  Propagation-based neutron phase-contrast tomography was demonstrated using
the ISIS pulsed spallation source. The proof-of-concept tomogram with
Paganin-type phase-retrieval filter applied exhibited an effective net boost of
$23\pm 1$ in the signal-to-noise ratio as compared to an attenuation-based
tomogram, implying a boost in the effective degree of neutron brilliance of
over two orders of magnitude. This comparison is for phase retrieval versus
conventional absorption with no additional collimation in place. Expressions
are provided for the optimal phase-contrast geometry as well as conditions for
the validity of the method. The underpinning theory is derived under the
assumption of the sample being composed of a single material. The effective
boost in brilliance may be employed to give reduced acquisition time, or may
instead be used to keep exposure times fixed while improving the measured
contrast.
