Analysis of a new, higher resolution data set from the Heavy Nuclei Experiment on

the HEA0-3 spacecraft has yielded the cosmic ray abundances relative to iron of oddeven

element pairs with atomic number, Z, in the range 33≤Z≤60. The abundances are

consistent with a solar-system source provided an allowance is made for a source

fraetionation based on first ionization potential (FIP). However, extending this analysis·

to element groups with Z>60, we find enhancements of the Pt group (74≤Z≤80)

abundance relative to the solar system and a corresponding increase in the largely

secondary nuclei in the range 62≤Z≤73, in agreement with recent Ariel-6 results. These

abundances suggest an enhancement of the r-process contribution to the source of the

Z > 60 nuclei

Binns, W. R.

Garrard, T. L.

Gibner, P. S.

Israel, M. H.

Kertzman, M. P.

Klarmann, J.

Newport, B. J.

Stone, E. C.

Waddington, C. J.

Caltech Authors - Main

OG 4.3-1 
THE ABUNDANCES OF ULTRAHEAVY ELEMENTS IN THE COSMJC RADIATION 
E. C. Stone~ C. J. Waddington~ W.R. Binns~ T. L. Garrard~ P. S. Gibfer~ 
M. H. Israel~ M. P. Kertzman~ J. Klarmann~ and B. J. Newport•• 
a) California Institute of Technology; Pasadena, California 91125 USA 
b) School of Physics and Astronomy, 
University of Minnesota; Minneapolis, Minnesota 55455 USA 
c) Department of Physics and McDonnell Center for the Space Sciences, 
Washington University; St. Louis, Missouri 63130 USA 
d) now at University of Chicago; Chicago, Illinois 60637 USA 
Abstract 
Analysis of a -new, higher resolution data set from the Heavy Nuclei Experiment on 
the HEA0-3 spacecraft has yielded the cosmic ray abundances relative to iron of odd-
even element pairs with atomic number, Z, in the range 33sZs60. The abundances are 
consistent 'Yith a solar-system source provided an allowance is made for a source 
fraetionation based on first ionization potential (FIP). However, extending this analysis· 
to element groups with Z>60, we find enhancements of the Pt group (74SZS80) 
abundance relative to the solar system and a corresponding increase in the largely 
secondary nuclei in the range 62sZS73, in agreement with recent Ariel-6 results. These 
abundances suggest an enhancement of the r-process contribution to the source of the 
Z > 60 nuclei. 
1. IntroduCtion. We have recently identified a subset of our data. with improved 
resolution and statistics in the region of the charge spectrum from 40 to 60 [l) where 
good resolution has not previously been achieved. We will discuss this new result in the 
context of two charge regions, 34 to 60 (Fig. 1), where we have even element resolution; 
and above 60 (Fig. 2), where the even elements are not well resolved. The data below 
charge 40. are presented primarily to demonstrate agreement with the previously 
published data [2-4). 
This data set consists only of nuclei which have energy greater than about 1 
r GeV /amu. All events are required to have consistency between two ion chambers on 
•iopposite sides of a Cherenkov detector, and between the ion chambers and the Cherenkov 
. '[5). Charge is determined for these events from the Cherenkov signal alone, with the 
ionization signal used only for consistency checks. The -number of iron nuclei 
corresponding to this data set is 8.0 x 106• 
2. Observations: 34SZS60. Figure 1 shows the ~harge histogram of this data set for 
Z=30 through 42 (upper) and for 40 through 62 (lower). Superimposed are smooth 
curves which show the results of fitting these histogram data with a gaussian res_olution 
function as described by Newport [1). The systematic error in the quoted abu~dances 
due to the choice of fitting functions and parameters is roughly 12% rms. The systematic 
errors are correlated, however, since a fit which yields an increased abundance for one 
element must yield a reduced abundance for neighboring elements in order to conserve 
particles. This uncertainty is in addition to the tabulated statistical errors. The 
preliminary abundances derived. from this fitting procedure are plotted in Fig. 3a in 
charge pairs, the abundance of each even charge being combined with the odd charge 
immediately below it, with the exceptions of those for Z=39 to 41 which are combined 
and plotted as a single point and that for 42 which is plotted by itself. The abundances 
are presented in this fashion since there may still be a residual tail extending down from 
the more abundant even charges which is not deconvolved using the gaussian fitting 
function. 
3. Observations: Z>60. In the Z>60 charge region (see Fig. 2), we do not see the 
