Pick a real isotope, choose a decay mode, and fire decays one at a time. The nuclide chart shows where the daughter lands; the histogram below fills in with individually sampled electron energies until the continuous beta spectrum emerges.
Decay energy Q
0.1565 MeV
endpoint 156.5 keV
Parent
C-14
A 14 · Z 6 · N 8
Daughter
N-14
A 14 · Z 7 · N 7
NuclideC-14
Decay modebeta-minus
This event · electron
—
fire a decay to sample an energy
Mean electron energy
—
0 events · converges to 54.4 keV
Greyed-out modes are energetically impossible for this nuclide.
Tip: fire 500 into H-3, then into Na-22. Same shape, wildly different width — that is why a quoted beta energy is a maximum, not a typical value. The dashed grey line is the mean the histogram converges to.