title: Determination of ²²⁶Ra, ²²⁸Ra and ²¹⁰Pb in NORM products from oil and gas exploration: problems in activity underestimation due to the presence of metals and self-absorption of photons.
abstract: Typical calibration of solid environmental samples for the determination of (226)Ra, (228)Ra and (210)Pb entails the use of standard reference materials which have a very similar matrix. However, TENORM samples from the oil and gas exploration contain unusually high amounts of calcium, strontium and barium which can severely attenuate the photons of (210)Pb and (226)Ra with their characteristic 46.1 keV and 186.2 keV gamma-rays, respectively and to some extent (228)Ra with the characteristic gamma-rays of 911.2 keV and 969.0 keV. We used neutron activation analysis to evaluate the content of TENORM for calcium, barium and strontium and then used a software program SELABS to determine the self-absorption. Our results confirm that even in Petrie containers with small dimensions the (210)Pb can be underestimated by almost by a factor of four while (226)Ra can be underestimated by 5%. The (228)Ra activities are virtually unaffected due to the higher energy gamma-rays. However, the implications for TENORM studies that employ large Marinelli containers having sample sizes between 0.25 and 1.0 L may be severely compromised by the presence of high Z elements in elevated concentrations. The usual spectral interferences on (226)Ra, (228)Ra and (210)Pb coming from other radionuclides in the (234)U, (235)U and (238)U decay chains are virtually nonexistent due the very high activity levels of (226)Ra, (228)Ra and (210)Pb in the tens of thousands of Bq/kg.
authors.affiliation: University of Texas at Austin, Nuclear Engineering Teaching Laboratory, Pickle Research Campus, R-9000, Austin, TX 78731, USA. Electronic address: s.landsberger@mail.utexas.edu.
authors.forename: S
authors.initials: S
authors.lastname: Landsberger
authors.forename: C
authors.initials: C
authors.lastname: Brabec
authors.forename: B
authors.initials: B
authors.lastname: Canion
authors.forename: J
authors.initials: J
authors.lastname: Hashem
authors.forename: C
authors.initials: C
authors.lastname: Lu
authors.forename: D
authors.initials: D
authors.lastname: Millsap
authors.forename: G
authors.initials: G
authors.lastname: George
mesh_terms: D007856:Lead Radioisotopes / Q000032:analysis*; D008670:Metals / Q000032:analysis; D061329:Oil and Gas Fields; D017785:Photons; D011834:Radiation Monitoring; D011883:Radium / Q000032:analysis*; D013051:Spectrometry, Gamma
chemical_list: D007856:Lead Radioisotopes; D008670:Metals; D011883:Radium
keywords: (226)Ra; (228)Ra and (210)Pb; NORM; Oil and gas industry