I OF
ORNL P
3052
.
2
EEEFE EFTER
:
1.25 1.4 14.5
MICROCOPY RESOLUTION TEST CHART
NATIONAL BUREAU OF STANDARDS - 1963
JUN: 3 1967
ORNn-f..zojn
Conf. 6165.24.-1
(Invited Paper - Symposium on the Origin and Distribution of the Elements,
Paris, France, May 8-11, 1967)

ICOS
CF92
Neutron Capture Cross Sections and the s-Process
60 23.00; mx 65
J. H. Gibbons and R. L. Macklin
Oak Ridge National Laboratory
Oak Ridge, Tennessee, USA
Ever since the discovery of neutrons it has been speculated that
they played a vital role in element synthesis, particularly for the heavy
elements. Over the past decade these speculations have evolved to highly
quantitative correlations between abundance and capture cross sections
of certain nuclides.
It is already clear that additional understanding
of the nucleosynthesis mechanisms and chronology will come from such studies.
In this paper we summarize the work on neutron capture cross sections and
present a few of the cosmological conclusions and extrapolations.
The first systematic measurements of fast neutron capture Cross
sections were made during the 1940's by Hughes and associates (Hu 53).
Wer
Their measurements, using MeV-range fission neutrons, showed that the
capture cross section increases smoothly with atomic weight except for
dips at several regions now known to be due to the closing of nuclear
shells. Alpher and Gamow (Al 48) showed that the capture results have a
rough correlation with elemental abundance (Fig. 1). Later, as appropriate
experimental techniques were developed, capture cross sections of many
elements were obtained in the many keV range characteristic of stellar
interiors. Burbidge, Burbidge, Fowler, and Hoyle (Bu 57) in their review
(frequently referred to as BʻFH) summarized the situation in 1957, showing
Research sponsored by the U.S. Atomic Energy Commission under contract
with Union Carbide Corporation.
.
DISTRIBUTION QE THIS DOCUMENI IS UNLIMITED.
.
2
.
More
r CO
a much more clear correlation between capture and abundance (Fig. 2).
BʻFH and Cameron (Ca 59) gave convincing evidence that the preponderance
of solar system elements heavier than about iron were created in one of
two general processes: (a) the s-process, involving ~ 30 keV neutron
capture at low rates (one neutron capture per nucleus per 100 - 10? years)
and (b) the r-process, involving rapid capture (~ seconds) of many neutrons.
The s-process rate was governed by the neutron flux history and the capture
S
cross sections of nuclides along the valley of teta stability.
The s- and
r-process paths can be rather accurately followed through the nuclides.
Certain isotopes can be identified as solely due to one process; others
are clearly mixtures of both processes. For example see Fig. 3.
The model of s-process syrithesis is relatively simple.
The end
products of charged particle reactions near maximum nuclear vinding are
the assumed starting material for the neutron capture synthesis mechanisms.
The most abundant is 5Fe. In s-process synthesis, the 5°Fe "seeds" are
immersed in a low density sea of neutrons whose average energy is several
tens of kilo-electron volts. Neutrons are captured at intervals long com-
ON.
pared to radioactive lifetimes of neutron-rich isotopes and the capture
cha in follows the valley of B-stability. Beyond Bi, alpha decay
terminates the process. The rate or change of the number of s-process
nuclei of weight A, N.(t), depends upon its capture rate (ov), the neutron
density n(t), and the abundance and capture rate of its lighter neighbor
(A-1). That is
an (t)
- = (ov)A-1"(t)NA-z(t) - kovan(t) wA(t)
at
LEGAL NOTICE
This report was prepared as an account of Government sponsored work. Nolther the United
States, nor the Commission, nor any person acting on beball of the Commission:
A. Makes any warranty or representation, expressed or implied, with respect to the accu-
racy, completeness, or usefulness of the information contained in this report, or that the we
of any information, apparatus, method, or process disclosed in this report may not infring
privately owned righta; or
B. Assumes any Habilities with respect to the use of, or for damages rosu ting from the
use of any information, apparatus, method, or proceso disclosed in this report.
As used in the above, "person acting on behalf of the Commission includes any m.
ployee or contractor of the Commisalon, or employee of such contractor, to the extent that
such employee or contractor of the Commission, or employee of much contructor preparos,
disseminates, or provides access to, any information pursuant to his employmeat or contract
with the Commission, or his employment with such contractor.
.
.
3
If we define the average capture cross section for weight A at temperature
T as (o)= (ov) /v.m and define the neutron flux exposure history (number
