Elements with even atomic number ( Z) in the interval 50 ~ Z ~ 56 have been resolved in the

cosmic radiation using the Heavy Nuclei Experiment on the HEAO 3 satellite. The observation that

50Sn and 56Ba are more abundant than 52Te Elements with even atomic number ( Z) in the interval 50 ~ Z ~ 56 have been resolved in the

cosmic radiation using the Heavy Nuclei Experiment on the HEAO 3 satellite. The observation that

50Sn and 56Ba are more abundant than 52Te 

and 54Xe is inconsistent with a purer-process cosmic-ray

source. Adjustment of source abundances for an enhancement of those elements with a low first

ionization potential does not change this conclusion and 54Xe is inconsistent with a purer-process cosmic-ray

source. Adjustment of source abundances for an enhancement of those elements with a low first

ionization potential does not change this conclusion

Binns, W. R.

Fickle, R. K.

Garrard, T. L.

Israel, M. H.

Klarmann, J.

Krombel, K. E.

Stone, E. C.

Waddington, C. J.

Elements with even atomic number (Z) in the interval 50 ≤ Z ≤ 56 have been resolved in the cosmic radiation using the Heavy Nuclei Experiment on the HEAO 3 satellite. The observation that _(50)Sn and _(56)Ba are more abundant than _(52)Te and _(54)Xe is inconsistent with a pure r-process cosmic-ray source. Adjustment of source abundances for an enhancement of those elements with a low first ionization potential does not change this conclusion

