Detailed Notes on Nuclear Decay

Nuclear Decay Processes

Introduction to Nuclear Decay

• Nuclear decay involves the emission of particles and/or energy, leading to the transformation of one atom into another.
• In most cases, nuclear decay results in the atom changing its identity to become a new element.
• There are four primary types of emissions: alpha, beta, positron, and gamma.

Alpha Emission (α Decay)

• Alpha decay involves the release of helium ions ($He^{2+}$) from the nucleus of an atom. An alpha particle consists of two protons and two neutrons, giving it a 2+ charge.
• The release of an α-particle results in a new atom with an atomic number that is two less than the original atom and an atomic weight that is four less.
• An example of alpha decay is the conversion of uranium-238 to thorium:
  • $^{238}<em>{92}U {\longrightarrow} ^{234}</em>{90}Th + \alpha$
  • The atomic number decreases from 92 (uranium) to 90 (thorium), and the atomic weight decreases from 238 to 234.
• The alpha emission is often accompanied by gamma (γ) radiation, which is a form of energy release.
• Many of the largest elements in the periodic table are alpha emitters.

Beta Emission (β Decay)

• Beta decay is more complex than alpha emission; it involves the transformation of a neutron in the nucleus into a proton and an electron.
• The electron is then ejected from the nucleus.
• During this process, the atomic number increases by one, while the atomic weight remains the same.
• Similar to α-emissions, β-emissions are often accompanied by γ-radiation.
• A typical beta decay process involves carbon-14, which is often used in radioactive dating techniques. The reaction forms nitrogen-14 and an electron:
  • $^{14}<em>{6}C \longrightarrow ^{14}</em>{7}N + \beta$

Positron Emission

• A positron is a positive electron (a form of antimatter).
• This type of emission occurs when a proton is converted into a neutron and a positron in the nucleus, with the positron being ejected.
• As a result, the atomic number decreases by one, while the atomic weight does not change.
• A positron is often designated by $\beta^+$.
• Carbon-11 emits a positron to become boron-11:
  • $^{11}<em>{6}C \longrightarrow ^{11}</em>{5}B + \beta^+$

Electron Capture

• Electron capture is an alternative way for a nuclide to increase its neutron-to-proton ratio.
• In electron capture, an electron from an inner orbital is captured by the nucleus of the atom and combined with a proton to form a neutron.
• For example, silver-106 undergoes electron capture to become palladium-106.
• The overall result of electron capture is identical to positron emission: the atomic number decreases by one, while the mass number remains the same.
• $^{106}<em>{47}Ag + e^- \longrightarrow ^{106}</em>{46}Pd$

Gamma Emission (γ Emission)

• Gamma (γ) radiation is purely energy.
• It may be released by itself or, more commonly, in association with other radiation events.
• There is no change in atomic number or atomic weight in a simple γ-emission.
• Often, an isotope may produce γ-radiation as a result of a transition in a metastable isotope.
• This type of isotope may undergo a shift of particles in the nucleus, increasing its stability.
• This shift increases the stability of the isotope from the energetically unstable (or “metastable”) isotope to a more stable form of the nucleus.