per em?) as 7 = 5 * n(t')vyat' then (1) becomes
Puss
N,.O.N. Clayton, Fowler, Hull, and Zimmerman
A-1A-I APA
dt
showed that on for s-process nuclei should be a smooth, slowly varying
function of atomic weight. CFHZ also showed that the observed distribution
of oN products could not have been produced by a uniform exposure of 5°Fe
to a single neutron flux. Instead an exposure to a distribution of flux
histories was called for by the data. Let the oN product per litial Fe
nucleus that results from a neutron exposure I be
*(T) = QN(*)/N.
where N is the total initial nuclei. Then, if plThat is the number
exposed to an integrated flux between T and (t + dT) the on products
produced are
f(A) = oN(A) = S(+)(r)ar
Thus the function f(A) is a measure of the integrated flux-time to which
JI
seed nuclei have been exposed. Given capture cross sections and abundances
one should be able to deduce e(T), the "history" of solar system s-process
SS
material synthesis.
More accurate values for elemental abundances and capture cross
sections of separated isotopes have become available in recent years
4
.
(Ma 65). The smoothly decreasing trend of the data given by B'H is now
known to have a ledge/precipice structure - as predicted by the model - due
to the minima in capture cross sections caused by nucleer sheli effects
(ci 61). The data can be fitted using a distribution, pl ), of either
exponential or power law form (Se 65). The most impressive f'it to data
is a power law with a cut-off for large values of (Fig. 4), compatible
with stellar models (Se 66). The cut-off term is necessary in order to
obtain agreement along the shelf between A = 140 und A = 200. Note that
there are two points changed on this curve since its publication in 1966.
These points are tellurium and
Pb (Ma 67a).
The earlier results had been
ohtained using estimates for the cross sections from systematics. l'he
tellurium result changed by only 15% but the lead-204 changed by 60%. We
will see later why the estimate for lead was 30 uncertain.
The limit of accuracy of data for the capture cross section vs
elemental abundance is different for different elements. Relative solar
system abundances are rather well-known for some specific elements but
rea
very poorly known for others for such reasons as volatility and degree
of segregation. Similarly the capture cross sections are not determinabie
to a uniform accuracy. This is principally a function of the magnitude
of the cross section. Those nuclides near closed shells have considerably
smaller cross sections than those between shells (Fig. 5). The intriguing
precipices in the oN curve are just the place where our ability to accurately
determine the capture cross sections is minimum.
The region around lead is a case in point. Lead has 82 protons,
a closed shell. In addition the neutron shell N = 126 is filled for 20% Pb
- 5-
and also strongly influences the lighter lead isotopes. The combined
effect of the proton and neutron shells causes the 30 keV capture cross
section to be as small as a few millibarns, compared to about two barns
for some of the rare earths. Since several millibarns 18 near the present
limit of our experimental sensitivity the lead cross sections are con-
siderably less well determined than most of the rest.
The problem of
nucleosynthesis of lead is very intriguing and its cross sections are
worthy of a rather careful experimental study. The strong nuclear shell
effects cause a level spacing similar to light elements. In this case
individual resonances, rather than averages over many states, must be
studied. The neutron total cross sections for the various isotopes are
shown in Figs. 6, 7, 8, and 9. The average level spacing varies from
about two key for 204po to about 50 keV for 208 pb. By comparison, level
spacirig for rare earth elements is several ev. In order to derive
temperature averaged cross sections for the lead isotopes we cannot use
averaging techniques in the experiment; instead we must measure individual
resonances in detail and then average the results.
The lead total cross
sections, obtainable with much higher resolution than capture, are used in
connection with capture gamma-ray studies (see for example Fig. 10) to
interpret the capture cross section data (for example Figs. 11 and 12).
Total cross section results (Ma 64, Gi 67) give the location, angular
momentum (sometimes), parity (sometimes) and total width (usually) of the
resonances. The capture gamma spectra (Bi 67) give unique isotopic
identification and aid in spin/parity assignment. The capture cross section
O
data per se, give the integrated resonance capture area, subject to scattering
.6.
and self-shielding corrections which in turn are deperdent upon the spin,
and capture and scattering widths of each resonance.
