Critical Nuclear Physics Needs for
Astrophysical Nucleosynthesis Studies
James W. Truran
Physics Division
Argonne National Laboratory
and
Department of Astronomy and Astrophysics
University of Chicago
March 23rd, 2010
Cosmic Nucleosynthesis Perspective
 The Universe emerged from the Big Bang with a composition consisting of hydrogen,
CRL-41
helium, 2D, 3He, and 7Li. The first stars and galaxies were born with this “primordial”
composition.
 The heavy elements with which we are familiar - from carbon and oxygen, to iron, .. to
uranium - are the products of nuclear processes associated with the evolution of stars and
supernovae of Types Ia and II.
 The classic papers by Burbidge, Burbidge, Fowler, and Hoyle (1957) and Cameron (1957)
provided the perspective from which we now view this nucleosynthesis history.
 The respective efforts by Cameron and Fowler to improve the nuclear physics input for
nucleosynthesis studies largely reflect today’s needs for both theory and experiment:
 Fowler and his collaborators focused during the 1950s and 1960s on nuclear
experiments involving light element reactions relevant to early stages of stellar energy
generation - efforts which have established the empirical foundations of stellar
evolution theory.
 Strongly motivated by Paul Merrill’s identification of the presence of technetium in red
giant stars, Cameron focused rather on the mechanisms of heavy element synthesis
and the need for theoretical estimates of reaction rates and other nuclear properties.
“Cosmic” Abundances of the Elements
Signatures of
nuclear systematics:
-particle nuclei are
dominant 12C --- 40Ca
dominance of unstable
 -nuclei decay products:
44Ti44Ca,
48Cr48Ti
60Zn60Ni,
64Ge64Zn
52Fe52Cr,
r-process
Massive Stars & SNe
56Ni56Fe
68Se68Zn, 72Kr72Ge
s-process
nuclear statistical
equilibrium centered on
mass A=56 (56Ni in situ)
neutron shell structure
reflected in the heavy
element region at magic
numbers N=50, 82, and
126 (s- and r-processes)
Outline

Helium Burning Reactions
CNO hydrogen burning in novae and X-ray bursts
Explosive Nucleosynthesis in supernovae: SNe Ia and SNe II
Some interesting long lived radioactivities
Heavy element (A>60) nucleosynthesis mechanisms
s-process
r-process
p-process
Clues from abundance studies
12C
Stellar helium burning proceeds mainly by
the two reactions: 3  12C and 12C(,)16O.
synthesis realized in red giant (AGB)
stars in ‘incomplete’ helium burning
regions (helium burning shells).
beam
target
bubbles
 + 16O --> 12C + 
•Superheated water will nucleate from  and 12C recoils
•The detector is insensitive to -rays from the beam.
•The target density is 1000x higher than that of
previous experiments.
•-ray beam provided by the HIS
facility at Duke University.
•Water has been depleted in heavy
isotopes of oxygen and deuterium.
•Backgrounds such as -emitters can
be rejected effectively.
•First experiment has been
scheduled for April 2010
Outline
Helium burning reactions
 CNO Hydrogen Burning and “breakout:”
Novae and X-ray Bursts
Explosive Nucleosynthesis in supernovae: SNe Ia and SNe II
Some interesting long lived radioactivities
Heavy element (A>60) nucleosynthesis mechanisms
s-process
r-process
p-process
Clues from abundance studies
Novae & X-Ray Bursts: Standard Models
 Classical Novae and X-Ray Bursters
involve thermonuclear explosions in
accreted hydrogen-rich envelopes of white
dwarfs and neutron stars, respectively, in
close binary systems.
 Accretion of matter from their companion
leads to growth of the envelope until a
critical pressure is achieved at its base to
trigger a thermonuclear runaway.
 The violence of the ensuing outbursts
depends strongly on the degree of
degeneracy at the base of the envelope
and the composition of the available
nuclear fuel. The early stages of the
outbursts of both novae and X-ray bursts
witness rapid energy release on a dynamic
time scale, moderated in a critical way by
the operation of the hot (+-limited) CNO
cycles.
