Probing Radiation Damage in Plutonium Alloys with Multiple Measurement Techniques
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Probing Radiation Damage in Plutonium Alloys with Multiple Measurement Techniques 1
S.K. McCall1, M.J. Fluss1 and B.W. Chung1 Lawrence Livermore National Laboratory, Livermore CA 94550 U.S.A.
ABSTRACT A material subjected to radiation damage will usually experience changes in its physical properties. Measuring these changes in the physical properties provides a basis to study radiation damage in a material which is important for a variety of real world applications from reactor materials to semiconducting devices. When investigating radiation damage, the relative sensitivity of any given property can vary considerably based on the concentration and type of damage present as well as external parameters such as the temperature and starting material composition. By measuring multiple physical properties, these differing sensitivities can be leveraged to provide greater insight into the different aspects of radiation damage accumulation, thereby providing a broader understanding of the mechanisms involved. In this report, selfdamage from α-particle decay in Pu is investigated by measuring two different properties: magnetic susceptibility and resistivity. The results suggest that while the first annealing stage obeys second order chemical kinetics, the primary mechanism is not the recombination of vacancy-interstitial close pairs. INTRODUCTION For most materials, radiation damage results only from external bombardment by a particle beam or flux of electrons, neutrons, or heavier ions. Particularly for the lighter particle irradiations, the damage created consists largely of collections of Frenkel pairs—a vacancy and an interstitial. A second, much less common form of radiation damage is self damage arising from naturally radioactive elements, such as occurs in the actinides. While many of the actinides decay by emission of an α-particle, which approximates a high energy light particle in terms of the damage created, it will also involve the recoil of a heavy ion quite comparable in mass to the other atoms of the lattice. This recoiling ion careens through the lattice like a roller-skating bear in a china shop, initiating dense cascades rich in vacancies and interstitials which are more complex than the relatively dilute concentration of Frenkel pairs created by the α-particle. In the study of radiation damage, radioactive systems have some advantages over those requiring external sources. The damage tends to be uniform and isotropic within the specimen since the decays are equally probable for any atom in the system. This allows samples of any shape to be studied, as well as investigating properties in environments where employing a particle beam is challenging, such as in high magnetic fields, or under high pressure. This makes practical the measurement of some physical properties that are not easily coupled to a particle accelerator, such as magnetization and specific heat. There are also inherent challenges in studying radioactive specimens. If the sample has an extremely long half life, such as 238U at
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