Physic Labs

Frontier physics

Nuclear reactions and fission

Model a fission event and its neutron multiplication: vary the model parameter to move the multiplication factor keffk_{\mathrm{eff}} below, at, and above 1, and estimate released energy from Q=(minitial−mfinal)c2Q=(m_{\mathrm{initial}}-m_{\mathrm{final}})c^2.

Advanced

⚠ Real fission experiments involve ionizing radiation and neutron sources; they require licensed facilities, shielding, and dosimetry — never handle radioactive material outside them.

Equipment

  • 3D fission model emitting fragments and secondary neutrons
  • Slider “Tham số” (model parameter controlling neutron multiplication)
  • Slider “Độ nhiễu” (noise level) and “Tham số vật lý” (physical parameter)
  • “Chạy thời gian” (run time) control for the chain evolution

Procedure

  1. Watch one fission

    Trigger the event and watch a heavy nucleus split into two fragments plus secondary neutrons. Charge and nucleon number are conserved; for a typical 235^{235}U event the fragments carry about 200 MeV of kinetic energy, consistent with Q=Δm c2Q=\Delta m\,c^2.

  2. Tune the multiplication factor

    Sweep the parameter slider while the time evolution runs. Below criticality (keff<1k_{\mathrm{eff}}<1) the neutron population dies out; at keff=1k_{\mathrm{eff}}=1 it self-sustains; above 1 it grows exponentially — identify the setting where the chain is just self-sustaining.

  3. Add noise and compare regimes

    Raise the noise slider and rerun near keff=1k_{\mathrm{eff}}=1: statistical fluctuations decide whether individual chains survive. Estimate the energy per fission (about 200 MeV =3.2×10−11=3.2\times10^{-11} J) and compute how many fissions per second a 1 GW reactor needs.

Simulation

Experiment history

Otto Hahn and Fritz Strassmann observed barium among the products of neutron-bombarded uranium in December 1938 — a chemically impossible result unless the nucleus had split. Lise Meitner and Otto Frisch explained it weeks later as nuclear fission and estimated the released energy; Frisch confirmed it experimentally in early 1939. Leo Szilárd immediately saw the chain-reaction possibility, and Enrico Fermi's Chicago Pile-1 achieved the first self-sustaining chain on 2 December 1942. The physics then branched into reactors for power and weapons — and into safeguards, since the same keff>1k_{\mathrm{eff}}>1 regime underlies both.

Related physicists

Marie CurieAlbert Einstein

Related library topics

Nuclear reactions and fission