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Questions and Answers
What is the approximate number of known radionuclides?
What happens to the atomic number of a nucleus when an additional neutron is forced into it?
What type of particles are accelerated in a cyclotron?
What happens to the mass number of a nucleus when a proton is forced into it?
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What is a characteristic of radionuclides produced in a cyclotron?
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What is the reason why radionuclides produced in a cyclotron can only be used reasonably close to the cyclotron?
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What is the reaction that occurs in a nuclear reactor?
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What is the product of the reaction 18O +p?
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What is the result of a positron (β+) decay in a radionuclide?
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What happens when a nucleus undergoes K-electron capture?
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What is emitted when an electron from an outer shell fills the created vacancy in the K-shell?
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What is the energy of the gamma rays emitted by Iodine-131 (131I)?
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What is the difference between gamma rays and X-rays?
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What happens when a positron comes to the end of its range?
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What is the characteristic of the gamma rays emitted by a given radionuclide?
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What is the mode of decay of Iodine-123 (123I)?
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What happens to the atomic number of a radionuclide during β- decay?
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What is the term for the nucleus that remains in an excited state for a variable length of time?
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What is the energy of the gamma ray emitted during the decay of 99mTc to 99Tc?
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What is the half-life of 99Tc?
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What is the process by which a radionuclide with a neutron deficit loses energy and becomes stable?
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What is the term for nuclei having different energy states and half-lives, but otherwise indistinguishable as regards mass number, atomic number, and other properties?
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What is the daughter nuclide produced during the decay of 99mTc?
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What is the term for the emission of a positive electron from the nucleus with high energy?
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What is the energy equivalent to the mass of an electron according to Einstein's formula?
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What is the result of the annihilation of a positive and negative electron?
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Why is it impossible to predict which unstable nucleus in a sample will disintegrate next?
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What is the quantity of radioactivity measured by?
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What is the unit of measurement for the activity of a radioactive sample?
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What is the rate of disintegration of a radioactive sample?
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What is the purpose of positron emitters in medical imaging?
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What is the characteristic of radioactive decay that makes it possible to predict the fraction of nuclei that will disintegrate?
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What is the unit of measurement used for most radionuclide administrations in medical gamma imaging?
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What is the relationship between the count rate and the activity of a radioactive sample?
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What is the fundamental law of radioactive decay?
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What is the unit of measurement used for radionuclide generators?
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What happens to the activity of a radioactive sample over time?
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What is the relationship between the count rate and the number of radioactive atoms in a sample?
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What is the conversion rate from curie to megabecquerels?
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What happens to the gamma rays when they enter a detector?
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Study Notes
Production of Radionuclides
- Over 2700 known radionuclides exist.
- Medical imaging radionuclides are artificially produced using nuclear reactors or cyclotrons.
Methods of Production
- Neutron Addition: In nuclear reactors, stable nuclei capture additional neutrons, resulting in neutron excess (e.g., 98Mo + n → 99Mo).
- Proton Addition: Cyclotrons accelerate protons that force an additional proton into a stable nucleus, creating a neutron deficit (e.g., 18O + p → 18F + n).
Characteristics of Radionuclides
- Radionuclides produced in cyclotrons typically have short half-lives, ranging from less than a minute to a few hours, limiting their use to proximity to the cyclotron.
- Radionuclides with a neutron deficit can undergo positron decay or K-electron capture, converting into more stable forms (e.g., Fluorine-18 (18F) transforms into Oxygen-18 (18O)).
Decay Processes
- Positron Emission: Positive beta particles (positrons) annihilate upon encountering negative electrons, neutralizing without changing mass number but increasing atomic number.
- K-Electron Capture: Nuclei capture an electron which may increase neutron count relative to protons, emitting X-rays when an outer-shell electron fills the vacancy.
Gamma Rays
- Emission involves gamma rays that possess specific energies unique to each radionuclide (e.g., Iodine-131 emits 364 keV gamma rays).
- Gamma rays share properties with X-rays.
Isomeric Transitions
- Some radionuclides, such as 99Mo, emit beta particles and may remain in an excited state before emitting gamma rays (99mTc).
- 99mTc decays to stable 99Tc, emitting a gamma ray at 140 keV.
Radioactive Decay
- Radioactive decay is a random process, making it impossible to predict individual nucleus disintegration while allowing for statistical predictions about sample fractions.
- Activity measures the disintegration rate of radioactive samples, not the number of remaining atoms.
Measurement of Activity
- Activity is measured in Becquerels (Bq), with 1 Bq equivalent to 1 disintegration per second.
- Common units in medical contexts include megabecquerels (MBq) and gigabecquerels (GBq).
- Counts measured by detectors may not reflect true activity due to detection inefficiencies, but there is a proportionality between count rate and activity.
Exponential Decay Law
- The activity of radioactive samples decreases by equal fractions over equal time intervals, known as the exponential law; activity never fully reaches zero.
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Description
Learn about the production of radionuclides, including the ways they are artificially produced for medical imaging. Discover how neutron excess occurs in a nuclear reactor.
