Introduction
Summary
- The notes provide an expanded overview of radioactivity, emphasizing radionuclides and their natural occurrence in elements with atomic numbers greater than 83. They explain alpha and beta decay processes, including their mechanisms and energy spectra, alongside gamma radiation and its specific spectra. Furthermore, the notes elaborate on the concept of metastable states and isomeric transitions, detailing how these states contribute to nuclear stability and the emission processes involved.
Radioactivity and Radionuclides
- Radioactivity: The spontaneous emission of particles or radiation from an unstable atomic nucleus aiming for a stable state.
- Radionuclides: These are isotopes with unstable nuclei that emit radiation, existing naturally in elements with an atomic number over 83, such as Bismuth-209.
Alpha- and Beta-Nuclear Transformations
- Alpha Decay:
- Involves emission of alpha particles (helium-4 nuclei).
- Results in a decrease of atomic mass by 4 units and atomic number by 2.
- Low penetration; stopped by a thin sheet of paper or a few centimeters of air.
- Beta Decay:
- Beta-minus Decay: Neutron converts into a proton, electron, and anti-neutrino.
- Beta-plus Decay: Proton converts into a neutron, positron, and neutrino.
- Energy Spectra: Beta particles exhibit a range of energies, shared with neutrinos, unlike the discrete energy levels of alpha particles.
- Equations :
- The α decay equation is AZXN⇒A−4Z−2YN−2+42He2 Z A X N ⇒Z − 2 A − 4 Y N − 2 + 2 4 He 2 . Nuclear decay releases an amount of energy E related to the mass destroyed ∆m by E = (∆m)c2.
- There are three forms of beta decay. The β− decay equation is AZXN ⇒ AZ+1YN−1+β−+¯νe Z A X N ⇒Z + 1 A Y N − 1 + β − + ν ¯ e .
Gamma-Radiation and Spectra
- Gamma Radiation: High-frequency, high-energy electromagnetic radiation emitted from a nucleus transitioning from a higher energy state to a lower one.
- Gamma Spectra: Characterized by discrete energy peaks specific to nuclear transitions, crucial for identifying isotopes in nuclear spectroscopy.
Metastable State and Isomeric Transition
- Metastable State: An unusually long-lived excited nuclear state, ranging from milliseconds to years, before decaying.
- Isomeric Transition: Involves the emission of a gamma ray by a nucleus in a metastable state, transitioning to a lower energy state without altering its atomic or mass numbers, leading to nuclear stability.