Lecture 8 spectrum and radioactivity

• Electron Energy is the energy that will be converted into x-ray and heat is carried to the x-ray tube by a current of flowing electrons.
• The energy carried by each electron is determined by the voltage or KV, between the anode and cathode.
• For each kV of voltage, each electron has 1 keV of energy.
• The x-ray machine operator assigns a specific amount of energy to each electron by adjusting the KV.
• The electron volt (eV) is a unit of energy equal to approximately 1.602 × 10−19 joule.
• The Joule is a huge unit of energy when dealing with radiation energies.
• The SI unit for activity is one decay per second and is given the name becquerel (Bq), so: 1 Bq = 1 decay/s.
• One of the most common units for activity is the curie (Ci).
• 1 Ci = 3.70 × 10^18 Bq.
• Activity is often expressed in other units, such as decays per minute or decays per year.
• Electron volt is a unit of energy commonly used in radiology, equal to the energy gained by an electron when the electrical potential at the electron increases by one volt.
• After the electrons are emitted from the cathode, they come under the influence of an electrical force pulling them toward the anode.
• This force accelerates them, causing an increase in velocity and kinetic energy.
• The increase in kinetic energy continues as the electrons travel from the cathode to the anode.
• Just as the electron arrives at the surface of the anode its potential energy is lost, and all its energy is kinetic.
• A 100-keV electron reaches the anode surface traveling at more than one half the velocity of light.
• When the electrons strike the surface of the anode, they are slowed very quickly and lose their kinetic energy; the kinetic energy is converted into either x-ray or heat.
• The electrons interact with individual atoms of the anode material.
• The strength (energy emission) of a radioactive source is called its activity, which is defined as the rate at which the isotope decays.
• PET Scan and Gamma Cameras are used in nuclear medicine.
• Alpha decay is used in radiotherapy, such as inserting tiny amounts of radium - 226 into cancerous masses.
• Isotopes are different forms of an element that have the same number of protons but different numbers of neutrons.
• A stable atom has a net charge of 0, meaning it has an equal number of protons and neutrons.
• Two types of interactions produce radiation: an interaction with electron shells produces characteristic x-ray photons; interactions with the atomic nucleus produce Bremsstrahlung x-ray photons.
• Many elements, such as carbon, potassium, and uranium, have multiple naturally occurring isotopes.
• Neutrons are important for stabilising the nucleus.
• The number of neutrons increases as the atomic number increases.
• Some isotopes are stable, but others can emit, or kick out, subatomic particles to be more stable.
• Nuclei which lie above the line of stability contain too many neutrons to be stable and are referred to as “neutron rich”.
• Nuclei which lie below the line of stability contain too many protons to be stable and are called “proton rich”.
• The stability of an isotope can be determined by calculating the ratio of neutrons to protons present in a nucleus (N/Z).
• Radioactivity is the process by which atoms that are unstable decay and eventually become stable through the emission of particles or electromagnetic radiation or both.
• Gamma ray is used in radiotherapy, such as gamma knife surgery.
• The unstable nuclei lie above and below the line of stability.
• Cobalt - 60 decays by beta - minus emission, with the decay products being Nickel - 60 plus an electron and an electron antineutrino.
• Too many neutrons or protons upset this balance disrupting the binding energy from the strong nuclear forces making the nucleus unstable.
• Beta decay is used in Positron Emission Tomography (PET) and radiotherapy, by killing nearby cancer cells.
• Radioactivity may be thought of as the volume of radiation produced in a given amount of time.
• The interaction that produces the most photons is the Bremsstrahlung process.
• Electrons that penetrate the anode material and pass close to a nucleus are deflected and slowed down by the attractive force from the nucleus.