Caltech Authors - Main

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THE ASTROPHYSICAL JOURNAL, 267:L93-L96, 1983 April 15 
'E' 1983. The American Astronomical Society. All rights reserved. Printed in U.S.A. 
COSMIC-RAY ABUNDANCES OF Sn, Te, Xe, AND Ba NUCLEI MEASURED ON HEAO 3 
w. R. BINNS, 1•2 R. K. FICKLE,3 T. L. GARRARD,4 M. H. ISRAEL,1 J. KLARMANN, 1 K. E. KROMBEL,4 
E. C. STONE,4 AND C. J. W ADDINGTON3 
Received 1982 November 8; accepted 1982 December 15 
ABSTRACT 
Elements with even atomic number ( Z) in the interval 50 ~ Z ~ 56 have been resolved in the 
cosmic radiation using the Heavy Nuclei Experiment on the HEAO 3 satellite. The observation that 
50 Sn and 56 Ba are more abundant than 52Te and 54 Xe is inconsistent with a purer-process cosmic-ray 
source. Adjustment of source abundances for an enhancement of those elements with a low first 
ionization potential does not change this conclusion. 
Subject headings: cosmic rays: abundances- nucleosynthesis 
I. INTRODUCTION 
Since the early work of Burbidge eta/. (1957), the 
elements heavier than iron and nickel are assumed to 
have been formed primarily by neutron capture nucleo-
synthesis processes. These processes can be separated 
into two extreme classes depending on the intensity of 
the neutron flux involved. The r, or rapid, process, 
characterized by .l high neutron flux, forms highly neu-
tron-rich nuclei which decay back to the valley of beta 
stability only after the completion of nucleosynthesis. 
The s, or slow, process has a much lower flux of 
neutrons and allows for the decay of beta unstable 
nuclides before subsequent neutron captures. A specific 
astrophysical site for a pure r-process has not yet been 
established, but it has usually been associated with 
supernova explosions, which are also often assumed to 
be a source of cosmic rays. The s-process, on the other 
hand, is usually attributed to milder environments. 
Both these processes produce a characteristic signa-
ture in the resulting elemental composition. These signa-
tures are particularly evident in the relative abundances 
of 50 Sn, 52Te, 54 Xe, and 56 Ba. The s-process produces a 
greater abundance of Sn and Ba than of Te and Xe, 
while the r-process results in an overabundance of Te 
and Xe. A decomposition of solar system material into 
r-process and s-process contributions (e.g., Cameron 
1982 a) clearly shows these differences. In both processes, 
the odd-charge elements are significantly less abundant 
than the adjacent even-charge elements. 
The HEAO 3 Heavy Nuclei Experiment was designed 
to measure the abundances of the elements heavier than 
1 Department of Physics and the McDonnell Center for the 
Space Sciences, Washington University. 
2 Formerly at McDonnell Douglas Research Laboratories, St. 
Louis, Missouri. 
3School of Physics and Astronomy, University of Minnesota. 
4 California Institute of Technology. 
L93 
iron in the cosmic radiation. We report here on the 
results of an analysis in the Sn to Ba region of a subset 
of data obtained over approximately 440 days of opera-
tion. 
II. DATA 
The detector was a large area particle telescope on the 
third High Energy Astronomy Observatory which was 
placed in orbit at 43?6 inclination and 495 km altitude 
on 1979 September 20. It consisted of six parallel plate 
ionization chambers, four pairs of multiwire ionization 
hodoscopes, and a dual radiator Cerenkov detector 
arranged symmetrically about the detector midplane 
(Binns et a[. 1981 b). 
In this data subset, all the particles triggered the 
Cerenkov detector, at least one of the six ion chambers, 
and a minimum of two hodoscopes. Background from 
nuclear interactions within the instrument has been sup-
pressed by requiring consistency between the sig11als 
from the ion chambers and the Cerenkov counter. Charge 
has been determined from the Cerenkov signal using 
Z-squared scaling normalized at iron. Sixty percent of 
the particles have been collected from directions and 
locations which correspond to a high geomagnetic cutoff 
( > 8 GV), ensuring that the Cerenkov signal is nearly 
independent of energy (/3 ;::: 0.96). The remainder of the 
particles have been selected to be high energy by com-
paring the Cerenkov and ion signals. 
The resulting data set is shown in Figure 1. The main 
histogram exhibits peaks in the lower charges, thereby 
establishing our charge scale. Figure I a is an enlarge-
ment of the region of interest which shows peaks at the 
even elements Sn, Te, Xe, and Ba. This measurement is 
the first to show resolved even-element peaks in this 
charge region. 
The particles with assigned charge between 49.0 and 
59.0 have been superposed in the modulo 2 histogram in 
© American Astronomical Society • Provided by the NASA Astrophysics Data System 
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20 a) 
FIG. I.-Histogram of the data from charge 30.0 to 60.0 in 0.25 charge unit bins. Although negligible over the limited range from 50Sn to 
56 Ba, charge-dependent biases in the consistency and energy selections are such that relative abundances of widely separated charges cannot 
be determined from this plot. Insets show (a) the region of interest in 0.5 charge unit bins and {b) a modulo 2 histogram of the data from 
charge 49.0-59.0 in 0.25 charge unit bins. 
Figure lb. This procedure, which bins each particle 
