Pacific Northwest National Laboratory has recently opened a shallow underground laboratory intended for measurement of lowconcentration levels of radioactive isotopes in samples collected from the environment. The development of a low-background liquid scintillation counter is currently underway to further augment the measurement capabilities within this underground laboratory. Liquid scintillation counting is especially useful for measuring charged particle (e.g., β, α) emitting isotopes with no (or very weak) gamma-ray yields. The combination of high-efficiency detection of charged particle emission in a liquid scintillation cocktail coupled with the low-background environment of an appropriately-designed shield located in a clean underground laboratory provides the opportunity for increased-sensitivity measurements of a range of isotopes. To take advantage of the 35 meters-waterequivalent overburden of the underground laboratory, a series of simulations have evaluated the scintillation counter's shield design requirements to assess the possible background rate achievable. This report presents the design and background evaluation for a shallow underground, low background liquid scintillation counter design for sample measurements.

Liquid scintillation counting (LSC) supports a range of environmental science measurements. At Pacific Northwest National Laboratory, we are constructing an LSC system with an expected background reduction of 10-100 relative to values reported in the literature. In this paper, a number of current measurement applications of LSC have been considered with an emphasis on determining which aspects of such measurements would gain the greatest benefit: improved minimum detectable activity (MDA), reduction in sample size, and reduction in total analysis time.

The Ultra-Low Background Liquid Scintillation Counter developed by Pacific Northwest National Laboratory will expand the application of liquid scintillation counting by enabling lower detection limits and smaller sample volumes. By reducing the overall count rate of the background environment approximately 2 orders of magnitude below that of commercially available systems, backgrounds on the order of tens of counts per day over an energy range of ~3-3600keV can be realized. Initial test results of the ULB LSC show promising results for ultra-low background detection with liquid scintillation counting.

Liquid scintillation counters measure charged particle-emitting radioactive isotopes and are used for environmental studies, nuclear chemistry, and life science. Alpha and beta emissions arising from the material under study interact with the scintillation cocktail to produce light. The prototypical liquid scintillation counter employs low-level photon-counting detectors to measure the arrival of the scintillation. For reliable operation, the counting instrument must convey the scintillation light to the detectors efficiently and predictably. Current best practices employ the use of two or more detectors for coincidence processing to discriminate true scintillation events from background events due to instrumental effects such as photomultiplier tube dark rates, tube flashing, or other light emission not generated in the scintillation cocktail vial. In low-background liquid scintillation counters, additional attention is paid to shielding the scintillation cocktail from naturally occurring radioactive material present in the laboratory and within the instrument's construction materials. Low-background design is generally at odds with optimal light collection. This study presents the evolution of a light collection design for liquid scintillation counting (LSC) in a low-background shield. The basic approach to achieve both good light collection and a low-background measurement is described. The baseline signals arising from the scintillation vial are modeled and methods to efficiently collect scintillation light are presented as part of the development of a customized low-background, high-sensitivity LSC system.

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The monitoring and decontamination of livestock has been an emerging topic in emergency response planning in recent years. Under the National Response Framework, the U.S. Department of Agriculture is tasked with providing support to the states during a radiological incident for the "assessment, control, and decontamination of contaminated animals, including companion animals, livestock, poultry, and wildlife." While there are currently no protocols in place on a national level for coordinated animal response, working groups have been developing a command structure and task force procedures, and some states have issued their own guidelines. A customized Bovine Screening Portal was manufactured and tested at Texas A&M University to investigate the operational capabilities in detecting, identifying, and localizing external contamination on livestock. An array of six sodium iodide detectors attached to power-over-Ethernet Multi-Channel Analyzers was used to collect time-stamped count rates, and spectral data were collected as a heifer was led past the detector panel. A 1.85 × 10(5) Bq 137Cs source was placed in four locations on a heifer, which was led through a cattle chute adjacent to the detector panel. The trials were repeated walking the heifer through a walkway with detectors hung on cattle pens lining a walkway. The Bovine Screening Portal observed increased count rates (>10σ) from the 1.85 × 10(5) Bq 137Cs source in live time. The identification capabilities with the intuitive software interface of the BSP are consistent with the requirements of a detection system for radiological emergency management of livestock.