well resolved peaks observed below 60. A likely cause for the lack of peaks is a 'larger 
366 
OG 4 • .3-1 
fraction of odd Z nuclei. Other possible causes include a greater fraction of low energy 
nuclei, resolution worsened by instrumental problems such as mapping, and deviations 
from z2 scaling in the Cherenkov response. These problems are compounded by poor 
statistics. As a result, we have grouped the nuclei into four charge regions rather than·-
fitting individual elements. The relative abundances of these groups are shown in Fig. 3. 
The groups are labeled "LS", 61.5SZS69.5; "HS 8 , 69.5 to.73.5; "Pt", 73.5 to 80.5; and 
"Pb n, 80.5 to 86.5. . ..----~-r--· "T"""""T--r----r-r----r----.-""T"----.-~ 
4. Comparisons. In Fig. 3a 
(and· in Table 1), we compare our 
new results with our previously 
published abundances (2-4) and find 
generally good agreement with en 
these earlier data sets. In the ~ 
Bii.ngalore Zs42 data (2), we 5 
required better knowledge of the u 
particle energy, and could correct 
the Cherenkov signal to its high 
energy value. In that data set we 
had better resolution but 
significantly less statistical 
prec1s1on. For the earlier 
50SZS58 data set (3), we required 
an energy above about 2.5 
GeV /nuc, but events with only one 
ion chamber were accepted. These 
data are comparable in both I!? 
resolution and statistics to those ~ 
presented here. In Binns et al., '85 8 
(4), the energy cut w~ -1.5 
GeV/nuc (cutoff rigidity ~ 5 GV) 
and only one ion chamber was 
required because of the extreme 
rarity of the Z>60 events. That 
data set had statistical weight 
comparable to this one. Binns (6) 
has reviewed data . from [1-4) in 
greater detail. 
After a small correction for 
interactions in the lids of the 
detector system as described by 
Newport (1), we also find good 
agreement (Fig. 3b, Table 1) with 
the Ariel-6 abundances [7). To 
compare these abundances with 
those of a solar system source, we 
have taken the Anders and Ebihara 
meteoritic abundances [8), 
fractionated according to the Letaw 
et al. step-FIP model [9), and 
propagated to earth using a leaky 
box model [1,10) with a rigidity 
dependent path length. The ratio 
100 
BO 
60 
40 
20 
0 31 
I 
\ 
16 
12 
B 
4 
Figure 1, Charge histogra~a. The dotted lines show 
the fit; from which the abundances are determined 
\ 
6 
2 
z 
Figure 2, Charge histogram for Z > 60 
367 
I J. ~ ~ 
10 
iO 
0 
To 
~ 
UI 
.. 
u 
~ Prevlou1 HNE 
/11111 ~ I ~ j ~ 
I 
li 
OG 4.3-1 
of our measured abundances to these 
fractionated and propagated solar 
system abundances is plotted versus 
charge in the upper panel of Fig. 4. 
There is agreement to within ± 30% 
from charge 34 to 60. In particular, 
.this is true for the newly measured 
abundances in the 40's. Similar 
comparisons to pure r- and pure s-
a 100 
LL_J_LJ._J_Ll_L.LJ_L_[_JLL_J_LL_L_LL--'--'--'---'-.L:.1-' process sources [4] are shown in the 
lower panels of Fig. 4. The 
observations in this charge range are 
inconsistent with a source composition 
which is dominated by either r-process 
or s-process material. The best fit is 
obtained with a source enriched 
slightly in r-process material, i.e., a 
source having an r- to s-process ratio 
'tJ 
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<( 
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. 2: 
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} Arlol 6 ;: I 
Ll-L.LJ-L_LJLL_J_jLL_J_L.l._J_Ll_L.LJ~_[_J-=-'-''--' of 1.22+~i.~1, relative to the solar 
38 44 
50 56 62 68 74 80 system. Note that the observations do 
10 
,rhl;' I I 
. ~I R 
z 
not exclude a source containing the Figure 3. A comparison of relative abundances 
A · 1 k same mixture of · r- and s-process with previous HNE ,publications and Tie 6 wor . . 
Plotted as a function of atomic number Z material as in the solar system. 
2 
w 
u 
~ .5 
0 
II) 
fil 
!;;: 
(!) 
ct. 0 2 
If 
"-I 
w 
u 
~ .5 
0 
z 
::::> 
m 
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er: 
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I 
-+--+--t-
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SOLAR SYSTEM 
-+-- ___:y-: 
I + 
S-PROCESS 
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--f-
A-PROCESS t 
36 40 44 48 52 56 60 64 68 72 76 BO 
z 
Figure 4. Ratios of measured abundances 
to calcu_lated abundances using 3 different 
models for the source 
Comparisons using no FIP or using an 
exponential-FIP fractionation give 
poorer agreement for any or' the three 
source possibilities. · 
In the Z > 60 region, the agreement 
with the solar system is not as good. If 
