超导量子干涉装置检测到核磁共振和核四极共振。超导量子干涉装置。

SQUID detected NMR and NQR. Superconducting Quantum Interference Device.

作者信息

Augustine M P, TonThat D M, Clarke J

机构信息

Department of Chemistry, University of California, Lawrence Berkeley National Laboratory, Berkeley 94720, USA.

出版信息

Solid State Nucl Magn Reson. 1998 Mar;11(1-2):139-56. doi: 10.1016/s0926-2040(97)00103-3.

DOI:10.1016/s0926-2040(97)00103-3

PMID:9650797

Abstract

The dc Superconducting QUantum Interference Device (SQUID) is a sensitive detector of magnetic flux, with a typical flux noise of the order 1 muphi0 Hz(-1/2) at liquid helium temperatures. Here phi0 = h/2e is the flux quantum. In our NMR or NQR spectrometer, a niobium wire coil wrapped around the sample is coupled to a thin film superconducting coil deposited on the SQUID to form a flux transformer. With this untuned input circuit the SQUID measures the flux, rather than the rate of change of flux, and thus retains its high sensitivity down to arbitrarily low frequencies. This feature is exploited in a cw spectrometer that monitors the change in the static magnetization of a sample induced by radio frequency irradiation. Examples of this technique are the detection of NQR in 27Al in sapphire and 11B in boron nitride, and a level crossing technique to enhance the signal of 14N in peptides. Research is now focused on a SQUID-based spectrometer for pulsed NQR and NMR, which has a bandwidth of 0-5 MHz. This spectrometer is used with spin-echo techniques to measure the NQR longitudinal and transverse relaxation times of 14N in NH4ClO4, 63+/-6 ms and 22+/-2 ms, respectively. With the aid of two-frequency pulses to excite the 359 kHz and 714 kHz resonances in ruby simultaneously, it is possible to obtain a two-dimensional NQR spectrum. As a third example, the pulsed spectrometer is used to study NMR spectrum of 129Xe after polariza-tion with optically pumped Rb. The NMR line can be detected at frequencies as low as 200 Hz. At fields below about 2 mT the longitudinal relaxation time saturates at about 2000 s. Two recent experiments in other laboratories have extended these pulsed NMR techniques to higher temperatures and smaller samples. In the first, images were obtained of mineral oil floating on water at room temperature. In the second, a SQUID configured as a thin film gradiometer was used to detect NMR in a 50 microm particle of 195Pt at 6 mT and 4.2 K.

摘要

直流超导量子干涉器件（SQUID）是一种灵敏的磁通量探测器，在液氦温度下，其典型的磁通噪声约为1μΦ₀Hz⁻¹/²。这里，Φ₀ = h/2e是磁通量子。在我们的核磁共振（NMR）或核四极共振（NQR）光谱仪中，缠绕在样品周围的铌丝线圈与沉积在SQUID上的薄膜超导线圈耦合，形成一个磁通变压器。通过这种非调谐输入电路，SQUID测量的是磁通量，而非磁通量的变化率，因此在任意低频率下都能保持其高灵敏度。这一特性被用于连续波光谱仪中，该光谱仪可监测由射频辐射引起的样品静态磁化强度的变化。这种技术的实例包括检测蓝宝石中的²⁷Al和氮化硼中的¹¹B的NQR，以及一种用于增强肽中¹⁴N信号的能级交叉技术。目前的研究重点是一种基于SQUID的脉冲NQR和NMR光谱仪，其带宽为0 - 5MHz。该光谱仪与自旋回波技术一起用于测量高氯酸铵中¹⁴N的NQR纵向和横向弛豫时间，分别为63±6ms和22±2ms。借助双频脉冲同时激发红宝石中359kHz和714kHz的共振，可以获得二维NQR光谱。作为第三个例子，脉冲光谱仪用于研究用光学泵浦铷极化后的¹²⁹Xe的NMR光谱。NMR谱线在低至200Hz的频率下即可被检测到。在低于约2mT的磁场下，纵向弛豫时间在约2000s时达到饱和。其他实验室最近的两项实验已将这些脉冲NMR技术扩展到更高温度和更小的样品。在第一个实验中，获得了室温下漂浮在水上的矿物油的图像。在第二个实验中，一个配置为薄膜梯度计的SQUID被用于在6mT和4.2K下检测50微米的¹⁹⁵Pt颗粒中的NMR。