Preliminary results are reported from 430 days of exposure of the heavy nuclei experiment on the HEAO-3 spacecraft. These results are confined to the heavy nuclei with Z ≥ 50 and emphasize the conclusions obtained on the relative numbers of actinides and heavy stable elements in the lead-platinum region. The extreme paucity of actinides found is inconsistent with the predictions of a cosmic ray source that is highly enriched in r-process material, but quite consistent with a source whose composition is similar to that of normal solar system material. An upper limit, at the. 95% confidence level, is placed in the ratio of nuclei with Z ≥ 88/(74 ≤ Z ≤87) of 0.03

Binns, W. R.

Fickle, R. K.

Garrard, T. L.

Israel, M. H.

Klarmann, J.

Stone, E. C.

Waddington, C. J.

Caltech Authors - Main

19
81
IC
RC
..
..
9.
.1
09
W - 109 -
OG H.2~9 
ABUNDANCES OF COSMIC RAY NUCLEI HEAVIER THAN 50sn 
C.J. Waddington and R.K. Fickle, School of Physics and 
Astronomy, University of Minnesota, Mpls. , MN 55455, tJ. S .A.; 
T.L. Garrard and E.C. Stone, 220-47 Downs Laboratory, Cali-
fornia Institute of Technology, Pasadena, CA 91125, U.S.A.; -
W.R. Binns, M.H. Israel and J. Klarmann,Department of Physics, 
Washington University, St. Louis, MO 63130, U.S.A. 
ABSTRACT 
Preliminary results are reported from 430 days of exposure of 
the heavy nuclei experiment on the HEA0-3 spacecraft. These 
results are confined to the heavy nuclei with Z~50 and emphasize 
the conclusions obtained on the relative numbers of actinides 
and heavy stable elements in the lead-platinum region. The 
extreme paucity of actinides found is inconsistent with the 
predictions of a cosmic ray source that is highly enriched in 
r-process material, but quite consistent with a source whose 
composition is similar to that of normal solar system material. 
An upper limit, at the. 95% confidence level, is placed in the 
ratio of nuclei with Z~88/(74sZs87) of 0.03. 
1. Introduction 
The heavy nuclei experiment on the HEA0-3 satellite was designed to 
determine the charge spectrum of cosmic ray nuclei from silicon to the 
actinides and to compare the elemental composition with those predicted 
for various hypothetical cosmic ray sources. In particular, the pro-
cesses of nucleosynthesis that are responsible for the cosmic ray nuclei 
should determine the observed composition and hence be revealed by a 
measurement. Additionally, the heavy nuclei are strongly influenced by 
the processes of interstellar propagation and these processes can be 
investigated in terms of the various models of propagation. 
This detector consisted of two pressure chambers, each containing 
two layers of x-y hodoscopes and three parallel plate ion chambers. 
Mounted between the chambers were two thin plastic Cherenkov radiators, 
Binns et al. (198la). In orbit approximately 5 x 104 iron nuclei were 
detected per day. These nuclei have to satisfy the coincidence require-
ments that they transverse at least two of the four hodoscope layers 
and at least two of the seven charge measuring modules, but otherwise 
have no restrictions on angle or direction of motion. The minimum 
charge detectable is angle dependent but roughly corresponds to Z~14, 
while a full scale signal would correspond to a nucleus of z=l20 at 60°. 
2. Experimental Data 
As a consequence of the loose coincidence requirements imposed, the 
data obtained are of widely varying quality. The charge resolution 
© IUP AP • Provided by the NASA Astrophysics Data System 
19
81
IC
RC
..
..
9.
.1
09
W - 110 -
OG H.2-9 
attainable depends critically on the subset of data chosen. For example, 
in the charge region 30~Zs40, where the abundances are relatively large, 