according to the difference between its assigned charge 
and the nearest even integer, superposes the even (and 
odd) element charge peaks, thus allowing a statistically 
significant determination of the instrument resolution. A 
Gaussian fit to this modulo 2 histogram, taking into 
account the spillover from the neighboring elements, 
indicates an rms charge resolution of 0.56 charge units. 
This verification of a peak at even charges, coupled with 
the peak at charge 38, shows that our assumption of 
Z-squared scaling cannot be significantly in error. Since 
elements with even charge dominate any suggested 
source, we are not likely to have an error of one charge 
unit, but an error of approximately two charge units 
cannot immediately be ruled out. However, if there were 
a two-charge unit error for any one of the peaks in 
Figure la, while the peak at 38 was correct, then the 
separation between even-element peaks in this interval 
would be approximately 1.7 or 2.3 charge units (depend-
ing of the direction of the error) rather than 2.0, with the 
result that the modulo 2 histogram would not have such 
a well-defined structure. Furthermore, such a large error 
in the charge estimate is not consistent with calculations 
of non-Z-squared Cerenkov effects by Derrickson, Eby, 
and Watts (1981). Our own earlier results (Binns eta/. 
1981 a) using a different data subset have also shown the 
approximate validity of Z-squared scaling up to charge 
40. 
Table 1 gives the abundances of 50Sn, 54 Xe, and 56 Ba 
(normalized to our best estimate of the abundance of 
52Te) obtained from a least-squares Gaussian fit to the 
data in Figure 1 having an assigned charge between 45.0 
and 60.0 using 0.25 charge unit bins. The fit was made 
to both odd and even charge abundances, and the 
Element 
50 Sn ....... . 
52Te ....... . 
54Xe ....... . 
56 Ba ....... . 
TABLE I 
RELATIVE ABUNDANCES {52Te "' I) 
HEAO 
1.33 ± 0.31 
1.00 ± 0.27 
1.03 ± 0.25 
1.52 ± 0.32 
Arie/6 
0.66 ± 0.22 
1.00 ± 0.23 
0.34 ± 0.17 
1.18 ± 0.23 
Balloon 
1.21 ± 0.37 
1.00 ± 0.32 
0.89 ± 0.27 
0.87 ± 0.27 
standard deviation of the assumed Gaussian charge 
resolution was parametrically varied to obtain a mini-
mum x2• The x2 value as a function of the assumed 
standard deviation has a wide minimum between 0.4 
and 0.6 charge units. The relative abundances of the 
even charge elements typically vary by less than 10% 
within this minimum, while the odd charge elements 
show a much greater variation, consistent with their not 
being resolved. The errors cited in the table are derived 
from this fit. No corrections have been applied to the 
abundances for fragmentation in the instrument since, 
over such a limited charge range, the relative adjustment 
factors for the even elements are less than - 3%. Also 
shown are results from Ariel 6 and balloons (Fowler 
et a/. 1981 ). The balloon data are "subject to significant 
and rapidly charge-dependent corrections" (Fowler 
et a/.), while there has been no claim of resolution of the 
individual even-element peaks in the Sn-Ba region for 
the Ariel 6 data. 
III. DISCUSSION 
Figure 2 shows the data and the propagated abun-
dances of the even elements from a calculation by 
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No.2, 1983 COSMIC-RAY ABUNDANCES OF Sn, Te, Xe, AND Ba L95 
Ill 
~I 
w 
u 
z 
<( 
0 
z 
:::> 
R-PROCESS 
m .4 -FIP 
<( ---NOFIP 
SOLAR SYSTEM 
-FIP 
---NO FIP 
·2 50 52 54 56 50 52 54 56 
ATOMIC NUMBER 
FIG. 2.-0ur data compared to results of propagating an as-
sumed r-process source and a solar system source through 5.5 
g em- 2 of hydrogen (Brewster et a!., private communication; 
Brewster, Freier, and Waddington 1983). Solid line has adjust-
ments applied for first-ionization-potential effects (FIP); dotted 
line does not. 
Brewster et a/. (private communication; see also 
Brewster, Freier, and Waddington 1983) using various 
sources and an exponential pathlength distribution with 
a mean of 5.5 gem- 2 of hydrogen. Since other results 
from lower charge regions indicate that there is an 
anticorrelation between first ionization potential and 
cosmic-ray elemental abundances relative to those of the 
solar system (Casse and Goret 1978; Binns eta/. 198la), 
Figure 2 also includes the results of propagating r-pro-
cess and solar system source abundances which have 
been adjusted to account for first-ionization-potential 
3.0 
2.5 
effects (Brewster, Freier, and Waddington 1983). The 
data are not consistent with the assumed r-process source 
material in either case, but reasonable agreement is 
obtained with solar system source material adjusted for 
first-ionization-potential effects. Although the large 
abundance of 58Ce shown in Figure 1 is also consistent 
with this conclusion, we have not considered it further 
here because its abundance is more affected by fragmen-
tation of heavier nuclei. 
The large abundance of either Sn or Ba relative to the 
other elements in this group argues against a source 
dominated by the r-process. This conclusion is empha-
sized in Figure 3, which compares the ratio of Sn to Te 
with the BajTe ratio. Our observed values are shown 
as the large diamond surrounded by error ellipses. 
Also shown are various calculated values derived from 
several assumptions regarding the source composition. 
Points are plotted for pure r-process abundances, pure 
