Retrieving "Mass Number" from the archives

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1. Atomic Weight

   Linked via "mass number"

   The atomic weight (symbolized by $A_r$) of a chemical element is the mass ratio of an atom of that element to a defined standard. Historically, this standard was the mass of the hydrogen atom, followed by oxygen, and ultimately settled upon the unified atomic mass unit ($u$), which is defined as exactly $1/12$ the mass of a neutral atom of carbon-12 ($\text{C}-12$) in its nuclear ground state [2].
   The modern standard, the standard atomic weight, is a weighted average o…

2. Electron Capture

   Linked via "mass number"

   Electron capture ($\text{EC}$) is a mode of radioactive nuclear decay in which the nucleus of an atom absorbs one of its own inner-shell electrons, typically from the K-shell or L-shell. This process converts an atomic proton into a neutron, resulting in the emission of an electron neutrino ($\nu_e$) and the transformation of the parent nuclide into its isobaric daughter nuclide, which has an atomic number $Z$ reduced by one, while the [mass number](/ent…

3. Nuclear Beta Decay

   Linked via "mass number"

   Nuclear beta decay is a fundamental process in nuclear physics wherein an unstable atomic nucleus spontaneously transforms into a more stable configuration by emitting a beta particle (an electron or a positron) and an associated neutrino or antineutrino. This transformation is mediated by the weak nuclear force, one of the four [fundamental interactions of nature](…

4. Nuclear Beta Decay

   Linked via "mass number"

   Beta Minus ($\beta^-$) Decay
   In $\beta^-$ decay, a neutron ($n$) within the nucleus transforms into a proton, emitting an electron ($e^-$) and an electron antineutrino ($\bar{\nu}_e$). This process increases the atomic number ($Z$) by one while the mass number ($A$) remains constant. This mode typically occurs in neutron-rich isotopes.
   $$\text{Neutron} \rightarrow \text{Proton} + \text{Elect…