FIG. 3.

The total data set, neutron phase from 1456 interferograms for target in with gas (ϕ_full, green), target in empty (ϕ_empty, gold), and target out (ϕ₀, black). The blue points are Φ_D = ϕ_full − ϕ₀. The red points are Φ_cell = ϕ_empty − ϕ₀. Subtracting Φ_cell from Φ_D gives the phase shift Φ_gas due to the gas only. Vertical lines delineate the runs used to compute Φ_gas for each pressure data set. The discontinuous jumps in ϕ₀ and ϕ_empty between 10.6 and 13.0 bar were due to a gap in time of about one month and an improvement in the facility’s environmental controls. All phase shifts are shown modulo 2π.