s-process abundances, and for solar system source abun-
dances, both with and without a bias due to first-ioniza-
tion-potential effects. Two different predictions are 
shown (Brewster, Freier, and Waddington 1983; and 
Blake and Margolis 1981, also private communication), 
and the differences between corresponding points from 
the two calculations are an indication of the range of 
uncertainty in the expectations due to different source 
assumptions and propagation models. (Note that, for a 
given propagation model and given assumption about 
first ionization bias, the three calculated points fall on a 
straight "mixing line" whose ends represent pure r or 
pure s material, with varying rjs mixtures falling along 
the line.) 
• HEAO 
1ll NO FIP 
FIP 
SOLAR 
SYSTEM 5 
;:f~_; QY \$.) NO F I 
® ® ~ FIP 
!:S.i NO FIP 
(SJ FIP 
FIG. 3.-0ur measurement of the abundance ratios plotted along with two propagations of r, s, and solar system material both with and 
without first-ionization-potential effects (FIP) included (see text). The solid error contour is the locus of abundance ratios which fit the data 
with the same x2 value such that there is a 68% probability that the actual value lies within the contour (50% for the dotted contour). 
© American Astronomical Society • Provided by the NASA Astrophysics Data System 
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L96 BINNSETAL. 
It is clear from this plot that our results are not 
consistent with pure r-process material either with or 
without first-ionization-potential effects. The difference 
between the closest r-process point and our measure-
ment is significant at the 93% level. When due account 
is taken of first-ionization-potential effects, our data 
are in reasonable agreement with solar system material, 
whereas ignoring these effects suggests an s-process-
dominated mixture. 
In Figure 3 we chose to plot ratios formed from Sn, 
Te, and Ba; the solar system Xe abundance is less 
certain than the other three because it is based on an 
interpolation of adjacent nuclides (Cameron 1982 b) 
rather than on measurements. However, our conclusions 
are not significantly altered if we include Xe. For each 
of the models represented by a point in Figure 3, we 
have made a least squares fit of the abundances of these 
four elements to our data. For any of the pure r-process 
models, the difference from our data is significant at 
least at the 93% level (reduced x2 ;::: 2.4), while models 
with solar system source abundances and first-ioniza-
tion-potential biases give reasonable fits to the data 
(reduced x2 ~ 1). 
The results in this charge interval are therefore con-
sistent with conclusions from measurements in other 
charge intervals since the measured elemental abun-
dances in the charge 26 to 40 region (Binns et al. l98la) 
show a similarity with solar system material adjusted for 
first-ionization-potential effects. Additionally, the low 
abundance of the "actinides" (88 ~ Z ~ 100) (Binns 
et al. 1982) is consistent with solar system material but 
not with freshly synthesized purer-process sources. 
We thank N. S. Collins, B. W. Gauld, D.P. Grossman, 
and B. J. Newport for assistance in programming for 
data analysis. The research was supported in part by 
NASA under contracts NAS 8-27976, 77, 78 and grants 
NGR 05-002-160, 24-005-050, and 26-008-001. 
REFERENCES 
Binns, W. R., Fickle, R. K., Garrard, T. L., Israel, M. H., 
Klarmann, J., Stone, E. C., and Waddington, C. J. 1981a, Ap. J. 
(Letters), 247, Ll15. 
__ . 1982, Ap. J. (Letters), 261, Lll7. 
Binns, W. R., Israel, M. H., Klarmann, J., Scarlett, W. R., Stone, 
E. C., and Waddington, C. J. 1981b, Nucl. lnst. Meth., 185, 415. 
Blake, J. B., and Margolis, S. H., 1981, Ap. J., 251, 402. 
Brewster, N. R., Freier, P. S., and Waddington, C. J. 1983, Ap. J., 
264, 324. 
Burbidge, E. M., Burbidge, G. R., Fowler, W. A., and Hoyle, F. 
1957, Rev. Mod. Phys., 29, 547. 
Cameron, A G. W. 1973, in Explosive Nucleosynthesis, ed. D. N. 
Schramm and W. D. Arnett (Austin: University of Texas Press), 
~3. . 
Cameron, A G. W. 1982a, Ap. Space Sci., 82, 123. 
__ . 1982b, in Essays in Nuclear Astrophysics, ed. C. A Barnes, 
D. D. Clayton, and D. N. Schramm (New York: Cambridge 
University Press), p. 23. 
Casse, M., and Goret, P. 1978, Ap. J., 221, 703. 
Derrickson, J. H., Eby, P. B., and Watts, J. W. 1981, Proc.llth Int. 
Cosmic Ray Conf. (Paris), 8, 88. 
Fowler, P. H., Walker, R. N. F., Masheder, M. R. W., Moses, 
R. T., and Worley, A 1981, Nature, 291, 45. 
Note added in proof.-Our results are also inconsistent at the ~ 99% level with the r-process abundances derived by 
subtracting the s-process values of F. Kappeler, H. Beer, K. Wisshak, D. D. Clayton, R. L. Macklin, and Richard A. 
Ward (1982, Ap. J., 257, 821) from those of the solar system recently compiled by Edward Anders and Mitsuru 
Ebihara (1982, Geochim. Cosmochim. Acta, 46, 2363). 
W. R. BINNS, M. H. ISRAEL, and J. KLARMANN: Department of Physics, Washington University, St. Louis, MO 63130 
R. K. FICKLE and C. J. WADDINGTON: School of Physics and Astronomy, University of Minnesota, 116 Church Street, 
S.E., Minneapolis, MN 55455 
T. L. GARRARD, K. E. KROMBEL, and E. C. STONE: 220-47 Downs Laboratory, California Institute of Technology, 
Pasadena, CA 91125 
© American Astronomical Society • Provided by the NASA Astrophysics Data System 