Nova V1974 Cygni 1992
X-ray Burst GS 1826-24
Hot CNO Cycles and Breakout Reactions
Break-Out Reactions
14O(
p)17F(p,)18Ne(β+ν)18F(p,α)15O
15O(
CNO Cycles)
)19Ne(p,γ)20Na
(T > 80 million K)
+-Decay Constrained
Implications for: novae and X-ray bursts
Nucleosynthesis Processes
Supernovae
Supernovae?
np-process
10
Courtesy: H. Schatz
Classical Nova Explosions under Extreme Conditions
 Townsley and Bildsten (2004) have shown that their exists a subclass of
nova events occurring on massive white dwarfs accreting at extremely low
rates and characterized by high densities and low central temperatures (T ≈ 5
million Kelvin).
 Glasner and Truran (2009; 2010) have shown that such conditions lead to
violent nova events with peak temperatures exceeding 400 million Kelvin,
such that “breakout” from the conventional CNO cycles can occur. This may
explain the anomalous abundance patterns seen in the ejecta of such systems.
 Glasner and Truran have also demonstrated the sensitivities of breakout to
critical reaction rates in the hot CNO sequences. We find a particularly strong
dependence on the rate of the 15O(α,γ)19Ne and a weaker sensitivity to the rate
of the 14O(α,γ)17F reaction. Also we note a constraint on flow past the iron
peak at 64Ge.
“Breakout,” the 15O(α,γ)19Ne Rate, and Nova Abundances
(The accreted matter was
assumed to include no
elements past oxygen.)
(Glasner and Truran 2009)
Note that heavier elements synthesized in nova events are
observable in nebular remnants > a direct observational test.
(Glasner and Truran 2010)
Outline
Helium burning reactions
CNO hydrogen burning in novae and X-ray bursts
Explosive Nucleosynthesis in SNe Ia and SNe II
Heavy element (A>60) nucleosynthesis mechanisms
s-process
r-process
p-process
Clues from abundance studies
Synthesis of Intermediate Mass and Iron-Peak Nuclei
 Following helium burning, the elements from neon to zinc are
formed in late stages of energy generation (carbon, neon, oxygen,
and silicon burning) in massive stars (M ≥ 10 M) and in
supernovae Type Ia and Type II.
 The critical first step here involves the fusion reactions
12C(12C,p)23Na
and 12C(12C,α)20Ne.
 Currently utilized reaction rates are obtained by extrapolation
from higher energy ranges that do not involve resonances. Recent
experimental investigations of the 12C+12C rate (e.g. Zickefoose et
al. 2010) are focusing on extending the studied region down to the
vicinity of the Gamow window. (See also Spillane et al. 2007).
 Challenges remain to confirm the production levels of
intermediate mass and iron nuclei formed under explosive
burning conditions in Type Ia and Type II supernova events.
COSMIC ABUNDANCES
The abundance history of the “intermediate mass” nuclei Si-Ca relative to “iron-peak”
nuclei (56Fe/56Ni) provides important constraints on SNe Ia and SNe II models.
“Explosive Iron-Peak Nucleosynthesis”
 Explosive nucleosynthesis is a complicated process. The nuclear
products are sensitively dependent upon:
 thermonuclear reaction rates (level densities are critical),
 weak interaction rates (which serve to convert protons to neutrons neutronization - and thereby reduce Ye and decrease the abundances
of proton rich nuclei), and
 the (short) dynamic timescales appropriate to supernovae.
 Cameron (1963) recognized that the products of heavy element
synthesis under explosive conditions were sensitive to the relative rates of
strong and weak interactions and to the timescale on which synthesis
occurred. This has ultimately led to the appreciation of the fact that
the production of iron-peak nuclei in supernovae occurs under
neutron-poor conditions (e.g. Ye ~ 0.5) such that the dominant
products are proton-rich nuclei (e.g. 56Ni).
