Rb-Xe spin relaxation in dilute Xe mixtures

Abstract

We present measurements of spin-relaxation of Rb atoms in He(98%)-N 2 (1%)-Xe(1%) mixtures similar to those used in magnetic resonance imaging polarizers. The pressure dependence allows us to separate out contributions from Rb-Xe van der Waals molecules and binary collisions. For the first time, we observe the predicted increase in the molecular contribution at high pressure. Our data suggest that the deduced molecular breakup rate has a strong temperature dependence.

Near-unity nuclear polarization with an open-source 129 Xe hyperpolarizer for NMR and MRI

“…For example, ongoing simulations predict a high Γ SD value of ∼134,300 s −1 for the experimental conditions of the 65°C data in Fig. 2, dominated by Xe collisions (25)(26)(27). However, the high resonant photon flux at the front of the cell should give nearly a ninefold greater optical pumping rate (γ OP ∼ 1.16 × 10 6 s −1…”

“…where γ OP (r) is the local OP rate [given by the integrated product of the laser flux and the Rb absorption cross-section (31)], and Γ SD is the Rb electronic spin destruction rate, which is dominated by nonspin-conserving collisions with Xe [via the spinrotation interaction (25,27)] and is high under our conditions because of its proportionality to [Xe]. Correspondingly, the laser power used here is also high-usually ∼170 W, mostly resonant with the Rb D 1 line.…”

“…† HP 129 Xe is usually created via spin-exchange optical pumping (SEOP) (23), whereby the unpaired electronic spins of an alkali metal vapor (e.g., Rb) are polarized via optical pumping with circularly polarized light, and the polarization is transferred to noble gas nuclear spins during collisions. It is generally anticipated that high P Xe is achievable only in the low xenon-density regime (18,24), because (i) higher Xe densities increase the destruction of Rb polarization from nonspin-conserving collisions at a rate that is orders of magnitude worse than those of other gases like N 2 and He (25)(26)(27); and (ii) higher total pressures tend to quench the threebody van der Waals contribution to Rb-Xe spin exchange-leaving the less-efficient two-body term (18,23). Most large-scale polarizers, in particular all that are available commercially, operate in this low-Xe density regime.…”

Spin polarization of 87Rb atoms with ultranarrow linewidth diode laser: Numerical simulation

“…Since spin destruction due to Van der Waals molecules is so complex that exact value is hard to obtain, we use R vdW ≈ 3240 Hz for an estimate. 18 For spherical cell without anti-relaxation coating R wall can be expressed as,…”

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

“…al. measured this rate in the "short lifetime" region [23] (total gas pressure on the order of an amagat). They reported that with a gas mixture of 1% Xe, 1% N 2 and 98% He, the vdW spin destruction rate is 2049 s −1 at 150 • C and 3240 s −1 at 80 • C. These rates are independent of the total gas pressure, but dependent on the gas composition.…”