  The focus of this paper is on optimizing the electron-antineutrino source for
the IsoDAR (Isotope Decay at Rest) experimental program. IsoDAR will perform
sensitive short-baseline neutrino oscillation and electroweak measurements,
among other Beyond Standard Model searches, in combination with KamLAND and/or
other suitable detectors. IsoDAR will rely on the high-$Q$ $\beta^-$ decay of
the $^{8}$Li isotope for producing electron-antineutrinos, created mainly via
neutron capture in an isotopically enriched $^{7}$Li sleeve surrounding the Be
target. In particular, this paper examines the performance, defined in terms of
absolute $^{8}$Li (or, equivalently, electron-antineutrino) production rate, of
various candidate sleeve materials, including a lithium-fluoride,
beryllium-fluoride mixture ("FLiBe") sleeve and a homogeneous mixture of
lithium and beryllium ("Li-Be"). These studies show that the $^{8}$Li yield can
be increased substantially by employing a Li-Be sleeve and therefore motivate
significant changes to the nominal IsoDAR design.
