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Intro to Chemistry
Table of Contents
Unit 21 Overview: Nuclear Chemistry
21.1 Nuclear Structure and Stability
21.2 Nuclear Equations
21.3 Radioactive Decay
21.4 Transmutation and Nuclear Energy
21.5 Uses of Radioisotopes
21.6 Biological Effects of Radiation

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21.6 Biological Effects of Radiation

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Ionizing radiation can wreak havoc on living organisms, damaging DNA and other crucial molecules. It's measured in various units like grays and sieverts, which help us understand its impact on different tissues and organs.

We encounter radiation daily from natural and artificial sources. Special detectors like Geiger counters and scintillators help us measure it. Understanding radiation's effects and measurement is key to protecting ourselves and harnessing its benefits safely.

Biological Effects and Measurement of Radiation

Effects of ionizing radiation

  • Ionizing radiation damages living organisms through direct and indirect mechanisms
    • Directly interacts with and ionizes biological molecules (DNA, proteins, lipids) leading to structural and functional changes
    • Indirectly produces free radicals and reactive oxygen species (ROS) by interacting with water molecules, which can damage biological molecules
  • Radiation-induced DNA damage is particularly harmful causing single-strand and double-strand breaks, mutations, and chromosomal aberrations
    • Can lead to cell death, impaired cell function, or uncontrolled cell growth (cancer)
  • Biological impact of radiation depends on type (alpha, beta, gamma, X-rays), energy, dose, dose rate, and radiosensitivity of exposed cells or tissues
    • High doses can cause acute radiation syndrome, characterized by nausea, vomiting, and potential organ failure

Units of radiation measurement

  • Radiation exposure measures ionization produced in air by X-rays or gamma rays in roentgens (R)
    • 1 R = 2.58 × 10^-4 coulombs/kg of air
  • Absorbed dose measures energy deposited per unit mass in grays (Gy) or rads
    • 1 Gy = 1 J/kg, 1 rad = 0.01 Gy
  • Equivalent dose accounts for biological effectiveness of different radiation types in sieverts (Sv) or rems
    • Equivalent dose = absorbed dose × radiation weighting factor (WR)
    • 1 Sv = 1 J/kg × WR, 1 rem = 0.01 Sv
  • Effective dose considers radiosensitivity of different tissues and organs also in sieverts (Sv) or rems
    • Effective dose = sum of (equivalent dose to each organ × tissue weighting factor)

Methods for radioactivity detection

  • Geiger-Müller counters detect ionizing radiation (alpha, beta, gamma) by producing electrical pulses
    • Used in radiation surveys and contamination monitoring
  • Scintillation detectors detect gamma rays and X-rays using scintillator materials that emit light converted to electrical signals
    • Used in medical imaging (PET scans) and radiation spectroscopy
  • Solid-state detectors (germanium) detect gamma rays and X-rays by creating electron-hole pairs in semiconductors producing energy-proportional electrical signals
    • Used in high-resolution gamma spectroscopy and environmental monitoring
  • Film badges and thermoluminescent dosimeters (TLDs) measure accumulated radiation dose over time
    • Film badges darken radiation-sensitive film, TLDs release stored energy as light when heated
    • Used for personal dosimetry monitoring and radiation protection in occupational settings

Sources of everyday radiation exposure

  • Natural background radiation from cosmic radiation, terrestrial radiation from radioactive materials in earth's crust (uranium, thorium, radon), and internal radiation from radioactive isotopes in the body (potassium-40, carbon-14)
  • Medical sources include diagnostic X-rays (dental, chest, CT scans), nuclear medicine procedures (PET scans, thyroid scans), and radiation therapy for cancer treatment
  • Consumer products like tobacco (polonium-210), building materials (granite, concrete), and luminous watches (tritium, promethium-147) contain radioactive materials
  • Occupational sources affect nuclear power plant workers, medical professionals (radiologists, nuclear medicine technicians), and researchers working with radioactive materials
  • Fallout from nuclear weapons testing and accidents (Chernobyl, Fukushima) can also contribute to radiation exposure

Radiation dose-response models

  • Linear no-threshold model assumes any radiation dose, no matter how small, increases cancer risk
  • Radiation hormesis hypothesis suggests low doses of radiation may have beneficial effects on health
  • Threshold model proposes a safe level of radiation exposure below which no harmful effects occur
  • These models inform radiation protection guidelines and regulations for public and occupational exposure

Key Terms to Review (54)

