Speaker
Dr
Jay W. Grate
(Pacific Northwest National Laboratory)
Description
Ultra low-background radiation measurements are essential to several large scale physics investigations, including dark matter detection (e.g. SuperCDMS). To drive down background noise levels, radioactive contaminant species in the materials used to make and house radiation detectors must be minimized. Low background materials have been affirmed as an infrastructure requirement at recent workshops.(e.g. Snowmass 2013) The radioisotopic purity required goes well beyond even the best industry practices for chemical purity. Prior work has addressed many issues with semiconductor detector materials, shielding, and metallic conductors(copper).
There remain needs for insulating dielectric materials with extremely low background radioactivity, a need best met with polymer plastics. Past plastics found to have reasonable radiopurity, i.e., certain polyethylene and polytetrafluoroethylene (Teflon) materials, have very poor mechanical properties. There is a need to move from materials with milliBq/kg levels toward those with low microBq/kg levels. It is required that the materials be especially low in U, Th, and K.
In addition, the assay of polymer materials for extremely low levels of radioactive elements presents new challenges. There are, for example, no certified reference materials for U or Th in thermoplastics. Typical methods for sample preparation for analysis of ppm to ppb levels of metals in plastic are not always directly applicable to the determination of ppt levels of U in plastics, because sample preparation processes can introduce contamination using conventional methods and containers.
This talk will describe PNNL’s program in sourcing and analyzing polymers for low background applications. We will describe the multifaceted criteria for selecting potential polymers, and sourcing them to find low contaminant materials that are not subsequently contaminated by post-production processing. We will also describe a variety of assay methods, under use or in development, including radiation counting and various mass spectrometric techniques.
Primary author
Dr
Jay W. Grate
(Pacific Northwest National Laboratory)
Co-authors
Eric W. Hoppe
(Pacific Northwest National Laboratory)
Dr
Isaac Arnquist
(Pacific Northwest National Laboratory)
Dr
Mary Bliss
(Pacific Northwest National Laboratory)
May-Lin P. Thomas
(Pacific Northwest National Laboratory)
Orville Thomas Farmer III
(Pacific Northwest National Laboratory)
