Ultracold Neutron Storage Simulation Using the Kassiopeia Software Package

The Kassiopeia software package was originally developed to simulate electromagnetic fields and charged particle trajectories for neutrino mass measurement experiments. Recent additions to Kassiopeia also allow it to simulate neutral particle trajectories in magnetic fields based on their magnetic moments. Two different methods were implemented: an exact method that can work for arbitrary fields and an adiabatic method that is limited to slowly-varying fields but is much faster for large precession frequencies. Additional interactions to simulate reflection of ultracold neutrons from material walls and to allow spin-flip pulses were also added. These tools were used to simulate neutron precession in a room temperature neutron electric dipole moment experiment and predict the values of the longitudinal and transverse relaxation times as well as the trapping lifetime. All three parameters are found to closely match the experimentally determined values when simulated with both the exact and adiabatic methods, confirming that Kassiopeia is able to accurately simulate neutral particles. This opens the door for future uses of Kassiopeia to prototype the next generation of atomic traps and ultracold neutron experiments.

Transient electromagnetically induced transparency spectroscopy of 87Rb atom in buffer gas

We have studied the transient response dynamics of 87Rb atomic vapor buffered in 8 Torr Ne gas through an electromagnetically induced transparency configured in Λ-scheme. Experimentally, the temporal transmission spectra versus probe detuning by switching on and off the coupling one show complex structures. The transmitted probe light intensity drops to a minimum value when the coupling light turns off, showing a strong absorption. While at the moment of turning on the coupling light at a subsequent delayed time, the atomic medium shows a fast transient response. To account for the transient switching feature, in the time-dependent optical Bloch equation, we have to take the transverse relaxation dephasing process of atomic vapor into account, as well as the fluorescence relaxation along with the optical absorption. This work supplies a technique to quantify the transverse relaxation time scale and sensitively monitor its variation along the environment by observing the transient dynamics of coherent medium, which is helpful in characterizing the coherent feature of the atomic medium.

Temperature Dependence of Nuclear Magnetic Resonance Relaxation Time in Carbonate Reservoirs

Summary Nuclear magnetic resonance (NMR)-based interpretation models are commonly calibrated using laboratory ambient core NMR measurements. For applying the core calibrated models to downhole NMR logging interpretation, the difference between the NMR responses measured at ambient and reservoir temperature needs to be evaluated. The temperature dependence of NMR relaxation time in high-quality (HQ) carbonate reservoirs has been studied, and NMR temperature dependence models were established using data analytic methods. In this paper, we extend our early studies on temperature dependence of NMR relaxation time to low-quality (LQ) carbonate formations. For more than 95% of the LQ samples investigated, NMR relaxation time shows a positive correlation with temperature. The correlation is similar to that observed in HQ carbonate rocks but slightly less significant. Temperature-dependent correlations for predicting the geometric mean of NMR transverse relaxation time (T2,GM) from a measured temperature to any other temperature were derived from HQ to LQ carbonate rocks independently first, then a unified T2,GM correlation was derived including both the HQ and LQ carbonate reservoirs. Predicting NMR transverse relaxation time T2 distribution from one temperature to other temperatures was achieved using a dimension reduction approach involving the principal component analysis (PCA) technique. It was found that the T2 distributions at any given temperature for both HQ and LQ carbonate reservoirs can be predicted robustly from the T2 distributions at the ambient temperature by representing the T2 distributions with principal components (PCs) at the ambient temperature and then using these PCs to predict the PCs at a different temperature. The optimal number of PC components depends on the multimodality of the T2distribution. This work extends the validity range of the data analytic methods, in particular parameter and dimension reduction methods, that quantify the temperature dependence of carbonate NMR properties. The new NMR temperature model enables the integration of NMR laboratory studies and downhole measurements for advanced petrophysical analyses in a wide range of carbonate reservoirs.

Spin noise gradient echoes

Nuclear spin noise spectroscopy in the absence of radio frequency pulses was studied under the influence of pulsed field gradients (PFGs) on pure and mixed liquids. Under conditions where the radiation-damping-induced line broadening is smaller than the gradient-dependent inhomogeneous broadening, echo responses can be observed in difference spectra between experiments employing pulsed field gradient pairs of the same and opposite signs. These observed spin noise gradient echoes (SNGEs) were analyzed through a simple model to describe the effects of transient phenomena. Experiments performed on high-resolution nuclear magnetic resonance (NMR) probes demonstrate how refocused spin noise behaves and how it can be exploited to determine sample properties. In bulk liquids and their mixtures, transverse relaxation times and translational diffusion constants can be determined from SNGE spectra recorded following tailored sequences of magnetic field gradient pulses.