it is possible to select a subset that contains only some 10% of the data 
and still obtain statistically significant abundances with individual 
charge resolution , Binns et al. (1981b). However, in the next charge 
region, 40~Zs58, the same selection gives results of marginal statistical 
significance, while relaxing the selection criteria degrades the charge 
resolution. Fig. 1 shows the data for the high resolution selection and 
shows marginally significant abundance peaks at soSn and sGBa. 2 The charge scale on Fig. 1 was derived assuming a strict Z scaling 
from the normalization at the 2sFe peak. For these high Z nuclei, the 
energy loss equations would be expected to contain higher order Z terms 
due to the breakdown of the first Born approximation which in the limit 
requires that Z/S<<l37. A sununary of the theory has been given by Ahlen 
(1980), while Eby (1980) has calculated the effects that might be 
observed in our detectors. However, the validity of these corrections 
applied to a specific detector is not fully understood and ultimately a 
calibration, internal or external, will be essential. The effects of 
applying corrections based on the Ahlen formalism are shown in Fig. 1, 
where each particle has been re-assigned a charge based on its individ-
ual history. The result seems encouraging but unphysical. The small 
peaks at soSn and sGBa appear better defined, but shifted in mean charge 
to non-integral and unreasonable charges. The magnitude of these 
corrections at these charges is quite small, but rapidly increases with 
increasing Z, becoming several charge units at z~so. Typical calculated 
values are shown in Fig. 2, for several energies and for charges 
determined from the Cherenkov signal, C, and from ion chamber signal 
combined with the Cherenkov signal, CI. 
40 
(/) 
~ 30 
w 
> w 
~ 20 
a:: 
~ 
3 
z 10 
HEA0-3 DATA (June, 1981) 
Combination of E .s 2 GeV/amu 
and P > 8 GV Data Sets 
Data set corresponds to 
2.7x I06 Fe 
32 36 40 44 48 
ATOMIC NUMBER 
20 
10 
Fig.I. High resolution for Z~58. 
Lower charge scale assumes only 
z2 scaling, upper includes higher 
order terms. 
3. Results 
s--~~-----~~~~~~~~-----:-
1 GeV/amu } 
0.8 Ge V/amu Z Cl 
0.6 GeV/amu 
4 
5 
N 
<J 3 
/ /2 GeV/arnu } 
/ Zc 
2 / /GGeV/amu / / 
:.---:::::// 
:;..---:;.---
0 30 4;~0 60 70 80 90 
Fig.2. Charge overest!mates 
due to assuming only z2 scaling 
as a function of Z. 
In order to obtain results of greater statistical significance, it 
is essential to relax the selection criteria and accept the resulting 
loss of charge resolution. The entire data set has been subdivided in 
some 25 bins, each characterized by various selection criteria. The 
© IUP AP • Provided by the NASA Astrophysics Data System 
19
81
IC
RC
..
..
9.
.1
09
W - 111 -
OG H. 2-9 
resolution and charge measurement obtained in each bin has been deter-
mined by examining the iron peak observed in that bin and the bins then 
ranked on the basis of the sharpness of the iron peak. In fig. 3 we 
show the charge spectra obtained for three groups of bins progressively 
110 
SELECTED (107) 
75 80 85 
Z "CORRECTED" 
Zr !BOO MeV/amu) 
65 70 75 BO 85 90 
65 70 75 80 85 90 z2 
65 70 75 80 85 90 
20 Zc!6 GeV/amu) 
10 
~ ro ~ ro ~ oo ~ oo~ 
CHARGE, Z SQUARED TERMS 
Fig.3. Charge spectra for three sets 
of data. Also shown are two alterna-
tive charge scales. The insets show 
the heaviest nuclei for two different 
charge assignments. 
35 
30 
25 
20 
15 
10 
5 
50 
SOLAR SYSTEM 
r- .PROCESS 
Fig.4. A comparison between 
predicted and measured charge 
spectra. 
summing from the highest resolution set to those of lower resolution. 
No results are shown for bins characterized by an iron peak having 
cr > O.~S charge units. These bins include 70% of the iron, or about 
