Session L7: Cosmic Ray Abundances and Electron/Positron Measurements

Student Observations of Cosmic Rays using Balloon Platforms

One hundred years ago Victor Hess used a balloon platform to carry simple instrumentation up to an altitude of 17,000 feet and in the process discovered a source of ionizing radiation originating from the Cosmos. Since then undergraduate student access to altitudes exceeding 100,000 feet has become feasible and over the last 15 years a number of programs using lightweight ballooning technology have been implemented to provide the next generation of scientists and engineers with hands-on experience in the development of near-space payloads. Over the years various student payloads weighing between 500 grams and 20 kilograms have been carried aloft by various classes of helium filled balloons to study cosmic ray shower development in the atmosphere, the generation of secondary neutrons, the east-west effect and the light cosmic ray charge spectrum. This presentation will discuss three such student ballooning programs implemented at Louisiana State University as well as the different cosmic ray experiments that students have developed under these programs.   

Spacecraft Measurements of the Relative Abundances of Cosmic-Ray Nuclides from Boron through Nickel

Since the original discovery of heavy nuclei in the cosmic radiation more than 60 years ago (Freier et al., Phys. Rev. 74, 213, 1948), the composition of this nuclear component has been providing important clues to the origin of the cosmic rays. Over the past two solar minima, the Cosmic Ray Isotope Spectrometer (CRIS) on NASA's Advanced Composition Explorer (ACE) mission has been measuring the relative abundances and energy spectra of essentially all stable and long-lived nuclides (both elements and isotopes) from He to beyond Ni in the energy range between $\sim$50 and $\sim$500 MeV/nuc. We report precise determinations of nuclidic composition obtained from this 14-year data set. In addition, we discuss the implications of these data for the composition of cosmic-ray source material and for the time scales associated with the acceleration and transport of cosmic-rays in the Galaxy.   

Elemental and isotopic abundance measurements of nuclei with Z$>$28 from the ACE-CRIS experiment and the OB association origin of galactic cosmic rays

We summarize measurements made of the elemental and isotopic abundances of galactic cosmic ray nuclei by the Cosmic Ray Isotope Spectrometer (CRIS) on the NASA Advanced Composition Explorer (ACE) satellite over a period of 14 years in space. We have measured the isotopic abundances of Ga (Z=31) and Ge (Z=32) for the first time and have obtained greatly improved measurements of the Cu (Z=29) and Zn (Z=30) isotopes. We have also measured the elemental abundances of nuclei up to Sr (Z=38). A total of $\sim $700 nuclei heavier than Ni (Z=28) have been collected with energies in the range of $\sim $150 to 600 MeV/nucleon. Our earlier published work on isotopes with Z$<$28 has shown abundances consistent with an OB association origin of a substantial fraction of galactic cosmic rays. This is based primarily on the enhanced $^{22}$Ne/$^{20}$Ne and $^{58}$Fe/$^{56}$Fe ratios relative to solar system abundances. $^{22}$Ne and $^{58}$Fe are copiously produced in Wolf-Rayet stars, which are found primarily in OB associations. The elemental abundances of Z$>$29 nuclei provide completely independent evidence that also points to an OB association origin. The isotopic abundances of Cu, Zn, Ga, and Ge are consistent with either an OB association or normal interstellar medium origin. This research was supported by NASA under grant NNX11AC49G.   

The Super-TIGER Instrument to Probe Galactic Cosmic-Ray Origins

Super-TIGER is a large area (5.4 m$^2$) balloon-borne instrument designed to measure ultra-heavy cosmic-ray nuclei (Z = 30 and above) with individual-element resolution and high statistical precision. These measurements will provide sensitive tests of the emerging model of cosmic-ray origins in OB associations and models of the mechanism for selection of nuclei for acceleration. Furthermore, Super-TIGER will measure the energy spectra of the more abundant elements in the interval 10 $\le Z \le$ 28 at energies 0.8 $<$ E $<$ 10 GeV/nucleon to test the hypothesis that microquasars or other sources could superpose spectral features. Super-TIGER, which builds on the heritage of the smaller TIGER, is expected to launch from Antarctica in December 2012. The particle charge and energy will be measured with a combination of plastic scintillators, acrylic and silica-aerogel Cherenkov detectors, and a scintillating fiber hodoscope. The design, expected performance and current status of the instrument along with the scientific implications of the Super-TIGER measurements will be presented.   

