  The SPI anticoincidence shield consists of 91 BGO crystals and is operated as
a nearly omnidirectional gamma-ray burst detector above ~75 keV. Since the
start of the mission 269 gamma-ray burst candidates have been detected. 110
bursts have been confirmed with the instruments included in the 3rd
Interplanetary Network. Here we present a preliminary statistical analysis of
the SPI-ACS sample of gamma-ray bursts and gamma-ray burst candidates; in
particular we discuss the duration distribution of the bursts. A prominent
population of short burst candidates (duration <200ms) is found which is
discovered to be strongly contaminated by cosmic-ray nuclei interacting in the
detectors.

Astrophysics