  The first lithium-drifted silicon (Si(Li)) detectors to satisfy the unique
geometric, performance, and cost requirements of the General Antiparticle
Spectrometer (GAPS) experiment have been produced by Shimadzu Corporation. The
GAPS Si(Li) detectors will form the first large-area, relatively
high-temperature Si(Li) detector system with sensitivity to X-rays to operate
at high altitude. These 10 cm-diameter, 2.5 mm-thick, 4- or 8-strip detectors
provide the active area, X-ray absorption efficiency, energy resolution, and
particle tracking capability necessary for the GAPS exotic-atom particle
identification technique. In this paper, the detector performance is validated
on the bases of X-ray energy resolution and reconstruction of cosmic minimum
ionizing particle (MIP) signals. We use the established noise model for
semiconductor detectors to distinguish sources of noise due to the detector
from those due to signal processing electronics. We demonstrate that detectors
with either 4 strips or 8 strips can provide the required $\lesssim$4 keV
(FWHM) X-ray energy resolution at flight temperatures of $-35$ to
$-45^{\circ}$C, given the proper choice of signal processing electronics.
Approximately 1000 8-strip detectors will be used for the first GAPS Antarctic
balloon flight, scheduled for late 2021.
