Alpha-Particle-Induced Prompt Gamma-Ray Analysis of Plutonium-Bearing Materials Packaged in 3013 Containers

More than 5,500 containers of excess plutonium-bearing materialshave been packaged for long-term storage following the requirementsoutlined in the DOE-STD-3013. Knowledge of thechemical impurities in the packaged materials is important becausecertain impurities, such as chloride salts, affect the behaviorof the material in storage leading to gas generation and corrosionwhen sufficient moisture also is present. In most cases, the packagedmaterials are not well characterized, and information aboutthe chemical impurities is limited to knowledge of the material’sprocessing history. The alpha-particle activity from the plutoniumand americium isotopes provides a method of nondestructiveself-interrogation to identify certain light elements through thecharacteristic, prompt gamma rays that are emitted from alphaparticle-induced reactions with these elements. Gamma-ray spectraare obtained for each 3013 container using a high-resolution,coaxial high-purity germanium detector. These gamma-ray spectraare scanned from 800 to 5,000 keV for characteristic, promptgamma rays from the detectable elements, which include lithium,beryllium, boron, nitrogen, oxygen, fluorine, sodium, magnesium,aluminum, silicon, phosphorus, chlorine, and potassium.The lower limits of detection for these elements in a plutonium-oxide matrix increase with atomic number and range from100 or 200 ppm for the lightest elements such as lithium andberyllium, to 19,000 ppm for potassium. The peak areas fromthe characteristic, prompt gamma rays can be used to estimatethe concentration of the light-element impurities detected in thematerial on a semiquantitative basis. The use of prompt gammaanalysis to assess impurity concentrations avoids the expense andthe risks generally associated with performing chemical analysison radioactive materials. The analyzed containers are grouped byimpurity content, which helps to identify high risk containers forsurveillance and in sorting materials before packaging.