In-Situ Measurement of the Density Ratio of the K-Rb-21Ne Comagnetometer Based on Electron Spin Relaxation Rate

Accurate measurement of alkali metal density ratio in hybrid vapor cells is essential for high sensitivity of comagnetometers. We introduce and investigate a new method of measuring the density ratio based on electron spin-relaxation rate. The Bloch equations including the parameter of density ratio are studied, and the density measurement results show that measurement uncertainty is less than 12%. The advantage of this method is measuring the in-situ density ratio, which is more precise and useful for optimizing sensitivity of comagnetometers by adjusting the density ratio in real time.

Detection of Two Phenomena Opposite to the Expected Ones

Both phenomena mentioned in the title were revealed by the electron paramagnetic resonance (EPR) method. The first phenomenon was found in superconducting La metal with Er impurities—the spin relaxation rate of the erbium impurities was sharply decreasing after transition into the superconducting state instead of the expected, i.e., the well-known Hebel–Slichter peak. The second unexpected phenomenon was discovered in the YbRh2Si2 compound—an excellent EPR signal from the Yb ions was observed at temperatures below the Kondo temperature determined thermodynamically, while according to the existing belief the EPR signal should not be observed at these temperatures due to the Kondo effect. In this tribute to K. Alex Müller, I describe the nature of the detected phenomena.

Solids Content of Black Liquor Measured by Online Time-Domain NMR

Black liquor, a valuable by-product of the pulp production process, is used for the recovery of chemicals and serves as an energy source for the pulp mill. Before entering the recovery unit, black liquor runs through several stages of evaporation, wherein the solids content (SC) can be used to control the evaporation effectiveness. In the current study, the time-domain nuclear magnetic resonance (TD-NMR) technique was applied to determine the SC of black liquor. The TD-NMR system was modified for flowing samples, so that the black liquor could be pumped through the system, followed by the measurement of the spin-spin relaxation rate, R2. A temperature correction was also applied to reduce deviations in the R2 caused by the sample temperature. The SC was calculated based on a linear model between the R2 and the SC values determined gravimetrically, where good agreement was shown. The online TD-NMR system was tested at a pulp mill for the SC estimation of weak black liquor over seven days without any fouling, which demonstrated the feasibility of the method in a harsh industrial environment. Therefore, the potential of the TD-NMR technology as a technique for controlling the black liquor evaporation process was demonstrated.