English

Cosmic-ray abundances of Sn, Te, Xe, and BA nuclei measured on HEAO 3

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THE ASTROPHYSICAL JOURNAL, 267:L93-L96, 1983 April 15 
'E' 1983. The American Astronomical Society. All rights reserved. Printed in U.S.A. 
COSMIC-RAY ABUNDANCES OF Sn, Te, Xe, AND Ba NUCLEI MEASURED ON HEAO 3 
w. R. BINNS, 1•2 R. K. FICKLE,3 T. L. GARRARD,4 M. H. ISRAEL,1 J. KLARMANN, 1 K. E. KROMBEL,4 
E. C. STONE,4 AND C. J. W ADDINGTON3 
Received 1982 November 8; accepted 1982 December 15 
ABSTRACT 
Elements with even atomic number ( Z) in the interval 50 ~ Z ~ 56 have been resolved in the 
cosmic radiation using the Heavy Nuclei Experiment on the HEAO 3 satellite. The observation that 
50 Sn and 56 Ba are more abundant than 52Te and 54 Xe is inconsistent with a purer-process cosmic-ray 
source. Adjustment of source abundances for an enhancement of those elements with a low first 
ionization potential does not change this conclusion. 
Subject headings: cosmic rays: abundances- nucleosynthesis 
I. INTRODUCTION 
Since the early work of Burbidge eta/. (1957), the 
elements heavier than iron and nickel are assumed to 
have been formed primarily by neutron capture nucleo-
synthesis processes. These processes can be separated 
into two extreme classes depending on the intensity of 
the neutron flux involved. The r, or rapid, process, 
characterized by .l high neutron flux, forms highly neu-
tron-rich nuclei which decay back to the valley of beta 
stability only after the completion of nucleosynthesis. 
The s, or slow, process has a much lower flux of 
neutrons and allows for the decay of beta unstable 
nuclides before subsequent neutron captures. A specific 
astrophysical site for a pure r-process has not yet been 
established, but it has usually been associated with 
supernova explosions, which are also often assumed to 
be a source of cosmic rays. The s-process, on the other 
hand, is usually attributed to milder environments. 
Both these processes produce a characteristic signa-
ture in the resulting elemental composition. These signa-
tures are particularly evident in the relative abundances 
of 50 Sn, 52Te, 54 Xe, and 56 Ba. The s-process produces a 
greater abundance of Sn and Ba than of Te and Xe, 
while the r-process results in an overabundance of Te 
and Xe. A decomposition of solar system material into 
r-process and s-process contributions (e.g., Cameron 
1982 a) clearly shows these differences. In both processes, 
the odd-charge elements are significantly less abundant 
than the adjacent even-charge elements. 
The HEAO 3 Heavy Nuclei Experiment was designed 
to measure the abundances of the elements heavier than 
1 Department of Physics and the McDonnell Center for the 
Space Sciences, Washington University. 
2 Formerly at McDonnell Douglas Research Laboratories, St. 
Louis, Missouri. 
3School of Physics and Astronomy, University of Minnesota. 
4 California Institute of Technology. 
L93 
iron in the cosmic radiation. We report here on the 
results of an analysis in the Sn to Ba region of a subset 
of data obtained over approximately 440 days of opera-
tion. 
II. DATA 
The detector was a large area particle telescope on the 
third High Energy Astronomy Observatory which was 
placed in orbit at 43?6 inclination and 495 km altitude 
on 1979 September 20. It consisted of six parallel plate 
ionization chambers, four pairs of multiwire ionization 
hodoscopes, and a dual radiator Cerenkov detector 
arranged symmetrically about the detector midplane 
(Binns et a[. 1981 b). 
In this data subset, all the particles triggered the 
Cerenkov detector, at least one of the six ion chambers, 
and a minimum of two hodoscopes. Background from 
nuclear interactions within the instrument has been sup-
pressed by requiring consistency between the sig11als 
from the ion chambers and the Cerenkov counter. Charge 
has been determined from the Cerenkov signal using 
Z-squared scaling normalized at iron. Sixty percent of 
the particles have been collected from directions and 
locations which correspond to a high geomagnetic cutoff 
