Most hazardous common radionuclide emitter: which one releases α, β, and γ radiation? Select the radioactive waste that emits all three types of ionising radiation, making it especially hazardous during handling and shielding design.

Introduction / Context:
Radiation safety in environmental engineering and nuclear waste management hinges on knowing the emission type of radionuclides. Alpha (α), beta (β), and gamma (γ) radiations differ strongly in penetration and shielding requirements. A nuclide (or its decay chain) that presents all three poses broader hazards for storage and transport.

Given Data / Assumptions:

• Compare I-131, Sr-90, Au-198, and Ra-226 with respect to emitted radiation.
• Consider both the parent and immediate daughters in practical handling scenarios.

Concept / Approach:
Ra-226 is an alpha emitter whose decay chain rapidly produces gamma-emitting daughters; in practice, the stored material presents α, β, and γ fields. By contrast, Sr-90 is a strong β emitter (with Y-90) and minimal γ; I-131 mainly emits β and γ; Au-198 emits β with notable γ but not α.

Step-by-Step Solution:

Verification / Alternative check:
Standard decay scheme charts show Ra-226 (half-life ~1600 years) decays to Rn-222 and further daughters producing penetrating γ; alpha contamination and gamma fields both require attention.

Why Other Options Are Wrong:

Common Pitfalls:
Overlooking daughter products when planning shielding. With Ra-226, both contamination control (α) and external dose (γ) must be managed.

Final Answer:
Ra-226