Physics: Electromagnetic Waves and X-Rays
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Questions and Answers

What is the speed at which x-rays travel?

  • 1x10^6 m/s
  • 3x10^5 m/s
  • 3x10^8 m/s (correct)
  • 2x10^7 m/s

    • What is the characteristic of electromagnetic waves that allows them to transmit energy?

  • Electric or magnetic field is changing periodically at a particular point in space (correct)
  • Changing magnetic field
  • Constant rate of change of electric field
  • Changing electric field

    • How does the frequency of electromagnetic waves relate to their energy?

  • High frequency corresponds to high energy (correct)
  • High frequency corresponds to low energy
  • Low frequency corresponds to high energy
  • Frequency is unrelated to energy

    • What is the amplitude of a wave?

    <p>The maximum excursion of a particle of the medium from its undisturbed position</p> Signup and view all the answers

    What is the relationship between the period and frequency of a wave?

    <p>Frequency is inversely proportional to period</p> Signup and view all the answers

    How do electromagnetic waves differ from one another?

    <p>In wavelength, frequency, and energy</p> Signup and view all the answers

    What is the primary difference in mass between electrons and protons/neutrons?

    <p>Electrons are 1/1840 the mass of protons and neutrons</p> Signup and view all the answers

    What is the main problem with Rutherford's model of the atom?

    <p>Electrons lose energy and spiral into the nucleus</p> Signup and view all the answers

    What did Rutherford's experiments show about the structure of the atom?

    <p>The nucleus is highly concentrated and positively charged</p> Signup and view all the answers

    What is the main component of the atom that is positively charged?

    <p>Nucleus</p> Signup and view all the answers

    What is the primary problem with the idea of electrons orbiting the nucleus?

    <p>Electrons would lose energy and spiral into the nucleus</p> Signup and view all the answers

    Who developed new rules to explain the behavior of electrons after Rutherford's model?

    <p>Neils Bohr</p> Signup and view all the answers

    What is the primary component of an x-ray tube that generates heat when a current is passed through it?

    <p>Filament</p> Signup and view all the answers

    What is the purpose of filtration in an x-ray beam?

    <p>To filter out some of the x-rays</p> Signup and view all the answers

    What is the main factor that affects the quality of an x-ray image?

    <p>the kilovoltage peak</p> Signup and view all the answers

    What is the goal of maximizing the signal to noise ratio in an x-ray image?

    <p>To minimize the background noise</p> Signup and view all the answers

    What is the term for the scattered radiation that does not contribute to the x-ray image?

    <p>Scattered radiation</p> Signup and view all the answers

    What is the purpose of the collimator in an x-ray imaging system?

    <p>To change the size of the x-ray beam</p> Signup and view all the answers

    What is the term for the ability of an x-ray detector to capture as many x-rays as possible?

    <p>Quantum detection efficiency</p> Signup and view all the answers

    What is the purpose of the display system in an x-ray imaging system?

    <p>To display the x-ray image</p> Signup and view all the answers

    What is the effect of increasing the distance between the object and the receptor on unsharpness?

    <p>It increases unsharpness</p> Signup and view all the answers

    What is the purpose of keeping the receptor close to the patient?

    <p>To reduce magnification</p> Signup and view all the answers

    What is the term for the degree of penumbra around the image?

    <p>Unsharpness</p> Signup and view all the answers

    What is the purpose of using filters and collimators in x-ray production?

    <p>To improve image quality</p> Signup and view all the answers

    What is the term for the ability to distinguish two close objects or specific anatomy in an image?

    <p>Resolution</p> Signup and view all the answers

    What is the effect of increasing energy on contrast in an image?

    <p>It decreases contrast</p> Signup and view all the answers

    What is the purpose of radiation measurement in medical imaging?

    <p>To determine patient dose</p> Signup and view all the answers

    What is the term for the difference between signal and background noise in an image?

    <p>Contrast</p> Signup and view all the answers

    What is the purpose of using a detector in medical imaging?

