Physics Chapter on Atomic Structure and Radiation

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Questions and Answers

What defines the atomic number of an atom?

The number of protons in the nucleus (correct)

The combined mass of protons and neutrons

The total number of neutrons in the nucleus

The total number of electrons surrounding the nucleus

Which statement best describes isotopes?

Atoms that have the same chemical properties regardless of mass

Atoms with different numbers of protons

Atoms that are chemically unstable

Atoms of the same element with different masses (correct)

What effect does electron binding energy have on the stability of an atom?

Higher binding energy means the atom is less stable

Higher binding energy means more energy is needed to remove an electron (correct)

Binding energy does not affect atom stability

Higher binding energy means electrons are more loosely bound

Which of the following particles accounts for most of an atom's mass?

Neutrons and protons Signup and view all the answers

How does electron arrangement affect an atom?

It influences the atom's chemical properties and stability Signup and view all the answers

What is the maximum number of electrons that can occupy the first shell of an atom?

2 Signup and view all the answers

In relation to medical imaging, what is the primary interaction involved with an atom's electrons?

Photoelectric effect Signup and view all the answers

What is true regarding electron orbits and their binding energy?

Electrons in the first shell have the lowest binding energy Signup and view all the answers

What happens when high-energy electrons collide with inner-shell electrons in the anode?

Inner-shell electrons are knocked out of their orbit. Signup and view all the answers

What is the energy release when higher energy shell electrons drop to fill a vacancy in the inner shell?

The energy is released as X-ray photons. Signup and view all the answers

Which of the following is a characteristic of X-rays produced through characteristic radiation?

They have discrete energies specific to the target material. Signup and view all the answers

Which statement about the inverse square law is correct?

Radiation intensity decreases proportionally to the square of the distance from the source. Signup and view all the answers

What is meant by attenuation in the context of radiation?

The gradual reduction in radiation intensity as it passes through a material. Signup and view all the answers

What defines the photoelectric effect in X-ray interactions?

An X-ray photon completely transfers its energy to an inner-shell electron. Signup and view all the answers

During the process of characteristic radiation, which electrons are primarily involved in creating X-rays?

Inner-shell electrons. Signup and view all the answers

Which property is NOT shared by all types of radiation?

They can be completely stopped. Signup and view all the answers

What happens to the photon during the photoelectric effect?

The photon transfers all its energy to the electron, leading to its ejection. Signup and view all the answers

Which statement correctly describes the process of Compton scattering?

The photon collides with an outer-shell electron and transfers some energy, causing both to scatter. Signup and view all the answers

What is the relationship between the energy of the incident photon and the binding energy of the electron in the photoelectric effect?

The energy of the incident photon must be greater than or equal to the binding energy to eject the electron. Signup and view all the answers

Which factor increases the probability of the photoelectric effect occurring?

Lower energy X-rays and denser materials. Signup and view all the answers

What is true about the energy of the scattered photon in Compton scattering?

The scattered photon has less energy than the incident photon. Signup and view all the answers

What type of radiation can cause ionization in atoms?

Gamma Signup and view all the answers

Which of the following is a method used in radiation therapy?

Iodine-131 Signup and view all the answers

Natural sources of radiation include which of the following?

Terrestrial radiation from radon Signup and view all the answers

What is the primary source of electrons in the X-ray tube?

Cathode Signup and view all the answers

What characterizes non-ionizing radiation?

It does not cause ionisations in atoms Signup and view all the answers

What occurs when high-speed electrons pass near the nucleus in the anode?

Electrons lose kinetic energy Signup and view all the answers

Which radioactive process involves the emission of particles from the nucleus?

Alpha decay Signup and view all the answers

Which isotope is commonly utilized in SPECT imaging?

Technitium-99m Signup and view all the answers

What type of radiation is primarily produced in an X-ray tube?

Bremsstrahlung radiation Signup and view all the answers

How does radioactivity relate to unstable isotopes?

They spontaneously break down, releasing radiation Signup and view all the answers

Which element is most commonly used for the anode target in X-ray tubes?

Tungsten Signup and view all the answers

What form does the energy released from decelerating electrons take?

X-ray photons Signup and view all the answers

What distinguishes ionizing radiation from non-ionizing radiation?

Ionizing radiation can damage biological tissue Signup and view all the answers

What is the effect of increasing the tube voltage (kVp) on the produced X-rays?

Increases the maximum energy of X-rays Signup and view all the answers

How do Bremsstrahlung radiation X-rays vary in energy?

They have a continuous spectrum of energies Signup and view all the answers

Which process occurs as electrons interact with atoms in the anode?

