Handling, transfer, storage, and shipping of commercial thin film hydride disk target samples

Abstract

Thin film hydride (i.e., elements that can react with hydrogen or its isotopes to form a chemical compound) targets are important for many applications, including accelerator research, oil-well logging, cancer research, various neutron devices, nuclear waste assay, process control studies, contraband detection, and for many other novel uses. They are very sensitive to air-oxidation and easily contaminated by improper handling. Targets must be handled very carefully after processing to minimize contamination from physical handling, particulate contamination, and air-exposure, which oxidize sensitive groups IIIB, IVB, and rare earth thin film materials, thus reducing their operating characteristics such as neutron output, and can produce arcing if used in neutron devices. This paper will discuss the development of handling techniques, special vacuum transfer, and shipping containers for thin film hydride target samples from postprocessing to transfer and shipment to a customer. Initial work began at the General Electric Neutron Devices Department, in Largo, FL, in the mid-1970s and was refined at the Los Alamos National Laboratory in Los Alamos, NM, in the mid to late 1990s. Studies were performed to determine the best physical handling techniques, procedures for reducing particulate contamination and for reducing air-exposure and moisture from targets. Items studied were argon or dry nitrogen filled gloveboxes, desiccators, vacuum shipping containers, and a new design loader in a glovebox (in 1993), with an International Organization for Standardization class 4 clean room dry nitrogen environment, with particle and moisture removal and measurements. Test samples of hydride thin films were used to study surface oxide contamination as a function of handling, transfer, and storage times utilizing Auger argon sputter thin film depth profiling techniques. Results have shown that argon filled gloveboxes and dry nitrogen filled desiccators, along with techniques used to minimize target air-exposure, and various vacuum ∼≤1 × 10−3 Torr (1.33 × 10−1 Pa) internal environment shipping containers initially pumped down to ∼1 × 10−7 Torr (1.33 × 10−5 Pa) or less, were adequate to supply customers with thin film hydride targets with surface oxides from 70 to 475 Å or 7.0 to 47.5 nm, as it takes ∼>500 nm to affect neutron output in neutron devices. A special dry nitrogen glovebox controlled clean room loader with a high-efficiency particulate air filter/fan module, and oxygen and water vapor monitors was developed to produce a pristine super clean environment with very low particulate and film surface oxide contamination. The authors demonstrated that we can ship thin film hydride targets of optimum quality adequate for many applications and can supply pristine targets when requested which are in a condition very close to that as processed directly out of a non-air-exposed loader. In addition, our results showed the relative oxidation susceptibility for the four occluder thin films studied: Sc > Zr > Er > Ti.