sensitivity studies for
r-process nucleosynthesis
Rebecca Surman
Union College
University of Notre Dame
ARIS 20142014 June 4

R Surman
ARIS 20142014 June 4

r-process nucleosynthesis

β(n, γ )(γ ,n)€€

N=50	  	  	  	  	  	  	  	  	  N=82	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  N=126	  	  	  	  rare	  earth	  peak	  abundances from
Anders and Grevesse (1988)

r-process observations

R Surman
ARIS 20142014 June 4

Observations suggest
the r-process site:• produces a robust
A>130 abundance
pattern• was in operation earlyin galactic history

Cowan et al (2011)
Roederer & Lawler (2012)r-process astrophysical site: compact object mergers?

R Surman
ARIS 20142014 June 4

neutron star-neutron star or
black hole-neutron starmergers

Goriely et al (2012)

Korobkin et al(2012)

e.g., Lattimer & Schramm (1974, 1976), Meyer (1989), Frieburghaus et al (1999), Goriely et al(2005), Wanajo & Ishimaru (2006), Oechslin et al (2007), Nakamura et al (2011), Goriely et al(2012), Korobkin et al (2012), Rosswog el at (2013), Wanajo et al (2014)

r-process astrophysical site: core-collapse supernovae?

R Surman
ARIS 20142014 June 4

supernova neutrino-driven windPNS

νlate-time ν fluxes from Keil et al (2003)

p + ν e ↔ n + e+n + ν e ↔ p + e−e.g., Meyer et al (1992), Woosley et al (1994), Takahashi et al (1994), Witti et al (1994), Fuller &Meyer (1995), McLaughlin et al (1996), Meyer et al (1998), Qian & Woosley (1996), Hoffman et al(1997), Cardall & Fuller (1997), Otsuki et al (2000), Thompson et al (2001), Terasawa et al (2002),Liebendorfer et al (2005), Wanajo (2006), Arcones€
et al (2007), Huedepohl et al (2010), Fischer et al(2010), Roberts & Reddy (2012), Wanajo (2013), Martinez-Pinedo et al (2014), etc.

r-process astrophysical site: current status

Compact object mergers have plenty of neutrons, but may not
evolve on short enough timescales to explain the halo star data
Core-collapse supernovae evolve on the correct timescale toexplain the halo star data, but may not produce enough neutrons

R Surman
ARIS 20142014 June 4r-process abundance pattern: site vs nuclear data

Nuclear masses

iven astrophysical conditions,omparison of abundances
ased different mass models‣ FRDM (Möller et al. 1995)

Mumpower, Cass, Passucci,
Surman, Aprahamian (2014)

hot wind

Arcones & Martinez-Pinedo, 2011

neutron star merger
hot windcold wind

R Surman
ARIS 20142014 June 4

classic (n,γ)-(γ,n) equilibrium r processequilibrium path:
3/2(*2 % ,"*ρ N AYn 2π Sn ( Z, Apath ) ~ −kT ln )$' *+ 2 # mn kT & *.

steady beta flow:λβ ( Z, Apath ) Y ( Z, Apath ) ~ constant

R Surman
ARIS 20142014 June 4

freezeout from (n,γ)-(γ,n) equilibrium

R Surman
ARIS 20142014 June 4 rare earth peak forms main peaks can shift, spread,or narrow

Mumpower, McLaughlin, &Surman (2012)

Surman & Engel (2001)

R Surman
ARIS 20142014 June 4

freezeout and nuclear data

Mumpower, McLaughlin, and Surman, PRC(2012)

HFB-17FRDM
β decay contours
neutron separation energy
contours

no REP formation

mercury isotopes [46].
SPY has now been applied to all the neutron-rich nucleiof relevance for r-process nucleosynthesis. It is found that
the A ’ 278 fissioning nuclei, which are main progenitorsof the 110 & A & 170 nuclei in the decompression of NSmatter, present an unexpected doubly asymmetric fission
mode with a characteristic four-hump pattern, as illustrated
in Fig. 2. Such fragment distributions have never been
observed experimentally and can be traced back to thepredicted potential energies at large deformations of
the neutron-rich fragments favored by the A ’ 278 fission.
The two asymmetric fission modes can also be seen on thepotential energy surface (Fig. 3) obtained from a detailed
microscopic calculation [50] for 278 Cf in the deformation
subspace (elongation hQ^ 20 i, asymmetry hQ^ 30 i). This calculation uses a state-of-the-art mean-field model with theGogny interaction. The two fission valleys indicated byarrows in Fig. 3 lead to asymmetries similar to the distributions presented in Fig. 2 obtained with SPY. The