Once the individual resonance capture area results have been obtained
they are averaged over a Maxwellian distribution of neutron energies in a
manner similar to that used with resonance-averaged cross sections. We
use the Max.vell-Boltzman weighting function
(v)av - 72
de exp -
where von = (2KT/m) 1/2, T is the absolute temperature, m is the reduced
neutron mass, and k is the Boltzman constant. We calculate
Foov) = o-ve(var
isut express, for convenience, the results in cross section units:
(o) = (o.v)/ver
The results for the lead isotopes as a function of energy, kt, are
given in Fig. 13. Normally, for nuclei with closely spaced levels, the
temperature dependence of the Maxwellian averageä cross section is very
similar from one element to another. But in lead the temperature dependence
is strongly different since the cross sections are due to so few resonances.
- This is particularly true for 20°pb because, to our knowledge, its neutron
capture at stellar temperatures is completely dominated by the two p-wave
resonances near 75 keV.
-7-
The correlations between elemental abundance and capture cross
J00
section seemed so promising that we undertook a more quantitative experi-
mental test of the model. We avoided the inherent uncertainties of
elemental abundance in our next series of measurements by testing the
correlations between capture cross sections of separated, stable isotopes
and th: ir isotopic abundance. The s-process mudel makes very specific
predictions about the o•N value for certain closely neighboring isotopes.
For example (Fig. 3) there are two isotopes of samarium that could only
be produced by the s-process since they are shielded from r-process
production by other stable nuclides. The oN values should differ, there-
fore, only by the amount indicated by the small slope of the distribution
function (about 2% in the case of samarium). Our experimental results
(Ma 63) (Table 1) for the (oN),28/(on), 50 ratio (0.98 0.06) give strong
support to the theory.
The techniques for measuring cross sections in the keV energy range
involve fast neutron pulsing and time-of-flight (Mo 64) combined with
fast, high efficiency capture gamma ray detection (Ma 67b). We have been
able to use samples as small as two grams.
The accuracy obtainable, while
dependent upon sample size, is mostly dependent upon the size of the cross
section. In the case of samarium, a high cross section element, relative
cross sections were obtainable to about 5% and absolute cross sections
to about 20%. Both of these uncertainties should be reduced by a factor
of 2 as a result of improvements in instrumentation and standards now
underway and by a factor of 4 when sufficiently large samples become
available.
I
.
8
.
We have also made capture cross section measurements with isotopes
of strontium, zirconium, tin (Ma 62), and tellurium in addition to samarium
and r’ind that the predicted correlations are verified in every case (Fig.
14). Details of these experimental results are given in Figs. 3, 15, 16,
and 17 and in Tables 2, 3, 4, and 5, and are discussed in more detail in
a forthcoming publication (Ma 67c). If we make a similar plot of cross
section times abundance for non s-process nuclides (Fig. 18) it is clear
that, as expected from the theory, no such correlation is obtained. Suess
(su 64) has suggested that abundance may be correlated with nuclear
SS
properties other than neutron capture, for example with binding energy of
the last neutron or the last alpha particle. To test this suggestion we
plotted our isotopic capture cross section results as a function of neutron
and alpha binding energies (Figs. 20 and ĉl). The circled points are
those for which the s-process ivypothesis is so closely followed. They
appear typical, showing no better correlation than the other isotopes.
The medien spread is about a factor of ten, in sharp contrast to the few
percent spread of the relevant data around the s-process predictions.
We conclude from these studies that the s-process hypothesis is in
highly quantitative agreement with experimental tests. Additional testing
will broaden this confirmation and will help toward a more clear under-
standing of the events that led to the synthesis of solar system material.
It is interesting to note that there is strong evidence (Da 66) that while
elemental abundance distribution can be considerably different in other
stars, their abundance distributions show the same characteristics of
ledge and precipice, due to the influence of neutron shells on capture
cross sections.
9
-
One immediate side benefit of the isotopic correlation studies art
101
are
r-process abundances for isotopes whose origin is mixed r, s (for example
see Table 1). The r-process abundance distribution is a prime starting
point in unravelling the threads of r-process synthesis. Another
