Fundamental mechanisms of 3 He relaxation on glass R.E. Jacob a, * , B. Driehuys b , B. Saam a a UniversityofUtah,115S.1400E.,SaltLakeCity,UT84112,USA b AmershamHealth,2500MeridianPkwy.Suite150,Durham,NC27713,USA Received 9 August 2002; in final form 26 December 2002 Abstract We present a model of 3 He relaxation on the surface of borosilicate glass which accurately predicts observed re- laxation rates and their temperature dependence. Above room temperature 3 He dissolves into Pyrex, where interactions with Fe 3þ ions result in a relaxation time of 1 ms. Gas exchange across the glass surface of an enclosed vessel leads to T 1 1 ¼ A=V ð3:9  1:4Þ 10 2 cm/h at room temperature, where A=V is the surface-to-volume ratio. The activation energy for relaxation is 13:7  0:7 kJ/mol and is dominated by the activation energy of 3 He diffusion in glass. This is the first successful confirmation of predicted 3 He relaxation rates in glass vessels. Ó 2003 Elsevier Science B.V. All rights reserved. 1. Introduction Spin-exchange optical pumping (SEOP) [1] and metastability-exchange optical pumping (MEOP) [2] are common methods of producing very high, non-equilibrium nuclear polarization in certain noble gas nuclei. The gas is typically polarized and/or stored in glass vessels, or cells. Workers in the field have long attempted to determine a quantitative and predictive model of 3 He surface relaxation on glass. Since 3 He surface relaxation has proven to be a very complex problem, under- standing even a single-model system would be critical progress. The ultimate goal is a better un- derstanding of 3 He relaxation in spin-exchange cells (cells containing an alkali metal), where magnetic inclusions in the glass can dominate re- laxation [3]. Researchers who use bare glass cells of all types, and Pyrex in particular, as storage cells for polarized gas research may find these re- sults especially pertinent. Previous measurements of 3 He relaxation as a function of temperature on glass surfaces have been made in bare (containing no Rb or surface coatings), sealed Pyrex, aluminosilicate, and quartz cells [4,5]. For Pyrex, Fitzsimmons et al. provided significant insight into 3 He relaxation mechanisms by showing that adsorption domi- nates relaxation below about 130 K and absorp- tion dominates at higher temperatures. They derived and verified a model for adsorption-based relaxation. However, a quantitative understanding of the absorption regime, which is relevant for most practical experiments, has eluded research- Chemical Physics Letters 370 (2003) 261–267 www.elsevier.com/locate/cplett * Corresponding author. Fax: 801-581-4801. E-mailaddress: rjacob@physics.utah.edu (R.E. Jacob). 0009-2614/03/$ - see front matter Ó 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0009-2614(03)00110-6