  The structure and $B(E1)$ transition strength of $^{19}$B are investigated in
a $^{17}\text{B}+n+n$ model, triggered by a recent experiment showing that
$^{19}$B exhibits a well pronounced two-neutron halo structure. Preliminary
analysis of the experimental data was performed by employing contact $n$-$n$
interactions, which are known to underestimate the $s$-wave content in other
halo nuclei such as $^{11}$Li. In the present work, the three-body
hyperspherical formalism with finite-range two-body interactions is used to
describe $^{19}$B. In particular, two different finite-range $n$-$n$
interactions will be used, as well as a simple central Gaussian potential whose
range is progressively reduced. The purpose is to determine the main properties
of the nucleus and investigate how they change when using contact-like $n$-$n$
potentials. Special attention is also paid to the dependence on the
prescription used to account for three-body effects, i.e., a three-body force
or a density-dependent $n$-$n$ potential. We have found that the three-body
model plus finite-range potentials provide a description of $^{19}$B consistent
with the experimental data. The results are essentially independent of the
short-distance details of the two-body potentials, giving rise to an
$(s_{1/2})^2$ content of about 55%, clearly larger than the initial estimates.
Very little dependence has been found as well on the prescription used for the
three-body effects. The total computed $B(E1)$ strength is compatible with the
experimental result, although we slightly overestimate the data around the
low-energy peak of the $dB(E1)/d\varepsilon$ distribution. Finally, we show
that a reduction of the $n$-$n$ interaction range produces a significant
reduction of the $s$-wave contribution, which then should be expected in
calculations using contact interactions.