The International Space Station CALorimetric Electron Telescope (CALET) Experiment

The CALET space experiment, currently being developed by collaborators in Japan, Italy and the United States, will study electrons to 20 TeV, gamma rays above 10 GeV and nuclei with Z=1 to 40 up to 1,000 TeV during a five year mission on the International Space Station. The instrument consists of a particle charge identification module, a thin imaging calorimeter (3 r.l. in total) with tungsten plates interleaving scintillating fiber planes, and a thick calorimeter (27 r.l.) composed of lead tungstate logs. CALET has the depth, imaging capabilities and energy resolution for excellent separation between hadrons, electrons and gamma rays and is expected to be launched in 2014 as an attached payload on the International Space Station (ISS) Japanese Experiment Module -- Exposed Facility (JEM-EF). CALET will investigate possible nearby sources of high energy electrons, study the details of galactic particle propagation and search for dark matter signatures. This presentation summarizes the expected instrument design and performance.   

Predicted CALET Measurements of Ultra-Heavy Cosmic Ray Abundances and Electron and Positron Fluxes Using the Geomagnetic Field

The CALorimetric Electron Telescope (CALET) is an imaging calorimeter under construction for launch to the ISS in 2014 for a planned 5 year mission. CALET consists of a charge detection module (CHD) with two segmented planes of 1 cm thick plastic scintillator, an imaging calorimeter (IMC) with a total of 3 radiation lengths (r.l.) of tungsten plates read out with 8 planes of interleaved scintillating fibers, and a total absorption calorimeter (TASC) with 27 r.l. of lead tungstate (PWO) logs. The primary objectives of the experiment are to measure electron energy spectra from 1 GeV to 20 TeV, to detect gamma-rays above 10 GeV, and to measure the energy spectra of nuclei from protons through iron up to 1,000 TeV. In this paper we discuss the capability of CALET to make additional measurements by exploiting the geomagnetic field it will be exposed to in the ISS 51.6$^{\circ}$ inclination orbit. The rare nuclei heavier than nickel (Z=28) can be resolved using the CHD and top IMC layers without requiring particle energy determination in the TASC in field regions where the rigidity cutoffs are above minimum ionization in the scintillator. CALET can also measure the distinct fluxes of cosmic ray positrons and electrons using the earth shadow of the geomagnetic field.   

Validation and Calibration of the Fermi Large Area Telescope Instrument Performance

We describe the $Fermi$-LAT instrument performance, for an updated event selection the LAT team developed in light of experience gained from on-orbit observations. Furthermore, we also describe both the Instrument Response Functions (IRFs) derived solely from Monte Carlo simulations of $\gamma$-rays interactions with the LAT as well as corrections to those IRFs which were motivated by discrepancies we observed between flight and simulated data. We also give details of the numerous validations we have preformed using flight data and quantify the residual uncertainties in the IRFs. Finally, we describe some techniques the LAT team has developed to propagate those uncertainties into estimates of the systematic errors on high level science measurements such as fluxes and spectral indices.   

Saturated Dispersive Extinction Theory of Red Shift

The Dispersive Extinction Theory (DET) proposed by Wang\footnote{Wang, Ling Jun, Physics Essays, \textbf{18}, No. 2, (2005).} offers an alternative to the Big Bang. According to DET, the cosmic red shift is caused by the dispersive extinction of the star light during the propagation from the stars to the earth, instead of being caused by the Doppler shift due to the expansion of the universe.\footnote{Hubble, E., Astrophys. J. \textbf{64}, 321 (1926).}$^,$\footnote{Hubble, E., \textit{The Realm of the Nebulae}, (Yale University Press, New Haven, 1936).} DET allows an infinite, stable, non expanding universe, and is immune of the fundamental problems inherent to the Big Bang such as the horizon problem, the extreme violation of the conservation of mass, energy and charge, and the geocentric nature which violates the principle of relativity.\footnote{Wang, Ling Jun, Physics Essays, \textbf{20}, No. 2, (2007).} The scenario dealt with in Reference (1) is a one in which the extinction by the space medium is not saturated. This work deals with a different scenario when the extinction is saturated. The saturated extinction causes limited energy loss, and the star light can travel a much greater distance than in the unsaturated scenario.