Calet measurement of ultra-heavy cosmic rays

The CALorimetric Electron Telescope (CALET) is under construction for launch to the International Space Station (ISS) in 2014, and beam-test components of its main calorimeter (CAL) instrument have recently undergone calibration at the CERN SPS using a lead-fragment beam. One of the primary science objectives of the CAL is to measure the energy spectra of nuclei from protons through iron up to 1,000 TeV, and a secondary objective will be to measure the rare ultra-heavy (UH) cosmic ray (CR) abundances that provide important clues for the CR source and acceleration mechanism. The CAL will supplement the UH statistics it can measure with events passing within the full instrument geometry by utilizing the Earth’s geomagnetic field at the 51.6^◦ inclination orbit of the ISS to select events that do not need energy determination in the Total Absorption Calorimeter (TASC). Ion-beam test data show that the Charge Detector (CHD) scintillator response is relatively insensitive to energy above minimum ionization, and the angle dependent rigidity as a function of geomagnetic latitude can be exploited to discriminate individual elements above this energy threshold. Such events require corrections for trajectory in the instrument that can be made with only the top 4 layers of the Imaging Calorimeter (IMC), which allows for considerably greater geometric acceptance than for events that require passage through the TASC for energy determination. Using this approach CALET will be able to measure UH CR relative abundances over its expected mission with ∼ 2 − 4 times the statistics of TIGER.