Nuclear astrophysics
A survey in 3 acts
Jeff Blackmon, Physics Division, ORNL
Nuclear physics plays an important role in astrophysics:
Energy generation
astronomical observables
Synthesis of elements
I
1. Introduction
2. Big Bang
3. Stellar structure & solar neutrinos
II
4. Stellar evolution & s process
5. Supernovae & r process
III 6. Binary systems: Type Ia, novae, x-ray bursts
Interdisciplinary research
A variety of new tools in many areas are driving progress
Laboratory measurements
New beams &
experimental
techniques
Observations
New orbiting
instruments,
increased optical
power, presolar
grains
Nuclear theory and data
Improved shell
model, reaction
theory, rates,
libraries &
dissemination via
the web
Astrophysics
Advancing
computing
power more
realistic
simulations
Solar system abundances
log (abundance)
One of the most fundamental
and important observables
This year
marks the 50th
anniversary of
“B2FH”
Mass
Nuclear reactions in the lab & in space
What you are used to in the lab:
cross section
reactions/s
reactions ions atoms


2
s
s cm
ions/s
atoms/cm2
reaction rate
reactions
nx ny

v v  v dv

3
3
3
cm s
cm cm
In astrophysical events:
3/2
 v 2 



2
 v   4 v 
 exp

2kT 
 2kT 

reactions n x n y

v
3
3
3
cm s
cm cm

v 

kT  EeE /kT dE

8
3/2
0
The Coulomb barrier
Energy of particles in astrophysical
environments is much lower than the
Coulomb barrier
Vc 

1.44Z a Z b
MeV·fm
r
T (106 K) kT (keV)
Reaction
site
rturn (fm)
r (fm)
p+p
sun
15
1.3
1100
2.5
p+14N
CNO
30
2.6
3900
4.3
+12C
red giant
190
16
1060
4.8
p+17F
nova
300
26
500
4.5
+30S
x-ray burst
1000
86
500
5.9
3He+4He
big bang
2000
170
33
3.8
The Gamow window

kT  EeE /kT dE

8
v 
3/2
0
S 
 e
E
v 
2
EG 
EG / E

2
kT  Se

8
3/2
Z Z e 
2 2
1
2
EG / E E /kT 
e
dE
0

T (106 K) kT (keV)
Reaction
site
rturn (fm)
r (fm)
E0 (keV)
p+p
sun
15
1.3
1100
2.5
6
p+14N
CNO
30
2.6
3900
4.3
42
+12C
red giant
190
16
1060
4.8
300
p+17F
nova
300
26
500
4.5
230
+30S
x-ray burst
1000
86
500
5.9
1800
3He+4He
big bang
2000
170
33
3.8
580
Why the S-factor is useful
Example: 3He(,)7Be
Important for:
The sun ( production)
Big Bang (Li production)
Rolfs&Rodney, p. 157.
Data from Kräwinkel et al.,
ZPA 304 (1982) 307.
Limit of experiments
Need  here for sun
But be careful…
Identifying resonances is crucial

kT  EeE /kT dE

8
v 
3/2
0
 E   
2
GxGy
2J  1
2Jx  12Jy  1 E  E r 2  G /22
 2   p2 
Gp  2
 2
2 

R
F

G



Keiser, Azuma & Jackson,
NPA331 (1979) 155.
Lecture 3
Gp>>G
If resonance is narrow
G>>Gp
2 
v   kT
 

3/2
 

2
 eE
GxGy
2J  1
2Jx  12Jy  1 G
“resonance strength”

r
/ kT
Solving a reaction rate network
The CN cycle: hydrogen burning
dN12C
 N15N N p v
dt
Identify important reactions
14O
15O
1m
2m
16O

13N
14N
10 m
12C
15N

13C
Network of many coupled equations
15Np
 N12C N p v
12Cp
dN13N
 N12C N p v 12Cp  N13N N p v 13Np  13N N13N
dt
dN13C
 13N N13N  N13C N p v 13Cp
dt
dN14O
 N13N N p v
dt
13Np
 14O N14O
dN14N
 N13C N p v 13Cp  14O N14O  N14N N p v
dt
dN15O

 N14N N p v 14Np  15O N15O
Nuclear physics  reaction rates
dt
 the
Astrophysical model to define
dN15N
 15O N15O  N15N N p v 15Np
equations of state: , T
dt