 Critical input nuclear physics includes experimental and theoretical
rates and/or lifetimes for nuclei near the alpha-line, for both nuclear
reactions and weak interactions.
Why 56Ni ?
56Ni
Production in Explosive Nucleosynthesis
 Pre-explosion compositions involve largely nuclei of Z  N, viz. 12C, 16O,
28Si
(for SNe II).
 Explosive burning at temperatures T > 4x109 K typically occurs on
timescales  seconds.
 Supernova nucleosynthesis sees reactions occurring on a dynamical
timescale. (Experimental rate determinations and Hauser-Feshbach
calculations are critical input.)
 Weak interactions proceed too slowly to convert any significant fraction of
protons to neutrons. (Weak interaction rates are critical input.)
 It follows that the main (in situ) iron-peak products of explosive
nucleosynthesis in supernovae are proton-rich nuclei of ZN, viz. 44Ti, 48Cr,
52Fe, 56Ni, 60Zn, and 64Ge (Cameron 1963; Truran, Arnett, and Cameron 1967).
Explosive Nucleosynthesis of Fe-Peak Nuclei
68Se
72Kr
67As
72Ge
63Ga
69Ga
71Ga
70Zn
64Zn
66Zn 67Zn 68Zn
59Cu
63Cu
65Cu
56Ni 57Ni 58Ni
60Ni 61Ni 62Ni
64Ni
55Co
59Co
52Fe 53Fe 54Fe
56Fe 57Fe 58Fe
51Mn
55Mn
48Cr 49Cr 50Cr
52Cr 53Cr 54Cr
Z
47V
50V
51V
44Ti 45Ti 46Ti 47Ti 48Ti 49Ti 50Ti
40Ca
70Ge
60Zn 61Zn 62Zn

43Sc
64Ge 65Ge 66Ge
45Sc
42Ca 43Ca 44Ca
46Ca
48Ca
Iron peak nucleosynthesis occurs
at Ye≈0.5 in both SNe Ia and SNe II
N 
74Ge
Supernova Nucleosynthesis Contributions
 Type Ia Supernovae: Thermonuclear explosions of CO white dwarfs.
 Type II Supernovae: Core collapse driven events in massive stars.
 In both instances,the formation of iron peak elements in explosive
nucleosynthesis occurs under neutron-poor conditions. This is reflected in
the 56Ni56Co56Fe signatures in both Type Ia and Type II supernova light
curves … and in the isotopic compositions of iron-peak elements in Solar
matter.
SNe Ia
(Iwamoto et al. 1999)
SNe 1987A
(Thielemann et al. 1992)
56Ni
Production in SNe Ia / Nomoto
Neutron
Rich
Matter
56Ni
(Ye ≅ 0)
Intermediate Mass
Elements: Si - Ca
(Timmes, Brown, and Truran 2003)
Interesting Long Lived Radioactivities
 Long lived radioactivities that are products of explosive nucleosynthesis (e.g. 7Be,
22Na, 26Al, 44Ti, 56Ni, 57Ni, 60Fe,
.. 232Th,235U, 238U ..) can test and constrain models. Both
7Be (53.28 d) and 22Na (2.604 a) are anticipated products of classical nova explosions.
Their abundance levels are sensitive functions of the convective/temperature history. The
three long lived actinide isotopes 232Th,235U, 238U constitute important chronometers of the
earliest stages of star formation activity in our Galaxy.
 Supernovae represent the source of the interesting radioactivities 44Ti, 56Ni, and 57Ni in
nucleosynthesis. Detections of gamma rays from 56Ni and 57Ni have informed us both of the
mass of 56Fe in Type II supernova ejecta and of the 56Fe/57Fe ratio emerging from these
events. We also understand the role of 56Ni in powering the light curves of Type Ia
supernovae, utilized as distance indicators.