    <p>To detect x-rays</p> Signup and view all the answers

    What is the term for the removal of electrons from an atom

    <p>Ionisation</p> Signup and view all the answers

    What is the main difference between ionisation and excitation of atoms?

    <p>Ionisation is when an electron is removed from the atom, while excitation is when an electron moves to a higher energy level</p> Signup and view all the answers

    What determines the electron binding energy in an atom?

    <p>The number of protons in the nucleus</p> Signup and view all the answers

    What is the process by which an unstable nucleus becomes stable?

    <p>Radioactive decay</p> Signup and view all the answers

    What is the term for the unique energy changes that occur when electrons transition between shells in an atom?

    <p>Characteristic x-rays</p> Signup and view all the answers

    What is the term for a nucleus that is unstable and spontaneously decays?

    <p>Radioactive</p> Signup and view all the answers

    What is the purpose of gamma spectroscopy?

    <p>To identify the gamma energies emitted by a nucleus</p> Signup and view all the answers

    What is the unit of measurement for the activity of a radioactive sample?

    <p>Becquerel (Bq)</p> Signup and view all the answers

    What is the term for the time it takes for half of the nuclei in a sample to undergo radioactive decay?

    <p>Half-life</p> Signup and view all the answers

    What type of radiation is emitted when an electron moves from a higher energy level to a lower energy level?

    <p>Characteristic x-rays</p> Signup and view all the answers

    What is the difference between alpha and beta decay?

    <p>Alpha decay involves the emission of a helium nucleus, while beta decay involves the emission of an electron</p> Signup and view all the answers

    What type of radiation is produced when electrons interact with the positive electric field of the nuclei in the target atoms?

    <p>Bremsstrahlung x-rays</p> Signup and view all the answers

    What happens to the energy of electrons when they interact with the positive electric field of the nuclei in the target atoms?

    <p>It is absorbed by the nucleus and emitted as electromagnetic radiation</p> Signup and view all the answers

    What is the main reason for the attenuation of an x-ray beam as it passes through a patient's anatomy?

    <p>Absorption and scattering of x-rays by atoms in the patient</p> Signup and view all the answers

    What determines whether an x-ray interacts with an atom in the patient's anatomy?

    <p>The energy of the x-ray</p> Signup and view all the answers

    What type of x-rays are produced when electrons transition to a lower energy state in the target metal?

    <p>Characteristic x-rays</p> Signup and view all the answers

    What happens to the x-ray beam as it passes through the patient's anatomy?

    <p>It is differently attenuated due to absorption and scattering</p> Signup and view all the answers

    What is the main purpose of the linear attenuation coefficient?

    <p>To quantify the fraction of x-rays removed per unit thickness of a material</p> Signup and view all the answers

    What is the significance of the mass attenuation coefficient?

    <p>It accounts for the number of atoms per unit volume of a material</p> Signup and view all the answers

    What is the primary difference between Compton scattering and the photoelectric effect?

    <p>The type of orbital electron involved in the interaction</p> Signup and view all the answers

    What is the threshold energy required for pair production to occur?

    <p>1.02 MeV</p> Signup and view all the answers

    What is the primary mechanism of energy loss for electrons in matter?

    <p>Ionization and excitation of orbital electrons</p> Signup and view all the answers

    What is the purpose of a dosimeter in radiation detection?

    <p>To measure the dose of radiation exposure</p> Signup and view all the answers

    What is the primary function of an ionization chamber?

    <p>To quantify the dose of radiation exposure</p> Signup and view all the answers

    What is the importance of recording radiation dose and exposure?

    <p>To minimize radiation exposure to patients and staff</p> Signup and view all the answers

    What is the primary interaction of electrons with the nucleus in matter?

    <p>Electrostatic attraction</p> Signup and view all the answers

    What is the term for the process of ejection of an orbital electron from an atom?

    <p>Atomic ionization</p> Signup and view all the answers

    What is the primary mechanism of heat transfer in conduction?

