An isolated sample of ground-state nickel-60 (atomic number 28) undergoes a two-step radioactive sequence that ultimately produces ground-state iron-60 (atomic number 26). Instrument readings reveal the following time-ordered signals:
• Within the first few seconds, a positron is detected emerging from the sample.
• Approximately 10−12s later, a single 1.17MeV photon is recorded.
No other nuclear particles are observed during the sequence.
(a) For each of the two observed emissions, identify the type of radiation.
(b) Write the nuclide symbol (mass number and atomic number) for the intermediate nucleus formed after the first emission.
(c) Using conservation of nucleon number, electric charge, and lepton number, demonstrate why the overall transformation from nickel-60 to iron-60 cannot occur in a single decay but must proceed through the two-step sequence observed.
(d) Give a qualitative explanation for why the second step releases a photon instead of another nuclear particle.