benefit that may accrue, first mentioned by Clayton (ci 64), is an
independent measure of the time since solar system r-process synthesis by
O
means of the Re-Os correlation (Fig. 18). Osmium has two s-cnly isotopes
but the aburdance of the heavier one has been increased through radioactive
decay of 107 Re produced in the r-process. Therefore, given the osmium
capture cross sections, the 10 Re half-life, and the Re/Os abundance, then
the time since to Re was formed can be calculated. This measureme:at awaits
the rather difficult production of sufficient quantities of the osmium
isotopes, but experimental studies of capture systematics in this region
of atomic weight may soon allow an estimate good to about 20%.
Finally, the confidence gained in the s-process hypothesis,
particularly through the isotope measurements, can be used to accurately
calculate some solar system primordial elemental abundances. This is
especially appealing for gaseous, volatile, and strongly segregated elements
whose abundances are difficult, at best, to measure in a straightforward
fashion. Assuming the validity of the s-process correlations, the relative
abundance of two elements is straightforward if the capture cross section
of at least one s-only isotope is known for each element. Elements which
we hope to examine by this technique include krypton, xenon, osmium, and
mercury. The empirical correlations found to date (Fig. 4) are, in a way,
a good confirmation of the relative abundance values obtained from geochemical,
- 10 -
geophysical, spectroscopic, and astrophysical studies. We feel, however,
that the s-process correlations are so promising that capture cross sections
are a new, if limited, and highly quantitative tool in determining some
primordial solar system elemental abundances.
Summary and Conclusions.
The correlaticns found between abundance and neutron capture cross
COM
sections corresponding to interior stellar temperatures have demonstratec.
the validity of the s-process theory of heavy element nucleosynthesis and
have disclosed the form of the neutron flux to which our solar system
material has been exposed. Additional tests, using separated isotopes,
have bypassed the sometimes large uncertainties in elemental abundance
and have shown, for several sets of isotopes, highly quantitative agree-
ment with s-process calculations. Alternative abundance correlations, such
as with neutron binding energy, were tested and found to show no significance.
As s-process abundances have become available a number of new r-
process abundances have been derived by subtraction. In one instance (Re/os)
it appears that an independent measure of the time lapsed since the last
r-processing of solar system material is given directly from s-process
considerations.
The detailed mapping of the s-process can be used to
accurately, if indirectly, measure relative elemental abundance of those
elements that have one or more s-process isotope.
Finally, Danziger's study of absorption spectra from other stars
shows that the s-process undoubtedly operates as an important nucleosynthesis
'.
mechanism in other parts of our galaxy.
*.
-
-
'.'.
'.
-
. -
'.*
s
e
..1-R
.
- 11 -
REFERENCES
S
Alpher, R. A. 1948, Phys. Rev. 74, 1577. A preliminary account of this
work was given by R. A. Alpher, H. Bethe, and G. Gamow, ibid. 73,
803 (1948).
Biggerstaff, J. A., Bird, J. R., Gibbons, J. H., and Good, W. M. 1967,
Phys. Rev. to be published.
Burbidge, E. M., Burbidge, G. R., Fowler, W. A., and Hoyle, F. 1957,
Rev. Mod. Phys. 29; 547.
Cameron, A. G. W. 1959, Ap. J. 129, 676; and earlier references
contained therein.
Clayton, D. D., Fowler, W. A., Hull, T. E., and Zimmerman, B. A.
1961, Ann. Phys. 12, 331.
Clayton, D. D. 1964, Ap. J. 139, 637.
Danziger, I. J. 1966, Ap. J. 143, 527.
Gibbons, J, H. and Macklin, R. L. 1967, Phys. Rev. 153, 1356.
Hughes, D. J., Garth, R. C., and Levin, J. S. 1953, Phys. Rev. 91, 1423.
Macklin, R. L., Inada, T., and Gibbons, J. H. 1962, Nature 194, 1272.
Macklin, R. Ion, Gibbons, J. H., and Inada, T. 1963, Nature 191, 369.
Macklin, R. L., Pasma, P. J., and Gibbons, J. H. 1964, Phys. Rev.
1.36, 695.
Macklin, R. L. and Gibbons, J. H. 1965, Rev. Mod. Phys. 37, 166.
Macklin, R. L. and Gibbons, J. H. 1967a, submitted to Astrophysical Notes.
Macklin, R. L. and Gibbons, J. H. 19675, Phys. Rev. (to be published).
Macklin, R. L. and Gibbons, J. H. 1967c, Astrophysical Journal (to be
published).
- 12 -
Moak, C. D., Good, W. M., King, R. F., Johnson, J. W., Banta, H. E.,
Judish, J., and duPreez, W. H. 1964, Rev. Sci. Instr. 35, 672.
Seeger, P. A., Fowler, W. A., and Clayton, D. D. 1965, Ap. J. Suppl.
91, 121.
Seeger, P. A. and Fowler, W. A. 1966, Ap. J. 144, 822.
Suess, H. E. 1964, Proc. National Academy Science 52, 387.
- 13 -
Table 1
Samarium Isotopes at kt = 30 kev

