Hideyuki Fuke

Abstract The Calorimetric Electron Telescope (CALET), launched to the International Space Station (ISS) in 2015 August and continuously operating since, measures cosmic-ray (CR) electrons, nuclei, and gamma rays. CALET, with its 27 radiation length deep Total Absorption Calorimeter, measures particle energy and allows for the measurement of spectra, secondary to primary ratios of the more abundant CR nuclei through ₂₈Ni, while the main charge detector can measure ultra-heavy CR nuclei through ₄₄Ru. The results for the abundances of elements from Z = 14 to Z = 44 relative to ₂₆Fe over 7.5 yr of observation are presented here and compared to previous measurements from ACE-CRIS, SuperTIGER, and HEAO-3.

The Calorimetric Electron Telescope (CALET), in operation on the International Space Station since 2015, collected a large sample of cosmic-ray (CR) iron and sub-iron events over a wide energy interval. In this Letter, we report an update of our previous measurement of the iron flux and we present—for the first time—a high statistics measurement of the spectra of two sub-iron elements Cr and Ti in the energy interval from 10 to 250  GeV/n. The analyses are based on 8 years of data. Differently from older generations of cosmic-ray instruments which, in most cases, could not resolve individual sub-iron elements, CALET can identify each nuclear species from proton to nickel (and beyond) with a measurement of their electric charge. Thanks to the improvement in statistics and a more refined assessment of systematic uncertainties, the iron spectral shape is better resolved, at high energy, than in our previous paper, and we report its flux ratio to chromium and titanium. The measured fluxes of Cr and Ti show energy dependences compatible with a single power law with spectral indices −2.74±0.06 and −2.88±0.06, respectively.

Recent direct measurements of the energy spectra of the charged cosmic ray have revealed unexpected spectral features, most notably the onset of a progressive hardening at few hundreds of GeV/n not only of proton and He spectra but also observable for heavier nuclei. Thus, the study of the spectra behavior of heavy elements may shed light on understanding propagation and acceleration phenomena in our Galaxy. In particular, Fe and Ni provide favorable conditions for observations thanks to the low background contamination from spallation of higher mass elements they are affected by. The CALorimetric Electron Telescope, CALET, has been measuring high-energy cosmic rays on the International Space Station since October 2015. The instrument consists of two layers of segmented plastic scintillators, a 3 radiation length thick tungsten-scintillating fiber imaging calorimeter and a 27 radiation length thick PWO calorimeter. It identifies the charge of individual elements up to Ni and beyond and it measures the energy of cosmic-ray nuclei providing a direct measurement of their spectra. In this contribution, the iron and nickel spectra, resulted after 5 years of data acquisition, are presented in the energy range between 10 and 2000 GeV/n and between 8.8 and 240 GeV/n, respectively. The analysis procedure and the assessment of systematic errors are detailed, in addition to the ratio between the two fluxes. Both spectra show similar shape and energy dependence.