Glossary

9.1 Types of radioactive decay and nuclear equations

3 min read•july 22, 2024

is a fascinating process where unstable atomic nuclei shed particles or energy to become more stable. There are several types, including alpha, beta, and , each with unique characteristics and effects on the nucleus.

Understanding is key to grasping why radioactive decay happens. The ratio of protons to neutrons in a nucleus determines its stability, with unstable nuclei undergoing decay to reach a more balanced state. This process is crucial in various fields, from medicine to energy production.

Types of Radioactive Decay

Types of radioactive decay

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  • involves emission of alpha particle (helium nucleus, 24He^4_2He) from nucleus of heavy elements (uranium, radium) with too many protons, decreasing by 2 and by 4
  • occurs in nuclei with imbalanced -to- ratio
    • Beta minus (β−\beta^-) decay involves emission of from nucleus due to conversion of neutron into proton (), increasing atomic number by 1 while remains unchanged
    • Beta plus (β+\beta^+) decay involves emission of positron from nucleus due to conversion of proton into neutron (potassium-40), decreasing atomic number by 1 while mass number remains unchanged
  • Gamma radiation involves emission of high-energy photons from nucleus when it transitions from excited state to lower energy state (cobalt-60), not changing atomic number or mass number

Balanced nuclear equations

  • : ZAX→Z−2A−4Y+24He^A_ZX \rightarrow ^{A-4}_{Z-2}Y + ^4_2He
  • Beta minus decay: ZAX→Z+1AY+β−+νˉ^A_ZX \rightarrow ^A_{Z+1}Y + \beta^- + \bar{\nu} where νˉ\bar{\nu} represents antineutrino
  • Beta plus decay: ZAX→Z−1AY+β++ν^A_ZX \rightarrow ^A_{Z-1}Y + \beta^+ + \nu where ν\nu represents neutrino
  • Gamma radiation: ZAX∗→ZAX+γ^A_ZX^* \rightarrow ^A_ZX + \gamma where asterisk (∗^*) indicates excited nuclear state

Products of radioactive decay

  • Determine atomic number and mass number of parent
  • Apply changes to atomic number and mass number based on decay mode
    1. Alpha decay: Zdaughter=Zparent−2Z_{daughter} = Z_{parent} - 2, Adaughter=Aparent−4A_{daughter} = A_{parent} - 4
    2. Beta minus decay: Zdaughter=Zparent+1Z_{daughter} = Z_{parent} + 1, Adaughter=AparentA_{daughter} = A_{parent}
    3. Beta plus decay: Zdaughter=Zparent−1Z_{daughter} = Z_{parent} - 1, Adaughter=AparentA_{daughter} = A_{parent}
  • Identify daughter nuclide using periodic table (lead-206 from alpha decay)

Nuclear Stability and Radioactive Decay

Nuclear stability and decay

  • Nuclear stability determined by ratio of protons to neutrons in nucleus
    • Stable nuclei have specific range of proton-to-neutron ratios (1:1 for light nuclei, 1:1.5 for heavy nuclei)
    • Unstable nuclei outside this range undergo radioactive decay (carbon-14, uranium-235)
  • Nuclear stability curve (band of stability) shows relationship between number of protons and neutrons in stable nuclei
    • Nuclei above curve have too many neutrons and undergo beta minus decay (carbon-14)
    • Nuclei below curve have too many protons and undergo beta plus decay (potassium-40) or alpha decay for heavy nuclei (uranium-238)
  • Factors affecting nuclear stability include nuclear forces (strong nuclear force binds nucleons, electrostatic repulsion between protons destabilizes nucleus) and neutron-to-proton ratio (more neutrons needed to maintain stability as number of protons increases)
  • Radioactive decay occurs when unstable nucleus emits particles or energy to reach more stable configuration (uranium-238 to lead-206 through series of alpha and beta decays)

Key Terms to Review (37)