I (), mb IN (atom %)
Ns oc
144p(m)
rs
150 £ 70
1170 = 190
257 50
1620 1 280
370 € 72
420 = 70
325 = 60
2.87
14.9
11.24
13.85
7.36
-
12.5 1 0.4* | 2.4 1 0.4* |(2810)*
11.24 2900 + 560
12.1 1 0.3* 1.7 + 0.3* (2810)*
7.36 2720 + 530
20.0 + 1.0* 6.9 11.0* (2810)*
22.8
26.90
22.84
*Inferred from the 148sm and 150sm results.
- 14 -
Table 2
Tin Isotopes at kt = 30 keV

Ko), mb
N (atom%)
116
Ş-0
104 1 21
14.2
7.6
sr
418 ¢
118
sr
24.0
(4.0)*
(4.5)*
(4.0)*
14.2
3.6
19.5
4.6
28.5
14.8 + 3
15.0 + 3
12.7 + 2.6
11.8 1 2.5
11.7 1 2.3
119
sr
8.6
120
S1
8
33.0
(4.5)*
122
r-o
4.7
4.7
124
r-o
5.9
5.9
"Errors do not include uncertainties arising from r-process estimates.
"W. A. Fowler, private communication.
- 15 -
Table 3
Strontium Isotopes at KT = 30 keV

