As the United States continues to reduce its cache of nuclear weapons, the importance of safely storing radioactive components has become a frontline issue. Our nation must ensure the storage methods we use for disassembled weapons are safe. Decaying plutonium isotopes emit energetic alpha particles which continually introduce helium into metal that comes into contact with plutonium. This process may possibly lead to a breakdown of the metal's mechanical properties. In the the study just completed, researchers investigated the effects of radiation upon the surface and microstructure of stainless steel by high fluence alpha particle irradiation from plutonium.
Stainless steel is the metal most often used to encase plutonium pits.
To calculate the alpha particle emission rate from WGPu, researchers developed a Monte Carlo code that yielded information pertaining to the alpha particle source strength at the WGPu - stainless steel interface. The code also produced data regarding the helium concentration depth profiles within the stainless steel. Because stainless steel has a high iron content, iron is a suitable surrogate material. Given the sensitivity of RBS and channeling analysis, the possibility of bubble cluster formation cannot be eliminated. This fluence level corresponds to a storage period of 107 years, suggesting that there was no significant propagation of possible micro-cracks formed between bubble sites which would allow diffusion of helium within the metal.