Using the relativistic rise of energy loss as a measure of energy, we have

determined the energy dependence of the abundances relative to _(26)Fe of the elements _(18)Ar,

_(19)K, _(20)Ca, _(21)Sc, _(22)Ti, _(23)V, and _(28)Ni, from 10 to several hundred Ge V /amu. From the energy

dependence of the observed Ar/Fe and Ca/Fe ratios we infer primary source ratios for these

elements

Binns, W. R.

Garrard, T. L.

Israel, M. H.

Jones, M. D.

Kamionkowski, M. P.

Klarmann, J.

Stone, E. C.

Waddington, C. J.

Caltech Authors - Main

Page 1 OG-4.1-4 
COSMIC-RAY ENERGY SPECTRA BETWEEN TEN AND SEVERAL 
HUNDRED GeV/amu FOR ELEMENTS FROM 18Ar TO 28Ni - RESULTS FROM HEA0-3 
M. H. Israel, 1 Michael D. Jones, l.4 M. P. Kamionkowski, 1 J. K.lannann, 1 
E. C. Stone,2 C. J. Waddington,3 W. R. Binns, 1 and T. L. Garrard,2 
1Dept. of Phys. and McDonnell Center for Space Sci., Washington U., St. Louis, MO 63130 USA 
2George W. Downs Lab., Calif. Inst. of Technology, Pasadena, CA 91125 USA 
3School of Physics and Astronomy, Univ. of Minnesota, Minneapolis, MN 55455 USA 
4Present address: LASP, Campus Box 392, Univ. of Colorado, Boulder co 80309 USA 
Abstract. Using the relativistic rise of energy loss as a measure of energy, we have 
determined the energy dependence of the abundances relative to 26Fe of the elements 18Ar, 
19K, 20Ca, 21 Sc, 22 Ti, 23 V, and 28Ni, from 10 to several hundred Ge V /amu. From the energy 
dependence of the observed Ar/Fe and Ca/Fe ratios we infer primary source ratios for these 
elements. 
1. Introduction. The energy-loss of a charged particle in gas exhibits a logarithmic 
increase with increasing energy over the interval from a few GeV/amu to several hundred 
GeV/amu. We have used this relativistic rise in the ionization chambers of the Heavy Nuclei 
Experiment (HNE) on HEA0-3 [1] to measure particle energies above 10 GeV/amu. For 
more detail see [2,3]. The present paper differs from preliminary results [4] in that we have 
evaluated the uncertainties caused by various assumptions and we have corrected an error in 
the calculation of the effects of interactions in the detector. 
2. Instrument Description and Data Selection. The HNE had six ionization chambers, a 
Cherenkov detector, and four multiwire ionization hodoscop~s. The results presented here 
come from a 1 m2sr-yr, high resolution subset of our data, consisting of nuclei that penetrated 
the Cherenkov detector and all six ionization chambers. We consider only particles with 
geomagnetic cutoff >8 GV. The atomic number, Z, of each nucleus is determined from Zc, 
the square-root of the Cherenkov signal, normalized so Zc =Z for high energy. The energy of 
each nucleus is derived from· the relativistic rise, p, defined by p = Z1 /Z, where Z1 is the 
square-root of the ionization signal normalized so that Z1=Z near 2.5 GeV/amu. Consistency 
checks were applied to exclude most of the nuclei which suffered nuclear interactions in the 
instrument. 
3. Analysis. We found the number of events of each Z in narrow intervals of p. We 
derived an energy calibration of p by comparing our Fe observations with those expected 
from folding a trial calibration with a differential Fe energy spectrum derived from a 
compilation of previously published measurements [5]. While the implied energy calibration 
curve depended upon the assumed Fe energy spectrum, our results for the energy dependence 
of secondary-to-primary abundance ratios and primary values of Ar/Fe and Ca/Fe were 
insensitive to the shape of the assumed Fe spectrum. We adopted a spectrum which went as 
E-2·7 at high energy, but our final results were essentially the same if we used E-2·5. 
The slope of the calibration curve (heavy line in fig. 1), implies that the Z1 resolution, 
0.4 charge units (cu) rms, corresponds to an energy resolution of a factor of 1.5 below 
50 GeV/amu and 1.9 above 50 GeV/amu. When this resolution and the steep energy spectrum 
are taken into account, the mean energy of particles observed in any p bin is significantly 
lower than that corresponding to the center of the bin. The light solid line in fig. 1 shows the 
mean energy for particles observed within a bin of width 0.2 cu in Z1 centered at each value 
