2.1 Types of radioactive decay

Radioactive decay is a fundamental process in nuclear physics, involving unstable atomic nuclei releasing energy and transforming into more stable forms. Understanding different decay modes provides insights into nuclear structure, particle interactions, and energy release mechanisms.

This topic explores various types of radioactive decay, including alpha, beta, gamma, and spontaneous fission. Each decay mode has unique characteristics, affecting atomic numbers and mass numbers differently, and plays crucial roles in nuclear applications and natural phenomena.

Types of radioactive decay

• Radioactive decay encompasses various processes by which unstable atomic nuclei release energy and transform into more stable configurations
• Understanding different decay modes provides crucial insights into nuclear structure, particle interactions, and energy release mechanisms
• Applied nuclear physics utilizes knowledge of decay types to develop technologies for energy production, medical diagnostics, and materials analysis

Alpha decay

Top images from around the web for Alpha decay

• 

  Modes of Radioactive Decay | Introduction to Chemistry View original

  Is this image relevant?

• 

  Radioactive Decay | Chemistry View original

  Is this image relevant?

• 

  Modes of Radioactive Decay | Introduction to Chemistry View original

  Is this image relevant?

• 

  Radioactive Decay | Chemistry View original

  Is this image relevant?

1 of 2

Top images from around the web for Alpha decay

• 

  Modes of Radioactive Decay | Introduction to Chemistry View original

  Is this image relevant?

• 

  Radioactive Decay | Chemistry View original

  Is this image relevant?

• 

  Modes of Radioactive Decay | Introduction to Chemistry View original

  Is this image relevant?

• 

  Radioactive Decay | Chemistry View original

  Is this image relevant?

1 of 2

• Occurs in heavy nuclei when two protons and two neutrons are emitted as an alpha particle (helium-4 nucleus)
• Reduces the atomic number of the parent nucleus by 2 and the mass number by 4
• Characterized by discrete energy spectra due to quantized nuclear energy levels
• Typically observed in elements with atomic numbers greater than 82 (lead)

Beta decay

• Involves the transformation of a neutron into a proton or vice versa, accompanied by the emission of an electron or positron
• Mediated by the weak nuclear force, allowing for flavor-changing interactions
• Results in the change of atomic number by 1 while maintaining the same mass number

Beta minus decay

• Neutron converts to a proton, emitting an electron and an antineutrino
• Increases the atomic number of the nucleus by 1
• Common in neutron-rich nuclei, often produced in nuclear fission reactions
• Energy spectrum of emitted electrons continuous due to three-body decay process

Beta plus decay

• Proton converts to a neutron, emitting a positron and a neutrino
• Decreases the atomic number of the nucleus by 1
• Occurs in proton-rich nuclei, often produced in particle accelerators
• Requires sufficient energy to overcome the mass difference between proton and neutron

Electron capture

• Proton in the nucleus captures an inner-shell electron, converting to a neutron
• Decreases the atomic number by 1 without changing the mass number
• Competes with beta plus decay in proton-rich nuclei
• Characterized by emission of characteristic X-rays or Auger electrons

Gamma decay

• Involves the emission of high-energy photons (gamma rays) from excited nuclear states
• Does not change the atomic number or mass number of the nucleus
• Plays a crucial role in nuclear spectroscopy and medical imaging techniques
• Often occurs in conjunction with other decay modes as nuclei de-excite

Isomeric transitions

• Gamma emission from long-lived excited nuclear states called isomers
• Metastable states can have half-lives ranging from nanoseconds to years
• Important in nuclear medicine for producing radioisotopes with desired decay properties
• Technetium-99m used extensively in medical imaging undergoes isomeric transition

Internal conversion

• Excited nucleus transfers energy directly to an atomic electron, ejecting it from the atom
• Competes with gamma emission, especially in heavy nuclei and for low-energy transitions
• Produces characteristic X-rays or Auger electrons as atomic electrons rearrange
• Conversion coefficient depends on atomic number, transition energy, and multipolarity

Spontaneous fission

• Occurs in very heavy nuclei when they split into two or more lighter fragments
• Releases significant energy in the form of kinetic energy of fragments and neutrons
• Important process in nuclear reactors and weapons, as well as in stellar nucleosynthesis
• Probability of spontaneous fission increases with atomic number and neutron-to-proton ratio

Characteristics of fission

• Asymmetric mass distribution of fission fragments typically observed
• Emission of prompt neutrons (2-3 on average) accompanies the fission process
• Total energy release approximately 200 MeV per fission event
• Fission cross-section varies greatly with incident neutron energy (thermal vs fast neutrons)

Fission products

• Wide range of isotopes produced, often neutron-rich and unstable
• Fission product yields depend on the fissioning nucleus and neutron energy
• Many fission products undergo subsequent beta decay, forming decay chains
• Accumulation of fission products in nuclear reactors leads to poisoning effects (xenon-135)

Neutron emission

• Process where a nucleus emits one or more neutrons, reducing its mass number
• Occurs in very neutron-rich nuclei or as a result of nuclear reactions
• Important in nuclear astrophysics for understanding stellar nucleosynthesis
• Neutron emission can be prompt (immediate) or delayed (following beta decay)

Delayed neutron emission

• Occurs when a beta-decay daughter nucleus is formed in a neutron-unbound state
• Critical for control of nuclear reactors, allowing time for control rod adjustments
• Typically represents a small fraction (< 1%) of total neutrons in fission
• Characterized by six delayed neutron groups with different half-lives and energies

Prompt neutron emission

• Neutrons emitted immediately (< 10^-14 s) following nuclear fission or other reactions
• Carries away excess energy and helps stabilize the excited fission fragments
• Energy spectrum of prompt neutrons follows a Maxwellian distribution (Watt spectrum)
• Average number of prompt neutrons per fission increases with incident neutron energy