title: First results of a simultaneous measurement of tritium and (14)C in an ultra-low-background proportional counter for environmental sources of methane.
abstract: Simultaneous measurement of tritium and (14)C would provide an added tool for tracing organic compounds through environmental systems and is possible via beta energy spectroscopy of sample-derived methane in internal-source gas proportional counters. Since the mid-1960's atmospheric tritium and (14)C have fallen dramatically as the isotopic injections from aboveground nuclear testing have been diluted into the ocean and biosphere. In this work, the feasibility of simultaneous tritium and (14)C measurements via proportional counters is revisited in light of significant changes in both the atmospheric and biosphere isotopics and the development of new ultra-low-background gas proportional counting capabilities for small samples (roughly 50 cc methane). A Geant4 Monte Carlo model of a Pacific Northwest National Laboratory (PNNL) proportional counter response to tritium and (14)C is used to analyze small samples of two different methane sources to illustrate the range of applicability of contemporary simultaneous measurements and their limitations. Because the two methane sources examined were not sample size limited, we could compare the small-sample measurements performed at PNNL with analysis of larger samples performed at a commercial laboratory. These first results show that the dual-isotope simultaneous measurement is well matched for methane samples that are atmospheric or have an elevated source of tritium (i.e. landfill gas). However, for samples with low/modern tritium isotopics (rainwater), commercial separation and counting is a better fit.
authors.affiliation: Pacific Northwest National Laboratory, 902 Battelle Blvd, P.O. Box 999, MSIN J4-65, Richland, WA 99352, USA. Electronic address: emily.mace@pnnl.gov.
authors.forename: E K
authors.initials: EK
authors.lastname: Mace
authors.affiliation: Pacific Northwest National Laboratory, 902 Battelle Blvd, P.O. Box 999, MSIN J4-65, Richland, WA 99352, USA.
authors.forename: C E
authors.initials: CE
authors.lastname: Aalseth
authors.affiliation: Pacific Northwest National Laboratory, 902 Battelle Blvd, P.O. Box 999, MSIN J4-65, Richland, WA 99352, USA.
authors.forename: A R
authors.initials: AR
authors.lastname: Day
authors.affiliation: Pacific Northwest National Laboratory, 902 Battelle Blvd, P.O. Box 999, MSIN J4-65, Richland, WA 99352, USA.
authors.forename: E W
authors.initials: EW
authors.lastname: Hoppe
authors.affiliation: Pacific Northwest National Laboratory, 902 Battelle Blvd, P.O. Box 999, MSIN J4-65, Richland, WA 99352, USA.
authors.forename: M E
authors.initials: ME
authors.lastname: Keillor
authors.affiliation: Pacific Northwest National Laboratory, 902 Battelle Blvd, P.O. Box 999, MSIN J4-65, Richland, WA 99352, USA.
authors.forename: J J
authors.initials: JJ
authors.lastname: Moran
authors.affiliation: Pacific Northwest National Laboratory, 902 Battelle Blvd, P.O. Box 999, MSIN J4-65, Richland, WA 99352, USA.
authors.forename: M E
authors.initials: ME
authors.lastname: Panisko
authors.affiliation: Pacific Northwest National Laboratory, 902 Battelle Blvd, P.O. Box 999, MSIN J4-65, Richland, WA 99352, USA.
authors.forename: A
authors.initials: A
authors.lastname: Seifert
authors.affiliation: Pacific Northwest National Laboratory, 902 Battelle Blvd, P.O. Box 999, MSIN J4-65, Richland, WA 99352, USA.
authors.forename: G
authors.initials: G
authors.lastname: Tatishvili
authors.affiliation: Pacific Northwest National Laboratory, 902 Battelle Blvd, P.O. Box 999, MSIN J4-65, Richland, WA 99352, USA.
authors.forename: R M
authors.initials: RM
authors.lastname: Williams
mesh_terms: D002250:Carbon Radioisotopes / Q000032:analysis*; D005740:Gases / Q000032:analysis; D008697:Methane / Q000032:analysis*; D008962:Models, Theoretical; D011834:Radiation Monitoring / Q000379:methods*; D014316:Tritium / Q000032:analysis*; D064091:Waste Disposal Facilities; D018508:Water Purification
chemical_list: D002250:Carbon Radioisotopes; D005740:Gases; D014316:Tritium; D008697:Methane
keywords: Environmental sample; Proportional counter; Radiocarbon; Simultaneous measurement; Tritium; Ultra-low-background