The HEAO-3 Heavy Nuclei Experiment measures

cosmic-ray energy directly in the interval 400 to

~1200 MeV/amu. Geomagnetic cutoffs can also be

derived up to ~15 GV. We present preliminary

rigidity spectra of various ultraheavy cosmic-ray

elements relative to iron

Binns, W. R.

Fickle, R. K.

Garrard, T. L.

Israel, M. H.

Jones, M. D.

Klarmann, J.

Stone, E. C.

Waddington, C. J.

Caltech Authors - Main

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EBEl.GY SPECTRA 01' ULTRABEAVY COSlllC RAYS 
RESULTS 1'1.011 BEA0-3 
OG 1-23 
Israel. M. H •• Jones, M. D., Klarmann 1 J., Binns. W. R. 
Washington University. St. Louis • Missouri 63130. U.S.A. 
Garrard, T. L •• Stone. E. c. 
California Institute of Technology. Pasadena. 
California 91125. U.S.A. 
Fickle. R. K., Waddington. c. J. 
University of Minnesota, Minneapolis, Minnesota 55455. U.S.A. 
The HEA0-3 Heavy Nuclei Experiment measures 
cosmic-ray energy directly in the interval 400 to 
-1200 MeV/amu. Geomagnetic cutoffs can also be 
derived up to -15 GV. We present preliminary 
rigidity spectra of various ultraheavy cosmic-ray 
elements relative to iron. 
1. Introduction 
The HEA0-3 Heavy Nuclei Experiment {Binns 1981) has 
collected information about the ultraheavy cosmic-rays 
(charge Z > 30) with greater statistics and resolution than 
previous detectors. In this paper we examine the rigidity 
dependence of abundances of various elements relative to 
Iron. Using a combination of Cerenkov counter and gas ion 
chambers we can assign unique charges and energies to most 
heavy CR particles which enter our detector with energies 
between 400 and 1200 MeV/amu. For higher energies. we use a 
simple Stor~er model of geomagnetic cutoff to determine the 
minimum rigidity a particle requires to reach our detector 
at a given location from a given direction. This allows us 
to make selections of events with some minimum rigidity. 
When the sense of the trajectory is ambiguous we adopt the 
lower of the two possible cutoffs. 
2. Data Selection 
The data recorded for each cosmic-ray nucleus were 
required to meet several consistency requirements in order 
to be considered a valid event. Events were limited in 
geometry to those giving signals in at least one ionization 
chamber on each side of the Cerenkov counter. The trajec-
tory as determined by the multiwire ionization hodoscope 
must be unambiguous. The ratio of Cerenkov signal to ioniza-
tion signal must be in a physically meaningful range. The 
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signals in the ion chambers must be consistent within an ion 
chamber module and between modules on each side of the 
Cerenkov detector. Specifically indications of charge-
changing interactions within the detector of more than -5% 
in charge (one charge unit at Fe) have been eliminated. 
Corrections to the abundances for interactions within the 
instrument have not been made since our rejection criteria 
for charge changing interactions of more than 1 charge unit 
offsets the interaction correction leaving a residual 
correction of <5% over this charge region. We also require 
that the spacecraft be outside of the South Atlantic Ano-
maly. 
Data from 313 days starting in October of 1979 are 
included in this analysis. The data set from which these 
events were selected included all events of Z > 30 and 1/40 
of all events with Z S 30 (selected at random from 
throughout the time interval). This one-in-forey subset was 
originally developed to use as a workable tool to normalize 
the higher charge events to Iron. For ratios of elements 
with Z > 30 to Iron. the precision is limited by the statis~ 
tics of the higher charged elements. In this paper we also 
present abundances of , 1 Ti, 2 ~Cr, and 28Ni relative to 26 Fe; 
for these abundances tn~ staiistical precision is limited by 
the 1/40 factor. 
J. The Data 
The best charge resolution comes from· "low energy 
