Quantitative Analysis of Proton Content in Deuterated Poly(methyl methacrylate) for Thin Neutron Window Material Selection in Ultra-cold Neutron Experiments

A suitable material selection for a dPMMA window used in the nEDM@SNS experiment, which aims to make the world's best measurement of the neutron's electric dipole moment, is essential. nEDM@SNS will significantly improve our understanding of how matter was formed during the Big Bang. To achieve this, nEDM@SNS requires maximum delivery of cold neutrons to the inside of a cell containing superfluid helium-4, cooled to 0.5 K, to produce the ultra-cold neutrons (UCNs) needed for the experiment.The ratio of the Hydrogen/Deuteron cross-section of ~12 highlights that materials containing hydrogen are much more likely to scatter, absorb, or deflect neutrons. This could potentially reduce the number of UCNs needed and produce unwanted background signals. To investigate the proton content of the deuterated poly(methyl methacrylate) (d-PMMA) sample, a Nuclear Magnetic Resonance (NMR) technique is used. TMS (tetra-methyl silane) and a separate fully-protonated PMMA sample are used for calibration. By employing a standardized sample preparation protocol and a MATLAB algorithm to calculate the signal strength attributed to the NMR peaks, the amount of protons in the polymer can be identified.