Activity: Activity refers to the rate at which a radioactive substance decays or emits radiation, typically measured in disintegrations per second. This concept connects to the likelihood of nuclear reactions and helps quantify how much radioactive material is present, influencing calculations related to energy production and chemical equilibrium in electrochemical cells.
Alpha decay: Alpha decay is a type of radioactive decay in which an unstable nucleus emits an alpha particle, consisting of two protons and two neutrons, effectively transforming into a different element with a lower atomic number. This process not only changes the identity of the element but also decreases its mass, highlighting the transformation involved in nuclear reactions. Understanding alpha decay is crucial for grasping the broader concepts of radioactive decay and the nuclear equations that describe these transformations.
Alpha decay: Alpha decay is a type of radioactive decay in which an unstable atomic nucleus emits an alpha particle, consisting of two protons and two neutrons, thereby transforming into a new element. This process decreases the atomic number by two and the mass number by four, leading to a different element that is typically further down the periodic table. Understanding alpha decay is essential for analyzing nuclear reactions and calculating half-lives of radioactive isotopes.
Atomic Number: The atomic number is the number of protons found in the nucleus of an atom, which uniquely identifies an element and determines its position on the periodic table. It plays a crucial role in nuclear reactions, as it influences the behavior of atoms during radioactive decay and helps in understanding nuclear equations.
Beta Decay: Beta decay is a type of radioactive decay in which a beta particle, which can be an electron or a positron, is emitted from an unstable atomic nucleus. This process transforms a neutron into a proton or vice versa, resulting in a change in the atomic number of the element while maintaining the same mass number. Beta decay plays a crucial role in understanding nuclear reactions and the stability of isotopes, influencing half-life calculations and the kinetics of radioactive decay.
Beta decay: Beta decay is a type of radioactive decay where a beta particle, which can be an electron or a positron, is emitted from an unstable atomic nucleus. This process transforms one type of nucleon into another, resulting in a change in the atomic number and a different element. Understanding beta decay is crucial for analyzing nuclear equations and calculating the half-life and kinetics of radioactive substances.
Binding energy: Binding energy is the energy required to separate a nucleus into its individual protons and neutrons, reflecting the stability of that nucleus. A higher binding energy indicates a more stable nucleus, which is crucial in understanding various processes such as radioactive decay, nuclear fission, and fusion. Additionally, binding energy plays a significant role in computational chemistry and molecular modeling as it helps to analyze the stability of molecules and their interactions.
Carbon-14: Carbon-14 is a radioactive isotope of carbon with an atomic mass of 14, formed in the atmosphere through the interaction of cosmic rays with nitrogen-14. It is used as a key tool for dating ancient organic materials, allowing scientists to estimate the age of fossils and archaeological artifacts based on its decay over time.
Conservation of Nucleons: Conservation of nucleons is a fundamental principle in nuclear physics stating that the total number of nucleons (protons and neutrons) in a closed system remains constant during nuclear reactions. This principle implies that when a nucleus undergoes decay or transformation, the sum of the nucleons before and after the reaction must be equal, linking this concept directly to the stability and behavior of atomic nuclei.
Curie: The curie (Ci) is a unit of measurement for radioactivity, specifically representing the amount of radioactive decay occurring in a sample. It is defined as the activity of a quantity of radioactive material in which 3.7 × 10^10 disintegrations occur per second. This measurement is crucial when discussing types of radioactive decay and helps in understanding the kinetics involved in half-life calculations, as it provides a quantifiable way to express the rate at which unstable nuclei decay over time.
Decay Constant: The decay constant is a proportionality factor that represents the rate at which a radioactive substance undergoes decay, indicating how quickly a specific isotope will transform into another element or isotope. This constant is crucial in understanding the behavior of radioactive decay processes, as it helps quantify the likelihood of decay events occurring over time. The decay constant is directly related to half-life, allowing for a deeper insight into nuclear reactions and the stability of different isotopes.
Electron: An electron is a subatomic particle with a negative electric charge, found in the outer regions of atoms. These tiny particles play a crucial role in chemical bonding, electricity, and the behavior of atoms in various physical processes. Electrons are fundamental to understanding atomic structure and are involved in numerous types of radioactive decay processes.
