The ECCO Instrument

ECCO is a large array of passive glass-track-etch detectors, with the principal goal of measur­ing the abundances of the actinides—naturally occurring thorium, uranium, plutonium and curium—in the galactic cosmic rays, both with respect to each other and with respect to the Pt-group. The actinides will be used as clocks to measure the absolute age since nucleosynthesis of the GCR nuclei. ECCO is at least an order of magnitude less expensive than an electronic instrument with the same capability. ECCO is simple on orbit; the sophistication of the experi­ment is in the terrestrial laboratory.

ECCO is composed of 256 detector modules, each of which consists of a sandwich of five lay­ers of barium-phosphate glass detectors. The effective collecting power of ECCO is 53 m²sr. The detectors passively record the tracks of rela­tivistic ultraheavy galactic cosmic rays during exposure on orbit. After recovery, the detectors are calibrated, etched, and analyzed. The charge of each GCR actinide is measured with sufficient precision to resolve each individual element. Even if the GCR source is old, characteristic of the interstellar medium, ECCO will collect at least 60 actinides. This is more than an order of magnitude improvement in current world­wide statistics for high-precision elemental abundance measurements of GCR actinides. In addition, ECCO will perform an abundance measurement for elements with Z>70, overlap­ping with the ENTICE charge range.