Scintillating fibers and their use in the Cosmic Ray Isotope Spectrometer (CRIS) on the Advanced Composition Explorer (ACE)

The Cosmic Ray Isotope Spectrometer (CRIS) experiment was launched aboard the NASA Advanced Composition Explorer satellite on August 25, 1997. The experimental objective of CRIS is to measure the isotopic composition of galactic cosmic ray nuclei for elements with charge $3<Z<28$ over the energy range ∼50–500 MeV/nuc. The instrument consists of a scintillating fiber hodoscope to determine particle trajectory, and four stacks of silicon wafers for multiple dE/dx and $Etot$ measurements. This instrument is the first to use scintillating fibers in space. The CRIS instrument has a large geometrical factor of ∼250 cm² sr. The spatial resolution obtained by the fiber hodoscope is ∼100 μm. The mass resolution achieved is ∼0.12 amu for Carbon and 0.30 amu for the heaviest isotopes measured. Mass histograms of selected isotopes are presented.