Ernest Rutherford: Ernest Rutherford was a pioneering physicist known as the father of nuclear physics, who significantly contributed to the understanding of atomic structure and radioactivity in the early 20th century. His groundbreaking experiments led to the discovery of the nucleus and helped classify different types of radioactive decay, laying the foundation for nuclear equations used to represent these transformations. Rutherford's work was essential in understanding how radioactive elements emit particles and energy, which connects directly to concepts involving decay processes and nuclear reactions.
Exponential Decay: Exponential decay is a process where the quantity of a substance decreases at a rate proportional to its current value, leading to a rapid decrease over time. This concept is crucial in understanding how radioactive substances lose their radioactivity, with the decay process typically described by a mathematical function that demonstrates how the amount of substance diminishes exponentially, rather than linearly. As time progresses, the quantity approaches zero but never quite reaches it, emphasizing the unpredictable nature of radioactive decay.
Fission: Fission is a nuclear reaction in which the nucleus of an atom splits into two or more smaller nuclei, along with the release of a significant amount of energy. This process can occur spontaneously but is typically induced by bombarding the nucleus with neutrons. Fission is fundamental to nuclear power generation and atomic weaponry, marking its significance in both energy production and military applications.
Fusion: Fusion is the process in which two light atomic nuclei combine to form a heavier nucleus, releasing a significant amount of energy in the process. This reaction is the source of energy for stars, including our Sun, and is critical to understanding nuclear reactions and their applications in both nature and technology.
Gamma decay: Gamma decay is a type of radioactive decay where an unstable atomic nucleus releases energy in the form of gamma rays, which are high-energy electromagnetic radiation. This process occurs without changing the number of protons or neutrons in the nucleus, meaning the atomic number and mass number remain the same. It is often a result of other forms of decay, as nuclei transition from a higher energy state to a lower energy state, releasing excess energy as gamma radiation.
Half-life: Half-life is the time required for half of the radioactive nuclei in a sample to decay. This concept is crucial for understanding the behavior of radioactive materials as it helps predict how long it will take for a substance to diminish to a certain level, influencing various applications from nuclear reactions to medical uses.
Law of Radioactive Decay: The law of radioactive decay states that the rate at which a radioactive substance undergoes decay is proportional to the quantity of the substance present. This principle is fundamental in understanding how unstable nuclei transform into more stable forms through various types of radioactive decay, impacting the calculations of half-lives and the prediction of decay over time.
Marie Curie: Marie Curie was a pioneering physicist and chemist known for her groundbreaking research on radioactivity, a term she coined. Her work led to the discovery of the radioactive elements polonium and radium, which significantly advanced the understanding of radioactive decay processes and contributed to the development of medical applications involving radioisotopes.
Mass number: Mass number is the total count of protons and neutrons in an atomic nucleus, giving an indication of the atom's mass. It is represented as a whole number and is essential for identifying different isotopes of an element, which have the same number of protons but different numbers of neutrons. Understanding mass number is crucial for comprehending various types of radioactive decay and how nuclear equations are balanced.
Mass Number: The mass number is the total count of protons and neutrons in an atom's nucleus, indicating its isotopic identity. It plays a crucial role in nuclear chemistry as it helps define the stability and type of radioactive decay an isotope may undergo. By understanding mass number, one can also comprehend how it is represented in nuclear equations, which are essential for illustrating radioactive processes.
Neutron: A neutron is a subatomic particle found in the nucleus of an atom, which has no electric charge and a mass slightly greater than that of a proton. Neutrons play a crucial role in stabilizing the atomic nucleus by offsetting the repulsive forces between positively charged protons, allowing for the formation of different isotopes of elements. Understanding neutrons is essential when discussing nuclear reactions and types of radioactive decay.
Neutron capture: Neutron capture is a nuclear reaction in which an atomic nucleus absorbs a neutron, leading to the formation of a heavier isotope or a different element altogether. This process is significant in various nuclear reactions, particularly in the formation of heavy elements in stars and during nucleosynthesis. It can occur either through a slow capture process, where the nucleus captures neutrons slowly, or through a rapid capture process, known as the r-process.
