ISS-CREAM

Building on the success of the Cosmic Ray Energetics And Mass (CREAM) balloon flights, the instrument is being transformed for accommodation on the International Space Station (ISS). The CREAM on the ISS, ISS-CREAM, mission is planned for launch in 2016. The goal is to extend the energy reach of direct measurements of cosmic rays to the highest energy possible to probe their origin, acceleration and propagation. Its long exposure above the atmosphere offers orders of magnitude greater statistics without the secondary particle background inherent in balloon experiments investigating the origin of cosmic rays. The ISS-CREAM instrument consists of complementary and redundant particle detectors to measure elemental spectra of Z = 1–26 nuclei over the energy range 10¹⁰ to >10¹⁴ eV. An ionization calorimeter determines the energy of the cosmic ray particles, provide tracking, and event trigger. Silicon charge detectors provide precise charge measurements. Top/bottom counting detectors provide shower profiles for electron/hadron separation. The boronated scintillator detector provides additional electron/hadron discrimination using thermal neutrons produced by particles that interact within the calorimeter. ISS-CREAM will (1) determine how the observed spectral differences of protons and heavier nuclei evolve at higher energies approaching the “knee”; (2) be capable of measuring potential changes in the spectra of secondary nuclei resulting from the interactions of primary cosmic rays with the interstellar medium; and (3) conduct a sensitive search for spectral features, such as a bend in the proton spectrum.

TCD and BCD

Kyungpook National University is responsible for Top Counting Detector and Bttom Counting Detector (TCD/BCD).

The TCD/BCD are designed to measure scintillation lights produced when particles pass through the plastic scintillators. The photodiode (PD) has been chosen to convert scintillation lights to electric current. The PD measures not only the scintillation lights but also the ionization energy losses of incident charged particles.

The TCD is located between the carbon target and the Calorimeter, and the BCD is located below the Calorimeter. The TCD consists of a plastic scintillator with 500 x 500 x 5 mm³ dimension and 20 x 20 silicon photodiodes. The BCD is similar to the TCD except that the size of the plastic scintillator is 600 x 600 x 10 mm³. Dimensions of the Al enclosures for the TCD and BCD are 901 x 551 x 29 mm³ and 950 x 650 x 25 mm³, respectively. The mass of the TCD is 9.6 kg and BCD is 15.6 kg, respectively.

The T/BCD can separate electrons from the protons for electron and gamma-ray physics. Electrons can be separated from the protons by using the difference in shower shapes of the electromagnetic and hadronic interactions. Energy information in two dimensions from the photodiodes above and below the Calorimeter can provide a tool to distinguish electrons from protons.

The T/BCD can also give a redundant high energy trigger and a low energy electron trigger.

-- Jeongmin Park - 2016-01-12

Comments