For SCO-1 Object, what is the nonfixed contamination limit on the accessible surface averaged over 300 cm2?

• A. The nonfixed contamination on the accessible surface averaged over 300 cm2 does not exceed 400 Bq/cm2 for beta and gamma and low toxicity alpha emitters, or 40 Bq/cm2 for all other alpha emitters.
• B. The nonfixed contamination on the accessible surface averaged over 300 cm2 does not exceed 40 Bq/cm2.
• C. The nonfixed contamination on the accessible surface averaged over 300 cm2 does not exceed 800 Bq/cm2.
• D. The nonfixed contamination on the accessible surface averaged over 300 cm2 does not exceed 4 Bq/cm2.

Answer: (A)

Nonfixed contamination is the portion of radioactive material that can be removed from a surface by wiping or washing. For SCO-1 Objects, regulations express this as an average contamination over a defined accessible surface area, typically 300 cm2, to provide a fair assessment of the whole surface rather than a single spot.

The best answer reflects the two-tier limit based on the type of radionuclide. For beta and gamma emitters and alpha emitters of low radiotoxicity, the surface average must not exceed 400 Bq per cm2 over the 300 cm2 area. For all other alpha emitters, the limit is much stricter: 40 Bq per cm2 over the same area. This distinction accounts for differing radiotoxicities—higher risk alpha emitters require tighter control of removable contamination.

Other proposed limits don’t match this regulatory structure: one-size-fits-all values or much lower figures don’t reflect the two-category approach or the correct numerical thresholds.