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First Multilayer-type Neutron Interferometry Measurements of Gases at J-PARC
What is it about?
This study reports the first application of a newly developed measurement system to determine the coherent scattering lengths (bc) of gaseous samples (^3He and ^4He) using a multilayer-type neutron interferometer at J-PARC. While conventional interferometry studies have typically used silicon-crystal interferometers and monochromatic neutrons supplied from reactors, our group developed a multilayer-based neutron interferometer and utilize pulsed neutrons from the J-PARC accelerator. Through 10-minute cycle time-of-flight measurements, we observed significant phase shifts induced by the helium gas samples. This establishes a definitive proof of principle for this methodology and allows us to clarify the specific experimental issues that must be resolved for high-precision experiments.
Why is it important?
Determining the precise coherent scattering lengths of light nuclei is vital for modern nuclear physics. These values serve as a crucial benchmark for testing advanced phenomenological nuclear models and chiral effective field theories, which attempt to describe the nuclear forces, including three-nucleon forces. Despite their importance, a long-standing mystery persists: past measurements using conventional interferometers show discrepancies for helium isotopes (^3He and ^4He). To resolve these puzzles, a completely new and independent experimental approach is required. This paper lays the essential foundation for a novel methodology utilizing pulsed cold neutrons. By overcoming the limitations of previous experiments, this ongoing project aims to achieve a relative precision of 10^{−3}, providing the data needed to improve nuclear theories.