Fundamental research for rare gas MRI

研制了一种圆柱形蓝宝石单晶池，用于核磁共振成像（MRI）研究的3 He核极化。用4个大气压的3 He气体、少量的铷液滴和100托的氮气填充该单元。单晶的c轴平行于圆柱的圆盘。该圆盘作为激光束的窗口，用于铷原子的偏振和光泵浦。蓝宝石单晶具有双折射。折射率取决于波振荡的方向。通过双折射窗口时的相移取决于振荡方向。由于相移，入射激光的圆偏振被退偏。相同尺寸的蓝宝石板补偿了相移。在原子碰撞过程中，铷原子的极化通过超精细相互作用转变为3 He原子核的极化。通过NMR检测监测3 He核极化。在~ 3 He核极化建立后，关闭激光器以观察~ 3 He极化弛豫。~ 3 He极化弛豫时间为40 h。在玻璃电池的情况下，我们通常从10个电池中获得一个这样的电池。结果表明，蓝宝石是一种很好的3 He极化材料。这是首次在蓝宝石电池中进行3 He极化测试

A cylindrical sapphire single crystal cell has been developed for 3He nuclear polarization for a MRI study. The cell was filled with 4-atm 3He gas, a small amount of rubidium droplet and 100 Torr nitrogen gas. The c axis of the single crystal was parallel to the disk of the cylinder. The disk worked as a widow for a laser beam for and optical pumping of rubidium atomic polarization. The sapphire single crystal has birefringence. The refractive index depends on the direction of the wave oscillation. The phase shift upon passage through the birefringence window depends on the oscillation direction. The circular polarization of incident laser is depolarized because of the phase shift. A same size of sapphire plate compensated for the phase shift. The rubidium polarization is transferred to 3He nuclear polarization upon atomic collision via a hyperfine interaction. The 3He nuclear polarization was monitored by a NMR detection. After the buid-up of the 3He nuclear polarization, the laser was switched off for an observation of 3He polarization relaxation. The relaxation time of the 3He polarization was 40 h. In the case of glass cell, we usually obtained one such cell from 10 cells. The result shows the sapphire is good material for 3He polarization. This is the first test of 3He polarization in sapphire cell