    <p>Transfer of energy at atomic level through collisions</p> Signup and view all the answers

    What is the name of the process in which heat is transferred by the bulk movement of a fluid?

    <p>Convection</p> Signup and view all the answers

    What type of wave is created by a vibrating object that compresses and decompresses the atoms/molecules in a material?

    <p>Longitudinal pressure wave</p> Signup and view all the answers

    What is the primary application of ultrasound in medicine?

    <p>Reconstructing images of internal tissues</p> Signup and view all the answers

    What is the purpose of the strong magnetic field in an MRI machine?

    <p>To image the protons in the patient</p> Signup and view all the answers

    What is the unit of activity of a radioactive sample?

    <p>Becquerel (Bq)</p> Signup and view all the answers

    What is the unit of measurement for electric current?

    <p>Ampere (A)</p> Signup and view all the answers

    What is the primary cause of statistical uncertainty in radioactivity measurements?

    <p>Random nature of radioactive decay</p> Signup and view all the answers

    What is the primary difference between a conductor and an insulator?

    <p>Conductors have loosely bound electrons</p> Signup and view all the answers

    What is the purpose of counting statistics in radioactivity measurements?

    <p>To calculate the average count rate and uncertainty</p> Signup and view all the answers

    What is the process by which electrons are emitted by a metal that is heated to a certain temperature?

    <p>Thermionic emission</p> Signup and view all the answers

    What is the formula for electrical power?

    <p>P = I × V</p> Signup and view all the answers

    What type of electric current flows in one direction only?

    <p>Direct current (DC)</p> Signup and view all the answers

    What is the unit of energy commonly used in radiation physics and medical imaging?

    <p>Electron volt (eV)</p> Signup and view all the answers

    What is the concept that describes the ability to move a stationary body or change the speed of a moving body?

    <p>Force</p> Signup and view all the answers

    What is the characteristic of electromagnetic waves that allows them to transmit energy through space?

    <p>Their ability to travel at the speed of light</p> Signup and view all the answers

    What is the relationship between energy and work?

    <p>Energy is the ability to do work, and work is the transfer of energy</p> Signup and view all the answers

    What is the concept that describes the rate at which energy is used?

    <p>Power</p> Signup and view all the answers

    What is the primary difference between kinetic energy and potential energy?

    <p>Kinetic energy is energy due to motion, while potential energy is stored energy</p> Signup and view all the answers

    What is the process by which electrical potential energy is transferred to electrons in an x-ray tube?

    <p>Electron acceleration</p> Signup and view all the answers

    What is the unit of measurement for the mass attenuation coefficient?

    <p>cm^2/g</p> Signup and view all the answers

    Which interaction process has a higher probability of occurrence at higher x-ray photon energies?

    <p>Pair production</p> Signup and view all the answers

    What is the result of an electron interacting with an orbital electron in an absorber atom?

    <p>Atomic ionisation</p> Signup and view all the answers

    What is the purpose of a collimator in an x-ray imaging system?

    <p>To shape the x-ray beam to match the detector size</p> Signup and view all the answers

    What is the term for the degree of penumbra around an image?

    <p>Unsharpness</p> Signup and view all the answers

    What is the primary factor that affects the quality of an x-ray image?

    <p>X-ray energy</p> Signup and view all the answers

    What is the purpose of filtration in an x-ray beam?

    <p>To remove low-energy x-rays</p> Signup and view all the answers

    What is the result of an electron interacting with the nucleus of an atom?

    <p>Bremsstrahlung</p> Signup and view all the answers

    What is the term for the ability of an x-ray detector to capture as many x-rays as possible?

    <p>Sensitivity</p> Signup and view all the answers

    What is the primary difference between the linear attenuation coefficient and the mass attenuation coefficient?