freezeout and nuclear data

[Fig. 1(a)] prohibiting the formation of super-heavy nuc
R Surmanand recycling the heavy material into lighter
fragmenARIS2014
which restart capturing the free neutrons. Fission
recycli2014 June 4
can take place up to three times before the neutrons
exhausted, depending on the expansion time scales. Wh
20
Mumpower,
McLaughlin,and Surman,
the neutron density
drops below
some 10PRC
cm"3 , the ti(2012)
scale of neutron capture becomes longer than a few s
onds, and the nuclear flow is dominated by ! decays ba
HFB-17to the stability line (as well as fission and " decay forheaviest species). The final abundance distribution of
3 $ 10"3 M% of ejecta during the NSM is compared w
the Solar System composition in Fig. 4. The similar
between the solar abundance pattern and the prediction
the 140 & A & 180 region is remarkable and strong
suggests that this pattern constitutes the standard signatu
of r processing under fission conditions.

100

Solar

10-3

FRDM
β decay contours
neutron separation energy
contours

Mass fraction

10-1

10

10-4-2

140

150

160

170

180

10-3
10-4

Goriely et al (2013)

80100

no 140
REP
160formation
180 200 220 240

120

Ar-process sensitivity studies

R Surman
ARIS 20142014 June 4

Choose a baseline simulation
Vary one piece of nuclear data by a set amount, rerun the simulation,and compare the final abundance pattern to the baseline
Repeat for each nucleus in the network
neutron capture rates
Beun, Blackmon, Hix, McLaughlin, Smith, Surman, J. Phys. G (2008)
Surman, Beun, McLaughlin, Hix, PRC (2009)
Surman, Sinclair, Hix, Jones, Mumpower, McLaughlin, CGS-14 (2011)
Mumpower, McLaughlin, Surman, PRC (2012)
Surman, Mumpower, Sinclair, Jones, Hix, McLaughlin, AIP ‘Stardust’ (2014)
masses/neutron separation energies
Brett, Bentley, Paul, Aprahamian, Surman, EPJA (2012)
Surman, Mumpower, Cass, Aprahamian, ICFN5 proceedings (2013)
Aprahamian, Bentley, Mumpower, Surman, AIP ‘Stardust’ (2014)
beta decay rates
Cass, Passucci, Surman, Aprahamian, NIC proceedings (2012)
Mumpower, Cass, Passucci, Surman, Aprahamian, AIP ‘Stardust’ (2014)
masses/capture rates/beta decay rates
Surman, Mumpower, Cass, Bentley, Aprahamian, McLaughlin, INPC proceedings(2013)

R Surman
ARIS 20142014 June 4

nuclear data uncertainties far from stability
one-neutron separation energies
for the tin isotopes, compared toFRDM values

PETER MÖLLER, BERND PFEIFFER, AND KARL-LUDWIG KRA
104
β− decay (Theory: GT)

103
102
101
100Tβ,calc /Tβ,exp

10 − 1Brett, Bentley, Paul, Aprahamian,Surman, EPJA (2012)10 − 210 − 3104
103

Total Error = 3.73 for 184 nuclei, Tβ,exp < 1 s
Total Error = 21.16 for 546 nuclei (13 clipped), Tβ,exp < 1000 sβ− decay (Theory: GT + ff)

102
101
100
10 − 1Möller et al (2003)

10 − 2

Total Error = 3.08 for 184 nuclei, Tβ,exp < 1 s
Total Error = 4.82 for 546 nuclei, Tβ,exp < 1000 s

10 − 310 − 3

10 − 210 − 1100
101102
Experimental β-Decay Half-life Tβ,exp (s)103r-process sensitivity studies: β-decay rates
hot wind r processparameterized as in Meyer (2002)
with s/k = 100, Ye = 0.25
F = 100 × ∑ X baseline (A) − X(A)Aequilibrium phase only

full simulation

Surman et al (2013)

R Surman
ARIS 20142014 June 4

R Surman
ARIS 20142014 June 4

r-process sensitivity studies: β-decay rates
hot wind r processparameterized as in Meyer (2002)
with s/k = 100, Ye = 0.25
F = 100 × ∑ X baseline (A) − X(A)Aequilibrium phase onlypreliminary
full simulation

Surman et al (2013)

