Abstract:
Background The assessment of gamma radiation dose released by strong explosions is an important direction in the research of nuclear emergency protection systems. Traditional research has mostly focused on dose assessment of prompt gamma radiation (with a duration of less that 1 μs）, while delayed gamma radiation (on the second timescale) is often overlooked due to time delay.
Purpose This article focuses on the study of the delayed gamma dose released by fission products after a strong explosion within 0.2–0.5 s, as well as the secondary gamma dose generated by neutron leakage, with the aim of systematically evaluating their radiation hazards in the near to medium range.
Methods Based on Monte Carlo (MC) method, a three-dimensional full-scale model coupling strong explosive source term atmospheric transport surface activation was constructed, and a dynamic dose assessment framework based on MC multi-step calculation was proposed. By modifying the importance card method, the variance of the simulation results at medium to close distances was effectively reduced, and a detailed comparison was made between the changing trends of delayed gamma and prompt gamma doses over time and distance.
Results The simulation results show that within a time window of 0.2– 0.5 s: at a distance of 500 m from the explosion source, the total dose of delayed gamma radiation reaches 0.829 Gy, which is 1.88 times that of the instantaneous gamma radiation dose (0.441 Gy); At a distance of 1000 m from the explosion source, the delayed gamma dose generated by fission products alone is 0.0318 Gy, which is 7.6 times that of the instantaneous gamma dose (0.0042 Gy), indicating that the hazard of delayed gamma is significantly higher than that of instantaneous gamma at longer distances. The secondary gamma dose generated by neutron leakage decays from 0.634 Gy at 500 m to 0.0485 Gy at 1000 m.
Conclusions The dynamic dose assessment framework proposed in this article effectively reveals the significant contribution of delayed gamma radiation in the early radiation field after a strong explosion, especially at a distance where its hazard far exceeds that of instantaneous gamma radiation. This study provides key data support for optimizing nuclear emergency protection strategies.
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