    <p>The units of measurement</p> Signup and view all the answers

    Study Notes

    Electricity and Magnetism

    • Electricity: the set of physical phenomena associated with the presence and flow of electric charge
    • Electric charge: a fundamental property of matter, can be positive or negative
    • Electric current: the flow of electric charge, measured in amperes (A)
    • Electric potential (voltage): the potential difference between two points, measured in volts (V)
    • Electric power: the rate at which electric energy is transferred, measured in watts (W)
    • Electric resistance: the opposition to the flow of electric current, measured in ohms (Ω)

    X-Rays

    • X-rays: high-energy electromagnetic waves with frequencies higher than visible light
    • Produced by accelerating electrons in a vacuum, e.g., in an x-ray tube
    • Characterized by high energy and short wavelength
    • Used in medical imaging, e.g., radiography and computed tomography (CT)
    • Can be filtered to reduce soft tissue absorption and improve image quality

    Atomic Structure

    • Atom: the smallest unit of a chemical element, consisting of protons, neutrons, and electrons
    • Protons and neutrons form the nucleus, while electrons orbit around it
    • Electrons occupy specific energy levels (shells) around the nucleus
    • Electron transitions between energy levels result in emission or absorption of electromagnetic radiation

    Ionisation and Excitation

    • Ionisation: the removal of an electron from an atom, resulting in an ion
    • Excitation: the transition of an electron to a higher energy level, followed by emission of a photon as it returns to its ground state
    • Characteristic x-rays: emitted when an electron transitions between energy levels, unique to each element
    • Ionisation energy (binding energy): the energy required to remove an electron from an atom

    Radioactive Decay

    • Radioactive decay: the spontaneous emission of ionising radiation from unstable atomic nuclei
    • Half-life: the time taken for half of the nuclei in a sample to undergo decay
    • Types of radioactive decay: alpha, beta, and gamma decay
    • Radioactive decay is a random process, leading to statistical uncertainty in measurements

    Imaging and Radiation Therapy

    • Medical imaging: the use of electromagnetic radiation to produce images of the body
    • Radiation therapy: the use of high-energy radiation to treat cancer and other diseases
    • Diagnostic imaging aims to produce an image of optimum quality for diagnosis and management
    • Factors influencing image quality and patient dose include x-ray beam characteristics, patient factors, and detector performance### Magnetism
    • A magnet has a north and south pole at opposite ends, and the Earth's core is made of molten iron ore, creating a magnetic field around the Earth.
    • Any magnetized object will orient itself along the magnetic field lines.

    Electricity and Electric Charge

    • Electric current is the flow of electrons around a circuit, and free electrons in a conducting metal wire enable this flow.
    • Applying a potential difference across a circuit causes electrons to flow from the negative electrode to the positive electrode.
    • The unit of electric current is the ampere (A), defined as a flow of 1 coulomb (C) of charge per second.

    Conductors and Insulators

    • Electrical conductors have loosely bound electrons in their outer shell, such as copper or silver.
    • Electrical insulators have electrons strongly bound to the atom, such as oil, plastics, or rubber.

    Electrical Power

    • Electrical power (P) is determined by the current (I) and voltage (V) on an electrical circuit, and is measured in kW.
    • Direct current (DC) flows in one direction, while alternating current (AC) flows in both directions.

    Electromagnetic Radiation

    • X-rays are electromagnetic waves that combine electric and magnetic fields at 90 degrees to each other.
    • X-rays travel at the speed of light and have no mass.
    • X-ray production involves accelerating a beam of electrons and directing them at a thin metal target, resulting in electromagnetic radiation.

    Attenuation of X-rays

    • X-ray beams are attenuated (absorbed) when directed at a patient's anatomy, resulting in a reduced beam intensity.
    • Attenuation occurs due to absorption and scattering, and is influenced by the x-ray energy and material properties.

    Linear Attenuation Coefficient (μ)

    • μ measures a material's ability to attenuate an x-ray beam per unit of thickness.
    • The mass attenuation coefficient (μ/ρ) takes into account the material's density.

    X-ray Interactions

    • The photoelectric effect involves the absorption of an x-ray photon by an inner electron, ejecting the electron from the atom.
    • Compton scattering involves the scattering of an x-ray photon by an outer electron, transferring energy to the electron.
    • Pair production involves the absorption of an x-ray photon by an atom, converting the energy into an electron-positron pair.

