Luo, P., DeVol, T.A., Sharp, J.L.(2012) Bayesian Analysis of Time-Interval Data for Environmental Radiation Monitoring. Health Physics. 102(6):637-645.
Three statistical control chart methods were investigated to determine the one with the highest detection probability and the best average run length (ARL). The three control charts include the Shewhart control chart of count data, cumulative sum (CUSUM) analysis of count data (Poisson CUSUM), and CUSUM analysis of time-interval (time difference between two consecutive radiation pulses) data (time-interval CUSUM). The time-interval CUSUM (CUSUMti) control chart was compared with the Poisson CUSUM (CUSUMcnt) and the Shewhart control charts with experimental and simulated data. The experimental data were acquired with a DGF-4C (XIA, Inc.) system in list mode. Simulated data were obtained by using Monte Carlo techniques to obtain a random sampling of a Poisson process. All statistical algorithms were developed using R (R Development Core Team). Detection probabilities and ARLs for the three methods were compared. The time-interval CUSUM control chart resulted in a similar detection probability as that of the Poisson CUSUM control chart but had the shortest ARL at relatively higher radiation levels; e.g., about 40% shorter than the Poisson CUSUM at 10.0 counts per second (cps) (five times above the background count rate). Both CUSUM control charts resulted in a higher detection probability than that of the Shewhart control chart; e.g., 100% greater than the Shewhart control method at 4.0 cps (two times above the background count rate). In addition, when time-interval information was used, the CUSUM control chart coupled with a modified runs rule (mrCUSUMti) showed the ability to further reduce the time needed to respond to changes in radiation levels and keep the false positive rate at a required level.
Seliman, A.F., Borai, E.H., Lasheen,Y.F., DeVol,T.A..(2012) Remobilization of 60Co, 85Sr, 137Cs, 152Eu and 241Am from a contaminated soil column by groundwater and organic ligands. Transport in Porous Media. 93(3), 799-813. DOI: 10.1007/s11242-012-9983-2
The desorption rate of 60Co, 85Sr, 137Cs, 152Eu, and 241Am from soil collected from Inshas disposal site in Egypt was investigated to understand the desorption and mobility of these radionuclides in the environment. Effect of a synthetic groundwater (GW) and the GW amended to 2 × 10−5M of ethylenediaminetetraacetic acid (EDTA) or ethylenediaminediacetic acid (EDDA), GW+ETDA and GW+EDDA, respectively, was studied in flow-through experiments. These experiments were designed to compare the influence of EDTA relative to one of its degradation products that can exist in natural water, EDDA. First-order desorption and two-site first-order desorption equations were used to describe the time-dependent desorption data. The desorption rate for 85Sr and 137Cs was high in the first 50 h followed by a slow release suggesting that two different mechanisms involved. The trace metal removal was not completely reversible for all radionuclides tracers except for 85Sr. The quantity of 85Sr, 137Cs, 152Eu, and 241Am desorbed from soil follows the order GW+EDTA > GW+EDDA > GW, while 60Co gives unexpected trends where the effect of EDDA is twice as high as that of EDTA. This behavior was discussed based on the aqueous species distribution of 60Co in both aqueous solutions.
Zavarin, M., Powell, B. A., Bourbin, M., Zhao, P., Kersting, A. B. (2012). Np(V) and PuV) Ion Exchange on Montmorillonite. Environ. Sci. Tech., 46, 2692-2698.
