In beta-minus decay, a neutron decays into three other particles. Write a nuclear equation for this process.

A student, supervised by their teacher, carries out an experiment with three unlabelled radioactive sources.

The student is told that each source emits only one type of radiation. One emits alpha particles, one emits beta-minus particles, and one emits gamma rays.

The student has the following equipment:

• a selection of materials with different thicknesses (including paper, aluminium sheets of a few millimetres, and thick lead)
• a strong magnet
• a radiation counter (GM tube and counter).

Explain how the student can use this equipment to determine safely which radiation each source emits.