( > 8 GV), ensuring that the Cerenkov signal is nearly 
independent of energy (/3 ;::: 0.96). The remainder of the 
particles have been selected to be high energy by com-
paring the Cerenkov and ion signals. 
The resulting data set is shown in Figure 1. The main 
histogram exhibits peaks in the lower charges, thereby 
establishing our charge scale. Figure I a is an enlarge-
ment of the region of interest which shows peaks at the 
even elements Sn, Te, Xe, and Ba. This measurement is 
the first to show resolved even-element peaks in this 
charge region. 
The particles with assigned charge between 49.0 and 
59.0 have been superposed in the modulo 2 histogram in 
© American Astronomical Society • Provided by the NASA Astrophysics Data System 
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L94 BINNSETAL. Vol. 267 
20 a) 
FIG. I.-Histogram of the data from charge 30.0 to 60.0 in 0.25 charge unit bins. Although negligible over the limited range from 50Sn to 
56 Ba, charge-dependent biases in the consistency and energy selections are such that relative abundances of widely separated charges cannot 
be determined from this plot. Insets show (a) the region of interest in 0.5 charge unit bins and {b) a modulo 2 histogram of the data from 
charge 49.0-59.0 in 0.25 charge unit bins. 
Figure lb. This procedure, which bins each particle 
according to the difference between its assigned charge 
and the nearest even integer, superposes the even (and 
odd) element charge peaks, thus allowing a statistically 
significant determination of the instrument resolution. A 
Gaussian fit to this modulo 2 histogram, taking into 
account the spillover from the neighboring elements, 
indicates an rms charge resolution of 0.56 charge units. 
This verification of a peak at even charges, coupled with 
the peak at charge 38, shows that our assumption of 
Z-squared scaling cannot be significantly in error. Since 
elements with even charge dominate any suggested 
source, we are not likely to have an error of one charge 
unit, but an error of approximately two charge units 
cannot immediately be ruled out. However, if there were 
a two-charge unit error for any one of the peaks in 
Figure la, while the peak at 38 was correct, then the 
separation between even-element peaks in this interval 
would be approximately 1.7 or 2.3 charge units (depend-
ing of the direction of the error) rather than 2.0, with the 
result that the modulo 2 histogram would not have such 
a well-defined structure. Furthermore, such a large error 
in the charge estimate is not consistent with calculations 
of non-Z-squared Cerenkov effects by Derrickson, Eby, 
and Watts (1981). Our own earlier results (Binns eta/. 
1981 a) using a different data subset have also shown the 
approximate validity of Z-squared scaling up to charge 
40. 
Table 1 gives the abundances of 50Sn, 54 Xe, and 56 Ba 
(normalized to our best estimate of the abundance of 
52Te) obtained from a least-squares Gaussian fit to the 
data in Figure 1 having an assigned charge between 45.0 
and 60.0 using 0.25 charge unit bins. The fit was made 
to both odd and even charge abundances, and the 
Element 
50 Sn ....... . 
52Te ....... . 
54Xe ....... . 
56 Ba ....... . 
TABLE I 
RELATIVE ABUNDANCES {52Te "' I) 
HEAO 
1.33 ± 0.31 
1.00 ± 0.27 
1.03 ± 0.25 
1.52 ± 0.32 
Arie/6 
0.66 ± 0.22 
1.00 ± 0.23 
0.34 ± 0.17 
1.18 ± 0.23 
Balloon 
1.21 ± 0.37 
1.00 ± 0.32 
0.89 ± 0.27 
0.87 ± 0.27 
standard deviation of the assumed Gaussian charge 
resolution was parametrically varied to obtain a mini-
mum x2• The x2 value as a function of the assumed 
standard deviation has a wide minimum between 0.4 
and 0.6 charge units. The relative abundances of the 
even charge elements typically vary by less than 10% 
within this minimum, while the odd charge elements 
show a much greater variation, consistent with their not 
being resolved. The errors cited in the table are derived 
from this fit. No corrections have been applied to the 
abundances for fragmentation in the instrument since, 
over such a limited charge range, the relative adjustment 
