Beta decay
The emission of beta radiation provides evidence that neutrons and protons are made up of quarks.
Beta (\(\beta^-\)) decay is the release of an electron by the change of a neutron to a proton.
- The neutron (charge = 0) is made up of one up quark (charge = \(\frac{2}{3}\)) and two down quarks (charge = \(2 \times \frac{1}{3}=\frac{2}{3}\)).
- One of the down quarks (charge = \(- \frac{1}{3}\)) is transformed into an up quark (charge = \(\frac{2}{3}\)). This difference in charge (\(+1\)) is conserved by the weak force boson \(W^{-}\).
- The new up quark moves away from the emitted \(W^{-}\). The neutron becomes a proton made up from two up quarks and one down quark (charge \(=2 \times \left(+\frac{2}{3}\right) - \frac{1}{3} =1\)).
- The short-lived \(W^{-}\) boson decays, forming an electron (charge =\(-1\)) and an electron neutrino (charge = 0).
- The proton, electron, and the antineutrino move away from one another emitting the electron as a beta particle.
The process is summarised by the equation:
\(_0^1n\rightarrow_1^1p+_{-1}^{\,\,\,\,\,0}e+\overline{v}_e\)
The evidence for the existence of quarks and other subatomic particles comes from the âdebrisâ moments after collisions between electrons, neutrons and protons in particle accelerators.
Each of particles in the standard model has an associated antiparticle.
When a particle and antiparticle combine to âannihilateâ each other the only result is energy. In hospitals, radioactive molecules that emit antimatter particles are used for imaging with positron emission tomography (PET scans).
Question
The above example is of beta negative decay. In beta positive decay a positron (positively charged lepton) is emitted along with a neutrino. What change must happen in the nucleus?
An up quark changes to a down quark so a proton changes to a neutron.