Class
ko.), mb
N (atom %)
No
g° | +
75
15
9.86
740 1 150
108
1 20
7.02
(0.7)
680 = 120
6.9 $
1.7
82.56
(7.8)
71.8
500 € 130
"Seeger, P. A., Fowler, W. F., and Clayton, D. D., Psr is s-only
but has a cosmoradiogenic decay contribution from the r-only 7Rb.
- 16 -
Table 4
Zirconium Isotopes at KT = 30 keV

Class
(o), mbN
(atom %)
Ng
No lost
s(m)
48.5
8.7
a
11 1 3
59 + 10
34 + 6
21 : 4
to fa 6 w
51.46
11.23
17.11
17.4
2.8
(3.0)
(2.5)
(3.0)
(2.8)
s 2.8
535 : 160
515 1 100
480 - 90
310 60
14.1
14.6
a
r-o(?)
41 I 12
MAN
Estimated from systematics.
Errors do not include uncertainties arising from r-process estimates.
- 17.
Table 5
Tellurium Isotopes at kT = 30 keV

Class
Co.), mb
N (atom %)
N.
NO
No
No God?
120
0.089
2.46
.089
.0454
122
248 2 40
2.0
123
0.87
.030
600 = 90
708 70
770 120
(695)*
4.61
25
(1.7)*
4.61
6.99
18.71
31.79
34.49
(5.3)*
(8.9)*
126
(2.8)*
(695)*
128
31.79
33 + 10
14 t 5
130
34.49
* Estimated from neighboring p-only isotopes. See text.
Obtained assuming the local approximation: NO. = 695.
• 18 -
FIGURE CAPTIONS
Fig. 1 - First correlations reported between fast capture cross section
and abundance (from Alpher 1948).
Fig. 2 - Correlations between cross section times abundance: (a) for
S-process nuclei as a function of atomic weight
n-s-process
S
nuclei. This figure shows our state of knowledge ten years ago
(Burbidge 1957).
Fig. 3 - The s-process path in the region of samarium. 14°Sm and +5°Sm
are due only to the s-process since they are shielded from
ar
r-process contribution by the corresponding isotopes of Nd.
Fig. 4 - Cross section times S-process abundances versus atomic weight.
The data points on this figure are derived from latest cross
section (Macklin 1965) and abundance (Seeger 1965) information.
The solid curve was calculated (Seeger 1966) assuming an
exponential distribution of neutron exposure histories of the
original material, with a cut-off for large flux exposures.
Fig. 5. Neutron capture cross sections near 65 keV as a function of
atomic weight. The deep minima are due to nuclear shell effects.
Fig. 6 - Neutron total cross section for
Fig. 7 - Neutron total cross section for
Fig. 8 - Neutron total cross section for 20 Pb.
Fig. 9. Neutron total cross section for
- 19 -
Fig. 10 - Neutron capture gamma spectra at several resonances in
These spectra are helpful in determining spin and parity of the
capturing state.
Fig. 11 - Capture cross section for (°°Pb + n). Individual resonance
effects are not clearly resolved.
Fig. 12 - Capture cross section for ( Pb + n). Individual resonance
effects are not clearly resolved.
Fig. 13 - Temperature-averaged capture cross sections of lead isotopes
as a function of energy, KT, where k is the Boltzman constant
and T the absolute temperature.
Fig. 14 - Correlations of neutron capture cross section times s-process
or predominantly s-process isotopic abundance for several
elements. The points are experimental results. Unlike the
elemental results (Fig. 4) there are negligible uncertainties
in relative isotopic abundances within a given element. Thus
VI
the only errors, due tij uns irtainties in relative capture
cross sections, are quite small and allow a highly quantitative
test. For convenience the data have been normalized to
ON = 1.0 for one isotope of each element.
The solid lines
indicate the trend expected from the semi-empirical s-process
theory. The agreement is remarkably good.
Fig. 15 - The s-process path in the region of tin. 110cd shields 110sn
from any r-process contribution since it terminates the chain
of beta decays with Z < 48 and mass 166.
The isotopes
41-6°Sn are clearly mixtures of s- and r-production. The
- 20 -
12
two heaviest stable isotopes are r-only since < Sn undergoes
Bº decay in a time very short compared to the mean s-process
neutron capture time (~ 103 - 103 years).
Fig. 16 - The s-process path in the region of strontium and zirconium.
Fig. 17 - The s-process path near tellurium. This element is unique
in that three of its isotopes are shielded from the r-process.
A major reason is the existence of an unusual number of
stable isotopes of tin, in turn due to nuclear shell effects.
Fig. 18 - The s-process path near osmium. our knowledge of the change of
No with atomic weight enables us to compute rather precisely
the no product for 107 Os given (1860s). The present abundance
of toros is due to two sources, one the s-process formation and
an additional component due to the beta decay of to Re. Therefore,
once No (107Os) is determined we can capture the effective time
since 107 Re (r-process) was produced.
Fig. 19 - No products versus atomic weight for non s-process nuclei.
S
The current theory of heavy element synthesis predicts no
significant correlation compared to the correlation between
s-process nuclei.
Fig. 20 - Comparison between neutron capture cross section and binding
energy of the added neutron. The circled data points are
s-process nuclei, whose close correlation with isotopic
(Fig. 14) and elemental (Fig. 4) abundance has been well
demonstrated. In clear contrast there is no correlation
evident with neutron binding energy. Such a correlation
- 21 -
has recently been suggested as a possible alternative to
On
ros
the s-process theory (Suess 1964).
Fig. 21 - Comparison between neutron capture cross section and binding
energy of the last alpha particle. The results are similar to
those in Fig. 20, namely that no correlation is evident,
particularly when compared to the strong correlations between
capture and abundance seen in Fig. 4 and Fig. 14.