Novel Multidimensional Inverse Laplace Nuclear Magnetic Resonance Spectroscopy Techniques

<p>This thesis presents the new development and application of multidimensional inverse Laplace nuclear magnetic resonance spectroscopy techniques. We present a new NMR technique which relates the longitudinal relaxation rate of the NMR signal to the internal gradients in the sample. We perform the experiment on a large range of magnet strengths to provide experimental evidence for the theory of how internal gradient intensity scales with pore size as a function of field strength. We make the first attempt of quantisation of two dimensional inverse Laplace experiments. We perform a transverse relaxation exchange experiment on several samples for a range of mixing times. We then integrate the peaks in the resulting spectra and plot them as a function of mixing time. By fitting the experimental results to theory, we can estimate the molecular exchange between pores of differing sizes. We then modify the transverse relaxation experiment to include diffusion attenuation so that we can see the separate signals for oil and water. We use this to look at the effect wettability has on the movement of the different fluids between pores. We then present the first experiment to combine two inverse Laplace dimensions with a Fourier dimension. We add a propagator dimension to the transverse relaxation exchange experiment to measure how far the molecules move during the mixing time. Quantisation of the results allows us to estimate the exchange rate between pores of similar sizes in addition the exchange rate between pores of different sizes. We are also able to estimate pore radii, inter-pore spacing and tortuosity. Lastly, we attempt a three dimensional inverse Laplace experiment by correlating transverse relaxation, diffusion, and internal gradients. While the three dimensional inversion techniques require more development, the results show resemblance to those seen from two dimensional experiments.</p>

Novel Multidimensional Inverse Laplace Nuclear Magnetic Resonance Spectroscopy Techniques

<p>This thesis presents the new development and application of multidimensional inverse Laplace nuclear magnetic resonance spectroscopy techniques. We present a new NMR technique which relates the longitudinal relaxation rate of the NMR signal to the internal gradients in the sample. We perform the experiment on a large range of magnet strengths to provide experimental evidence for the theory of how internal gradient intensity scales with pore size as a function of field strength. We make the first attempt of quantisation of two dimensional inverse Laplace experiments. We perform a transverse relaxation exchange experiment on several samples for a range of mixing times. We then integrate the peaks in the resulting spectra and plot them as a function of mixing time. By fitting the experimental results to theory, we can estimate the molecular exchange between pores of differing sizes. We then modify the transverse relaxation experiment to include diffusion attenuation so that we can see the separate signals for oil and water. We use this to look at the effect wettability has on the movement of the different fluids between pores. We then present the first experiment to combine two inverse Laplace dimensions with a Fourier dimension. We add a propagator dimension to the transverse relaxation exchange experiment to measure how far the molecules move during the mixing time. Quantisation of the results allows us to estimate the exchange rate between pores of similar sizes in addition the exchange rate between pores of different sizes. We are also able to estimate pore radii, inter-pore spacing and tortuosity. Lastly, we attempt a three dimensional inverse Laplace experiment by correlating transverse relaxation, diffusion, and internal gradients. While the three dimensional inversion techniques require more development, the results show resemblance to those seen from two dimensional experiments.</p>

Orientation dependent transverse relaxation in human brain white matter: The magic angle effect on a cylindrical helix

Purpose: To overcome limitations of prior orientation-dependent R2 and R2* formalisms in white matter (WM) with a novel framework based on magic angle effect. Methods: A cylindrical helix model was developed embracing both anisotropic rotational and translational diffusions of ordered water in WM, with the former characterized by an axially symmetric system. Both R2 and R2* were divided into isotropic (R2i) and anisotropic parts, R2a*f(ε-ε0,α), with α denoting a funnel opening angle and ε0 an orientation (ε) offset relative to DTI-derived primary diffusivity direction. The proposed framework (Fit A) was compared with prior model without ε0 (Fit B) and applied to published R2 and R2* in WM of underdeveloped, healthy, and diseased conditions. Goodness of fit was characterized by root-mean-square error (RMSE). F-test and Pearson correlation coefficient (PCC) were used with statistical significance set to P ≤ .05. Results: Fit A significantly outperformed Fit B as demonstrated by reduced RMSEs in myelin water (i.e., 0.349 vs. 0.724). The fitted ε0 was in good agreement with the calculated ε0 from DTI directional diffusivities. Significant positive (R2i) and negative (α and R2a) correlations were found with aging (demyelination) in adults while ε0 showed a weak positive correction (PCC=0.11, P= .28). Compared to those from healthy adult WM, the fits of R2i, R2a, and α from neonates were considerably reduced but ε0 increased, consistent with limited myelination. Conclusion: The developed framework can better characterize anisotropic transverse relaxation in WM, shedding new light on myelin microstructural alterations at the molecular level.