Measuring the diffusion of noble gases through a porous medium using prompt gamma activation analysis
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Measuring the diffusion of noble gases through a porous medium using prompt gamma activation analysis Carlos A. Rios Perez • Steven Biegalski Mark R. Deinert
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Received: 10 July 2012 / Published online: 17 August 2012 Ó Akade´miai Kiado´, Budapest, Hungary 2012
Abstract Detection of anthropogenic noble gas isotopes in the atmosphere is an important indication that a below ground nuclear-test has taken place. Diffusion plays a critical role in the transport of these gases through the geological media to the surface where they can be detected. Better techniques are need with which to study the diffusion of noble gases through porous systems. Here we demonstrate the suitability of using prompt gamma activation analysis to measure the time dependent concentration of argon as a result of its diffusion through a porous medium that is saturated with nitrogen at atmospheric pressure. The experiments were conducted in a 1 m long tube, 10 cm diameter, and packed with fine SiO2 sand. Prompt gamma activation analysis was used to measure the concentration of argon within the experimental system as a function of time. Keywords Noble gas Diffusion Prompt gamma activation analysis Concentration
Introduction The presence of anthropogenic radioisotopes provides the only definitive evidence that a clandestine nuclear weapon
This study was originally presented at the MARC IX conference. C. A. Rios Perez M. R. Deinert (&) The University of Texas at Austin, 1 University Station, C2200, Austin, TX 78712, USA e-mail: [email protected] S. Biegalski The University of Texas at Austin, 1 University Station, R9000, Austin, TX 78712, USA
test has taken place [1]. Noble gas isotopes are particularly useful in this regard as their non-reactive nature allows them to migrate to the surface after a below ground detonation. The International Monitoring System of the Comprehensive Nuclear-Test Ban Treaty Organization often uses the presence of anthropogenic xenon in the atmosphere [1, 2] to determine whether a below ground test has taken place. Recently, it has been suggested that anthropogenic argon could be also be used for this purpose. The detection of anthropogenic noble gas isotopes can also be useful as an indicator for underground contamination from buried radioactive materials [3]. In both cases, subsurface gas transport will affect the quantities of gas that reach the surface and the time required to do so [2, 4]. The time dependent concentration of a gas moving through a porous medium can be described using: oCA ¼ r ðCA V DAB rCA Þ þ RA ot
ð1Þ
Here CA is the concentration (moles m-3), v is the bulk velocity (m s-1), DAB is the binary diffusion coefficient (m2 s-1) of A through B, and RA is the rate at which A is produced or lost at a given location (moles m-3 s-1) [5, 6]. All experimental techniques that are used to study the diffusion of gases through a porous medium require the ability to measure the time dependent concentration of the gas [7–13]. Common methods for doing this include gas chromatography and mass
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