Numerically solve for Nx(t)
14Np
The Early Universe
Space, time, matter, & energy began with the Big Bang
Independent observations tell us about different epochs
Nucleosynthesis
Light Elements Formed
CMB -The afterglow
Stellar observations
New Cosmological Paradigm
(Lecture 3)
WMAP: CMB Observations
Type 1a supernova
redshift vs.
distance indicates
the expansion
rate of the
universe is
accelerating
DARK ENERGY (e.g. cosmological constant) exerts a
“negative pressure” causing the acceleration
Only 4% of matter is baryonic  test with nucleosynthesis
The Homogeneous BBN Model
proton
neutron
proton
2H
3He
neutron
2H
3He
4He
7Be
Assume adiabatic expansion ( flavors)
n/p ratio set by weak strength (n half-life)
Only free parameter is baryon/photon ratio
~All free neutrons into 4He
Mass 5 & 8 gaps inhibit formation of heavy elements
7Li
p ~75%
4He ~25%
2H,3He ~ 10-5
7Li ~ 10-10
A Typical Big Bang Network
Solve the reaction rate network
start
1
Time (sec)
100
300
finish
p
4He
d
3He
7Li
final
abundances
proton
neutron
d / H abundance ratio
2H
3He
4He
7Be
Theoretical
Abundance
Prediction
7Li
 = baryon / photon
Abundance Observations can be used to constrain the “normal” matter
density - the free parameter in the theory - independent of WMAP
Quasi-Stellar Object (QSO)
(absorbs light)
hydrogen
deuterium
D / H = 2.78 ± 0.4 • 10-5
d / H abundance ratio
“Primordial” Interstellar
Gas Cloud
Deuterium
abundance
observations
10-10
Theoretical
Abundance
Prediction
range of densities
consistent with
observations & theory
Keck Telescopes
 = baryon / photon
Abundance Observations can be used to constrain the “normal” matter
density - the free parameter in the theory - independent of WMAP
7Li: good constraint
relatively weak constraint
on baryonic matter
but good observations?
density
H abundance ratio
7Li
/ H = 1. 0 – 1.6 • 10-10
7Li /
Yp = 0.242 ± 0.002
4He
mass fraction
4He:


Comparing Matter Density Constraints
using 4He
Disagrees with WMAP
using 7Li
Disagrees with WMAP
WMAP
“Gold Standard”
Highest precision
Independent of
how light
Elements formed
in Big Bang
using 2H
Agrees with WMAP
Precision needs
improvement
1
2
3
4
5
6
• 1010 ~ normal matter density
7
8
Is our understanding of dark energy / dark
matter is wrong?
Are our observations / interpretations
New online suite of cosmology codes under
development at bigbangonline.org
Enables users to run and visualize BBN calculations with
choice of reaction rates
choice of primordial abundance observations
choice of standard BBN or some non-standard variants
Hydrogen burning in stars
Hydrostatic equilibrium
dP r
GMin rr

dr
r2
G
Energy conservation
DP


Large T,P gradient

dLr r r

dr
4 r 2
Pressure
P(r)  Pgasr  Prad r
For sun (non-degenerate)
k
Pgasr 
rT r
m
1
Prad r  aT 4 r  Pgas(r)
3
Opacity: photons
absorbed and
emitted at shorter 

Luminosity/opacity/T relationship

LM4
The sun
M=2x1030 kg
(0)=150 g/cm3
T(0)=1.5x107 K
T(surf)=5800 K
L=3.8x1026 W
5x104 yr for
energy produced
in sun’s core to
be radiated at
surface
Solar power:
Thanks to substantial efforts in experiment, theory & evaluation
5%
5%
7%
7%
13%
5-10%
6x109 e/cm2/s
only direct probe
of solar core
Homestake
Homestake
Super-K
2002 Nobel Prize
Davis & Koshiba
Radiochemical
Real-time counting
Homestake
Super-K
1967
Homestake Gold Mine
600kt perchloroethylene
100 events/yr
37Cl+  37Ar+e
e
~30% expectations
1996
Mozumi Mine
50,000 kt water
5,000 events/yr
e+ e- scattering
~40% expectations
SNO & SuperK measure only neutrinos from the decay of 8B
SNO
Flux measurements determine
neutrino properties

1998
Creighton Nickel Mine
1 kt heavy water
x + d  p + n
7Be(p,)8B
A accurate value for the predicted 8B neutrino flux is need
for comparison to the current generation of measurements
SuperK CC = (2.39  0.03stat  0.06sys) x 106 /(cm2s)
SNO NC = (5.21  0.27stat  0.38sys) x 106 /(cm2s)
SSM = 5.7 x 106 /(cm2s)
 ~15%
metallicity
reaction rates
Flavor oscillation
•
Neutrino mass eigenstates not the same as flavor
eigenstates
In vacuum
•
1.27Dm 2 eV 2 Lkm