    Mass Attenuation Coefficient

    • μ/ρ accounts for the material's density, and has units of cm²/g.

    Attenuation Processes

    • The sum of the mass attenuation coefficients for the photoelectric effect, Compton scattering, and pair production determines the total attenuation coefficient.

    Electron Interactions

    • Electrons interact with matter through collisions with nuclei and orbital electrons, resulting in energy losses and scattering.

    Diagnostic Imaging

    • X-rays are produced in a linear accelerator and detected using various methods, including ionization chambers, dose area product meters, and semiconductor detectors.

    Radiation Dose and Exposure

    • Radiation dose and exposure must be accurately measured and recorded to minimize risks to patients and the general population.
    • Dosimetry detectors measure the radiation dose, and various methods are used to detect and measure radiation exposure.

    Electromagnetic Waves

    • Travel at the speed of light (3x10^8 m/s or 1080 million km/h)
    • Have 0 mass
    • Can transmit energy through space
    • Electric or magnetic field changes periodically at a particular point in space
    • Electricity in the waves changes direction
    • Used for transmitting information (radio-waves)

    X-Rays

    • Produced when high-energy electrons collide with a metal target
    • Short wavelength, high frequency, and high energy
    • Originate from within atoms
    • Produced in a vacuum, but must pass through a filter to get out of the vacuum

    Diagnostic Imaging

    • Aims: produce an image of optimum quality for diagnosis and management/treatment of the patient
    • Factors influencing image quality and patient dose: x-ray beam characteristics, patient, detector and imaging system, and practitioner's skills and perception

    X-Ray Detectors

    • Ideally, all x-rays should be absorbed into the detector
    • 40-60% of x-rays are not detected (DQE)
    • Two main types of detector systems: CR and DR (computed radiography and digital radiography)
    • Detective quantum efficiency: a measure used to compare different imaging system performance

    Ionisation

    • Removal of electrons from an atom, leaving a positively charged ion
    • Different levels of energy cause ionisation in different materials

    Radiation Dose

    • Can have a biological effect on the patient due to high energy absorbed
    • Disrupts the cell and changes chemistry
    • Recording image parameters (kV, mA, exposure time, field size, FOD and FRD)

    Human Perception

    • Experience and skill of practitioner affect the ability to see abnormalities and pathology in the image

    Atomic Structure

    • Consists of a nucleus (protons and neutrons) and an electron cloud (electrons)
    • Electrons exist in discrete orbitals/shells and energy levels
    • The Rutherford model: negatively charged electrons surround the nucleus of an atom
    • The Bohr model: same concepts as the Rutherford model, but with new rules for orbiting electrons

    Electron Transitions

    • If an electron is forcibly removed from an inner shell, an electron from a more distal shell will transition inwards
    • Electromagnetic wave will be emitted (photon)
    • Wavelength of EM wave depends on the difference between energy levels

    Electron Binding Energy (Ionisation Energy)

    • The amount of energy required to completely remove an electron from an atom
    • The process of removing an electron is called ionisation
    • Transitions of electrons between shells will be unique energy changes, characteristic to a particular atom

    Forces Acting in the Atomic Nucleus

    • Electrostatic repulsive force
    • Strong nuclear force holds the nucleus together

    Radioactivity and Radioactive Decay

    • Unstable nuclei spontaneously rearrange to become stable
    • Radioactive decay: nuclides that are unstable will spontaneously rearrange their nuclei to attempt to become stable
    • Types of radioactive decay: alpha, beta, and gamma decay
    • Half-life: time taken for half of the nuclei in a sample to undergo decay

    Counting Statistics for Radioactivity Measurements

    • Make measurement for one minute
    • Measurement will be a number of counts/minute
    • Convert to counts/s (Bq)
    • Repeat three times
    • Calculate average and standard deviation

    Force, Work, Energy, and Power

    • Force: ability to move a stationary body or change the speed of a moving body
    • Work: required to be done to move an object
    • Energy: measure of the ability to do work
    • Power: rate at which energy is used### Magnetism
    • A permanent magnet has a north magnetic pole and a south magnetic pole at opposite ends.
    • The Earth's core contains molten iron ore, generating a magnetic field around the Earth.
    • Any magnetized object will align itself with the magnetic field lines.