we assume a solar system source, the 
observed Pb abundance is notably lower 
while the Pt, BS, and LS abundances 
are higher than predicted. One possible 
explanation for the low Pb abundance 
is the suggestion of Grevesse and Meyer 
(11] that the photospheric abundance of 
Pb is about 0.63 of the standard 
meteoritic [8] abundance. Another is a 
volatility related fractionation (4]. 
The high abundance of th~ Pt 
group appears to indicate an additional 
admixture of r-process source material 
in this charge region. The high HS, LS 
abundances lend additional credence to 
the idea of an enhancement in the r-
process component. This conclusion 
does not depend on the step-FIP mod~! 
used; the enhancement also is seen if 
the FIP correction is omitted. 
If we assume an r-process sourc.e, then tl\e 11 secondary 11 (LS, HS) to 11 primary 11 (Pt) 
ratio is consistent with the st_and.ard leaky box model. No more elaborate models are 
OG 4.3-1 
.justified, especially in view of the paucity of the statistics and the uncertainties in the 
cross-sections (see OG7 .2-11, 12; this conference). We note that our previously published 
HEAO data [4] have smaller LS and HS abundances. The differei;ice may indicate an 
energy dependence in these abundance ratios. Such an energy dependence might also 
explain the lack of resolution in the 60's for this data set. 
We also note that this data set does not contain an actinide. The one actinide in 
Binns et al., '82 (12], using a data set of greater statistical significance (corresponding to 
-18 x 106 Fe ~vents), did not meet the geometry criteria required for this work. Neither 
result is in.consistent with the Ariel work (7]. 
5. Conclusions. We find that the cosmic ray abundances in bhe Z=34 to 60 region 
(including the new 40 to 60 data) are in generally good agreement with solar system 
abundances with a step-FIP fractionation model applied, as we had earlier concluded 
looking separately at the 30's and 50's. We have seen that the cosmic ray source is 
definitely not dominated by the r-process for Z~60. The newly resolved elements in the 
charge region 40 to 48 are largely secondary assuming a solar system source and the 
observations agree well with the calculatious; in this charge region it is unnecessary to 
iuvoke anything more elaborate than the standard leaky box model. 
In the Z>60 region, abundances of the Pt group and the corresponding "secondary 11 
groups (LS, HS) seem to indicate an enhancement of r-process nuclei compared to the 
solar system. 
4. Acknowledgements. This research was supported in part by NASA under grants 
NAG 8-498, 500, and 502 and NCR 05-002-160, 24-005,050, and 26-008-001. 
References 
1. Newport B. J., Thesis, California Institute 
of Technology, 1986. 
2, Binns et al., Proc. 18th ICRC (Bangalore}, 
9, 1983, 106. 
3, Stone et al., Proc. 18th ICRG (Bangalore), 
9, 1983, 115. 
4. Binns W. R., N. R. B~ewster, D. J, Fixsen, 
T. L. Garrard, M. H. Israel, J, K\armann, 
B. J, Newport, E. C. Stone, and C. J, 
Waddington, Ap. J., 297, 1985, 111. 
5. Binns et al., Nucl. Instr. Meth., 185, 
1981, 415. 
6, Binns W. R., "Ultra Heavy Nuclei in the 
Cosmic Radiation", Genesis and Propa-
gation of Cosmic Rays, Reidel & Co., 
Dordrecht, 1987 1 in press 
7, Fowler P. H., R. N. F. Walker, M. R. W. 
Masheder R. T. Moses, A. Worley, and A. 
M. Gay, to be pub. Ap. J., March 1987. 
8 , Andera E. and M. Ebihara, Geochim, et 
Cosmochim., 461 1982, 2363. 
9, Letaw J. R., R. Silberberg, and C. H. Tsao, 
Ap. J., 279, 1984, 144. 
10, Brewster et al., Ap. J., 294, 1985, 419. · 
11; Grevesse N. and J, P. Meyer, Proc. 19th 
IGRC (La Jolla}, 3, 1985, 5. 
12, Binns et al., Ap. J., 261, 19.82, 1117. 
24.3aK. 1613 369 
Table 1 
Relative Abundances (Fe=106) 
element this work Ariel previous 
(71 12 3 4] 
33-34 44.9±4.1 66 ±5 52 ±6 
35-36 35.1±2.4 39 ±4 30 ±8 
37-38 38.1±2.4 36 ±4 43 ±6 
39-40-41 24.7± 1.9 32 ±4 21 ±5 
42 4.2±0.9 9 ±4 8 ±2 
43-44 6.1± 1.1 3 ±2 
- -
45-46 5.2±0.9 5 ±2 - -
47-48 5.9±0.9 6 ±1.3 
- -
49-50 5.1±0.8 3 ±1.0 5.7 ±1.3 
51-52 5.1±0.9 7.4± 1.0 3.0 ±1.0 
53-54 3.6±0.7 4.3±1.1 3.5 ±0.9 
55-56 5.8±0.9 7.9±1.2 6.2 ±1.0 
57-58 2.3±0.5 1.8± 1.0. 2.8 ±0.9 
59-60 1.5±0.4 2.3±0.8 - -
LS 6.0±0.7 7.4±0.9 3.54±0.63 
HS 1.9+0.6 1.9±0.5 104+0.45 
- 0.5 . - 0.33 
Pt 4.6±0.8 5.7±0.8 4.38±0.71 
Pb i.o+o.5 2.0±0.6 1 04+0.45 
- 0.4 . - 0.33 


The Abundances of Ultraheavy Elements in the Cosmic Radiation

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The Abundances of Ultraheavy Elements in the Cosmic Radiation

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