The Russian-US INTREPID Project

INTREPID (Ionization-Neutron Transition-Radiation Electron-Protonnucleus Investigation Detector) is a potential joint Russian-US balloon project. INTREPID is meant (1) to integrate and cross-calibrate the transition radiation detection and ionization-neutron calorimetry techniques and (2) to study the spectra of primary cosmic-ray (PCR) electrons from ∼ 2 × 10 9 to ∼ 10 12 eV and of the nuclear component at energies up to 10 14 eV. The potential capabilities of the instrument are discussed. protons and nuclei below and in the ”knee” range can potentially provide information on local nearby sources of high-energy PCRs and their propagation in the Galaxy. Experimental techniques applied so far have been unable to provide a final solution of these problems. As regards the electron spectrum, there is significant scatter among the data obtained by various experiments, and no case where a single instrument has obtained results across the entire energy range. An additional problem is that the high energies of particles intiating cascades in standard calorimeters can be only be estimated with the use of model-based simulations. So it would be very useful to measure energies with two independent methods. The technique of Compton Scatter Transition-Radiation Detectors (CSTRD) [1,2] provides the possibility of extending the range of measured values of particle Lorentz factors γ (and thus energy) independently of the cascade development up to γ ∼ 10 5 . The INCA project has developed the technique of the ionization-neutron calorimeter (INCA) to (1) determine the cascade energy by measuring both the ionization and the yield of thermalized neutrons, (2) select electrons against the proton-produced background, and (3) enlarge significantly the acceptance of potential space instrument designs [3-6]. The integration of