factors for the even elements are less than - 3%. Also 
shown are results from Ariel 6 and balloons (Fowler 
et a/. 1981 ). The balloon data are "subject to significant 
and rapidly charge-dependent corrections" (Fowler 
et a/.), while there has been no claim of resolution of the 
individual even-element peaks in the Sn-Ba region for 
the Ariel 6 data. 
III. DISCUSSION 
Figure 2 shows the data and the propagated abun-
dances of the even elements from a calculation by 
© American Astronomical Society • Provided by the NASA Astrophysics Data System 
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No.2, 1983 COSMIC-RAY ABUNDANCES OF Sn, Te, Xe, AND Ba L95 
Ill 
~I 
w 
u 
z 
<( 
0 
z 
:::> 
R-PROCESS 
m .4 -FIP 
<( ---NOFIP 
SOLAR SYSTEM 
-FIP 
---NO FIP 
·
2 50 52 54 56 50 52 54 56 
ATOMIC NUMBER 
FIG. 2.-0ur data compared to results of propagating an as-
sumed r-process source and a solar system source through 5.5 
g em- 2 of hydrogen (Brewster et a!., private communication; 
Brewster, Freier, and Waddington 1983). Solid line has adjust-
ments applied for first-ionization-potential effects (FIP); dotted 
line does not. 
Brewster et a/. (private communication; see also 
Brewster, Freier, and Waddington 1983) using various 
sources and an exponential pathlength distribution with 
a mean of 5.5 gem- 2 of hydrogen. Since other results 
from lower charge regions indicate that there is an 
anticorrelation between first ionization potential and 
cosmic-ray elemental abundances relative to those of the 
solar system (Casse and Goret 1978; Binns eta/. 198la), 
Figure 2 also includes the results of propagating r-pro-
cess and solar system source abundances which have 
been adjusted to account for first-ionization-potential 
3.0 
2.5 
effects (Brewster, Freier, and Waddington 1983). The 
data are not consistent with the assumed r-process source 
material in either case, but reasonable agreement is 
obtained with solar system source material adjusted for 
first-ionization-potential effects. Although the large 
abundance of 58Ce shown in Figure 1 is also consistent 
with this conclusion, we have not considered it further 
here because its abundance is more affected by fragmen-
tation of heavier nuclei. 
The large abundance of either Sn or Ba relative to the 
other elements in this group argues against a source 
dominated by the r-process. This conclusion is empha-
sized in Figure 3, which compares the ratio of Sn to Te 
with the BajTe ratio. Our observed values are shown 
as the large diamond surrounded by error ellipses. 
Also shown are various calculated values derived from 
several assumptions regarding the source composition. 
Points are plotted for pure r-process abundances, pure 
s-process abundances, and for solar system source abun-
dances, both with and without a bias due to first-ioniza-
tion-potential effects. Two different predictions are 
shown (Brewster, Freier, and Waddington 1983; and 
Blake and Margolis 1981, also private communication), 
and the differences between corresponding points from 
the two calculations are an indication of the range of 
uncertainty in the expectations due to different source 
assumptions and propagation models. (Note that, for a 
given propagation model and given assumption about 
first ionization bias, the three calculated points fall on a 
straight "mixing line" whose ends represent pure r or 
pure s material, with varying rjs mixtures falling along 
the line.) 
• HEAO 
1ll NO FIP 
FIP 
SOLAR 
SYSTEM 5 
;:f~_; QY \$.) NO F I 
® ® ~ FIP 
!:S.i NO FIP 
(SJ FIP 
FIG. 3.-0ur measurement of the abundance ratios plotted along with two propagations of r, s, and solar system material both with and 
without first-ionization-potential effects (FIP) included (see text). The solid error contour is the locus of abundance ratios which fit the data 
with the same x2 value such that there is a 68% probability that the actual value lies within the contour (50% for the dotted contour). 
© American Astronomical Society • Provided by the NASA Astrophysics Data System 
19
83
Ap
J.
..
26
7L
..
93
B
L96 BINNSETAL. 
It is clear from this plot that our results are not 
