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Particle Astrophysics: ISS CREAM
Scott Nutter Dr Nutter at NASA Wallops Flight Facility near Chincoteague, VA.

ISS-CREAM (Cosmic Ray Energetics And Mass for the International Space Station) is a NASA-sponsored instrument being prepared for installation on the International Space Station. The goal is to better understand the details of how cosmic rays are accelerated out of supernova remnants. ISS-CREAM must be above the atmosphere in order to measure the spectrum of individual atomic elements in the cosmic rays at high energies, where the cosmic ray spectrum shows currently unexplained anomalies. The ISS-CREAM project is a direct descendant of the CREAM balloon-borne instrument, which has flown from Antarctica many times at the extreme upper limits of the atmosphere (above 99.5% of its mass). Placing a similar instrument on the ISS greatly reduces backgrounds due to interactions of the cosmic rays in the atmosphere. It is both exciting and a privilege to have an instrument accepted for the ISS.

There are four instruments on ISS-CREAM. The two primary instruments are the multi-layered tungsten-scintillator calorimeter (CAL), measuring particle energy, and the Silicon Charge Detector (SCD), which measures particle charge using a thin layer of silicon. Two additional detector systems distinguish between electrons and hadrons (protons and other atomic nuclei) that enter the instrument: the Top and Bottom Charge Detectors (TCD/BCD), which lie above and below the CAL and help determine particle shower shape, and the Boronated Scintillator Detector (BSD). The University of Maryland contributes the CAL, Korean collaborators provide the TCD/BCD and SCD, and NKU, Pennsylvania State University, and NASA-Goddard share responsibility for the BSD.

These detectors were integrated into the ISS-CREAM instrument this past year. The complete instrument was subjected to a battery of tests, including shaking (simulating a rocket launch), electromagnetic interference tests, and thermal vacuum. Work was done in a clean room environment and required a “bunny suit” for entry. Special training to protect against accidental static electricity discharge while handling the detector and its sensitive electronics was also required. After more than a year of testing and modifications, the instrument is ready for launch, and currently resides at Kennedy Space Center (aka Cape Canaveral) and is being considered for next summer (2016).

NKU’s participation is led by Professor Scott Nutter, who spent sabbatical this year participating in the readiness efforts. In addition, he is the lead scientist on the detector simulations. While readying the full instrument, the BSD team also worked on clearing up a few mysteries discovered in beam tests of a BSD prototype at CERN in 2012.  (Special thanks go to NKU student Kirk Wallace for his help during that test at CERN, the European particle accelerator facility near Geneva, Switzerland.) Those tests showed that the detector worked well at discriminating between electrons and protons – in fact, better than simulations could explain. Further tests of the prototype this past fall (2015) have revealed the reason: the scintillation light emitted as the initial particle shower passes through the BSD lasts much longer than realized. With this enhanced understanding, a paper describing the unique detector is in the works.