Becquerel (Bq): The becquerel (Bq) is the SI unit of radioactive decay, defined as one disintegration per second. It measures the activity of a quantity of radioactive material.
Alpha particles: Alpha particles are a type of ionizing radiation consisting of two protons and two neutrons bound together. They are emitted from the nucleus of certain radioactive elements during alpha decay.
Curie (Ci): The curie (Ci) is a unit of radioactivity, defined as the quantity of any radioactive substance in which 3.7 × 10^{10} disintegrations occur per second. It is named after the pioneering scientist Marie Curie.
Gamma rays (γ): Gamma rays ($\gamma$) are high-energy electromagnetic waves emitted from the nucleus of an atom during radioactive decay. They have no mass and no charge but can penetrate most materials.
Geiger counter: A Geiger counter is an instrument used for detecting and measuring ionizing radiation. It consists of a Geiger-Müller tube that produces an audible or visible signal when radiation is detected.
Gray (Gy): Gray (Gy) is a unit of absorbed radiation dose in the International System of Units (SI). It measures the amount of radiation energy absorbed per kilogram of matter, where 1 Gy equals 1 joule per kilogram.
Ionizing radiation: Ionizing radiation is a type of energy released by atoms that travels in the form of electromagnetic waves or particles and has enough energy to ionize atoms or molecules by detaching electrons. It can cause damage to living tissue, which makes it significant in both medical applications and environmental contexts.
Millicurie (mCi): A millicurie (mCi) is a unit of radioactivity equal to one-thousandth of a curie. It measures the rate of radioactive decay or disintegration of unstable atomic nuclei.
Radiation dosimeters: Radiation dosimeters are devices used to measure an individual's exposure to ionizing radiation over a specific period. They are essential for monitoring and ensuring safety in environments where radiation is present.
Radiation absorbed dose (rad): Radiation absorbed dose (rad) is a unit of measurement for the amount of energy deposited by ionizing radiation in a substance, typically human tissue. One rad is equivalent to 0.01 joules of energy absorbed per kilogram of tissue.
Roentgen equivalent for man (rem): Roentgen Equivalent for Man (rem) is a unit of measurement for the dose of ionizing radiation that factors in its effect on human tissue. It accounts for both the energy deposited and the biological impact.
RBE: Relative Biological Effectiveness (RBE) is a measure of the relative damage caused by different types of ionizing radiation on biological tissue. It compares the biological effectiveness of one type of radiation to another, usually using X-rays or gamma rays as a reference.
Relative biological effectiveness: Relative Biological Effectiveness (RBE) is a measure of the effectiveness of ionizing radiation in causing biological damage. It compares the dose of a test radiation to the dose of a reference radiation (usually X-rays or gamma rays) that produces the same biological effect.
Sievert (Sv): A sievert (Sv) is the SI unit used to measure the biological effect of ionizing radiation on human tissue. It quantifies the risk of radiation exposure by considering both the dose and its impact on different types of tissues.
Scintillation counter: A scintillation counter is an instrument used to detect and measure ionizing radiation by using a scintillator material that emits light when it absorbs radiation. The emitted light is then converted into an electrical signal for measurement.
Radon: Radon is a dense, radioactive, naturally-occurring noble gas that is formed from the radioactive decay of radium. It is a significant environmental and health concern due to its potential to cause lung cancer through inhalation exposure.
Alpha Particles: Alpha particles are a type of ionizing radiation consisting of two protons and two neutrons, emitted during the radioactive decay of certain elements. They are the largest and most heavily charged particles released in radioactive processes and have a limited range in matter.
Gamma Rays: Gamma rays are a type of high-energy electromagnetic radiation, similar to X-rays, that are emitted during radioactive decay. They have the highest frequency and shortest wavelength in the electromagnetic spectrum, making them highly penetrating and capable of causing significant biological damage.
Carbon-14: Carbon-14 is a radioactive isotope of carbon with a nucleus containing 6 protons and 8 neutrons. It is used extensively in radiometric dating techniques to determine the age of various materials, as it undergoes radioactive decay over time.
Potassium-40: Potassium-40 is a radioactive isotope of the element potassium that undergoes radioactive decay. It is a naturally occurring radioisotope found in the environment and within living organisms, making it relevant to the topics of radioactive decay and the biological effects of radiation.
Tritium: Tritium is a radioactive isotope of hydrogen with a nucleus containing one proton and two neutrons. It is a key term in the context of transmutation and nuclear energy, as well as the biological effects of radiation.
Promethium-147: Promethium-147 is a radioactive isotope of the element promethium, which is a rare earth metal. It is primarily used in medical and industrial applications due to its unique radioactive properties.
Single-Strand Breaks: Single-strand breaks (SSBs) refer to a type of DNA damage where the phosphodiester backbone of one strand of the DNA double helix is severed, leaving the complementary strand intact. This disruption in the DNA structure can have significant biological effects, particularly in the context of radiation exposure.
