Neutron Phase Contrast Imaging of PbWO${}_4$ Crystals for G Experiment Test Masses Using a Talbot-Lau Neutron Interferometer

Abstract

The use of transparent test/source masses can benefit future measurements of Newton's gravitational constant $G$. Such transparent test mass materials can enable nondestructive, quantitative internal density gradient measurements using optical interferometry and allow in-situ optical metrology methods to be realized for the critical distance measurements often needed in a $G$ apparatus. To confirm the sensitivity of such optical interferometry measurements to internal density gradients it is desirable to conduct a check with a totally independent technique. We present an upper bound on possible internal density gradients in lead tungstate (PbWO${}_4$) crystals using a Talbot-Lau neutron interferometer on the Cold Neutron Imaging Facility (CNIF) at NIST. We placed an upper bound on a fractional atomic density gradient in two PbWO${}_4$ test crystals of $\frac{1}{N}\frac{dN}{dx}<0.5\times 10^{-6}$ cm${}^{-1}$. This value is about two orders of magnitude smaller than required for $G$ measurements. We discuss the implications of this result and of other nondestructive methods for characterization of internal density inhomogeneties which can be applied to test masses in $G$ experiments.

10 pages, 8 figures, submitted to Classical and Quantum Gravity

References in corpus (1)

• Imaging of PbWO4 Crystals for G Experiment Test Masses Using a Laser Interferometer