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Physics Colloquium: Michael Huber

February 8, 2021 | 4:00 pm - 5:00 pm

Title: Studying Fundamental Physics and Material Science using Neutron Interference

Abstract: The National Institute of Standards and Technology (NIST) in Gaithersburg, MD operates a 20 MW reactor for neutron research.  Neutrons have several advantages over more common material probes like x-rays and electrons.  These include:  (1) neutrons transmit through most materials making them ideal to study bulk properties, (2) the neutron carries a magnetic dipole moment enabling the study of magnetic samples, and (3) with de Broglie wavelengths of a few angstroms, neutrons are ideal probes of atomic structure.  It is the neutron’s wave-like property that allows for the use of interferometric techniques to be employed in high precision measurements.  

Neutron interferometry is commonly done using a perfect-crystal silicon ingot machined to produce 2 or more blades on a common base.  Neutrons diffract inside the crystal blades to create 2 spatially separate paths. This type of interferometer is analogous to a Mach-Zehnder interferometer in optics.   Differences along the paths of the interferometer whether caused by physical samples or other forces change the relative phase between the 2 paths.   What makes perfect-crystal interferometry a compelling technique is its simple-to-interpret results and ability to manipulate neutrons by simple macroscopic elements.  Perfect-crystal neutron interferometry has been used to study nuclear physics, quantum information, gravity, and place limits on cosmological models.    

Another popular neutron technique is that of neutron imaging. Neutron tomography has been successfully employed in such areas as the study of concrete, lithium battery technology and in the development of hydrogen fuel cells.   Recently, researchers at NIST and the NIH have demonstrated a neutron interferometer operating in the far-field using a series of phase gratings instead of perfect crystals. Combined with dark field imaging, this type of interferometer allows access to structural features in a neutron image. In one sense, this far-field interferometer bridges the gap between interferometric and imaging techniques.  The use of phase gratings eliminates the micron precision manufacturing and angstrom-level alignment requirements for perfect crystals potentially making the far-field interferometer a more prolific instrument.   Combined with the ability to obtain tomography, dark field imaging with a far field interferometer opens the possibility of three-dimensional, multi-scale data sets, with pair correlation functions ranging from 1 nm to 10 µm. 

NIST is developing the far-field interferometer denoted as INFER as a potential new user instrument to study inhomogeneous structures, such as additively manufactured metal parts, lithium batteries, and porous media.  INFER’s advantages may prove invaluable for several experiments including a precision measurement of gravity.  The speaker will discuss using perfect-crystal, neutron interferometry for fundamental physics and the development of the new far-field grating-based interferometer for material science. 

Bio: Dr. Michael G. Huber has been working in the field of neutron optics and interferometry since 2003.  His earliest work in neutron interferometry focused on providing high precision data for nuclear models.    In addition to interferometry, Dr. Huber has worked on other experiments in fundamental physics such as measuring the neutron lifetime, Schwinger scattering, and the generation of spin-orbit states. He is the principle investigator for the 2 perfect-crystal interferometer facilities at NIST which operate with the generous support of several graduate students, post-docs, and external collaborators including NC State.  He is part of the INFER team developing far-field interferometry for wider scientific use.

Host: Albert Young

Details

Date:
February 8, 2021
Time:
4:00 pm - 5:00 pm
Event Category: