3.3 Gamma decay and internal conversion
2 min read•august 7, 2024
and are two ways excited atomic nuclei release energy. Gamma decay emits high-energy photons, while internal conversion transfers energy directly to an electron, ejecting it from the atom.
These processes help nuclei reach stable ground states after radioactive decay. Understanding them is crucial for grasping how atoms shed excess energy and achieve stability in various nuclear reactions.
Gamma Decay
Emission of High-Energy Photons
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- Gamma decay involves the emission of high-energy photons called gamma rays from an atomic nucleus
- Gamma rays are a form of electromagnetic radiation with the highest energy and shortest wavelength in the electromagnetic spectrum
- During gamma decay, the atomic nucleus transitions from an excited nuclear state to a lower energy state
- The energy difference between the initial and final nuclear states determines the energy of the emitted gamma ray
Nuclear Excited States and Isomeric Transitions
- Atomic nuclei can exist in various excited states with higher energy levels than the
- These excited states are often populated following other radioactive decay processes such as alpha or beta decay
- Nuclei in excited states are unstable and will eventually transition to lower energy states through the emission of gamma rays
- are a specific type of gamma decay where the initial and final nuclear states have the same spin and parity (angular momentum and symmetry properties)
Internal Conversion
Conversion Electrons and Competing Process
- Internal conversion is a competing process to gamma decay, where the excitation energy of the nucleus is directly transferred to an atomic electron
- Instead of emitting a gamma ray, the nucleus ejects an electron from one of the inner atomic shells (K, L, M, etc.)
- The ejected electron is called a conversion electron and has a specific energy equal to the difference between the nuclear transition energy and the binding energy of the electron shell
Multipolarity and Selection Rules
- The probability of internal conversion depends on the of the nuclear transition, which describes the angular momentum and parity change between the initial and final nuclear states
- Electric monopole (E0) transitions can only occur through internal conversion, as they do not involve a change in angular momentum or parity
- Higher-order multipole transitions (dipole, quadrupole, etc.) are less likely to undergo internal conversion compared to lower-order transitions
- based on conservation of angular momentum and parity govern the allowed transitions and determine the multipolarity of the
Key Terms to Review (22)
Attenuation: Attenuation refers to the reduction in intensity or energy of gamma rays as they pass through matter. This process is crucial in understanding how gamma radiation interacts with different materials, as it determines the effectiveness of shielding and the potential exposure levels to radiation. Factors such as the material's density, atomic number, and thickness all play a significant role in how much attenuation occurs.
Conversion electrons: Conversion electrons are high-energy electrons that are ejected from an atom during the internal conversion process, a form of radioactive decay where an excited nucleus transfers its energy to an orbiting electron instead of emitting a gamma photon. This phenomenon is particularly significant in the context of nuclear reactions, as it provides an alternative pathway for energy release, impacting the overall decay scheme of certain isotopes and influencing radiation detection methods.
Dosimetry: Dosimetry is the measurement and calculation of the absorbed doses of radiation in a material, typically biological tissue, due to ionizing radiation exposure. Understanding dosimetry is crucial for assessing the potential biological effects of radiation, helping to establish safe exposure limits, and optimizing therapeutic applications. The principles of dosimetry are linked to the processes of gamma decay, internal conversion, and the interaction of gamma rays with matter, ultimately informing the study of radiation's impact on living organisms.
Excited State: An excited state refers to a condition of an atom or nucleus where it possesses more energy than its ground state, often due to the absorption of energy. In this higher energy configuration, electrons may occupy higher energy levels or nucleons may be in higher energy configurations, making the system unstable and prone to returning to its more stable ground state through processes such as gamma decay or internal conversion.
Gamma Decay: Gamma decay is a type of radioactive decay where an unstable nucleus releases energy in the form of gamma rays, which are high-energy electromagnetic radiation. This process typically occurs after alpha or beta decay when the nucleus is left in an excited state, allowing it to transition to a more stable state by emitting gamma radiation. This decay is important in understanding the behavior of radioactive isotopes and their applications in medicine and industry.
Gamma Spectroscopy: Gamma spectroscopy is an analytical technique used to measure the energy and intensity of gamma radiation emitted by radioactive substances. This method helps identify isotopes and determine their concentrations by analyzing the gamma-ray spectrum, providing crucial insights into nuclear processes and applications.
Geiger counter: A Geiger counter is a device used for detecting and measuring ionizing radiation, such as alpha, beta, and gamma radiation. It works by detecting the ionization produced when radiation passes through a gas within the detector, providing an audible click or a visual reading to indicate the presence of radiation. This instrument is crucial in various fields, helping to assess exposure levels, monitor radioactive environments, and ensure safety during radiation-related activities.
Ground State: The ground state is the lowest energy state of an atom or nucleus, where it is most stable and at its minimum energy level. In the context of nuclear decay processes such as gamma decay and internal conversion, the ground state plays a crucial role as it represents the final configuration after these transitions, providing insight into the energy changes involved in radioactive decay.
