The HEAO-3 Heavy Nuclei Experiment (Binns, et al., 1981) is

composed of ionization chambers above and below a plastic Cherenkov counter. We

have measured the energy dependence of the abundances of elements with atomic

number, Z, between 18 and 28 at very high energies where they are rare and thus need

the large area x time of this experiment. We extend the measurements of the Danish French

HEAO-3 experiment (Englemann, et al., 19S3) to higher energies, using the

relativistic rise of ionization signal as a measure of energy, and determine source

abundances for Ar and Ca

Binns, W. R.

Garrard, T. L.

Israel, M. H.

Jones, Michael D.

Klarmann, J.

Stone, E. C.

Waddington, C. J.

Caltech Authors - Main

19
85
IC
RC
..
..
2.
..
28
J
OG 4.1-8 
28 
ENERGY SPECTRA OF ELEMENTS WITH 18 < Z < 28 
BETWEEN 10 AND 300 GeV /amu 
Michael D. Jogesa, J. Klarmanna, E. C. Stoneb, C. J. Waddingtonc, W. R. Binnsa, 
T. L. Garrard , M. H. Israela 
a) Washington University, St. Louis, MO 63130, USA 
b) California Institute of Technology, Pasadena, CA 91125 USA 
c) University of Minnesota, Minneapolis, MN 55455, USA 
1. Introduction. The HEA0-3 Heavy Nuclei Experiment (Binns, et al., 1981) is 
composed of ionization chambers above and below a plastic Cherenkov counter. We 
have measured the energy dependence of the abundances of elements with atomic 
number, Z, between 18 and 28 at very high energies where they are rare and thus need 
the large area x time of this experiment. We extend the measurements of the Danish-
French HEA0-3 experiment (Englemann, et al., 19S3) to higher energies, using the 
relativistic rise of ionization signal as a measure of energy, and determine source 
abundances for Ar and Ca. 
2. Data Analysis. We confine this analysis to events in the 1.1 m2sr in which the 
cosmic rays penetrate all six ionization chambers, and to the first 370 days of the flight, 
when all six ionization chambers were functioning properly. These selections give the 
highest possible ionization resolution. We select only events incident with geomagnetic 
cutoff greater than 8 GV, so Z is determined by the Cherenkov signal. We further 
require agreement between the means of the three ionization chamber signals above the 
Cherenkov and those below, to eliminate most nuclear interactions inside the 
instrument. 
:: = = = = =) J f 
2~ 
::J 
20 22 24 26 28 
Zc 
Figure 1 
·300 
Ni 
200 
I&J 
~ g 
! 
ID 
<[ 
100 
Figure 2 
Figure 1 is a schematic plot showing the locus of events for each element, 20 < Z 
< 28. Zc is the square-root of the Cherenkov signal normalized so Zc ~ Z at high 
energy. Zi is the square-root of the ionization normalized so Zi = Z at minimum-
ionizing. Figure 2 is a histogram of Zc for events with 29.3 < Zi < 29.5, the region 
between the dashed lines in figure 1. This histogram includes Fe, Co, and Ni at about 
130, 34, and 12 GeV /amu respectively. The abundance of each element in each of 
eighty such histograms is determined by maximum-likelihood fitting. 
© NASA/STI • Provided by the NASA Astrophysics Data System 
19
85
IC
RC
..
..
2.
..
28
J 29 
OG 4.1-8 
Corrections to these raw abundances were calculated to account for interactions 
both in the lid in front of the first ionization chamber and in the Cherenkov counter 
and other material between the ionization chambers. The latter calculation included 
only charge changes of one or two charge units, other interactions having been 
eliminated by the requirement for agreement between upper and lower ionization 
chambers. The calculation assumed that at all energies the total cross-sections were 
given by the formula of Westfall et al. {1979) and the partial cross-sections for changing 
by n charge units were the same fraction of the total cross-section for any projectile as 
was measured by Webber and Brautigam (1982) at 980 MeV /amu for Fe on C. These 
calculated corrections lowered the raw abundance ratios by typically 10 to 30 percent. 
3. Energy Scale. We used Zi/Z as a measure of energy, and derived an empirical 
energy calibration by comparing our Fe observations with an Fe energy spectrum 
derived from a compilation of previously published measurements (Webber, 1982). This 
Fe spectrum was multiplied by an empirical geomagnetic transmission function which 
represented the fraction of time when the geomagnetic cutoff permitted Fe of that 
energy to reach the instrument; the product was the effective Fe spectrum at the 
instrument, averaged over many orbits. This energy spectrum was then converted to a 
Zi/Z spectrum using a trial form of the energy dependence of Zi/Z. Finally this 
calculated spectrum was folded with the instrument's ionization resolution, and the 
resulting Zi/Z spectrum was compared with the data. The process was iterated, by 
