Radionuclide observables of underwater nuclear explosive tests

Area of Science:

• Nuclear Science
• Environmental Monitoring
• International Treaty Verification

Background:

• On-site Inspections (OSI) are crucial for verifying Comprehensive Nuclear-Test-Ban Treaty (CTBT) compliance.
• Terrestrial nuclear explosions have well-defined radionuclide signatures for detection.
• Underwater nuclear explosions introduce complexities due to neutron activation of seawater.

Purpose of the Study:

• To assess the impact of radionuclides induced by underwater nuclear explosions on OSI.
• To determine if activation products interfere with existing radionuclide observables for CTBT verification.
• To identify potential new indicators for underwater nuclear events.

Main Methods:

• Calculated inventories of relevant and activation radionuclides for a 1-kT underwater nuclear explosion.
• Utilized Monte Carlo techniques to model spectral interferences.
• Analyzed the decay rates of dominant activation products (38Cl and 24Na).

Main Results:

• Inventories of OSI-relevant (6.0 × 10^16 Bq) and activation (1.6 × 10^19 Bq) radionuclides were quantified.
• Predominant activation products 38Cl and 24Na decay significantly within 14 days.
• Spectral interferences from activation products were found to be negligible during this period.

Conclusions:

• Induced radionuclides from underwater nuclear explosions do not interfere with current CTBT OSI radionuclide measurements within 14 days.
• The activation product 24Na shows potential as a useful indicator for OSI purposes.
• Technical challenges for high-seas OSI are mitigated by understanding activation product behavior.