 Because a 129Xe nucleus has a spin of 1 / 2 , and therefore a zero electric <unk> moment , the 129Xe nucleus does not experience any <unk> interactions during collisions with other atoms , and thus its <unk> can be maintained for long periods of time even after the laser beam has been turned off and the alkali vapor removed by condensation on a room @-@ temperature surface . Spin polarization of 129Xe can persist from several seconds for xenon atoms dissolved in blood to several hours in the gas phase and several days in deeply frozen solid xenon . In contrast , <unk> has a nuclear spin value of 3 ⁄ 2 and a <unk> <unk> moment , and has t1 relaxation times in the <unk> and second ranges . 