44Ti
decay gamma rays have been detected from the Cas A Type II supernova remnant
(see figure). The measured flux implies that if 44Ti and 56Ni were formed in a ratio
consistent with the solar 44Ca/56Fe ratio, the Cas A supernova should have been brighter.
Alternatively, the 44Ti may simply have been overabundant relative to mass 56 in that Type
II event (the Ti/Ca ratio seen in halo stars is ≈ 3 times solar). Experimental
determinations of the rates of production and destruction of 44Ti remain critical input.
Outline
 Helium burning reactions
 CNO hydrogen burning in novae and X-ray bursts
 Explosive Nucleosynthesis in supernovae: SNe Ia and SNe II
 Some interesting long lived radioactivities
 Heavy Element (A>60) Nucleosynthesis Mechanisms
s-process
r-process
p-process
Clues from abundance studies
Neutron-Capture Processes of Heavy Element Synthesis
 Our picture of the processes of heavy
element synthesis has become considerably
more complicated with time. Early work
identified the s- and r-processes, with a
relatively small contribution from the pprocess.
 We now understand that there are two
distinguishable contributions (a “weak” and
a “main” component) to both of the
neutron capture processes: the s-process
and the r-process.
 The challenges to theorists include the need
to identify the astrophysical sites in which this
nucleosynthesis occurs and to explain the
distinctive features of the diverse components.
(Cameron 1963)
Neutron Capture Cross Sections: theory/experiment
Rauscher, Thielemann and Kratz (1996)
Truran and Cameron (1965)
Macklin and Gibbons (1957)
Thielemann, Arnould and
Truran (1987)
Bao and Kappeler (1986)
Note systematic trends through
positions of shell closures arising
from level density variations.
Neutron capture cross section uncertainties (Käppeler et al. 2007)
Identifying the r-Process Component in Solar System Matter
Neutron Capture Cross Sections
Search for a Second r-Process
“weak”
r-process
 The robust r-process abundance pattern in
the regime from barium through the actinides
does not extend below mass A ≈ 130,
although the classic r-process model extends
down to mass A ≈ 70. A second component is
thus essential. Two possibilities are:
 the νp-process (Fröhlich 2007)
 an r-process associated with the
mass shells ejected in Type II events
CS 22892-052
Nucleosynthesis Beyond Fe-group: νp-process
 Proton-rich matter is ejected under the
influence of neutrino interactions.
 Nuclei form at distances where a
substantial antineutrino flux is
present.
 True rp-process is limited by slow
decays, e.g. (64Ge).
 Antineutrinos help bridging long
waiting points via (n,p) reactions:
(Frebel et al. 2005)
• With neutrinos
o Without neutrinos
30
Numerical Effects of Rate Variations
Fröhlich, Tang, and Truran (2010)
(p,γ) rates
(n,p) rates