-
-
LOGARITHM OF CAPTURE
CROSS SECTION, IN BARNS
-3.0
-2.0 0 -1. 0
1.0 2.0
LOGARITHM OF RELATIVE ABUNDANCE
30
Fig. 1
ORNL-DWG 66 -12429

bot.
S-PROCESS NUCLEI
1
CROSS SECTION (mb) X ABUNDANCE (Si=106)
R-PROCESS NUCLEI
|
IL TT
melon
60
80
100
III II
120 140 160 180 200
ATOMIC WEIGHT (A)
Fig. 2

ORNL-LR-DWG 75283
.48
n=82
16 y
15
l
1.07
62
sm
0-%2650
1.27 1.12
.24
.08 L
·06
.06
60 END
s
ud
R-ONLY
e
R-ONLY
1.001 !
19h
T!
330
JR-ONLY
ATOMIC NUMBER
SUBSEQUENT B-
SLOW (ny) IN
RED GIANTS
54
E.C. niy
RAPID In, Y) IN
SUPERNOVAE
52
140
145
150
ATOMIC WEIGHT
Fig. 3
ORNL-DWG 67-1601
TTT NTTTTTT
THE S-PROCESS
oNs vs A
p= EXPOSURE
T = INTEGRATED NEUTRON FLUX
CROSS SECTION (mb) XABUNDANCE (Si = 10°)
T
POT-3.2, Tmax= 1.35x1027 NEUTRONS CM-2
'60
80
100
120 140 160
ATOMIC WEIGHT (A)
180
200
220

Fig. 4

108
UNCLASSIFIED
ORNL - LR-DWG 49866
O ODD Z TARGET NUCLEI -
• EVEN Z TARGET NUCLEI WITH
EVEN-EVEN COMPONENT WEIGHTED
MULTIPLYING BY FACTOR OF 2.4
103
"
effective AT 65 kev
100 L
0
10
20
30
40
50 60
Z (TARGET)
70
80
90
100
Fig. 5.

ORNL-DWG 65-3748
20
T
204 Pb +
TTTTTT
To ON 0
LIL
Of (barns)
Oy (barns)
5
6
7
8
9 10
15
20
En (kev)
30
40
50
60 70 80
Fig. 6
c
-
6 5ས-20
༡ དང་པ་ མར་པ་དང་ སྐར་མ་ ཅི་དགའ་གང་
or (barns)
web
s。 bབrs/com
ག
or
6080

TTTTTTTTTTTTTTTIT
20
30
En (kev)
0
Fig. 7
ORNL-DWG 64-4231
T
Of(borns)
207 Pb (93%)
46.1 barns/atom
16
-
MTTTT
TTTTTTTTTTTTTTT
TTTTTTIIM
20
30
40
60

En (kev)
Fig. 8
ORNL-DWG 64-753A
♡
Pb208
ã
8.08 barns/atom
ñ
Oy (barns)
o
0
w
o
o
10
20
30
70
80
90
100

40 50 60
NEUTRON ENERGY (kev)
Fig. 9
ORNL-DUG CA-5083

66-75 tev
POTPO 41 KOV
35-46 AeV
25 ker
Y NOW
-LII
16 KOV
TIME-OF-FLIGHT CHANNEL NUMBER
FLIGHT THULE DEGREASMOS-
10
ARBITRARY WHITS
o
Į LIubo
20 40 60 80 100 120
GAMMA RAY CHANNEL NUMBER
Yield of Gamma Rays as a Function of Neutron Energy for 206Pb Target (Neutrons in 20 Channel, Gamma Rays in 128 Channel).
Fig. 10

