• Journal of the Korean Magnetic Resonance Society
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• v.11 no.1
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• pp.1-9
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• 2007

An unequal site exchanging system induced by restricted rotation of 9-methyl group in 1,8-dichloro-9-triptycene has been studied by spin-lattice relaxation and 2D-EXSY experiments. The exchange rate obtained from relaxation studies is very well coincident to the result of line shape analysis, and the difference of the relaxation times ($T_1$) in two different sites has an important role to analyze 2D-EXSY experimental data.

• Journal of the Korean Magnetic Resonance Society
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• v.17 no.1
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• pp.24-29
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• 2013

The structural characteristics of 4-coordinate $BO_4$ [B(1)] and 3-coordinate $BO_3$ [B(2)] groups in $BiB_3O_6$ were studied by $^{11}B$ magic angle spinning (MAS) and single-crystal nuclear magnetic resonance (NMR) spectroscopy. The spin-lattice relaxation time in the laboratory frame, $T_1$, for $^{11}B$ decreased slowly with increasing temperature, whereas the spin-lattice relaxation times in the rotating frame, $T_{1{\rho}}$, for B(1) and B(2), which differed from $T_1$, were nearly constant. Further, $T_{1{\rho}}$ for B(1) and B(2) showed very similar trends, although the $T_{1{\rho}}$ value of B(2) was shorter than that of B(1). The 3-coordinate $BO_3$ and 4-coordinate $BO_4$ were distinguished by $^{11}B$ MAS NMR spectrum and $T_{1{\rho}}$.

• Journal of the Korean Magnetics Society
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• v.4 no.1
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• pp.52-55
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• 1994

The proton and deuteron spin-lattice relaxation times, $T_{1}(H)$ and $T_{1}(D)$, have been measured in HD between 30 K and 313 K in the pressure of 0.67 - 1.92 atm. The nuclear magnetic resonance frequencies are respectively 358.012 MHz for a proton and 58.958 MHz for a deuteron. From the measurements of $T_{1}(H)$ and $T_{1}(D)$ the ratio of the correlation times ${\tau}_{1}\;and\;{\tau}_{2}$ that are associated with the molecular angular momentum operators was obtained. The nuclear spin-lattice relaxation time at J = 1 state has been observed to have a temperature dependence being proportional to $T^{0.25}$.

• Journal of the Korean Magnetic Resonance Society
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• v.6 no.2
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• pp.132-141
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• 2002

$^1H$ nuclear magnetic resonance (NMR) relaxations have been investigated in ammonium sulfate $((NH_4)_2SO_4)$ power at temperatures ranging form 102 K to 440 K. There is a bottleneck in the spin-lattice relaxation between the nuclear spin system and the hindered rotation of ammonium ions, which is certified by measuring the relaxation according to the initial condition of the spin system. For temperatures below 318 K the $^1H$ spin-lattice relaxations have double-exponential behaviors with the exponent, n, having a value 2>n>1 initially and n=l after a long time. Above 318 K not only is the relaxation exponential initially with exponent n=1, but it is a single-exponential over the entire time, resulting in one $T_1$ value. The two types of $NH_4^+$ ions have different activation energies for hindered rotation, $E_a^1=0.27{\pm}0.02eV$ and $E_a^11=0.12{\pm}0.0eV$, in the ferroelectric phase.

• Food Science and Biotechnology
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• v.17 no.5
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• pp.895-898
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• 2008

The mobility of water in set yogurt during fermentation was studied using nuclear magnetic resonance (NMR) relaxometry. The spin-spin relaxation was analyzed using a 2-fraction model, resulting in 2 spin-spin relaxation time constants $T_{21}$ and $T_{22}$. Both $T_{21}$ and $T_{22}$ exhibited rapid changes between 2 and 4 hr of fermentation, coinciding with the drop in pH and the rise in lactic acid bacteria count. The spin-lattice relaxation time $T_1$ increased over the fermentation period. Both $T_1$ and $T_2$ showed an increase in the mobility of water upon gel formation during fermentation. Water redistribution within the gel matrix due to casein aggregation and structure forming may be responsible for the changes in mobility.

• Journal of Magnetics
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• v.19 no.2
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• pp.116-120
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• 2014

The spin-lattice relaxation time, $T_1$, for $^{69}Ga$, $^{71}Ga$, and $^{75}As$ nuclei in GaAs:$Mn^{2+}$ single crystals was measured as a function of temperature. The values of $T_1$ for $^{69}Ga$, $^{71}Ga$, and $^{75}As$ nuclei were found to decrease with increasing temperature. The $T_1$ values in GaAs:$Mn^{2+}$ crystal are similar to those in pure GaAs crystal. The calculated activation energies for the $^{69}Ga$, $^{71}Ga$, and $^{75}As$ nuclei are 4.34, 4.07, and 3.99 kJ/mol. It turns out that the paramagnetic impurity effect of $Mn^{2+}$ ion doped in GaAs single crystal was not strong on the spin-lattice relaxation time.

• Journal of the Korean Magnetic Resonance Society
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• v.14 no.1
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• pp.18-27
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• 2010

The NMR spectrum and spin-lattice relaxation times, $T_1$, of the $^{1}H$ nuclei in $(NH_{4})_{2}Cd_{2}(SO_{4})_{3}$ single crystals were obtained. The two minima in $T_1$ in the paraelectric phase are attributed to the reorientational motions of the $NH_{4}^{+}$ groups. The $^{1}H\;T_1$ of the $(NH_{4})_{2}Cd_{2}(SO_{4})_{3}$ crystals can be described with Bloembergen- Purcell-Pound (BPP) theory. The experimental value of $T_1$ can be expressed in terms of an isotropic correlation time ${\tau}_H$ for molecular motions by using the BPP theory, and determine the role of protons in these processes.

• Journal of the Korean Magnetic Resonance Society
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• v.18 no.1
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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.

• Journal of the Korean Magnetic Resonance Society
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• v.17 no.2
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• pp.86-91
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• 2013

Detailed information about the structural nature of three-coordinate borons in ${\beta}-BaB_2O_4$ is obtained through $^{11}B$ MAS NMR and $^{11}B$ single-crystal NMR. The three-coordinate $BO_3$ of the two borons B(1) and B(2) in ${\beta}-BaB_2O_4$ were distinguished. The spin-lattice relaxation time in the laboratory frame $T_1$ for B(1) and B(2) slowly decreases with increasing temperature, whereas the spin-lattice relaxation time in the rotating frame $T_{1{\rho}}$ for B(1) and B(2), which differs from $T_1$, is nearly constant. The B(1) and B(2) of the two types were distinguished by $^{11}B$ MAS NMR and $^{11}B$ single-crystal NMR.

• Journal of the Korean Magnetics Society
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• v.25 no.6
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• pp.185-188
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• 2015

We have investigated nuclear magnetic resonance of $^{23}Na$ nucleus in $NaMgCl_3$ single crystal in the temperature range 200 K~410 K using FT-NMR spectrometer. The spin-lattice relaxation times $T_1$ of $^{23}Na$ nucleus residing at cubic symmetry in the host crystal was measured as a function of temperature. The $T_1$ of $^{23}Na$ nucleus decreased with increasing temperature. The nuclear spin-lattice relaxation rate $1/T_1$ of $^{23}Na$ in $NaMgCl_3$ single crystal was proportional to the temperature T. This behavior is explained with the characteristic feature of the direct process between the nuclear spins and single phonon, $1/T_1$ being proportional to the absolute temperature. The activation energy calculated was $E_a=4.82J/mol$.