose and Biological Effect
- What did Rutherford scattering change?
- Most particles passed through while a small fraction scattered through large angles, which was incompatible with diffuse positive charge. The result required most mass and positive charge to occupy a very small nucleus. Chapter 05 · Atomic and Nuclear Structure
- Why check the state before its energy?
- A tuple outside the allowed quantum-number ranges represents no state in the model. Calculating its energy wastes time and can produce a plausible-looking number for an impossible configuration. Chapter 06 · Quantum Numbers and Electron Transitions
- Why do atomic levels become bands?
- Neighbouring atoms perturb one another when a solid forms, splitting formerly discrete states into many closely spaced levels. With many atoms those levels appear as quasi-continuous energy bands. Chapter 07 · Band Structure and Luminescence
- What does kVp mainly change?
- It sets the maximum electron kinetic energy and therefore the maximum possible photon energy and minimum wavelength. It also affects production efficiency and can cross thresholds needed for characteristic radiation. Chapter 08 · X-Ray Tube Physics and Spectra
- Is every attenuated photon absorbed?
- No. Attenuation removes photons from the uncollided primary beam through absorption or scattering away from that beam. Some scattered photons may still reach a detector from a different direction. Chapter 09 · Photon Interactions with Matter
- What remains unchanged in gamma decay?
- Mass number and atomic number remain unchanged because the nucleus moves between energy states of the same nuclide. Energy is released as a photon, so the nuclear state changes without changing element identity. Chapter 10 · Radioactivity and Electrical Physics
How to study for the exam
Start each revision session with one quantity chain rather than one chapter title. For example, follow a photon field through fluence, energy transfer, kerma, charged-particle transport, absorbed dose and biological weighting. On a blank page, define each quantity in words, write its unit and mark the physical event that separates it from the next.
Then solve one numerical problem using fresh values and finish with a sentence about the imaging consequence. On another day, follow the equipment chain from filament heating to electron acceleration, anode interaction, bremsstrahlung, characteristic radiation, heat and detector exposure. Use the question banks to check method order, but do not memorise their numbers.
End with paired contrasts spoken aloud: fluence versus flux, kerma versus absorbed dose, photoelectric versus Compton, kVp versus mAs, fluorescence versus phosphorescence. If you can state the difference, equation boundary and direction without notes, you are ready for both short and long responses.
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