Environmental Radioactivity and Radioecology
Gaetano Licitra, Giovanni d'Amore, Mauro Magnoni in Physical Agents in the Environment and Workplace, 2018
Radioactive decay takes place when the nuclear structure of an isotope is unstable. The reason for this instability is strictly related to the composition of the nucleus, i.e. the number of protons and neutrons. The stability of a nucleus is the result of the complex balance between the attractive short-range nuclear forces, acting indifferently among the nucleons (protons and neutrons), and the Coulombian repulsion forces due to the electrical charge of the protons. A detailed treatment of this issue is beyond the scope of this book and can be found in any introductory nuclear physics textbook (see for example, Johns and Cunningham, 1983). Let's discuss briefly only the most important outcomes of this instability. When a nucleus is unstable, the radioisotope spontaneously emits a corpuscular radiation in order to gain stability. There are two kinds of corpuscular radiation emitted by the radioactive elements: α radiation and β radiation (Lieser, 1997).
Biomedical Imaging Molecular Imaging
Lawrence S. Chan, William C. Tang in Engineering-Medicine, 2019
Unlike x-ray production for CT and x-ray radiography, where the emission of radiation is induced by an external force (a bombarding electron), the radiation used for SPECT and PET imaging comes from an internal source. Both SPECT and PET rely on radioactivity, which is based on a fundamental property of the substances being used, called nuclear instability. Nuclear instability leads to a process known as radioactive decay, and the type of radioactive decay depends on the type of instability of the isotope in question. There are five types of radioactive decay known as alpha decay, beta-minus (β−) decay, beta-plus (β+) decay or positron emission, electron capture, and isomeric transition. While all are important physical events, discussion in this chapter will be limited to β+ decay, electron capture, and isomeric transition for their uses in medical imaging, and we encourage readers to seek other resources to learn more regarding alpha and β− decay. β+ decay, electron capture, and isomeric transition are most important for medical imaging because for a radioisotope to be useful for medical imaging it must have a suitable half-life and with a decay pattern that results in photon emission with little to no associated particulate (subatomic emitting) radiation. These radioisotopes must also have photon energies which are high enough to penetrate the body and low enough energies for optimal detection by imaging systems (Hendee and Ritenour 2003).
External Beam Radiotherapy and Brachytherapy
Karl H. Pang, Nadir I. Osman, James W.F. Catto, Christopher R. Chapple in Basic Urological Sciences, 2021
The radioactive decay of an atomic nucleus results in:Alpha radiation: emission of alpha particles (two protons, two neutrons).Beta radiation: emission of beta particles.beta− = electronsbeta+ = protonsGamma radiation: emission of electromagnetic energy (photon).
Consequences of a large-scale nuclear accident and guidelines for evacuation: a cost-effectiveness analysis
Published in International Journal of Radiation Biology, 2020
Moshe Yanovskiy, Ori Nissim Levi, Yair Y. Shaki, Yehoshua Socol
Radiation contamination decreases with time due to radioactive decay. In case of NPP accident, many radionuclides are released. The longest-living relevant radionuclide—cesium-137 (Cs-137)—has a half-life of 30 years; thus, its radioactivity decreases rather slowly: 50% of the initial level after 30 years, 25% of the initial level after 60 years and so on. However, many short-living isotopes are also released, so the initial radiation level decreases rather rapidly during the first year. There is also another mechanism of radiation rate decrease—the migration of radionuclides from the contaminated surface due to rain, wind, road traffic etc. The data for Chernobyl and Fukushima is fairly consistent (Balonov 2016; IRSN 2016; Zoriy et al. 2016; WNA 2018b) and shown in Figure 1. As a result, radiation dose absorbed in 10 years is only twice higher than the first-year dose, and the lifetime dose is approximately equal to three first-year doses (UNSCEAR 2013, p. 209). Although this fact is well known, it is not always considered in the radiation-protection context. One year after the accident and onwards the dose-rate R(t) can be approximately described by R(t) = R(0)/(1 + 0.75 × t) where t – time in years. This approximation is illustrated in Figure 1. Table 1 summarizes doses absorbed during different periods of time after the accident relative to the dose absorbed during the first 12 months.
Gastrin-releasing peptide receptor agonists and antagonists for molecular imaging of breast and prostate cancer: from pre-clinical studies to translational perspectives
Published in Expert Review of Molecular Diagnostics, 2022
Joana Gorica, Maria Silvia De Feo, Luca Filippi, Viviana Frantellizzi, Orazio Schillaci, Giuseppe De Vincentis
The main objective of nuclear medicine is to investigate and gauge metabolic and molecular changes during pathological processes in living subjects through the administration of radiolabeled molecules as imaging probes [19]. Once the radiolabeled probe (i.e. radiopharmaceutical) has been administered, photons produced in the process of radioactive decay and interaction with neighboring tissues are detected by employing appropriate technologies. In the case of gamma-emitting radiopharmaceuticals, such as 99mTc or 111In, imaging is performed by employing the gamma-camera, also through single-photon emission tomography (SPECT) or SPECT/CT hybrid devices [20,21]. When positron-emitting radiopharmaceuticals are utilized, such as 18F or 68Ga, positron emission computed tomography (PET/CT), characterized by superior sensitivity and spatial resolution than SPECT or SPECT/CT, is applied. The use of GRPR analogs for the molecular imaging of prostate cancer patients has provided promising preliminary results. Various bombesin analogs have been labeled with different radioisotopes (64Cu, 18F, 68Ga, 66Ga). GRPR antagonists replaced agonists because of their more favorable pharmacokinetics; they block the receptor instead of activating it (as agonists do), resulting in no gastrointestinal side effects and increased binding [22].
Aptamer-based technology for radionuclide targeted imaging and therapy: a promising weapon against cancer
Published in Expert Review of Medical Devices, 2020
Luca Filippi, Oreste Bagni, Clara Nervi
The main purpose of nuclear imaging is represented by the detection and the quantification of metabolic and molecular changes due to different pathological conditions in living subjects. This approach entails the administration of radiolabeled probes and the detection of photons produced in the process of radioactive decay and interaction with neighboring tissues. Different modalities of detection can be applied, depending on the type of radionuclide bound to the probe. In case of a gamma-emitting probe, such as the already cited 99mTc, or indium-111 (111In) and iodine-123 (123I), the appropriate technological approach is represented by gamma-camera also through single-photon emission tomography (SPECT) or hybrid SPECT/CT system [19]. On the contrary, positron emission tomography (PET/CT) approach, which is characterized by superior sensitivity, spatial resolution, and quantification capabilities, is applied when molecular probes are labeled with positron emitting radionuclides, such as fluorine-18 (18 F) and gallium-68 (68 Ga).
Related Knowledge Centers
- Alpha Decay
- Beta Decay
- Gamma Ray
- Radionuclide
- Thorium
- Atomic Nucleus
- Half-Life
- Internal Conversion
- Nuclear Transmutation
- Potassium-40