Internal conversion: Internal conversion is a non-radiative process in which an excited nucleus transfers its energy to an inner shell electron, resulting in the ejection of that electron from the atom. This process occurs as an alternative to gamma decay, where instead of emitting a gamma photon, the excess energy is used to overcome the binding energy of an inner orbital electron, leading to its ionization. This phenomenon plays a critical role in nuclear de-excitation and influences the emission patterns of gamma rays.
Isomeric Transitions: Isomeric transitions refer to the process where an excited nuclear state transitions to a lower energy state, often involving the emission of gamma radiation. These transitions occur between different nuclear isomers, which are distinct states of the same nucleus that have the same number of protons and neutrons but differ in energy due to variations in their configurations or arrangements. This phenomenon is significant in understanding nuclear decay processes and the behavior of isotopes during radioactive decay.
Marie Curie: Marie Curie was a pioneering scientist known for her groundbreaking research on radioactivity, which laid the foundation for the field of radiochemistry. Her work led to the discovery of two elements, polonium and radium, and she was the first woman to win a Nobel Prize, as well as the only person to win Nobel Prizes in two different scientific fields—Physics and Chemistry. Her contributions to science not only advanced our understanding of atomic behavior but also influenced safety protocols and applications in nuclear forensics.
Multipolarity: Multipolarity refers to a situation in which multiple entities, such as nuclear states or energy levels, exert influence and power within a given system. In the context of radiation processes, particularly gamma decay and internal conversion, multipolarity describes the various ways that gamma radiation can be emitted, depending on the angular momentum and parity of the nuclear states involved. Understanding multipolarity is crucial for analyzing how different quantum transitions occur during these radioactive processes.
Niels Bohr: Niels Bohr was a Danish physicist who made foundational contributions to our understanding of atomic structure and quantum mechanics. He is best known for the Bohr model of the atom, which introduced the idea of quantized energy levels for electrons orbiting the nucleus. This model laid the groundwork for later developments in quantum theory and provided insights into processes like gamma decay and internal conversion, where energy transitions occur within atoms.
Nuclear excitation: Nuclear excitation refers to a state in which an atomic nucleus absorbs energy and moves to a higher energy level without undergoing a change in its number of protons or neutrons. This process can occur through interactions with incoming radiation, such as gamma rays, or through internal conversion processes. When a nucleus is excited, it can later return to a lower energy state by emitting gamma radiation or undergoing internal conversion, which are key phenomena in nuclear physics.
Nuclear fission: Nuclear fission is the process in which the nucleus of an atom splits into two or more smaller nuclei, along with the release of energy. This phenomenon is crucial in various applications, from generating power in nuclear reactors to influencing the behavior of radioactive isotopes during decay processes, and is linked to the overall energy balance in nuclear reactions.
Nuclear Fusion: Nuclear fusion is the process where two light atomic nuclei combine to form a heavier nucleus, releasing a significant amount of energy in the process. This reaction is the primary source of energy for stars, including our sun, as it converts mass into energy, which can be understood through concepts like nuclear binding energy and mass defect. Fusion is often contrasted with nuclear fission, where heavy nuclei split into lighter ones, and understanding fusion is crucial for advancements in both energy production and understanding stellar processes.
Photon Interaction: Photon interaction refers to the processes that occur when photons, which are particles of light or electromagnetic radiation, engage with matter. These interactions can lead to various outcomes, such as scattering, absorption, or the emission of secondary radiation. Understanding photon interactions is crucial for comprehending phenomena like gamma decay and internal conversion, as they explain how high-energy photons influence atomic and molecular structures.
Quantum Mechanics: Quantum mechanics is a fundamental theory in physics that describes the behavior of matter and energy at the smallest scales, such as atoms and subatomic particles. This theory introduces concepts like wave-particle duality, uncertainty principle, and quantization, which help explain phenomena that cannot be understood through classical physics. In the context of radioactive decay processes like gamma decay and internal conversion, quantum mechanics provides a framework to understand how particles interact and how energy is emitted or absorbed during these transformations.
Radiotherapy: Radiotherapy is a medical treatment that uses ionizing radiation to kill cancer cells or shrink tumors. By targeting cancerous tissues while minimizing damage to surrounding healthy tissues, radiotherapy plays a crucial role in cancer management. It can utilize different types of radiation, such as gamma rays from radioactive decay, making understanding the interaction of these radiation types with matter essential in maximizing treatment efficacy.
Scattering: Scattering is the process by which particles or waves are forced to deviate from a straight trajectory due to non-uniformities in the medium through which they pass. In the context of radiation interactions, scattering is essential as it influences how gamma rays and neutrons behave when they encounter different materials, affecting their absorption and transmission properties, which are critical in radiation detection and shielding.
Selection Rules: Selection rules are a set of criteria that dictate the allowed transitions between different energy states during processes like gamma decay and internal conversion. These rules arise from fundamental principles of quantum mechanics and are essential for predicting the probabilities of specific transitions, ultimately influencing the types of emissions observed in radioactive decay and nuclear reactions.
Transition States: Transition states are high-energy configurations of molecules that occur during a chemical reaction, representing a point where the reactants are in the process of being converted into products. These states are crucial as they determine the pathway and energy requirements of a reaction, influencing processes such as gamma decay and internal conversion. The stability and properties of these states can impact the efficiency and likelihood of specific decay processes.