  We present stellar parameters and chemical abundances of 47 elements detected
in the bright (V = 11.63) very metal-poor ([Fe/H] = -2.20 +- 0.12) star 2MASS
J22132050-5137385. We observed this star using the Magellan Inamori Kyocera
Echelle spectrograph as part of ongoing work by the R-Process Alliance. The
spectrum of 2MASS J22132050-5137385 exhibits unusually strong lines of elements
heavier than the iron group, and our analysis reveals that these elements were
produced by rapid neutron-capture (r-process) nucleosynthesis. We derive a
europium enhancement, [Eu/Fe] = +2.45 +- 0.08, that is higher than any other
r-process-enhanced star known at present. This star is only the eighth
r-process-enhanced star where both thorium and uranium are detected, and we
calculate the age of the r-process material, 13.6 +- 2.6 Gyr, from the
radioactive decay of these isotopes. This star contains relatively large
enhancements of elements that may be produced as transuranic fission fragments,
and we propose a new method using this characteristic to assess the r-process
yields and gas dilution in samples of r-process-enhanced stars. We conclude
that 2MASS J22132050-5137385 exhibits a high level of r-process enhancement
because it formed in an environment where the r-process material was less
diluted than average. Assuming a canonical baryonic minihalo mass of 10^6 M_sun
and a 1 percent metal retention rate, this star formed in a cloud of only ~ 600
M_sun.