consistent with pure r-process material either with or 
without first-ionization-potential effects. The difference 
between the closest r-process point and our measure-
ment is significant at the 93% level. When due account 
is taken of first-ionization-potential effects, our data 
are in reasonable agreement with solar system material, 
whereas ignoring these effects suggests an s-process-
dominated mixture. 
In Figure 3 we chose to plot ratios formed from Sn, 
Te, and Ba; the solar system Xe abundance is less 
certain than the other three because it is based on an 
interpolation of adjacent nuclides (Cameron 1982 b) 
rather than on measurements. However, our conclusions 
are not significantly altered if we include Xe. For each 
of the models represented by a point in Figure 3, we 
have made a least squares fit of the abundances of these 
four elements to our data. For any of the pure r-process 
models, the difference from our data is significant at 
least at the 93% level (reduced x2 ;::: 2.4), while models 
with solar system source abundances and first-ioniza-
tion-potential biases give reasonable fits to the data 
(reduced x2 ~ 1). 
The results in this charge interval are therefore con-
sistent with conclusions from measurements in other 
charge intervals since the measured elemental abun-
dances in the charge 26 to 40 region (Binns et al. l98la) 
show a similarity with solar system material adjusted for 
first-ionization-potential effects. Additionally, the low 
abundance of the "actinides" (88 ~ Z ~ 100) (Binns 
et al. 1982) is consistent with solar system material but 
not with freshly synthesized purer-process sources. 
We thank N. S. Collins, B. W. Gauld, D.P. Grossman, 
and B. J. Newport for assistance in programming for 
data analysis. The research was supported in part by 
NASA under contracts NAS 8-27976, 77, 78 and grants 
NGR 05-002-160, 24-005-050, and 26-008-001. 
REFERENCES 
Binns, W. R., Fickle, R. K., Garrard, T. L., Israel, M. H., 
Klarmann, J., Stone, E. C., and Waddington, C. J. 1981a, Ap. J. 
(Letters), 247, Ll15. 
__ . 1982, Ap. J. (Letters), 261, Lll7. 
Binns, W. R., Israel, M. H., Klarmann, J., Scarlett, W. R., Stone, 
E. C., and Waddington, C. J. 1981b, Nucl. lnst. Meth., 185, 415. 
Blake, J. B., and Margolis, S. H., 1981, Ap. J., 251, 402. 
Brewster, N. R., Freier, P. S., and Waddington, C. J. 1983, Ap. J., 
264, 324. 
Burbidge, E. M., Burbidge, G. R., Fowler, W. A., and Hoyle, F. 
1957, Rev. Mod. Phys., 29, 547. 
Cameron, A G. W. 1973, in Explosive Nucleosynthesis, ed. D. N. 
Schramm and W. D. Arnett (Austin: University of Texas Press), 
~3. . 
Cameron, A G. W. 1982a, Ap. Space Sci., 82, 123. 
__ . 1982b, in Essays in Nuclear Astrophysics, ed. C. A Barnes, 
D. D. Clayton, and D. N. Schramm (New York: Cambridge 
University Press), p. 23. 
Casse, M., and Goret, P. 1978, Ap. J., 221, 703. 
Derrickson, J. H., Eby, P. B., and Watts, J. W. 1981, Proc.llth Int. 
Cosmic Ray Conf. (Paris), 8, 88. 
Fowler, P. H., Walker, R. N. F., Masheder, M. R. W., Moses, 
R. T., and Worley, A 1981, Nature, 291, 45. 
Note added in proof.-Our results are also inconsistent at the ~ 99% level with the r-process abundances derived by 
subtracting the s-process values of F. Kappeler, H. Beer, K. Wisshak, D. D. Clayton, R. L. Macklin, and Richard A. 
Ward (1982, Ap. J., 257, 821) from those of the solar system recently compiled by Edward Anders and Mitsuru 
Ebihara (1982, Geochim. Cosmochim. Acta, 46, 2363). 
W. R. BINNS, M. H. ISRAEL, and J. KLARMANN: Department of Physics, Washington University, St. Louis, MO 63130 
R. K. FICKLE and C. J. WADDINGTON: School of Physics and Astronomy, University of Minnesota, 116 Church Street, 
S.E., Minneapolis, MN 55455 
T. L. GARRARD, K. E. KROMBEL, and E. C. STONE: 220-47 Downs Laboratory, California Institute of Technology, 
Pasadena, CA 91125 
© American Astronomical Society • Provided by the NASA Astrophysics Data System 


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Cosmic Ray Abundances of Sn, Te, Xe, and Ba Nuclei Measured on HEAO 3

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