अणूभट्ट्या हे किरणोत्सर्गाचे महत्वपूर्ण स्रोत आहेत, विशेषत :

The correct answer is Option D (Neutron radiation).

Key Points:
• Operational physics inside a nuclear fission reactor core:
• Continuous Fission Mechanism: In an operating reactor, fission reactions are triggered and sustained continuously by neutrons: ²³⁵₉₂U + ¹₀n → Fission Fragments + 2 to 3 ¹₀n + 200 MeV Energy.
• Radiation Field: The operating reactor core generates massive fluxes of free prompt and delayed neutrons (Neutron radiation) alongside gamma rays.
• Penetrating Power: Uncharged, highly penetrating neutron radiation induces secondary radioactivity in surrounding structural components through neutron activation, necessitating specialized biological shielding (heavy water, graphite, borated steel, thick concrete).
• Nuclear reactors are the pre-eminent artificial sources of Neutron radiation (Option 4).
• Key Takeaway: Operating nuclear reactors produce an intense flux of prompt and delayed neutron radiation alongside gamma rays.