• 한국자기공명학회논문지
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• 제7권1호
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• pp.16-24
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• 2003

Nuclei with the spin quantum number not smaller than unity have not only the nuclear magnetic moment but also the electric quadrupole moment. The quadrupole moment couples with the electric field gradient (EFG) to produce the nuclear quadrupole interaction. It is well known that two independent parameters, i.e. the quadrupole coupling constant (QCC) and the asymmetry parameter ($\eta$) together with the principal axis directions can fully describe the interaction and are very sensitive to the local symmetry and structure of the solid. In order to obtain quantitative estimates of the EFG tensor for various simple ionic configurations surrounding the nucleus under consideration, we employ the simple point charge approximation and apply the calculated results to some real crystals. General agreement is rather satisfactory.

• 대한화학회지
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• 제10권3호
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• pp.143-144
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• 1966

• 한국자기공명학회:학술대회논문집
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• 한국자기공명학회 1999년도 동계총회 및 제14회 자기공명 학술발표회
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• pp.2-3
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• 1999

• 한국자기공명학회:학술대회논문집
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• 한국자기공명학회 2002년도 제20회 학술발표회
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• pp.16-16
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• 2002

• Journal of Magnetics
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• 제20권4호
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• pp.342-346
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• 2015

The nuclear magnetic resonance of the $^{23}Na$ nucleus in a $NaBrO_3$ single crystal was investigated at the temperature range of 200 K~410 K. The tendencies of temperature dependence of the nuclear quadrupole coupling for the two magnetically inequivalent Na(I) and Na(II) centers are found to be opposite to each other. The nuclear spin-lattice relaxation mechanism of $^{23}Na$ in the $NaBrO_3$ crystal is investigated, and the result revealed that the Raman process is dominant in the temperature range investigated. The relaxation process of the $^{23}Na$ nuclear spins was well described by a single exponential function in time. The $T_1$ values of the $^{23}Na$ nuclei in the $NaBrO_3$ single crystal decreased with increasing temperature. The calculated activation energy for the $^{23}Na$ is $0.032{\pm}0.002eV$.

• 한국자기공명학회논문지
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• 제7권2호
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• pp.80-88
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• 2003

We have performed $^{11}$ B nuclear magnetic resonance (NMR) measurements to microscopically investigate an electronic structure of the ferromagnetic state in three different compositions of calcium-hexaboride single crystals. Although the crystal structure of Ca $B_{6}$ is cubic and three NMR lines may be expected for the nuclear spin 3/2 of $_{11}$ B, a larger number of NMR resonance peaks have been observed. The frequency and intensity of those peaks distinctively changes depending on the angle between crystalline axis and magnetic field. Analyzing this behavior, we find that the electric field gradient(EFG) tensor at the boron has its principal axis perpendicular to the six cubic faces with a quadrupole resonance frequency $v_{Q}$ 600 kHz. Even though the magnetization data highlight the ferromagnetic hysteresis, $^{11}$ B NMR linewidth data show no clear microscopic evidence of the ferromagnetic state in three different compositions of Ca $B_{6}$ single crystals.s.

• Nuclear Engineering and Technology
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• 제55권12호
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• pp.4570-4575
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• 2023

Noise and Radio-frequency interference or RFI causes a significant restriction on the Free induction Decay or FID signal detection of the Nuclear Quadrupole Resonance procedure. Therefore, using this method in non-isolated environments such as industry and ports requires extraordinary measures. For this purpose, noise reduction algorithms and increasing signal-to-noise-and-interference ratio or SNIR have been used. In this research, sodium nitrite has been used as a sample and algorithms have been tested in a non-isolated environment. The resonant frequencies for the 150 g of test sample were measured at 303 K at about 1 MHz and 3.4 MHz. The main novelty in this study was, (1) using two types of antennas in the receiver to improve adaptive noise and interference cancellation, (2) using a separate helical antenna in the transmitter to eliminate the duplexer, (3) estimating the noise before sending the pulse to calculate the weighting factors and reduce the noise by adaptive noise cancellation, (3) reject the interference by blanking algorithm, (4) pulse integration in the frequency domain to increase the SNR, and (5) increasing the detection speed by new pulse integration technique. By interference rejection and noise cancellation, the SNIR is improved to 9.24 dB at 1 MHz and to 7.28 dB at 3.4 MHz, and by pulse integration 44.8 dB FID signal amplification is achieved, and the FID signals are detected at 1.057 MHz and 3.402 MHz at room temperature.

• 한국자기학회지
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• 제5권2호
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• pp.99-102
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• 1995

전기장 기울기 텐서가 축대칭인 결정에 대칭인 방향으로 자기장을 가하면 핵사중극공명에 미치는 Zeeman 효과에 의하여 두 개의 분리된 공명진동수가 측정된다. 이 때 가해준 자기장과 두 공명진동수 간의 차이는 서로 비례하며, ${(CH_{2})}_{6}N_{4}$ 단결정의 $^{14}N$ 원자핵에 대한 비례상수는 0.16 mT/kHz 이다. 핵 사중극 공명장치 와 개인용 컴퓨터를 interface 하여 핵 사중극 공명신호의 모습을 모니터에 표시하여 측정되는 두 공명신호의 진동수 차이로 자기장을 직접 읽을 수 있도록 하였다. 여기로부터 핵 사중극 공명 Gaussmeter를 이용하여 실험적으로 측정한 최저 자기장은 0.20 mT 였다.

• 한국자기공명학회논문지
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• 제15권1호
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• pp.40-53
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• 2011

The NMR spectra of $Li_3Rb(SO_4)_2$ crystals and their relaxation processes were investigated by using $^7Li$ and $^{87}Rb$ NMR. The relaxation rates of the $^7Li$ and $^{87}Rb$ nuclei in the crystals were found to increase with increasing temperature, and can be described by the relation $T_1^{-1}{\propto}AT^2$. The dominant relaxation mechanism for these nuclei with electric quadrupole moments is provided by the coupling of these moments to the thermal fluctuations of the local electric field gradient via Raman spin-phonon processes.

• 한국자기공명학회논문지
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• 제18권1호
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• pp.15-23
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• 2014

The structural properties and relaxation processes of $MCsSO_4$ (M = Na, K, or Rb) crystals were investigated by measuring the NMR spectra and spin-lattice relaxation rates $1/T_1$ of their $^{23}Na$, $^{39}K$, $^{87}Rb$, and $^{133}Cs$ nuclei. According to the NMR spectra, the $MCsSO_4$ crystals contain two crystallographically inequivalent sites each for the M and Cs ions. Further, the relaxation rates of all these nuclei do not change significantly over the investigated temperature range, indicating that no phase transitions occur in these crystals in this range. The variations in the $1/T_1$ values of the $^{23}Na$, $^{39}K$, $^{87}Rb$, and $^{133}Cs$ nuclei in these three crystals with increasing temperature are approximately proportional to $T^2$, indicating that Raman processes may be responsible for the relaxation. Therefore, for nuclear quadrupole relaxation of the $^{23}Na$, $^{39}K$, $^{87}Rb$, and $^{133}Cs$ nuclei, Raman processes with n = 2 are more effective than direct processes.