    Magnetism in Imaging and Radiotherapy

    • MRI uses fields and waves to image the patient.
    • Strong magnetic fields are required, necessitating the use of superconducting magnets.
    • MRI essentially images the protons in the patient using non-ionizing radiation.

    Electricity and Electric Charge

    • Electric current is the flow of electrons around a circuit.
    • Free electrons in conducting metal wires facilitate this flow.
    • Applying a potential difference across a circuit causes electrons to flow from the negative electrode to the positive electrode.
    • Units: 1 Ampere (A) = flow of 1 Coulomb (C) of charge per second.

    Conductors and Insulators

    • Electrical conductors have loosely bound electrons in their outer shell, allowing easy electron flow (e.g., copper or silver).
    • Electrical insulators have strongly bound electrons, preventing electron flow (e.g., oil, plastics, or rubber).

    Electrical Power

    • Determined by the current and voltage in an electrical circuit.
    • P = IV (power = current x voltage), measured in kW.
    • Direct current (DC) flows in one direction, while alternating current (AC) flows in both directions.

    Electromagnetic Radiation

    • X-rays are a type of electromagnetic wave.
    • Combining electric and magnetic fields at a 90-degree angle generates electromagnetic radiation.
    • Electromagnetic radiation travels at the speed of light and has no mass.

    X-ray Production and Interactions

    • Accelerating electrons and directing them at a thin metal target produces x-rays.
    • X-rays interact with the positive electric field of the nucleus in target atoms.
    • Energy is absorbed by the nucleus and emitted as electromagnetic radiation (Bremsstrahlung x-rays).

    Attenuation of X-rays

    • X-rays interacting with the patient's anatomy are absorbed, transmitted, or scattered.
    • Attenuation occurs due to absorption and scattering.
    • The probability of interaction depends on x-ray energy and the material through which it travels.

    Linear Attenuation Coefficient (μ)

    • Measures a material's ability to attenuate an x-ray beam per unit of thickness.
    • μ is the fraction of x-rays removed from the beam per unit thickness of the irradiated material.

    Mass Attenuation Coefficient

    • Accounts for the density of the material: μ/ρ (density).
    • Units: cm^2/g.

    Compton Scattering, Photoelectric Effect, and Pair Production

    • Compton scattering: x-ray photons interact with outer electrons, transferring energy and causing scattering.
    • Photoelectric effect: x-ray photons collide with inner electrons, resulting in complete absorption and ejection of the electron.
    • Pair production: high-energy x-rays are absorbed by the nucleus, producing an electron-positron pair.

    Importance of Bremsstrahlung in Diagnostic Imaging

    • X-rays produced in a linear accelerator using an accelerating waveguide.

    Electrons and Dose

    • Electrons cause energy deposition in a material.
    • X-rays interact through the photoelectric effect, Compton scattering, or pair production.
    • Electrons then travel a short distance, losing energy through multiple collisions, resulting in absorbed dose.

    Factors Affecting Radiation Dose and Measurement

    • Diagnostic imaging contributes to radiation exposure in the general population.
    • Decision to order a procedure using ionizing radiation requires a risk-benefit analysis.
    • Dose and exposure must be recorded accurately.

    Detection and Measurement of Radiation

    • Dosimetry detectors measure the response to ionization in the active detector material.
    • Methods include ionization chambers, dose area product meters, automatic exposure devices, geiger-muller tubes, radiographic and radiochromic film, and thermoluminescent dosimeters.

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    Quiz about electromagnetic waves, including x-rays, their properties, and uses. Covers speed, energy transmission, and application in radio communication.

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