Background The spatial distribution of the neutron-induced gamma radiation field generated within the ground medium by intense pulsed neutrons is critically dependent on the neutron source location and the chemical composition of the soil. These distributional variations give rise to differential radiological hazards for personnel.

Purpose The objective of this study is to quantitatively assess the environmental levels of neutron-induced gamma radiation across diverse scenarios—specifically incorporating variations in neutron source location and ground medium composition—to facilitate research on intense pulsed neutron radiation environments and to inform evidence-based development of radiation protection protocols for personnel.

Methods Based on an atmospheric stratification model, a two-step Monte Carlo simulation methodology was implemented to quantify the dose distribution of neutron-induced radioactivity within the ground medium and the temporal evolution of dose rates at representative locations across diverse soil compositions. Subsequently, empirical formulas characterizing the dose contributions of individual radionuclides were derived through curve-fitting analysis. Numerical simulations were performed for three representative soil compositions to derive nuclide-specific activation coefficients, facilitating rapid estimation of activated atom populations within the soil matrix. The average dose contributions of individual radionuclides were quantitatively evaluated based on dose contribution per unit mass. Furthermore, two novel safety metrics—the Soil Safety Residence Index and Safety Residence Distance —were proposed to systematically assess the safety of the induced radioactivity environment caused by intense pulsed neutron under varying soil conditions across multiple temporal scales.

Results Results demonstrate that, for neutron source heights below 1000 m, the dose exhibits an exponential dependence on source altitude, while the activation coefficient shows pronounced variation with horizontal projection distance. Manganese (Mn) was identified as the element contributing the highest dose per unit mass. Soils with low aluminum (Al) content yielded a higher Soil Safety Residence Index, whereas soils enriched in manganese (Mn) and sodium (Na) exhibited shorter Safety Residence Distances, indicating elevated radiological risk under equivalent exposure conditions.

Conclusions This study confirms that the spatial distribution and temporal evolution of the gamma radiation field generated by intense pulsed neutrons are governed by source geometry and the chemical composition of the soil medium. Manganese (Mn) is identified as the predominant radionuclide contributing to dose per unit mass, underscoring the imperative for enhanced radiological protection protocols in manganese-enriched soil environments. Moreover, the Soil Safety Residence Index and Residence Distance serve as rapid, quantitative metrics to inform appropriate radiation protection strategies for personnel across diverse soil conditions.