R Surman
ARIS 20142014 June 4

r-process sensitivity studies: nuclear masses
cused on the uncertainties of nuclear inputs individually.
For instance, neutron separation energy and binding energy studies where mass influences have not been propagated to other properties have been performed in thecontext of both supernova and neutron star merger r
process scenarios [14, 15]. Individual neutron capture
rates have been studied in the context of both weak [16]and main r-process components [17–19]. Studies of betadecay rates have been performed around closed neutron
shells [20, 21] as well as for main r-process components[22]. In all of these studies the most influential nuclei are
populated either during equilibrium or during the laststage of the r process known as ‘freeze-out’, when nuclei decay back to stability. For a main r process theseimportant nuclei are found to lie near closed shells andin the rare earth region A ⇠ 160. Here we perform acomplete sensitivity study of nuclear masses focusing on
nuclei near the N = 82 shell closure.
In an r-process wind, extreme conditions activate nuclear reactions and can potentially produce equilibrium
between neutron captures and their inverse reaction,
photo-dissociation. In a ‘hot’ wind this equilibrium occurs for a long duration whereas in a ‘cold’ wind theequilibrium is short lived or non-existent [23]. Equilibrium occurs when temperatures are high and so -decays
which move the nuclear flow to higher atomic number,Z, control the timescale for heavy element production.
Nuclear masses are particularly important during thisphase as they directly set the r-process path along withthe temperature and density. In this special case, theabundances along an isotopic chain can be computed via
the nuclear Saha equation [2]. Once the supply of freeneutrons is consumed the r-process path, or set of mostabundant isotopes, begins to move back to stability. Thecriterion of neutron exhaustion signals the start of thefreeze-out phase of the r process in which key abundance

Neutron capture

Separation energy

β-decay

Pjna change in the mass of nucleus (Z, A) also modifies:neutron separation energies for (Z, A) and (Z, A+1)
neutron capture rates for (Z, A) and (Z, A-1)

beta decay rates for (Z, A) and (Z-1, A)
1: Shows A+3)
the quantities of neighboring nuclei of impo
beta-delayed neutron emission probabilities for (Z-1, FIG.
A)-(Z-1,
tance to the r-process that are altered by a change in mass
nucleus with Z protons and N neutrons.

tion (AME) [32]. We use these theoretical masses for anuclei in our network since an artificial jump would bintroduced by attempting to supplement with measuremasses. This is also why our results show sensitivitie
for known masses in the 2012 AME despite some bein
known to better than 100 keV.
In our study when a nuclear mass is varied we reca
culate all the relevant nuclear properties of neighborin
nuclei that depend on the changed mass. Specifically,
the mass of a nucleus (Z,N ) with Z protons and N neu
trons is varied then it leads to changes in the neutro
Mumpower,
capture rates of (Z,N) and (Z,NFang,1), the separatioenergies of (Z,N )Surman,and (Z,N +1), the -decay rates oBeard,(Z,N ) and (Z 1,N+ 1), and -delayed
neutron emi
Aprahamian,
submitted
sion probabilities of (Z,N ), (Z 1,N + 1), (Z 1,N + 2(2014)(Z 1,N + 3), (Z 1,N + 4) and (Z 1,N + 5). This
shown visually in Fig. 1.
Nuclear masses go into the calculation of neutron cap
ture rates via the dependence on separation energy o
the compound nucleus and reduced mass. The separar-process sensitivity studies: nuclear masses
Mumpower, Fang,Surman, Beard,
Aprahamian, inpreparation

R Surman
ARIS 20142014 June 4r-process sensitivity studies: nuclear masses

R Surman
ARIS 20142014 June 4

Mumpower, Fang,Surman, Beard,
Aprahamian, in
preparation

preliminary

Mumpower, Fang,Surman, Beard,
Aprahamian, in
preparation

r-process sensitivity studies: β-delayed neutron emission
hot wind r processparameterized as in Meyer (2002)
with s/k = 100, Ye = 0.25
F = 100 × ∑ X baseline (A) − X(A)
ASurman and Mumpower,in preparation

R Surman
ARIS 20142014 June 4

β-delayed neutron emission: instantaneous freezeout

no bdnewith bdne
Surman and Mumpower,in preparation

R Surman
ARIS 20142014 June 4

β-delayed neutron emission: dynamical freezeout
hot wind, fully dynamical calculation

no bdnewith bdne
Surman and Mumpower,in preparation

hot wind, instantaneous freezeout

R Surman
ARIS 20142014 June 4

β-delayed neutron emission: dynamical freezeout
hot windno bdnewith bdne
Surman and Mumpower,in preparation

cold wind

R Surman
ARIS 20142014 June 4

key Pn values

R Surman
ARIS 20142014 June 4

hot r process

Here BDNE isswitched off forranges of nuclei(0-5, 5-10, 10-15,etc. neutronsfrom stability)

cold r process

Surman and Mumpower,in preparation

summary

R Surman
ARIS 20142014 June 4

The site of the r process remains one of the greatest mysteries ofnuclear astrophysics
After decades of progress the question is still unanswered: mergers orsupernovae? (or both??)Advances in spectroscopic observations, radioactive beam
experiments, and the nuclear theory of neutron-rich nuclei haveopened up a new avenue of approach to solving this mystery
Once nuclear physics uncertainties are reduced, we can exploit how
the abundance pattern is finalized during freezeout to constrain the rprocess astrophysical conditions