of p, using our assumed energy spectrum for Fe. Since secondary elements are observed to 
have a steeper energy spectrum, the mean energy corresponding to the same value of p is 
slightly different for each element. For example, the dashed curve is the corresponding one 
for Ti. 
The abundance for each (Z ,p) bin was corrected for interactions in the detector system 
and then divided by the number in the Fe bin at the p corresponding to the same energy. 
Page 2 OG-4.1-4 
1.20 
s.. 
w 1.15 
(/) 
a:: 
u 1.10 ~ (/) 
5 
~ 1.05 
..J 
w 
a: 
1.00 
I 10 100 1000 
ENERGY (GeV/amu) 
Fig. 1. Calibration of relativistic rise (p) as a function of energy. 
Figures 2, 3, and 4 show (•, o) our resulting abundances relative to Fe. Also shown (X) are 
the results from the Danish-French (DF) experiment on the same spacecraft [6]. The two sets 
of data display good agreement where they overlap, 10 to 25 GeV/amu. The error bars on 
our data are statistical only. The light lines indicate the sensitivity of our results to the 
uncertainty of the corrections for interactions, by showing the locations of our data points 
under the extreme assumptions for the cross-sections. 
0.10 
lJ.J 
u 
z 
<l: 
0 
z 
::> 
CD 
<l: 
lJ.J 
> 
~ 0.02 
...J 
lJ.J 
a:: 2aNi 
0.01 
I 10 100 1000 
ENERGY (GeV/amu) 
Fig. 2. Abundance of Ni relative to Fe (Ni/Fe ratio) vs energy. 
4. Discussion. Our data for the Ni/Fe ratio between 10 and 500 Ge V /amu (fig. 2) suggest 
a slight energy dependence, with a best fit power law of exponent -0.050 ± 0.016. Ignoring 
this slight energy dependence, our data give a mean Ni/Fe ratio above 10 GeV/amu of 
0.054 ± 0.001. This result agrees with the highest energy points of the DF experiment. 
However, the data of that experiment suggest an energy dependence of this ratio, rising from 
about 0.045 at about 1 GeV/amu to about 0.055 at about 10 GeV/amu. Data from our HNE 
between 0.5 and 1 GeV/amu [2,7] also indicate a Ni/Fe ratio of about 0.045. 
For K/Fe, Sc/Fe, Ti/Fe,· and V/Fe (fig. 3), our data indicate an extension to about 
150 GeV/amu of the same power-law dependence as indicated by the OF data. The best fit 
exponents for these four ratios, combining the data plotted here from both experiments, are 
respectively -0.31 ± 0.01, -0.25 ± 0.02, -0.28 ± 0.01, and -0.23 ± 0.02. 
Page 3 
w 
u 
a ~ 0. 
~ 
w 
> i= 0.0 
<( 
_J 
w 
a: 
OG-4.1-4 
0.10------------------. 
(b) 21Sc 
0.01 '---'--"'---'-~--'--""---1....._....i.;...._, 
100 1000 I 10 100 IOOO 
w 
u 
z 
~ 0.1 
III 
<( 
~ 0. 
5 
w 
a: O.O,a......i.-_._....i._.1...-....i.-.1...-_.__..__. 
0.10-------------
(dl ~v 
0.0 
ODl'-_.__.._-1-.....i.-_.__.,_"'--__.,__, 
I 10 100 1000 l 10 100 1000 
ENERGY (GeV/amu) ENERGY (GeV/amul 
Fig. 3. Abundances of secondary elements relative to Fe. 
0.20-__,..-__,.._.,.....""""l"_""""I"_...-__ _..., __ 
(a) 18Ar 
0.10 
0.05 
IJ.J 
u ' 
z ---------~----~ ' z 0.02 .___._ _ _,,_ ...... _.__'---'---'-......1.--1 
.::::> I 10 100 1000 ID 
<( 0.50 -.....--~...,.......,-...,.-,--...,...-..,....., 
~ 
~ 
_J 
w 
a:: 
(b) 20Ca 
0.20 
0.10 
0.05 '--....L..-....L..-"'---""--'-....__.__....__...___. 
I 10 100 1000 
ENERGY (GeV/amu) 
Fig. 4. Abundances relative 
to Fe of elements with primary 
and secondary components. 
Our data for the Ar/Fe and Ca/Fe 
ratios (fig. 4) indicate a leveling above 
the energies of the OF experiment, as 
would be expected for an energy-
independent primary component that 
becomes increasingly significant at 
higher energies as the secondary 
component becomes less abundant. 
· We fitted the combined data from the 
two experiments to a function aEP +b, 
with p = -0.321 ± 0.028 for Ar/Fe 
and -0.291 ± 0.010 for Ca/Fe, and 
found primary abundance ratios, 
Ar/Fe = 0.026 ± 0.007 and 
Ca/Fe = 0.088 ± 0.007. These primary 
ratios are insensitive to whether or not 
we included our four or five highest 
energy points ( o) in the fitting, due to 
their low statistical weights. 
Our Ar/Fe and Ca/Fe primary ratios relative to the solar system value [8], are shown in 
fig. 5. The other points are from galactic propagation calculations on the OF data [9], a 
