PHYSICS · Single correct · A Level · Physics · Particles and radiation · Particles and radiation
Problem
In the decay 53131I→54131Xe+e−+νˉe, the mass number of the nucleus remains 131 while the atomic number increases by one. Which of the following best explains this observation?
(a) The nucleus absorbs an inner-shell electron, turning a neutron into a proton; the total number of nucleons stays the same while the proton count rises by one.
(b) Removing a negatively charged electron from the nucleus leaves one extra unit of positive charge, so A stays 131 but Z increases by 1.
(c) Inside the nucleus a neutron converts into a proton and emits an electron and an antineutrino, keeping the nucleon total the same while adding one proton.
(d) The antineutrino carries away a neutron’s worth of mass, compensating for the creation of a new proton so A is unchanged even as Z increases.