ABSTRACT
Neutron interferometry enables precision measurements that are typically operated within elaborate, multi-layered facilities which provide substantial shielding from environmental noise. These facilities are necessary to maintain the coherence requirements in a perfect crystal neutron interferometer which is extremely sensitive to local environmental conditions such as temperature gradients across the interferometer, external vibrations, and acoustic waves. The ease of operation and breadth of applications of perfect crystal neutron interferometry would greatly benefit from a mode of operation which relaxes these stringent isolation requirements. Here, the INDEX Collaboration and National Institute of Standards and Technology demonstrates the functionality of a neutron interferometer in vacuum and characterize the use of a compact vacuum chamber enclosure as a means to isolate the interferometer from spatial temperature gradients and time-dependent temperature fluctuations. The vacuum chamber is found to have no depreciable effect on the performance of the interferometer (contrast) while improving system stability, thereby showing that it is feasible to replace large temperature isolation and control systems with a compact vacuum enclosure for perfect crystal neutron interferometry.
ABSTRACT
The neutron index of refraction is generally derived theoretically in the Fermi approximation. However, the Fermi approximation neglects the effects of the binding of the nuclei of a material as well as multiple scattering. Calculations by Nowak introduced correction terms to the neutron index of refraction that are quadratic in the scattering length and of order 10(-3) fm for hydrogen and deuterium. These correction terms produce a small shift in the final value for the coherent scattering length of H2 in a recent neutron interferometry experiment.
ABSTRACT
In this paper, we will discuss a phase-contrast imaging method that avoids the complications of interferometry to provide phase contrast in weakly absorbing samples. A transversely coherent neutron beam is used with the traditional radiography scheme. Images taken with this scheme show dramatic intensity variations due to sharp changes in the neutron wave refractive index. With some numerical processing these images may be used to reconstruct a quantitative phase radiograph of specimens imaged with this technique.
ABSTRACT
We develop and experimentally demonstrate a formalism that allows accurate phase imaging using neutron sources producing highly polychromatic beams. The results of measurements from a rectangular block of silicon compare favorably with theoretical simulations based upon the known composition and geometry of the block. The increased flux and reduced exposure times will permit a simple extension of the technique to tomographic phase imaging.
ABSTRACT
We have performed the first high precision measurement of the coherent neutron scattering length of deuterium in a pure sample using neutron interferometry. We find b(nd)=(6.665+/-0.004) fm in agreement with the world average of previous measurements using different techniques, b(nd)=(6.6730+/-0.0045) fm. We compare the new world average for the nd coherent scattering length b(nd)=(6.669+/-0.003) fm to calculations of the doublet and quartet scattering lengths from several modern nucleon-nucleon potential models with three-nucleon force (3NF) additions and show that almost all theories are in serious disagreement with experiment. This comparison is a more stringent test of the models than past comparisons with the less precisely determined doublet scattering length of (2)a(nd)=(0.65+/-0.04) fm.