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Radionuclide Production
Published in Michael Ljungberg, Handbook of Nuclear Medicine and Molecular Imaging for Physicists, 2022
With the ‘Big Bang’, the cosmic explosion about 14 billion years ago, the process to create all matter started. Particles like protons and neutrons, which form the building blocks of nuclei, appeared as free particles during the first seconds. Various types of nuclear reactions formed different combinations of protons and neutrons to create light elements as 4He, 3He, and 7Li and later, in the stars, heavier elements. All matter around us was created in nuclear reactions as a mixture of stable and unstable (radioactive) combinations of protons and neutrons. Over time, the unstable combinations have undergone transformation (radioactive decay) to form stable combinations but some with exceptionally long half-lives (natural radioactivity) remain, potassium-40, lead-204, thorium-232 and the natural occurring isotopes of uranium. Some of these and their radioactive daughters were early applied in biology and medicine.
Radiation injuries
Published in Jan de Boer, Marcel Dubouloz, Handbook of Disaster Medicine, 2020
Yves Jouchoux, Christophe Boyer
Natural background radioactivity. The natural exposure of human beings to radioactivity is equivalent to 2mSv per year. The main source is radon 222 (a natural gas absorbed by inhalation). The irradiation increases in those areas that are rich in granite rocks. Other external sources from natural elements are uranium 238 and thorium 232. Internal sources include potassium 40. Natural external irradiation originates also from cosmic radiation from outside the Earth: this irradiation is greater at higher altitudes than at sea level (for example, in air travel, the irradiation dose is about 100 times greater).
Special Problems of Internal Radioactive Materials
Published in George W. Casarett, Radiation Histopathology, 2019
Thorium-232 is an alpha emitter with a physical half-life of 1.39 × 1010 years. After its introduction in 1928, thorotrast, a 20% colloidal suspension of thorium dioxide, became widely used as a contrast medium in diagnostic radiology. Amounts of 3 to 15 grams were administered intravenously. The colloidal particles are rapidly phagocytosed and concentrated in cells of the reticuloendothelial system. Looney76 found that the excretion of thorium dioxide is minimal. He estimated the biological half-life to be about 190 years. The colloid tends to remain fixed in the tissues, although there is some migration which is probably accomplished within the macrophages which are migrating.
Radiological risk assessment of the Hunters Point Naval Shipyard (HPNS)
Published in Critical Reviews in Toxicology, 2022
Dennis J. Paustenbach, Robert D. Gibbons
A traditional risk assessment approach was adopted to estimate cancer risks for various populations potentially exposed, both on- and off-site, to eight radionuclides of concern (ROCs) (americium-241 [Am-241], cobalt-60 [Co-60], cesium-137 [Cs-137], plutonium-239 [Pu-239], radium-226 [Ra-226], strontium-90 (Sr-90), thorium-232 [Th-232], and uranium-235 [U-235]) that were potentially present at the site due to site-related operations. These eight radionuclides were selected for this risk assessment based on the Navy’s 2006 Action Memo, recent Navy work plans (USN 2006, 2018), and professional judgment.
Lung damage by thoron progenies versus possible damage redemption by lung stem cells: a perspective
Published in International Journal of Radiation Biology, 2020
Debajit Chaudhury, Utsav Sen, Nagesh N. Bhat, Bijay Kumar Sahoo, Sudheer Shenoy P, Bipasha Bose
Thoron (220Rn) it is a radon isotope that belongs to the thorium (232Th) decay series (Figure 1). Inhalation of radon, thoron along with their progenies are the primary source of both occupational (thorium and uranium mining facility) and environmental exposure contributing a significant fraction of global effective dose (NCRP 1988, 1989). Thorium decay to form thoron (T1/2 = 55.6 s) terminating to a stable isotope lead (208Pb; Figure 1; Porstendörfer 1994; Mishra and Mayya 2008; Ramachandran 2010). The rate of thoron exhalation from the earth’s crust is generally higher than that of radon in terms of activity released per unit surface area per unit time. Once they reach the air, their progenies may attach to aerosol to either form attached fraction or unattached fraction depending on the aerosol size distribution (Bale 1980). Due to short half-life of thoron, its concentration rapidly decreases with distance from source and measurements are prone to high uncertainties (Porstendorfer and Mercer 1979; Steinhausler 1996; Meisenberg and Tschiersch 2011). Also due to its short half-life, the attachment of its progeny occurs only in limited space near the point of exhalation (source point) leading to very low and wide variation of equilibrium factor between thoron and its progeny in comparison to equilibrium factor between radon and its progeny. This is why the thoron and its progenies have been neglected in past while estimating dose rate from inhalation exposure (except at extreme levels). α-particles are the predominant forms of radiation followed by emissions of β and γ radiation as a result of the successive decay of thoron and its progenies (Figure 1; Fano 1963; Tavernier 2009). The α-particles owing to its high mass exhibit high Linear Energy Transfer (LET) with corresponding high relative biological effectiveness (RBE), which manifests itself by characteristics Bragg’s Peak (Okayasu 2012; Ghorai et al. 2016). The β and γ rays with minimal RBE compared to α are generally emitted by the other r progenies of Thoron namely 212Pb and 212 Bi. All these emissions interact with matter in the variety of established phenomenon such as photoelectric absorption, Compton scattering and by pair production (subatomic particles). Moreover, at a biological level, such effects are manifested either as direct effects such as single or double stranded DNA damage or indirect effects such as ionization of water molecules inside the living system leading to free radicals that finally may damage the DNA. The factors influencing the concentrations of thoron in the environment are (1) thorium specific activity in soil (2) ground cover (vegetations, buildings, and roads), (3) soil porosity and grain size, (4) temperature, (5) atmospheric pressure, (6) soil moisture, rainfall and snow cover, (7) ventilation rate in the atmosphere and (8) seasons (Shetty and Narayana 2010). Thoron and its progeny concentration are generally higher in the early mornings because of relatively higher soil moisture and the inversions in atmospheric temperature (Malakhov et al. 1966).