Development of high-performance alkali-hybrid polarizedHe3targets for electron scattering

Abstract

We present the development of high-performance polarized 3 He targets for use in electron scattering experiments that utilize the technique of alkali-hybrid spin-exchange optical pumping. We include data obtained during the characterization of 24 separate target cells, each of which was constructed while preparing for one of four experiments at Jefferson Laboratory in Newport News, Virginia. The results presented here document dramatic improvement in the performance of polarized 3 He targets, as well as the target properties and operating parameters that made those improvements possible. Included in our measurements were determinations of the so-called X-factors that quantify a temperature-dependent and as-yet poorly understood spin-relaxation mechanism that limits the maximum achievable 3 He polarization to well under 100%. The presence of this spinrelaxation mechanism was clearly evident in our data. We also present results from a simulation of the alkali-hydrid spin-exchange optical pumping process that was developed to provide guidance in the design of these targets. Good agreement with actual performance was obtained by including details such as off-resonant optical pumping. Now benchmarked against experimental data, the simulation is useful for the design of future targets. Included in our results is a measurement of the K-3 He spin-exchange rate coefficient k K se = (7.46 ± 0.62)×10 −20 cm 3 /s over the temperature range 503 K to 563 K.

Measurement of the Target-Normal Single-Spin Asymmetry in Quasielastic Scattering from the ReactionHe3↑(e,Zhang1, Long2, Mihovilovič3 et al. 2015Phys. Rev. Lett.352361View full textAdd to dashboardCite

“…Approximately 0.1 amg of N 2 gas was also included to aid in the polarization process. The target was polarized through spin-exchange optical pumping of a Rb-K mixture [14]. In order to reduce the systematic uncertainty, the direction of the target polarization vector was reversed every 20 min using adiabatic fast passage.…”

Synchronous Spin-Exchange Optical Pumping

“…When we introduce a transverse compensation field, we are able to eliminate the spin-exchange broadening and restore the usual NMR phase sensitivity. The projected quantum-limited sensitivity is better than 1 nHz// √ Hz.The ability to produce highly magnetized noble gases via spin-exchange collisions with spin-polarized alkali atoms [1] has greatly impacted scientific studies of magnetic resonance imaging [2], high-energy nuclear physics with spin-polarized targets [3], and chemical physics [4]. Applications in precision measurements began with NMR gyros [5] and have continued with fundamental symmetry tests using multiple cell free induction decay [6], dual-species masers [7,8], selfcompensating co-magnetometers [9], NMR oscillators [10], and free spin-precession co-magnetometers [11][12][13][14].…”

Low Field MRI and the Development of Polarized Nuclear Imaging (PNI)-A New Imaging Modality

“…For 3 He cells of a few atms, we've measured polarizations as high as 70% [16]. The achievable xenon polarization strongly depends on the xenon pressure in the cell.…”

“…All the glass tubings were "reblown", a process in which the diameter of the commercial tubings were enlarged using a glass lathe and a hand torch. The "reblown" process has been found to be critical in suppressing the wall relaxation rate [16,38,43], perhaps because it fixes microfissures on the interior glass surfaces. An alternative method of suppressing the wall relaxation is to coat the inner surface with sol-gel [44].…”

“…Perhaps the most widely used atom in optical pumping is Rubidium. Although in our lab sometimes an alkali hybrid of Rb/K is involved for 3 He target cells, Rb is the alkali metal that is directly polarized by the laser light, and its polarization is then transferred to Potassium [16]. Rb is suitable for optical pumping for several reasons.…”