Volume 15, Number 4, December 1999
By Joseph King
NSSDC's solar wind magnetic field and plasma parameter data are its most widely accessed and used space physics data. They are so widely used because they are needed as correlative data in a broad range of studies and are fairly easily understood and used.
In contrast, a majority of NSSDC space physics data sets are more difficult to use and understand, are often at a "lower processing level," and are not relevant to so broad a range of science analyses. However, these data sets often contain still-unmined science potential relevant to key current science questions.
An example of a data set that might have such potential is the Heavy Nuclei Experiment (HNE) flown on the High Energy Astrophysics Observatory (HEAO 3) in 1979-1981. The HNE was intended to measure high energy nuclei with atomic number (Z, nuclear charge) between 17 (chlorine) and 100 (fermium) with the ability to resolve individual elements. Such cosmic ray composition data are used in studies of nucleosynthesis (how elements are created) and in studies of the propagation of cosmic rays from their point of origin to the time and place of being observed.
Key scientists associated with the HNE experiment were co-PIs M. H. Israel (Washington University), E. C. Stone (Caltech), and C. J. Waddington (University of Minnesota), and co-PIs W. R. Binns (McDonnell Douglas Corporation) and J. Klarmann (Washington University). Data processing and management were largely done at Caltech under the leadership of the late T. L. Garrard.
The HNE is a very sophisticated package containing four multiwire hodoscopes for determining path direction, six ionization chambers, and two Cherenkov detectors. A given incident cosmic ray particle will penetrate some or all of these aligned elements. For each such particle is captured the following information: which pair of wires fired in each hodoscope (thus fixing the particle direction of motion); the amount of energy deposited in each of the ion chambers; the amount of energy recorded in each of eight photomultiplier tubes observing light emitted by the Cherenkov detectors. It is the combination of all these parameters that enables the determination of the atomic number and the energy of any given cosmic ray.
Scientific results of this investigation are given in Binns et al., Astrophysical Journal, Volume 346, page 997 (1989) and in the earlier papers referenced therein. According to Dr. Israel the three major scientific results of this investigation were as follows:
1. The flux of actinides (very high Z) in the cosmic rays is much lower than suggested by earlier balloon-borne plastic track and nuclear emulsion experiments.
2. The cosmic ray abundances of Z< 60 elements are broadly similar to solar system abundances, while abundances at Z > 60 suggest enhancement of "r-process" elements.
3. The abundance of Germanium (Ge, Z = 32) relative to Iron (Fe, Z = 26) in the cosmic rays is about half that in the solar system even though Ge and Fe have almost identical first-ionization-potential (FIP), suggesting that element fractionation according to FIP does not fully explain cosmic ray abundances.
NSSDC holds a set of 591 nine-track HNE "library tapes" (about 100 GBytes) provided by the experimenter with all these parameter values for each heavy cosmic ray observed over the 600-day HNE life. This information includes about 20 million iron nuclei and ten thousand nuclei with Z > 40. A great deal of documentation and software source code accompany the data. In addition, NSSDC holds two subsets of the data created initially by the PI team to support the majority of the analyses done by them. One, called "gold," contains data on 21 tapes (~ 4 GBytes) for all the cosmic rays reliably identified as Z > 30, and the other, called "cobalt," contains data on 11 (~ 2 GBytes) tapes for all cosmic rays passing most closely along the axis of the detector package and thus having the best resolution in atomic number.
NSSDC can provide a bibliography of the scientific papers done with these data to date. These HNE data (along with contemporaneous data from the UK Ariel 6 spacecraft) remain unique in terms of the range of atomic number and energy covered.
While NSSDC has provided electronic access to many recent data and selected older data in the past several years, it wants to identify and prioritize additional older data sets in its archive for promotion to electronic accessibility based on the likelihood of their contributing to significant new scientific results. The author of this article asks readers interested in the promotion of this HEAO 3 HNE data set or any other NSSDC data set still held off line identified in the Web-accessible NSSDC Master Catalog to let this author know. Expressions of even latent interest in the full HNE data set (as distinct from the much smaller "gold" and "cobalt" subsets) would be useful.
The author thanks to Dr. Israel for comments on a first draft of this article.
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