4.4 Natural and artificial radioactivity

Radioactivity, both natural and artificial, shapes our world in surprising ways. From cosmic rays to radon gas, we're surrounded by natural radiation. Primordial radionuclides, formed billions of years ago, still persist in our environment today.

Humans have also created artificial radioactivity through nuclear reactions and weapons testing. These man-made radionuclides have found applications in medicine, research, and industry. From cancer treatments to carbon dating, radioactivity plays a crucial role in modern life.

Natural Radioactivity

Primordial and Cosmogenic Radionuclides

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• Primordial radionuclides formed during nucleosynthesis in stars and supernovae before Earth's formation
• Uranium-238, thorium-232, and potassium-40 constitute primary primordial radionuclides on Earth
• Half-lives of primordial radionuclides exceed billions of years, allowing their continued presence
• Cosmogenic radionuclides produced by cosmic ray interactions with atmospheric gases
• Carbon-14, beryllium-7, and tritium represent common cosmogenic radionuclides
• Cosmic ray flux varies with altitude and latitude, affecting cosmogenic radionuclide production rates

Environmental Radioactivity Sources and Impacts

• Natural background radiation stems from terrestrial and cosmic sources
• Radon gas, a decay product of uranium, contributes significantly to indoor radiation exposure
• Granite-rich areas often exhibit higher levels of natural radioactivity due to uranium content
• Cosmic radiation intensity increases with altitude, leading to higher exposure for air travelers
• Natural radioactivity in soil and water affects plants and animals through bioaccumulation
• Human activities like mining and fossil fuel combustion can enhance natural radioactivity levels

Artificial Radioactivity

Anthropogenic Radionuclides and Nuclear Fission Products

• Anthropogenic radionuclides produced through human activities, primarily nuclear reactions
• Nuclear weapons testing released significant amounts of artificial radionuclides into the environment
• Cesium-137 and strontium-90 represent prominent artificial radionuclides from nuclear fission
• Nuclear power plant accidents (Chernobyl, Fukushima) contributed to environmental radioactivity
• Plutonium isotopes, created in nuclear reactors, persist in the environment due to long half-lives
• Artificial radionuclides used as environmental tracers to study oceanic and atmospheric processes

Activation Products and Radioisotope Production

• Activation products formed when stable nuclei absorb neutrons in nuclear reactors or accelerators
• Cobalt-60, a common activation product, widely used in industrial radiography and cancer treatment
• Particle accelerators produce short-lived radioisotopes for medical imaging (fluorine-18, carbon-11)
• Neutron activation analysis employs artificial radioactivity to determine elemental composition
• Radioisotope production methods include reactor irradiation, cyclotron bombardment, and generator systems
• Molybdenum-99/technetium-99m generator system crucial for nuclear medicine diagnostics

Applications of Radioactivity

Radioactive Tracers in Research and Industry

• Radioactive tracers allow non-invasive tracking of chemical and biological processes
• Carbon-14 dating determines age of organic materials up to approximately 50,000 years old
• Iodine-131 used to study thyroid function and treat thyroid disorders
• Tritium serves as a tracer in groundwater hydrology studies
• Industrial applications include leak detection in pipelines and wear analysis in engines
• Radioactive tracers aid in understanding metabolic pathways and drug metabolism in pharmaceutical research

Nuclear Medicine Diagnostics and Therapies

• Nuclear medicine utilizes radiopharmaceuticals for diagnosis and treatment of various diseases
• Technetium-99m, the most widely used medical radioisotope, employed in bone and organ scans
• Positron Emission Tomography (PET) scans use short-lived positron emitters (fluorine-18, gallium-68)
• Radioiodine therapy effectively treats thyroid cancer and hyperthyroidism
• Targeted radionuclide therapy delivers radiation directly to cancer cells (lutetium-177, yttrium-90)
• Brachytherapy involves placing sealed radioactive sources near tumors for localized treatment