ORNL-DWG 63 -7849
Pb 206
CAPTURE CROSS SECTION (mb)
10
15
20
50
55
60
25 30 35 40 45
NEUTRON ENERGY (keV)
Fig. 11
ORNL-DWG 63-7850
Pb 207
CAPTURE CROSS SECTION (mb)
10
15
20
50
55
60

25 30 35 40 45
NEUTRON ENERGY (keV).
Fig. 12
ORNL-DWG 67–3786

veta (mb)
206
208
0
10
20
50
60
70
30 40
KT (keV)
Fig. 13
ORNL-DWG 66-11323

.
.
O
ONS (NORMALIZED)
0.02
oor Lillimi Lulunullilulu
MASS: 86 90 95 | 116 120 125 130 145 150
Sn Te
ELEMENT: Sr
Zr
Sm
Fig. 14

ORNL-LR-DWG 75284
.57
i
R-
P30
50
ONLY
1.06
Sn
.01
1.05
.007.004.14 1.08 L.241.09 L.331_
is
27h
R.
ONLY!
In dit .04 1.96
27-13_:24.4.2_L29 L 1.08
13S
14738
48
sanl.08
I
54h
R-ONLY
-SLOW (
ny) IN
RED GIANTS
R-ONLY
T
SUBSEQUENT BC
ATOMIC NUMBER
ก
-RAPID (ny) IN
SUPERNOVAE
n = 82
38 Fi
110
115
120
ATOMIC WEIGHT
Fig. 15

ORNL-LR-DWG 75282
0:50
(Py).16
.09
.16
| .17 1.09
.
42 EMO
[
st-sh
1.00
ND
1 2x10^y 350
L1.71 .03
J106* L 650
L R
-ONLY
1.001.j
€56
.10 .07.831
ist st 500
38
Sr
1.287
190
R-ONLY
SUBSEQUENT B
ATOMIC NUMBER
ONLY
34
SLOW (ny) IN
RED GIANTS
32
RAPID (ny) IN
SUPERNOVAE
30
NY
85
90
95
ATOMIC WEIGHT
Fig. 16

ORNL-DWG 66-3367
SLOW (n, Y) IN
RED GIANTS
(S-PROCESS)
128 129 130 131 132
.02.26 .04.211.27
127_S
25m
| 128
9.3 9.32 67m
130
.34
ATOMIC NUMBER
120 122 123 124 | 125 | 126
10009 1 .02 .009.04.07 9
121 !
i 123
.57 30 .43
118 119 | 120
| 122
124
1241 L33 12
m .06
117
.08
48
B- FROM
R-PROCESS
-
198
118
120
120
122
122
124
126
128
128
126
ATOMIC WEIGHT
130
130
132
132
Fig. 17

ORNL-DWG 66-7302
1843
86716721881829
10.0160.0160.1336167167264
LILLI I
10002
ATOMIC NUMBER
E7x100
on) k.0.632
2842
1.7,)
184
186
190
192
188
ATOMIC WEIGHT
Fig. 18
ORNL-DWG 66-11324

دعا
ON (NORMALIZED)
0.02
الببلللللللللللللللللبلايابلابل بلييياليبيا 0
.
01
MASS: 86 90 95 | 10116 120 | 125 130 145 150
ELEMENT: Sr. ZrMo Sn Te Sm
Fig. 19
| 175 | 205
Lu' Pb
ORNL-DWG 66-11784

-
-
CAPTURE FOR KT = 30 kev, room (millibarnes)
5
6
14
7 8 9 10 11 12 13
BINDING ENERGY OF LAST NEUTRON (MeV)
Fig. 20
ORNL-DWG 66-11780

illibarnes)
w
CAPTURE FOR KT = 30
-2 0 2 4 6 8 10
BINDING ENERGY OF LAST ALPHA PARTICLE (MeV)
Fig. 21
.
---
--
-
-
..
.
."
i
-
-
--
.
wy
-
.
y
.
END




DATE FILMED
91 / 8 / 67