Nuclear fission: Nuclear fission is a process where the nucleus of an atom splits into two or more smaller nuclei, along with the release of energy and neutrons. This reaction can happen spontaneously or can be induced by bombarding the nucleus with neutrons. Fission is a key concept in understanding types of radioactive decay and plays a significant role in energy generation and weaponry.
Nuclear Fusion: Nuclear fusion is a process in which two light atomic nuclei combine to form a heavier nucleus, releasing a significant amount of energy in the process. This reaction is responsible for the energy produced by stars, including our sun, and has potential applications in clean energy generation on Earth. Understanding nuclear fusion also involves recognizing its contrast with nuclear fission, where heavy nuclei split apart, highlighting the differences in energy production methods.
Nuclear Medicine: Nuclear medicine is a medical specialty that uses radioactive substances for diagnosis and treatment of diseases. By incorporating the principles of radioactive decay and nuclear equations, this field allows for imaging techniques and targeted therapies that can effectively monitor and treat conditions such as cancer and heart disease. The ability to measure the half-life of these radioactive isotopes is crucial in determining their effectiveness and safety in medical applications.
Nuclear Stability: Nuclear stability refers to the balance and resilience of a nucleus against radioactive decay. It is determined by the ratio of neutrons to protons within an atom and the forces acting between them, which dictate whether a nucleus will remain stable or undergo transformations such as alpha, beta, or gamma decay. Understanding nuclear stability is crucial in predicting the behavior of isotopes and their tendency to decay, as well as the types of radiation they may emit.
Nuclide: A nuclide is a distinct atomic species characterized by its number of protons and neutrons in the nucleus, which determines its atomic number and mass number. Each nuclide represents a specific isotope of an element, and understanding nuclides is essential for studying different types of radioactive decay processes and the nuclear equations that describe these transformations.
Products: In chemistry, products are the substances that are formed as a result of a chemical reaction. They appear on the right side of a chemical equation and represent the outcome after reactants undergo transformation through various processes, including radioactive decay. Understanding products is crucial for analyzing nuclear equations and the types of decay that occur in unstable nuclei.
Proton: A proton is a subatomic particle found in the nucleus of an atom, carrying a positive electric charge equal in magnitude to that of an electron's negative charge. Protons play a crucial role in defining the identity of an element, as the number of protons determines the atomic number and thus the element itself. They are involved in various types of nuclear reactions and radioactive decay processes, influencing the stability of atomic nuclei.
Rad: The rad, short for radiation absorbed dose, is a unit of measurement that quantifies the amount of energy absorbed by a material when exposed to ionizing radiation. It is crucial in the context of radioactive decay and nuclear equations as it helps assess the effects of radiation on biological tissues and materials, determining safety levels and potential damage from exposure.
Radioactive decay: Radioactive decay is the process by which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves. This natural process transforms the original atom into a different element or isotope and is fundamental to understanding various nuclear processes, including types of decay and nuclear reactions. As atoms undergo radioactive decay, they emit alpha particles, beta particles, or gamma rays, which are important for both natural phenomena and technological applications.
Radiometric dating: Radiometric dating is a technique used to determine the age of materials by measuring the abundance of radioactive isotopes and their decay products. This method relies on the principles of radioactive decay, where unstable isotopes transform into stable ones over time at a predictable rate, allowing scientists to calculate how long it has been since a particular rock or fossil formed.
Reactants: Reactants are the starting substances in a chemical reaction that undergo transformation to create products. They are crucial in understanding chemical equations and reactions as they dictate what substances are involved and how they interact during the reaction process. Identifying reactants helps predict the outcomes and the behavior of the system during the reaction.
Symbol Notation: Symbol notation is a way to represent atomic and nuclear particles, showing their identity and properties through specific symbols. This notation is crucial in understanding radioactive decay processes, as it helps in writing nuclear equations that depict changes in atomic structure during various types of decay.
Uranium-238: Uranium-238 is a naturally occurring isotope of uranium with an atomic mass of approximately 238 atomic mass units. It is the most abundant isotope of uranium, making up about 99.3% of natural uranium, and plays a crucial role in nuclear processes and radioactive decay chains. Its long half-life of about 4.5 billion years makes it significant for understanding both geological time and nuclear reactions.
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