measurement of 4°Ca!Fe [10], and solar coronal abundances inferred from solar energetic 
particles (11]. Also, for Ar we display an upper limit taken directly from our data at 
100 Ge V /amu. It is clear that the Ar abundance has been subjected to a fractionation process. 
Page 4 OS-4.1-4 
The highest energy points in fig. 4 suggest that the Ar/Fe and Ca/Fe ratios increase 
significantly above about 200 Ge V /amu. These· apparent increases could be due to (a) a real 
increase in the primary abundance ratios, (b) a flattening or upturn in the secondary/primary 
ratios, or (c) an instrumental artifact. 
One possible instrumental effect could be: If the p vs energy calibration curve for 
elements lighter than Fe did not flatten off at the highest energies quite as much as did the 
curve for Fe, then at these highest energies the ratio of Ca at some p to Fe at the same p 
would be a ratio of Ca at some energy to Fe at a higher energy. Because of the steepness of 
the energy spectra and the flatness of the p vs energy curve at these highest energies, only a 
small difference is necessary to change the ratio by a factor of two. We do not believe that 
this problem affects the results below about 150 GeV/amu, because at these energies the 
different elements show different energy dependences (flat for Ni/Fe, power-law fall for 
secondaries/Fe) in a way that is not surprising. 
Ca/Fe 
2.0 Ar/Fe 
I 
i : 
1.0 f Ht! en 
en 
....... 
I 
I en I 
er 0.5 ' 
' 
t 
u ' I 
0.2 
0.1------------------
Fig. 5. Cosmic-ray source ratio divided by solar system 
ratio [8] for Ca/Fe and for Ar/Fe. Solid points are for 
galactic cosmic rays: circles, this experiment; triangles, 
[9]; square, [10]. Open circles, solar energetic 
particles (11]. Error bars plotted on data points ignore 
uncertainties in the solar-system ratio. Solid bars 
centered at 1.0 indicate uncertainties of solar-system 
ratios. Note that our Ar/Fe ratio derived from the fit 
in fig. 4 indicates a significant fractionation relative 
to Ca/Fe. This fractionation is also apparent in our 
upper limit to Ar/Fe which we derived by assuming 
that the entire observed.abundance at 100 GeV/amu 
is primary. 
If future studies demonstrate that our calibration is correct above 150 Ge V /amu then the 
turn-up in the data would imply a real effect in the cosmic rays. Because we have no data for 
the pure secondary elements above about 150 GeV/amu, we cannot exclude the possibility of 
a flattening or turn-up of the secondary/primary ratio at these higher energies. Indeed such an 
effect is predicted by the closed-galaxy model [12]. 
If the turn-up is due neither to an instrumental artifact nor to a change in the slope of the 
secondary/primary ratio, then it would indicate a difference between the cosmic-ray source 
composition at several hundred GeV/amu and that at lower energies. Evidence for such a 
heterogeneity of cosmic-ray sources would be important. 
This work was supported by NASA grants NAG 8-498, 500, 502, and NGR 05-002-160, 
24-005-050, and 26-008-001. 
References 
1. Binns, W. R., et al. 1981, Nucl. Instr. Meth., 185, 415. 
2. Jones, M. D. 1985, Ph. D. Thesis, Washington Univ. (St. Louis); 
3. Binns, et al. 1987, submitted to Ap. J. 
4. Jones, M. D., et al. 1985, 19 ICRC (La Jolla), 2, 28. 
5. Webber, W. R. 1983, in Comp. and Origin of Cosmic Rays, ed. M. M. Shapiro (Reidel), 
p. 83. 
6. Engelmann, J. J., et al. 1983, 18 ICRC (Bangalore), 2, 17. 
7. Israel, et al., 1983, 18 JCRC (Bangalore), 9, 123. 
8. Anders, E., and Ebihara, ·iv'L 1982, Geochim. Cosmochim. Acta, 46, 2362. 
9. Lund, N. 1984, Adv. Space Res., 4, (No. 2-3), 5. 
10. Krombel, K. E., and Wiedenbeck, M. E. 1985, 19 ICRC (La Jolla), 2, 92. 
11. Breneman, H. H., and Stone, E. C. 1985, Ap. J. (Letters), 299, L57. 
12. Peters, B., and Westergaard, N. J. 1977, Astrophys Space Sci, 48, 21. 


Cosmic-Ray Energy Spectra Between Ten and Several Hundred GeV/amu for Elements from _(18)Ar to _(25)Ni--Results from HEAO-3

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Cosmic-Ray Energy Spectra Between Ten and Several Hundred GeV/amu for Elements from _(18)Ar to _(25)Ni--Results from HEAO-3

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