Gray: Gray, or grey, is a neutral color that is a blend of black and white, often associated with a sense of balance, neutrality, and moderation. In the context of biological effects of radiation, gray refers to the unit of measurement used to quantify the amount of ionizing radiation absorbed by living tissue.
Polonium-210: Polonium-210 is a highly radioactive isotope of the element polonium. It is a naturally occurring, alpha-emitting radionuclide that has significant applications in various fields, but its high toxicity also makes it a potential health hazard.
Reactive Oxygen Species: Reactive oxygen species (ROS) are chemically reactive molecules containing oxygen, such as superoxide, hydrogen peroxide, and hydroxyl radicals. They are naturally produced in the body as byproducts of cellular metabolism and play important roles in biological processes, but can also cause oxidative damage if not properly regulated.
DNA Damage: DNA damage refers to alterations or lesions that occur in the DNA molecule, disrupting its normal structure and function. This type of damage can be caused by various environmental factors and cellular processes, and if left unrepaired, can lead to genetic mutations and potentially contribute to the development of diseases like cancer.
X-rays: X-rays are a type of electromagnetic radiation with wavelengths shorter than those of visible light. They are widely used in various fields, including medicine, industry, and research, due to their ability to penetrate matter and provide valuable information about the internal structure of objects.
Radiation Protection: Radiation protection refers to the measures and practices implemented to minimize the harmful effects of ionizing radiation on living organisms, including humans. It encompasses a set of principles and techniques designed to safeguard individuals and the environment from the potential risks associated with exposure to radiation.
Acute Radiation Syndrome: Acute Radiation Syndrome (ARS) is a serious illness that occurs when the entire body (or most of it) receives a high dose of radiation, such as from a nuclear accident or attack. It happens when radiation damages the body's cells, leading to widespread organ failure and potentially death if left untreated.
Rad: The rad (Radiation Absorbed Dose) is a unit of measurement used to quantify the amount of ionizing radiation absorbed by a person or material. It is a measure of the energy deposited per unit mass of the irradiated material, and it is used to assess the potential biological effects of radiation exposure.
Geiger-Müller Counters: Geiger-Müller counters are radiation detection devices that are commonly used to measure the intensity and type of ionizing radiation, such as alpha, beta, and gamma radiation. They play a crucial role in understanding the biological effects of radiation exposure.
Free Radicals: Free radicals are highly reactive molecules or atoms that have an unpaired electron in their outer shell. This instability causes them to aggressively seek out and react with other molecules in the body, potentially causing cellular damage and contributing to various health conditions.
Equivalent Dose: Equivalent dose is a measure used in radiation protection to quantify the biological effect of different types of ionizing radiation on the human body. It takes into account the varying levels of energy deposition and biological effectiveness of different types of radiation.
Film Badges: Film badges are small, portable devices used to monitor and measure an individual's exposure to ionizing radiation. They are commonly used in occupational settings where workers may be exposed to radiation, such as in medical facilities, nuclear power plants, and research laboratories.
Cosmic Radiation: Cosmic radiation refers to the high-energy particles and electromagnetic radiation that originate from outside the Earth's atmosphere, primarily from the Sun and other celestial bodies. This type of radiation is a significant factor in the context of the biological effects of radiation discussed in chapter 21.6.
Ionizing Radiation: Ionizing radiation refers to high-energy radiation that has enough power to remove electrons from atoms, creating positively charged ions. This type of radiation is capable of causing significant damage to living tissues and is an important consideration in the use of radioisotopes and the biological effects of radiation exposure.
Chromosomal Aberrations: Chromosomal aberrations are structural or numerical changes in the normal chromosome complement of a cell. These abnormalities can have significant impacts on an organism's health and development, particularly in the context of radiation exposure.
Effective Dose: The effective dose is a measure of the total amount of ionizing radiation energy absorbed by the human body, taking into account the different sensitivities of various tissues and organs. It is used to assess the potential health risks associated with exposure to radiation.
Sievert: The sievert (Sv) is a unit of measurement for ionizing radiation, specifically used to quantify the biological effects of radiation on human health. It takes into account the type of radiation and its impact on different tissues, making it essential for assessing risk associated with radiation exposure from sources like nuclear energy and medical treatments. Understanding the sievert is crucial in fields related to transmutation and nuclear energy, as well as in evaluating the biological effects of radiation exposure.
Double-strand breaks: Double-strand breaks (DSBs) are a type of DNA damage where both strands of the DNA helix are severed, resulting in a complete disruption of the DNA molecule. This can occur due to various factors including exposure to radiation, chemicals, or during normal cellular processes such as replication. DSBs are particularly significant in the context of biological effects of radiation because they can lead to mutations, chromosomal rearrangements, and even cell death if not properly repaired.
