represent α- and β-decay by a radioactive decay equation of the form UT h92238 90234

Atoms, Nuclei and Radiation

Objective

Represent α‑ and β‑decay by a radioactive decay equation of the form \$\,{Z}^{A}\text{X} \rightarrow \,{Z'}^{A'}\text{Y} + \text{particle}\,\$.

α‑Decay

In α‑decay the nucleus emits an α‑particle, which is a helium‑4 nucleus:

\$\$

\,{92}^{238}\text{U} \;\rightarrow\; \,{90}^{234}\text{Th} \;+\; \,_{2}^{4}\alpha

\$\$

• The mass number decreases by 4.
• The atomic number decreases by 2.

β‑Decay

In β‑decay a neutron is transformed into a proton with the emission of an electron (β⁻ particle) and an antineutrino (often omitted in simple equations):

\$\$

\,{6}^{14}\text{C} \;\rightarrow\; \,{7}^{14}\text{N} \;+\; \,_{-1}^{0}\beta

\$\$

• The mass number remains unchanged.
• The atomic number increases by 1.

Comparison of α‑ and β‑Decay

Practice Questions

1. Write the decay equation for the α‑decay of \$\,_{84}^{210}\text{Po}\$.
2. Write the decay equation for the β‑decay of \$\,_{11}^{22}\text{Na}\$.
3. Explain why the mass number does not change in β‑decay.