31
Penning Trap Mass Measurements (υp=process regime)
N=Z
CANADIAN Penning TRAP at ANL
Xe
110
Xe
111
Xe
112
Xe
113
Xe
114
I
108
I
109
I
110
I
111
I
112
I
113
N = 50
Te
105
Te
106
Te
107
Te
108
Te
109
Te
110
Te
111
Te
112
Sb
103
Sb
104
Sb
105
Sb
106
Sb
107
Sb
108
Sb
109
Sb
110
Sb
111
52
SHIPTRAP
51
Z = 50
49
JYFLTRAP
48
Sn
100
Sn
101
Sn
102
Sn
103
Sn
104
Sn
105
Sn
106
Sn
107
Sn
108
Sn
109
Sn
110
In
98
In
99
In
100
In
101
In
102
In
103
In
104
In
105
In
106
In
107
In
108
In
109
Cd
97
Cd
98
Cd
99
Cd
100
Cd
101
Cd
102
Cd
103
Cd
104
Cd
105
Cd
106
Cd
107
Cd
108
47
Ag
93
Ag
94
Ag
95
Ag
96
Ag
97
Ag
98
Ag
99
Ag
100
Ag
101
Ag
102
Ag
103
Ag
104
Ag
105
Ag
106
Ag
107
46
Pd
91
Pd
92
Pd
93
Pd
94
Pd
95
Pd
96
Pd
97
Pd
98
Pd
99
Pd
100
Pd
101
Pd
102
Pd
103
Pd
104
Pd
105
Pd
106
45
Rh
89
Rh
90
Rh
91
Rh
92
Rh
93
Rh
94
Rh
95
Rh
96
Rh
97
Rh
98
Rh
99
Rh
100
Rh
101
Rh
102
Rh
103
Rh
104
Rh
105
44
Ru
87
Ru
88
Ru
89
Ru
90
Ru
91
Ru
92
Ru
93
Ru
94
Ru
95
Ru
96
Ru
97
Ru
98
Ru
99
Ru
100
Ru
101
Ru
102
Ru
103
Ru
104
43
Tc
85
Tc
86
Tc
87
Tc
88
Tc
89
Tc
90
Tc
91
Tc
92
Tc
93
Tc
94
Tc
95
Tc
96
Tc
97
Tc
98
Tc
99
Tc
100
Tc
101
Tc
102
Tc
103
42
Mo
83
Mo
84
Mo
85
Mo
86
Mo
87
Mo
88
Mo
89
Mo
90
Mo
91
Mo
92
Mo
93
Mo
94
Mo
95
Mo
96
Mo
97
Mo
98
Mo
99
Mo
100
59
60
41
Nb
81
Nb
82
Nb
83
Nb
84
Nb
85
Nb
86
Nb
87
Nb
88
Nb
89
Nb
90
Nb
91
Nb
92
Nb
93
Nb
94
Nb
95
Nb
96
Nb
97
Nb
98
Nb
99
58
np – process
REFERENCE NUCLIDES
50
40
Zr
78
Zr
79
Zr
80
Zr
81
Zr
82
Zr
83
Zr
84
Zr
85
Zr
86
Zr
87
Zr
88
Zr
89
Zr
90
Zr
91
Zr
92
Zr
93
Zr
94
Zr
95
Zr
96
Zr
97
39
Y
76
Y
77
Y
78
Y
79
Y
80
Y
81
Y
82
Y
83
Y
84
Y
85
Y
86
Y
87
Y
88
Y
89
Y
90
Y
91
Y
92
Y
93
Y
94
Y
95
67
38
Sr
73
Sr
74
Sr
75
Sr
76
Sr
77
Sr
78
Sr
79
Sr
80
Sr
81
Sr
82
Sr
83
Sr
84
Sr
85
Sr
86
Sr
87
Sr
88
Sr
89
Sr
90
Sr
91
Sr
92
55
37
Rb
72
Rb
73
Rb
74
Rb
75
Rb
76
Rb
77
Rb
78
Rb
79
Rb
80
Rb
81
Rb
82
Rb
83
Rb
84
Rb
85
Rb
86
Rb
87
Rb
88
Rb
89
53
54
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
(adapted from C. Weber)
56
32
Main r-Process Nucleosynthesis Contributions
 Significant efforts have been made to understand the extremely
robust r-process abundance pattern observed in the mass range from
barium to uranium that characterizes both Solar matter and the oldest
(and r-process rich) stars in our Galaxy’s halo.
 This robustness strongly suggests – perhaps even demands – that
significant fission recycling enables an approach to a stable pattern.
This emphasizes the need for a more reliable treatment of fission
including an understanding of the fragment distribution.
 Critical nuclear input also includes masses (SN) for nuclei along
the capture path, a more refined treatment of nuclear level densities,
greater predictability of the behavior near shell closures, and a
more extensive study of the beta-decay systematics of deformed
nuclei (Möller, Nix, and Kratz 1997).
