W. R. Binns

Abundances of ultraheavy elements in the cosmic radiation: results from HEAO 3

We report here an analysis that, for the first time, systematically normalizes the data from the HEAO 3 Heavy Nuclei Experiment on .the cosmic-ray abundances of all the elements heavier than germanium to that of .iron. In the range of atomic number Z, 33 ≤Z ≤60, the analysis yields abundances of odd-even element pairs. These abundances are consistent with a cosmic-ray source having a composition similar to that of the solar system, but subject to source fractionation correlated with the first ionization potential (FIP) of each element. For Z > 60, the analysis yields abundances of element groups. For these heaviest nuclei, we find an enhancement of the abundance of the platinum group, elements with 74 ≤ Z ≤ 80, relative to that in a propagated solar system source, and a corresponding increase in the abundance of the largely secondary elements in the range 62 ≤ Z ≤ 73. These abundances suggest that there is an enhancement of the r-process contribution to the source nuclei in the Z > 60 charge region. Over the entire region of charge, standard leaky box models of propagation satisfactorily model secondary production.

Cosmic-ray abundances of elements with atomic number 26 less than or equal to 40 measured on HEAO 3

Individual elements in the cosmic radiation of even atomic number (Z) in the interval 26-40 have been resolved and their relative abundances measured. The results are inconsistent with a cosmic-ray source whose composition in this charge interval is dominated by r-process nucleosynthesis. The ratios of cosmic-ray source abundances to solar system abundances in this interval follow the same general correlation with first ionization potential as for the lighter elements, although there are deviations in detail.

Lead, platinum, and other heavy elements in the primary cosmic radiation - HEAO 3 results

An observation of the abundances of cosmic-ray lead and platinum-group nuclei using data from the HEAO-3 Heavy Nuclei Experiment (HNE) which consisted of ion chambers mounted on both sides of a plastic Cerenkov counter is reported. Further analysis with more stringent selections, inclusion of additional data, and a calibration at the LBL Bevalac, have allowed obtaining the abundance ratio of lead and the platinum group of elements for particles that had a cutoff rigidity R sub c 5 GV.

Radioactive Clocks and Cosmic-ray Transport in the Galaxy

There are a number of radioactive ‘clocks’ in the cosmic radiation that can be used to measure the time scales for cosmic ray processes in the Galaxy. With high-resolution isotope measurements available from ACE it is now possible to read these clocks with greatly improved accuracy and address key questions about the origin and lifetime of cosmic rays. This paper discusses the status of three such investigations.

Constraints on cosmic-ray acceleration and transport from isotope observations

Observations from the Cosmic Ray Isotope Spectrometer (CRIS) on ACE have been used to derive constraints on the locations, physical conditions, and time scales for cosmic-ray acceleration and transport. The isotopic composition of Fe, Co, and Ni is very similar to that of solar system material, indicating that cosmic rays contain contributions from supernovae of both Type II and Type Ia. The electron-capture primary ^(59)Ni produced in supernovae has decayed, demonstrating that a time ≳10^5 yr elapses before acceleration of the bulk of the cosmic rays and showing that most of the accelerated material is derived from old stellar or interstellar material rather than from fresh supernova ejecta.

The UH-nuclei cosmic ray detector on the third high energy astronomy observatory

The third High Energy Astronomy Observatory satellite (HEAO-3) carries a particle telescope for the detection of highly charged cosmic ray nuclei. These nuclei, which have Z ≳ 28, are much rarer than the lower charged nuclei in the cosmic radiation. As a consequence, this particle telescope was required to have a large collecting area as well as an ability to resolve individual elements. This paper describes the telescope, composed of large area parallel plate ionization chambers, multiwire ion chamber hodoscopes and a Cherenkov radiation detector. The resulting telescope has a total geometry factor of 59,000 cm^2 sr and is capable of measuring the charges of nuclei in the range 14 ≲ Z ≲ 120.

Cosmic-Ray Spectra in Interstellar Space

At energies below ~300 MeV/nuc our knowledge of cosmic-ray spectra outside the heliosphere is obscured by the energy loss that cosmic rays experience during transport through the heliosphere into the inner solar system. This paper compares measurements of secondary electron-capture isotope abundances and cosmic-ray spectra from ACE with a simple model of interstellar propagation and solar modulation in order to place limits on the range of interstellar spectra that are compatible with both sets of data.

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

Abundances of the cosmic ray β-decay secondaries and implications for cosmic ray transport

Galactic cosmic rays (GCRs) pass through the interstellar medium (ISM) and undergo nuclear interactions that produce secondary fragments. The abundances of radioactive secondary species can be used to derive a galactic confinement time for cosmic rays using the amount of ISM material traversed by the cosmic rays inferred from stable GCR secondary abundances. Abundance measurements of long-lived species such as ^(10)Be, ^(26)Al, ^(36)Cl, and ^(54)Mn allow a comparison of propagation histories for different parent nuclei. Abundances for these species, measured in the energy range ~ 50 - 500 MeV/nuc using the Cosmic Ray Isotope Spectrometer (CRIS) aboard the Advanced Composition Explorer (ACE) spacecraft, indicate a confinement time τ(esc) 16.2±0.8 Myr. We have modeled the production and propagation of the radioactive secondaries and discuss the implications for GCR transport.

Preliminary SuperTIGER Abundances of Galactic Cosmic-Rays for the Charge Interval Z=41-56 and Prospects for SuperTIGER-2

The SuperTIGER (Trans-Iron Galactic Element Recorder) instrument was launched from Williams Field, Antarctica on December 8, 2012 and flew for 55 days at a mean altitude of 125,000 feet on a long-duration balloon flight. SuperTIGER measured the relative abundances of Galactic cosmic-ray nuclei with high statistical precision and well resolved individual element peaks in the charge range Z=10-40. In addition, SuperTIGER made exploratory measurements of the relative abundances up to Z=56. Although the statistics are low for charges greater than Z=40, we will show how the relative abundances of charges Z=40-56 compare to those reported by HEAO3. A second flight, SuperTIGER-II, is planned for December 2017. As SuperTIGER-II will fly during solar minimum, we estimate a ~50% increase in the particles collected per unit time as compared to SuperTIGER-I. With the combined data sets of SuperTIGER-I and II we will improve statistics in the Z=30-40 range and measure individual elemental abundances up to Z=56.