L. M. Scott

Cosmic ray energy loss in the heliosphere: Direct evidence from electron‐capture‐decay secondary isotopes

Measurements by the Cosmic Ray Isotope Spectrometer (CRIS) on the Advanced Composition Explorer (ACE) spacecraft provide direct evidence that galactic cosmic rays lose energy as a result of their interactions with magnetic fields expanding with the solar wind. The secondary isotopes ^(49)V and ^(51)Cr can decay to ^(49)Ti and ^(51)V, respectively, only by electron capture. The observed abundances of these isotopes are directly related to the probability of attaching an electron from the interstellar medium; this probability decreases strongly with increasing energy around a few hundred MeV/nucleon. At the highest energies observed by CRIS, electron attachment on these nuclides is very unlikely, and thus ^(49)V and ^(51)Cr are essentially stable. At lower energies, attachment and decay do occur. Comparison of the energy dependence of the daughter/parent ratios ^(49)Ti/^(49)V and ^(51)V/^(51)Cr during solar minimum and solar maximum conditions confirms that increased energy loss occurs during solar maximum. This analysis indicates an increase in the modulation parameter ϕ of about 400 to 700 MV corresponding to an increase in average energy loss for these elements of about 200 to 300 MeV/nucleon.

ERRATUM: “COSMIC RAY ORIGIN IN OB ASSOCIATIONS AND PREFERENTIAL ACCELERATION OF REFRACTORY ELEMENTS: EVIDENCE FROM ABUNDANCES OF ELEMENTS 26Fe THROUGH 34Se” (2009, ApJ, 697, 2083)

B. F. Rauch1, J. T. Link1,2, K. Lodders1, M. H. Israel1, L. M. Barbier3, W. R. Binns1, E. R. Christian3, J. R. Cummings1,3, G. A. de Nolfo2, S. Geier4, R. A. Mewaldt4, J. W. Mitchell3, S. M. Schindler4, L. M. Scott1, E. C. Stone4, R. E. Streitmatter3, C. J. Waddington5, and M. E. Wiedenbeck6 1 Washington University, St. Louis, MO 63130, USA 2 GSFC/CRESST, Greenbelt, MD 20771, USA 3 NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA 4 California Institute of Technology, Pasadena, CA 91125, USA 5 University of Minnesota, Minneapolis, MN 55455, USA 6 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA

Measurement of the Relative Abundances of the Ultra-Heavy Galactic Cosmic Rays (30 ≤ Z ≤ 40) with TIGER

Observations of ultra-heavy (Z≥30) galactic cosmic rays (GCR) help to distinguish possible origins of GCR. The Trans-Iron Galactic Element Recorder (TIGER) measures the charge (Z) and energy of GCR using a combination of scintillators, Cherenkov detectors, and a scintillating fiber hodoscope. The two Cherenkov radiators, one acrylic and one aerogel, provide TIGER with an energy sensitivity between 0.3 and 10 GeV/nucleon in the instrument. The threshold at the top of the atmosphere is close to 0.8 GeV/nucleon for Fe. TIGER has accumulated data on two successful flights from McMurdo, Antarctica launched in D ecember 2001 and December 2003 with a total flight duration of 50 days. The combined dataset resolves ~140 nuclei with Z > 30, and provides the best measurements to date for 30Zn, 31Ga, 32Ge, and 34Se. The results for Ga and Ge taken together are inconsistent with a GCR source with Solar-System abundances modified either by preferential acceleration of elements of low first ionization potential or by preferential acceleration of refractory elements, suggesting that elemental composition of the GCR source is different from that of the Solar System

The attenuation length of cosmic ray iron in the atmosphere obtained by tiger experiment

A precise measurement of elemental abundances of galactic cosmic rays from charges Z = 20 to 34 was made by TIGER balloon experiment. Using the various path lengths in the atmosphere between 4 and 16 g/cm2 from the TIGER flight data, we derived the attenuation length of iron nuclei with the energy above 2.5 GeV/n in the atmosphere. As the result, we obtained the attenuation length of 15.5 ± 0.6 g/cm2 which is consistent with previous results of balloon measurements.