Acceleration of electrons Signup and view all the answers

Study Notes

Course Information

Course name: Introduction to Medical Imaging (HSMI 1211)
Lecture date: October 17, 2024
Day: Thursday
Instructor: Liyana Musa, PhD
Department: Diagnostic Imaging & Radiotherapy
Institution: International Islamic University Malaysia
Lecture topic: Atomic Structure and Medical Imaging

Atomic Structure Overview

Atom: The basic unit of matter, composed of a nucleus surrounded by electrons.
Nucleus: Contains positively charged protons and neutral neutrons, accounting for most of the atom's mass.
Electrons: Negatively charged particles orbiting the nucleus in various energy levels (shells).

Components of an Atom

Nucleus: Contains protons and neutrons.
Electrons: Negatively charged, orbit the nucleus.

Atomic Number and Mass Number

Atomic Number (Z): The number of protons in the nucleus, defining the element.
Mass Number (A): The total number of protons and neutrons in the nucleus.
Isotope: Different types of atoms of the same element, having the same number of protons but different numbers of neutrons.

Importance of Atomic Structure

Subatomic particle arrangement determines an atom's chemical properties, stability, and behavior in interactions with radiation.

Electron Binding Energy

Electron binding energy: The energy required to remove an electron from an atom's orbit, depending on the distance from the nucleus.
Electron shells: Fixed numbers of electrons (2n^2), with electrons closer to the nucleus having higher binding energy.
Inner and outer shells important in medical imaging interaction.

Types of Radiation

Ionizing Radiation:
- Alpha, Beta, Gamma, X-rays, High energy Neutrons
- Cause ionization in atoms it interacts with.
- Has enough energy to remove electrons from atoms or molecules.
- Can cause damage to biological tissues.
Non-ionizing Radiation
- Ultraviolet, Visible light, Infrared, Microwave, Radio waves
- Does not cause ionization in atoms they interact with.
- Less harmful.

Electromagnetic Spectrum

Electromagnetic spectrum: Arrangement of different types of electromagnetic radiation, characterized by wavelength and energy.
The shorter the wavelength the higher the energy (and vice versa).
X-rays and gamma rays are on the higher energy end of the spectrum.

Radioactivity

Definition: The process where unstable atomic nuclei break down, emitting radiation, to achieve a more stable state.
Types: Alpha decay, Beta decay, Gamma decay
Link to medical imaging:
- Radioactive isotopes (e.g., Technetium-99m) used in SPECT.
- Radioactive isotopes (e.g., Iodine-131) used in radiation therapy to treat cancer.

Source of Radiation in Medical Imaging

Natural Sources: Cosmic rays from the sun, terrestrial radiation from naturally occurring elements like radon, and internal radiation from radioactive isotopes in the body.
Artificial Sources:
- Diagnostic Imaging: X-ray machines (radiography, fluoroscopy, CT scans).
- Nuclear Medicine: Gamma-emitting radioisotopes injected or ingested (e.g., Technetium-99m, Fluorine-18).
- Radiation therapy: High-energy X-rays or gamma rays used to kill cancer cells.

How X-rays are Produced

X-ray tube:
- Cathode (electron source): Releases electrons through thermionic emission.
- Anode (target): Electrons accelerate toward the target (often tungsten), producing X-rays.

Primary Processes in the Atoms of the Anode

Bremsstrahlung radiation (braking radiation): High-speed electrons from the cathode, passing near the nucleus of anode atoms, lose kinetic energy and emit X-rays.
Characteristic radiation: Inner-shell electrons in the anode atoms are ejected, causing outer electrons to drop into the vacancy, emitting X-rays with specific energies.

Properties of Radiation

Travel at the speed of light in a straight line in free space (obeying the inverse square law).
Attenuation: Gradual reduction in intensity when passing through matter due to absorption and scattering.
Interaction with tissues (attenuation further):
- Penetration: Fraction of radiation passing through.
- Absorption: Transfer of energy from radiation to the medium.
- Scattering: Change in photon direction with or without energy loss.

Interaction of X-ray with Tissue (Photoelectric Effect)

Definition: Incoming X-ray photon completely transfers energy to an inner-shell electron, ejecting it; the ejected electron is called a photoelectron.
Process: X-ray photon interacts with inner-shell electron.
Energy Release: Energy must be equal to or greater than the electron's binding energy.
Ejected electron leaves a vacancy, filled by an outer electron, releasing characteristic radiation.

Interaction of X-ray with Tissue (Compton Scattering)

Definition: Interaction of an X-ray photon with an outer-shell electron, transferring part of its energy to the electron and causing the photon to scatter in a different direction with reduced energy.
Process: X-ray photon interacts with outer-shell electron.
Energy Release: Photon loses energy, and the electron is ejected (Compton electron).
Considerations: More likely with higher-energy X-rays, less dependent on the atomic number of the material.

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Test your understanding of atomic structure, electron behavior, and radiation concepts in this comprehensive quiz. Explore topics like atomic number, isotopes, electron binding energy, and X-ray interactions. Perfect for students studying physics or preparing for exams.