2 x 10 7 nuctei. This charge spectrum is based on charges assigned from 
a z2 scaling. Also shown are two alternative charge scales constructed 
from the curves in Fig. 2. It is clear that the net effect will be to 
smear any charge features in the e2Pb - 1ePt region. In order to 
examine this charge region with the best available statistics we have 
individually analyzed every event that was assigned a nominal charge of 
z~72 for.what ever reason. The resulting charge spectrum of acceptable 
events is shown as the left hand insert to Fig. 3. The right hand 
insert shows the effect of correcting each charge assignment by the 
most appropriate of the two charge scales shown. 
4. Discussion 
The charge spectra shown in Fig. 3 can be compared with those 
expected from various assumed source spectra after propagation through 
the interstellar medium. Fig. 4 shows the spectra calculated by 
Brewster et al. (1981) after correction for the effects of the first 
ionization potential (4.30 exp (-0.18 I (eV))) and for propagation with-
out energy loss through a simple leaky box with an escape path of 5 g/cm2 
© IUP AP • Provided by the NASA Astrophysics Data System 
19
81
IC
RC
..
..
9.
.1
09
W
VI 
N 
CJ) 
CJ) 
- - - - - - - - - - - - - - - - - - WITH FIP 
BALLOONS 
I 
HE Ji 
I 
I 
I 
I 
SKYLAB 
ARIEL 
- - - - - -.- - - - - -
.,. 
GROSS r- PROCESS 
SS r- PROCESS 
WITH FIP 
HEAQ 
SOLAR SYSTEM 
Fig.5. The actinide to lead-
platinum ratio as observed and 
predicted. 
- 112 -
OG H.2-9 
of hydrogen. Spectra are shown 
assuming a solar system source 
composition, Cameron (1981), and 
an r-process source composition. 
For clarity, only the even-charged 
elements are shown, with the odd 
charge abundances divided equally, 
and the spectra are normalized to 
the abundances of the 50~Z~56 
elements. 
The data shows the same main 
features .as the predicted spectra, 
with a steep decline in abundance 
around ssBa, an almost constant 
abundance in the lanthanides and 
subsidary Pt and Pb peaks, but is 
not in close correspondence with 
the details of either ther~process 
or SS prediction, nor could it be expected to until the charge assign-
ments have been corrected. The insert of Fig. 3 shows that the ratio 
of Z2:88/(74.SZS86), the "actinide to lead plus platinum" ratio is about 
1%, with a 84l confidence upper limit of 3%. Fig. 5 shows a comparison 
of this result with some of those made by other workers and some of the 
predictions of Blake et al. (1978). These data show that while the 
earlier results were consistent with the predictions of a r-process 
source our own data has an upper limit that is clearly more consistent 
with a source having a solar system composition. This conclusion is 
not in disagreement with either the high energy Skylab data or the 
Ariel results. 
5. Acknowledgments 
This research was supported in pa.rt by NASA under contract NASB-
27976, 77, 78 and grants NGR 05-002-160, 24-005-050 and 26-008-001. 
References 
Ahlen, S.P., (1980), Rev. Mod. Phys. 52, 121. 
Binns, W.R., et al., (198la) Nucl. Instr. Meth. (to be published) 
(198la) OG H.2-8. 
Blake, et al., (1978), Ap. J. 221, 694. 
Brewster et al., (1981), OG H.3-13. 
Cameron, A.G.W., (1980), Center for Astroph. Reprint No. 1357. 
Eby, P., (1980), private communication. 
Fowler et al., (1981), Nature 291, 45. (Ariel) 
Shirk, E.K. and P.B. Price, (1978), Ap. J. 220, 719. (Skylab) 
© IUP AP • Provided by the NASA Astrophysics Data System 


Abundances of Cosmic Ray Nuclei Heavier than _(50)Sn

http://authors.library.caltech.edu/45045/1/1981-24.pdf

Abundances of Cosmic Ray Nuclei Heavier than _(50)Sn

Abstract

Similar works

Full text

Available Versions

Caltech Authors - Main