Speaker
Description
Polarized neutron beams, generated using $^3$He spin filters, provide a valuable approach for separating coherent and incoherent scattering, nuclear and magnetic scattering, and for observing symmetry violations in nuclear reactions. The $^3$He spin filter is suitable for polarizing neutrons with energies ranging from meV to eV, making effective use of J-PARC's high-intensity pulsed neutron beams that cover a wide energy range. The number of user experiments with a $^3$He spin filter in J-PARC has increased annually [1], reaching about 10 experiments per year in recent years.
This presentation focuses on the application of the $^3$He spin filter for measurements of coherent scattering from hydrogen-containing samples. Hydrogen is a fundamental constituent of biomolecules, yet the underlying mechanisms of hydrogen bond formation remain an open question. However, incoherent scattering from hydrogen often affects significantly to background noise, complicating accurate structural analyses of samples in neutron experiments. The experiment was conducted at the BL21 NOVA beamline at J-PARC, which can perform measurements in the high-Q region with high-intensity neutron beams, facilitating precise pair distribution function (PDF) analyses. Integrating NOVA with $^3$He spin filters allows for separation of coherent and incoherent scattering components and high-precision PDF analysis. As part of our efforts to establish a method for separating the components of coherent and incoherent scattering by neutron spin analysis using the $^3$He spin filters, we have started to analyze the data in combination with Monte Carlo simulations. Incoherent scattering of neutrons in a sample is known to flip the neutron spin direction with a probability of 2/3. However, in cases of multiple scattering, the probability of spin flips may vary, which reduces the accuracy of the separation between coherent and incoherent scattering components. We have used Geant4, which is a toolkit for the simulation of the passage of particles through matter, to estimate the spin-flip probability due to multiple scattering. This presentation will report on the details of the polarized neutron spin analysis experiments carried out with the $^3$He spin filter in NOVA and the current status of the data analysis.