Due to their ubiquity and chemical reactivity, aluminosilicate clays play an important role in actinide retardation and colloid-facilitated transport in the environment. In this work, Pu(V) and Np(V) sorption to Na-montmorillonite was examined as a function of ionic strength, pH, and time. Np(V) sorption equilibrium was reached within 2 h. Sorption was relatively weak and showed a pH and ionic strength dependence. An approximate NpO2+ → Na+ Vanselow ion exchange coefficient (Kv) was determined on the basis of Np(V) sorption in 0.01 and 1.0 M NaCl solutions at pH < 5 (Kv 0.3). In contrast to Np(V), Pu(V) sorption equilibrium was not achieved on the time-scale of weeks. Pu(V) sorption was much stronger than Np(V), and sorption rates exhibited both a pH and ionic strength dependence. Differences in Np(V) and Pu(V) sorption behavior are indicative of surface-mediated transformation of Pu(V) to Pu(IV) which has been reported for a number of redox-active and redox-inactive minerals. A model of the pH and ionic strength dependence of Pu(V) sorption rates suggests that H+ exchangeable cations facilitate Pu(V) reduction. While surface complexation may play a dominant role in Pu sorption and colloid-facilitated transport under alkaline conditions, results from this study suggest that Pu(V) ion exchange and surface-mediated reduction to Pu(IV) can immobilize Pu or enhance its colloid-facilitated transport in the environment at neutral to mildly acidic pHs.
DeVol, T.A., Pruitt, L., Gallaird J., Sexton, L., Cordaro, J. Rao, A., Serkiz, S.M. (2011). Toward a carbon nanotube anode gas-filled radiation detector. Nuc. Instr. Meth. Physics A 652, 310-314.
Grogan, K.P., DeVol, T.A. (2011). Online Detection of Radioactive Iodine in Aqueous Systems through the Use of Scintillating Anion Exchange Resin. Analytical Chemistry, 83 (7), 2582-2588.
Jacobsohn, L. G., McPherson, C.L., Sprinkle, K. B., Yukihara, E.G., DeVol, T. A., Ballato, J. M. (2011). Scintillation of Rare Earth Doped Fluoride Nanoparticles,” Applied Physics Letters, Vol. 99, 113111.
Jacobsohn, L. G., Sprinkle, K. B., Roberts, S. A., Kucera, C. J., James, T. L., Yukihara, E.G., DeVol, T. A., Ballato, J. M. (2011). Fluoride Nanoscintillators. Journal of Nanomaterials, Vol. 2011, Article ID 523638, 6 pages, doi:10.1155/2011/523638.
Kaplan, D. I., Roberts, K. A., Schwehr, K. A., Lilley, M. S., Brinkmeyer, R., Denham, M. E., DiPrete, D., Li, H., Powell, B. A., Xu, C., Yeager, C. M., Zhang, S., Santschi, P. H. (2011). Cause of a Multi-species Radioiodine Plume that is Increasing in Concentration. Environ. Sci. Tech., 45(2), 489-495.
Powell, B. A., Dai, Z., Zavarin, M. Z., Zhao, P., Kersting, A. B. (2011). Stabilization of Plutonium Nano-colloids by Epitaxial Distortion on Mineral Surfaces. Environ. Sci. Tech., 45, 2698-2703.
Seliman, A.F., Samadi, A., Husson S.M., Borai, E.H., DeVol T.A. (2011). Preparation of Polymer-Coated, Scintillating Ion-Exchange Resins for Monitoring of 99Tc in Groundwater,” Anal. Chem. 83, 4759–4766.
Shuller, L.C., Ewing, R.C., Becker, U. (2011) Np-incorporation into uranyl phases: A quantum-mechanical evaluation. Journal of Nuclear Materials, 10.1016/j.jnucmat.2011.04.016.
Shuller, L.C., Ewing, R.C., Becker, U. (2011) Thermodynamic properties of ThxU1-xO2 (0 < x < 1) based on quantum-mechanical calculations and Monte-Carlo simulations. Journal of Nuclear Materials, 412: 13-21.
Tinnacher, R. M., Powell, B. A., Kersting, A. B., Zavarin, M. (2011). Kinetics of Neptunium(V) Sorption and Desorption Reactions on Goethite: Experiment and Modeling. Geochimica et Cosmochimica Acta, 75, 6854-6599.
Zhao, P., Zavarin, M., Leif, R., Powell, B. A., Singleton, M., Lindvall, R., Kersting, A. (2011). Mobilization of Actinides by Dissolved Organic Compounds at the Nevada Test Site. Applied Geochemistry, 26, 208-218.