Radiosensitivity: Radiosensitivity refers to the susceptibility of biological tissues and organisms to damage caused by ionizing radiation. This sensitivity varies across different types of cells and organisms, impacting how radiation exposure affects biological processes such as cell division, repair mechanisms, and overall health. Understanding radiosensitivity is crucial for assessing the biological effects of radiation exposure and its implications in medical treatments and radiation protection.
Radiation weighting factor: The radiation weighting factor, also known as the quality factor, is a numerical value that reflects the biological effect of different types of ionizing radiation on living tissue. This factor helps to quantify the potential for biological damage caused by radiation, as not all types of radiation have the same effect on human health. By considering this factor, health physicists can better assess the risks associated with exposure to various forms of radiation, leading to more effective safety standards and protective measures.
Roentgen: Roentgen is a unit of measurement for ionizing radiation exposure, named after the German physicist Wilhelm Conrad Roentgen, who discovered X-rays. This term is significant as it helps quantify the biological effects of radiation on human tissue, providing a basis for understanding the impact of radiation exposure in medical and environmental contexts.
Beta particles: Beta particles are high-energy, high-speed electrons or positrons emitted during the radioactive decay of an atomic nucleus. These particles play a significant role in transforming unstable isotopes into more stable forms and can impact biological systems due to their penetrating ability.
Scintillation Detectors: Scintillation detectors are devices used to detect and measure ionizing radiation by utilizing the phenomenon of scintillation, where certain materials emit light when exposed to radiation. These detectors convert the light emitted from scintillating materials into electrical signals, allowing for the quantification of radiation levels. They are widely used in various fields, including medical imaging and radiation safety, due to their sensitivity and speed in detecting radiation events.
Thermoluminescent dosimeters: Thermoluminescent dosimeters (TLDs) are devices used to measure ionizing radiation exposure by storing energy from radiation in a crystal lattice and releasing it as light when heated. This characteristic allows them to quantify doses of radiation, making them valuable tools in assessing biological effects of radiation exposure and ensuring safety in various environments, such as medical facilities and nuclear power plants.
Rem: The rem, or roentgen equivalent man, is a unit of measurement used to quantify the biological effects of ionizing radiation on human tissue. It takes into account the type of radiation and its impact on health, making it a crucial metric in assessing radiation exposure and potential harm. This measurement is vital for ensuring safety standards in environments where exposure to radiation is a concern.
Linear no-threshold model: The linear no-threshold model (LNT) is a risk assessment approach used to estimate the potential biological effects of ionizing radiation on human health, suggesting that there is no safe level of exposure and that even the smallest dose can increase the risk of cancer. This model posits a direct relationship between radiation dose and the probability of harmful effects, meaning that as exposure increases, so does the risk of adverse outcomes. This concept is critical for understanding radiation safety standards and public health policies regarding exposure limits.
Solid-state Detectors: Solid-state detectors are devices that use semiconductor materials to detect and measure radiation, converting the energy from radiation into an electrical signal. These detectors are vital in fields like medical imaging and radiation protection, as they provide high resolution and efficiency in detecting ionizing radiation.
Absorbed dose: Absorbed dose is a measure of the amount of energy deposited by ionizing radiation in a specific mass of tissue, typically expressed in grays (Gy). This concept is crucial in understanding how radiation interacts with biological systems and can lead to various biological effects, including cell damage, cancer, and tissue response to radiation exposure. The absorbed dose helps quantify the risk associated with different levels of radiation exposure and assists in assessing safety standards in medical and occupational settings.
Radiation hormesis: Radiation hormesis is the hypothesis that low doses of ionizing radiation may have beneficial effects on health and biological systems, as opposed to the traditional view that all radiation exposure is harmful. This concept suggests that small amounts of radiation can stimulate protective biological responses, potentially leading to improved health outcomes. The idea challenges the linear no-threshold model, which asserts that any exposure to radiation, no matter how small, increases cancer risk.
Terrestrial radiation: Terrestrial radiation refers to the thermal radiation emitted by the Earth as it absorbs solar energy and subsequently releases it in the form of infrared radiation. This process plays a crucial role in maintaining the planet's energy balance and is essential for regulating temperature and climate, influencing biological systems and ecological processes.
Tissue weighting factor: The tissue weighting factor is a numerical value that represents the relative sensitivity of different tissues and organs to the harmful effects of radiation exposure. It helps quantify the overall biological impact of radiation on the human body by taking into account how much damage each specific tissue can sustain, allowing for a more accurate assessment of risk associated with radiation exposure.