Before revision: Group Half-Life (s) Decay Constant (s−1) Energy (keV) Yield, Neutrons per Fission Fraction 1 55.72 0.0124 250 0.00052 0.000215 2 22.72 0.0305 560 0.00346 0.001424 3 6.22 0.111 405 0.00310 0.001274 4 2.30 0.301 450 0.00624 0.002568 5 0.610 1.14 - 0.00182 0.000748 6 0.230 3.01 - 0.00066 0.000273 Importance in nuclear reactors If a nuclear reactor happened to be prompt critical – even very slightly – the number of neutrons would increase exponentially at a high rate, and very quickly the reactor would become uncontrollable by means of external mechanisms.
After revision: Group Half–Life (s) Decay Constant (s−1) Energy (keV) Yield, Neutrons per Fission Fraction 1 55.72 0.0124 250 0.00052 0.000215 2 22.72 0.0305 560 0.00346 0.001424 3 6.22 0.111 405 0.00310 0.001274 4 2.30 0.301 450 0.00624 0.002568 5 0.610 1.14 – 0.00182 0.000748 6 0.230 3.01 - 0.00066 0.000273 Importance in nuclear reactors If a nuclear reactor happened to be prompt critical – even very slightly – the number of neutrons would increase exponentially at a high rate, and very quickly the reactor would become uncontrollable by means of external mechanisms.