CPT Fission Fragment Measurements
New CPT /
Previous CPT
measurements




Ongoing program of measurements since March 2008, target 15 keV uncertainty
38 species, 31 have never been measured by method other than β-endpoint
Typically improved precision by factor of 5-10
Adds to 30 measurements taken at CPT in past years with small gas catcher and
source
“Site-ing” r-Process Nucleosynthesis
Helium Shells
of SNe II
Neutron StarNeutron Star
Collisions
R-Process
Models
Identification of the r-process
sites remains a major challenge.
Low Mass
( Prompt Expl.)
SNe II
n- Driven Winds
SNe II
Synthesizing the r-Process Mass Region A = 110-238
Farouqi et al. (2010) r-process calculations in the context of the ‘high entropy
wind’ model for two choices of mass model. The possibility of achievement of
such high entropy conditions in Type II supernova environments remains a
challenging issue (Panov and Janka 2009).
Calculated Fit to Solar r-Process Pattern
Kratz et al. (2004)
Synthesizing the r-Process Mass Region A = 110-238
 The two most obvious constraints imposed on the r-process mechanism(s) by
spectroscopic studies are: First – that there exist at least two distinct astrophysical
sites. Second – that the process responsible for the synthesis of elements past Z = 56
is quite exttraordinarily robust. This points to fission recycling. Panov et al. (2004)
provide beta-delayed and neutron-induced fission rates and argue that fission leads to
the termination of the r-process. Petermann et al. (2009) have performed
representative r-process calculations for different neutron-to-seed ratios that provide
a measure of the importance of fission recycling to the robustness of this process.
Panov et al. (2004)
Petermann et al. (2009)
Fission Product Yields from Californium 252Cf Source at ANL
78Ni
(110 +100 -60 ms)
(Hosmer et al. 2005)
(162 ±30 ms)
(Hannawald et al. 2001)
130Cd
Concluding Remarks-I
 The nuclear physics input requirements for nucleosynthesis studies continue to
reflect the importance of both experimental studies of identified “critical” reaction
links and theoretical studies built upon statistical properties of nuclei.
 In the light mass regime, the 12C(α,γ)16O reaction is of particular importance.
The triple-alpha reaction and the 12C + 12C reaction also warrant further
experimental scrutiny.
 Studies of “breakout” from the hot CNO cycles, relevant to both X-ray bursts
and novae, will be greatly helped by an improved experimental determination of
the rate of the critical 15O(α,γ)19Ne reaction.
 Calculations of nucleosynthesis of Ne to Zn nuclei in massive stars and both
SNe II and SNe Ia are sensitive both to nuclear reaction rates and to weak
interaction rates. Both experimental and theoretical efforts are required.
Observations of halo stars provide clues to and constraints upon the ratio of
intermediate mass nuclei (Si-Ca) to iron peak nuclei while the range in peak
brightness of SNe Ia also reflects variations in the 56Ni/(Si-Ca) abundance ratio.
Concluding Remarks-II
 In the regime past the iron peak, a number of processes can contribute. We now know
that both the s-process and the r-process patterns demand contributions from at least two
different sites.
 A critical factor historically has been the separation of the s- and r-components using
theory together with experimental neutron capture cross determinations. This may be more
complicated in the mass regime A ≅ 60-90 where two s-process contributions may overlap.
The dependence of the ‘weak’ s-process on neutron capture cross sections has recently been
examined by Pignatari et al. (2010).
 The sites of the two (?) r-process contributions remain to be identified as do the range of
physical conditions that they may reflect. Required experimental studies include both mass
determinations on the proton-rich side relevant to the operation of the νp-process in the mass
range A ≅ 60-100 and those on the neutron-rich side relevant to determination of the betadecay timescales at the waiting points along the r-process path in the vicinity of e.g. 130Cd,
critical to the fission recycling that yields a robust r-process pattern in the extended mass
range A ≅ 130-238 such as is observed in “r-process rich” and iron-poor halo stars. Further
theoretical studies of beta-delayed and neutron-induced fission are also of interest.