changing the assumed form of the energy dependence of Zi/Z, until the calculated and 
observed spectra of Fe agreed. 
The resulting energy dependence is consistent, between about 10 and 100 
GeV /amu, with one derived independently for a different detector system by Barthelmy 
et al. (1985, OG 4.1-7). Above about 200 GeV /amu, the shape of our calibration curve 
depends upon the assumption we made that the Fe energy spectrum falls as a power-
law with exponent -2.7 at energies above those where it has been measured. 
Abundance ratios derived from data in a particular Zi/Z histogram were plotted 
at the mean energy from which those particles came, assuming the Fe energy spectrum 
and the calibration curve described above. The energy resolution implied by our 
ionization resolution of 0.40 charge units is comparable to the spacing of the points in 
figure 3. 
4. Results. Figure 3 gives the resulting abundances of several elements relative to Fe 
as a function of energy. The X symbols are the results of the DF experiment 
(Englemann, 1983), while the 0 symbols are the results of this experiment. In every case 
our results are consistent with those of the DF experiment in the interval where both 
experiments apply, 10 to 25 GeV /amu. At higher energies our data generally continue 
the DF trend. 
Our data above 10 GeV /amu suggest a Ni/Fe ratio slightly dependent upon 
energy, with a best fit power law of exponent -0.050 ± 0.016. If we ignore this slight 
variation with energy, then the mean value of the Ni/Fe ratio over our data is 0.054 ± 
0.001. 
For the secondary ratios, K/Fe, Sc/Fe, Ti/Fe, and V /Fe, our data indicate an 
extension to about 100 GeV /amu of the same power law dependence as was indicated 
by the OF data. Figure 4 shows the best fit exponent for each of these ratios combining 
the DF and our data. The steepening of the slope with decreasing Z is expected as 
lower Z elements have greater contributions from tertiary nuclei. 
© NASA/STI • Provided by the NASA Astrophysics Data System 
19
85
IC
RC
..
..
2.
..
28
J
30 
Ar 
I I 
I I 
• • • , t 
t • t 
t t t I 
I 
I I I I 
•• ,· ••• •tf 
I t f t 
O.,v..a...--~o-...___._.....L-....;_..__......_...J---&._J 
O.ZQ---r-.--.,-~--.---r--r--__, 
I I 
I I 
I I I 
I I I e 
•• • 
•• 
Ti 
Ni 
0. 
OG 4.1-8 
"'t. 
•• t t 
t t 
I 
t f 
I t 
... 
H ~ I 
. . ~ 
t t t 
t I 
' t tl ' v 
' ' . • • • t , • t 
t t 
ENERGY (GeVIamu) 
Figure 3 
Abundances relative to Fe 
x Englemann, et al. (1983) 
• This work. 
© NASA/STI • Provided by the NASA Astrophysics Data System 
19
85
IC
RC
..
..
2.
..
28
J
31 OG 4.1-8 
Our data indicate a leveling of the Ca/Fe ratio above the energies of the DF 
experiment, as would be expected from an energy-independent primary component 
becoming increasingly significant at higher energies as the secondary component 
becomes less abundant. We fitted the combination of the DF and our ratios to a 
function aEP +b. With p = -0.295 ± 0.010, interpolated from figure 4, the result is 
primary Ca/Fe = 0.094 ± 0.004. A galactic propagation calculation on the DF data 
(Lund, 1984) gives a source abundance of Ca/Fe = 0.065 ± 0.019. 
-0.22 
-o.24r f §~.2&r Figure 4 
f ~ :. Exponent of power law fit to ::5-o.2Br 
15 abundance of element z 
~-o.30 f relative to Fe. 
-0.32 
-0."-
18 19 20 21 22 23 24 
z 
A similar fit to the energy dependence of Ar /Fe, but with p = -0.33 ± 0.01, gives 
primary Ar /Fe = 0.026 ± 0.003. Propagation of the DF data (Lund, 1984) gives Ar /Fe 
= 0.032 ± 0.008. Source abundances inferred from such galactic propagations on 
observed abundances 2.5 to 5 times higher must depend critically upon the adopted 
fragmentation cross-sections, while our extension of observations above 100 GeV /amu 
permits inference of source abundances without galactic propagation calculations. 
5. Acknowledgement. This work was supported in part by NASA grants NAG 8-498, 
500, 502, and NCR 05-002-160, 24-005-050, and 26-008-001. 
6. References 
Barthelmy, S.D., M.H. Israel, J. Klarmann, 1985, this conference OG4.1-7. 
Binns, W.R., et al., 1981, Nucl. Instr. Meth., 185, 415. 
Englemann, J.J., et al., 1983, 18th ICRC {Bangalore) 2, 17. 
Lund, N., 1984, Adv. Space Res., 4, (No.2-3), 5. 
Webber, W.R., 1982, Comp. Origin of Cos. Rays, ed. M.M.Shapiro, 25. 
Webber, W.R. and D.A. Brautigam, 1982, Ap.J., 260, 894. 
Westfall, G.D., et al., 1979, Phys. Rev. C, 19, 1309. 
© NASA/STI • Provided by the NASA Astrophysics Data System 


Energy Spectra of Elements with 18 ≤ Z ≤ 28 Between 10 and 300 GeV/amu

http://authors.library.caltech.edu/45435/1/1985-18.pdf

Energy Spectra of Elements with 18 ≤ Z ≤ 28 Between 10 and 300 GeV/amu

Abstract

Similar works

Full text

Available Versions

Caltech Authors - Main