events with energies of -400-1100 MeV/amu and "high rigi-
dity" events with minimum rigidity cutoff of >8 GV. By 
dividing these data into four comparably sized sets limited 
relative rigidity spectra can be obtained. The cuts were 
made so t~gt set 1 ~as rigidity of 2.9-3.5 GV(0.61-0.84 
GeV/amu at Fe). ~gt 2 has rigidity of 3.5-4.0 GV(0.84-
1.08 GeV/amu at Fe). Set 3 contains those events with 
observed c~toff rigidities of 8-10 GV. Set 4 contains those 
events with >10 GV cutoff. 
We have used rigidity rather than energy as the 
independent parameter of our analysis because the geomag-
netic field acts as a rigidity filter and the motion of the 
spacecraft gives us different exposure times for different 
rigidities. We have used a piecewise linear, monotonic ~unc­
tion of Z as an approximation to Z/A in the conversion from 
observed energy per nucleon to rigidity. 
For each of the four sets, individual element abun-
dances were derived by fitting gaussians to charge peaks in 
a least-squares manner. These fit abundances are used for Z 
s 32. The charge group "34-42" was creaEed by_binni2g wit~ 
assigned charges from 33.0 to 43.0. The 44-48 and 50-58 
charge groups were constructed similarly. 
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Table l has abundance values for the charges 22. 24. 
26. 28. 32 and the charge groups 34-42. 44-48 and 50-58 nor-
malized to Fe. Figure l .gives plots of relative abundances 
versus rigidity. 
Table la : Abundances Relative to Fe ~ 1000 
Rigidity Rigidity Cutoff Cutoff 
--~----Z.Li-3~i_Q!_~~i~~~Q-~Y---~~1Q_~y_ __ _>J,.Jl _ _9_y_ 
2 2 180±14 156±11 l 06±2 97 ±3 
24 
26 
28 
177±11 
1000±.28 
45±4 
147±11 
1000±13 
52±5 
120±3 
1000±7 
52±2 
113±3 
1000±.9 
52±2 
Table lb : Abundances Relative to Fe _ 106 
Rigidity Rigidity Cutoff Cutoff 
___ z~--Z~i~1~i_Qy ___ 1~i~!~Q-~y ___ 8-!..Q._GV __ _>Jj)__!;_y_ 
32 108±23 71±19 75±13 85±17 
34-42 150±23 98±.18 141±13 155±16 
44-48 4+ 9 1o+10 14±4 12±.5 
50-58 31~~0 16~~ 1 19±5 14±5 
4. Conclusions 
The results for the abundances relative to Iron of the 
Iron secondaries and of Nickel are in agreement with results 
reported by the Saclay Copenhagen Collaboration{Kocb-
Miramond.Engelmann et al). The 22Ti and 24cr relative abun-
dances decrease with rigidity while the 28Ni relative abun-
dance is insensitive to rigidity in accord/4ith conventional 
propagation models. The results of the higher charges are 
new to this experiment. 
None df tbe Z > 30 charge groups demonstrates a rigi-
dity spectrum which is inconsistent with that of Iron within 
the statistical errrirs. 
5. Acknowle~ge•enta 
This research was supported in part by NASA under con-
tracts NAS8-27976,77.78 and grants NGR 05-002-160.24-005-050 
and 26-008-001. 
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40 
20 
10 
8 
~ 20 
i== 
<( 
_J 
w 
0:: 
w 
u 
z 
<( 
0 
z 
::::> 
co 
<( 
10 
8 
6 
4 
126 
44~Z~48 
5 10 20 
RIGIDITY (GV) 
0.15 
0.10 
0.08 
~ 0.06 
0 
0 
0 
Ge 
-----1--11~) )o 
~ 
w 
> 
~ 
_J 
::[ ~<0 °0 : ~ ~: 0 ~ 'o: hJ 
~ 200f 
u 150 
z 
<( 
0 100 z 
::::> 
co 
<( 200 
7~o:~~~~::J 
-b-i+o o 0 
Ti 
0 0 0 
0 
2 5 10 20 
RIGIDITY (GV) 
Figure 1: Relative abundances. +are our data; o are the 
data of the Saclay-Copenhagen Collaboration. 
6. B.eferences 
Binns. W.R., Israel. M.H., Klarmann, J., Scarlett, W.R., 
Stone. E.C. and Waddington, C.J., 1981, Nucl. Inst. Meth. 
185, 415. 
Koch-Miramond, L., 1981, 17th lCRC, Paris, 12, 20. 
Engelmann, J.J., Goret, P., Juliusson, Koch-Miramond, 
Masse, P •• Petrou, N., Rio, Y., Soutoul, A., Byrnak, B., 
Jakobsen H., Lund, N., Peters. B •• Rasmussen, I.L •• 
Rotenburg, M., Westergaard, N., 1981, 17th ICRC, Paris, 
'· 97. 
© INSDOC • Provided by the NASA Astrophysics Data System 


Energy Spectra of Ultraheavy Cosmic Rays Results from HEAO-3

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Energy Spectra of Ultraheavy Cosmic Rays Results from HEAO-3

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