Oct 04 2007
Analysis of: Dabbs, J. W. T. et al, “Gravitational Acceleration of Free Neutrons” Phys. Rev. 139B, pp. 756-760, 1965
The acceleration due to gravity was actually determined to be approximately 0.5 percent less than expected, from velocities at the “polycrystalline Be block”. It reads to me as though velocities less than what would be expected at the 14.587 cm drop from horizontal were missing after the second collimating slit, by design. It would be difficult to define the velocity limit perfectly, so there would have been some velocities just under, maybe even 0.5 percent under. Barrier diffraction of a straight path would allow some of these neutrons to reach the lower counter, and “the counting rates in the lower detector were not large (200 counts/min at the bottom of the travel and 30-MW reactor power)”. Also, the slow component is said to have dropped approx. 10-20 cm, quite a range, and may be partly due to single edge diffraction patterns.
Something interesting about Fig. 4 in the paper relating to the “fast” component is that for the top 9 data points for “counts/channel”, shifting the triangle to center over channel 65 would seem to be a better fit. With the complete set of data points used, the fit is effected by some of the higher near zero readings on the right side of the plot. These readings may again include neutrons directed by single edge diffraction at the edge of the barrier.