P       sin 2 sin 


E v GeV 


2
2
Strong evidence from observations of atmospheric
neutrinos (  )

•
Observed in reactor experiments: KamLAND & Chooz
•
Oscillations of solar (8B) neutrinos are enhanced by
interactions with the high density of electrons in the
solar core MSW: Mikheyev & Smirnow, SJNP 42 (85).
Wolfenstein, PRD 17 (78).
7Be
KamLAND
pp = Next-generation
CLEAN
LENS
7Be
P(e)
= Focus of current
experiments
KamLAND
Borexino
pp
“There are rare moments in science when a clear
road to discovery lies ahead and there is broad
consensus about the steps to take along that path
This is one such moment.”
October 2004
One of the 3 major
recommendations
• The pp neutrino flux is accurately predicted by the solar luminosity.
• pp neutrinos oscillate (primarily) by vacuum oscillations not MSW oscillations.
• Would provide a clear test of solar physics, hydrostatic equilibrium, etc.
• Is the sun’s energy output now the same as 50,000 years ago?
Measuring the pp flux: CLEAN
McKinsey & Coakley, Astroparticle Physics 22 (2005) 355.
Very high purity liquid Ne or Ar
Thin film of shifting flour in front of PMTs
Good recoil/electron discrimination
Very low threshold (few 10’s keV)
130 ton device proposed (either SNO-Lab or DUSEL)
MiniCLEAN now operating
65 liters
LENS: e from pp fusion
#1 prompt electron
 e energy (-like)
Buffer up to 10s
signal #1
signal #2
Shower
Time/space correlation
discrimination
Now: 8% In-loaded scintillator
Background
2x 115In decays
1 mimics prompt e
1 mimics  cascade
 high segmentation
air
3D array of transparent cells
(~6 m)3 fiducial volume = ~15 tons In
~ 500 pp events/yr
In-loaded
scintillator
Nuclear Physics Laboratory Measurements
beam
ion source
small
accelerator
detectors
target
Directly measure cross sections in the lab at the lowest
possible
energies energy range ~ 10 keV to 3
Bombarding
MeV (~ mA)
High currents
Long run times
Efficient detectors to obtain high
statistics
Pure, stable targets
Absolute cross section
measurements
Good normalization & careful
control of systematic
LNGS
LNGS
ROME
QuickTime™ and a
Photo - JPEG decompressor
are needed to see this picture.
Laboratory space adjacent
to highway tunnel
1400 m rock coverage
cosmic µ reduction= 10–6
µ rate ~ 1 (/m2 h)
Low-energy accelerators at LNGS
50 keV accelerator
First 
measurements
in solar
Gamow widow
3He()7Be
3He(3He,2p)
R. Bonetti et al., PRL
82 (1999) 5205.
with
400 keV accelerator
3He()7Be
@ LUNA
Gy. Gyürky, PRC 75 (2007) 035805.
PRL 48 (1982)
PRC 27 (1983)
ZPA 310 (1983)
PRL 93 (2004)
7Be(p,)8B
at Seattle
450mm2,Ep=305 keV
Junghans et al., PRC
68 (2003) 065803.
7Be Target
Rotating target
arm
Faraday Cup
150mm2,Ep=305 keV
22.3 ± 0.7 eV barn
Si detectors
Extraordinary
control over
systematic
uncertainties.
22.1 ± 0.6 eV barn
Proton beam going
through LN2 trap
New Coulomb dissociation result
Schumann et al., PRC 73 (2006) 015806.
Change in S17(E)
20.60.81.2 eV b
Schumann (CD 2006)
Trache (Glauber 2004)
Davids & Typel (CD 2003)
Junghans et al.
Schumann (CD 2003)
Azhari (ANC 2001)
Recent 7Be(p,)8B results
Evaluated S17 (eV b)
Junghans PRC 68 (2003) 065803.
21.40.50.6
Davids & Typel PRC 68 (2003) 045802. 18.60.41.1
Cyburt et al., PRC 70 (2004) 045801.
19.3  21.4
with ~ 6-7% 
• Precision has been significantly improved.
• Some questions remain.
• Additional high-precision measurement(s) are desired.
Solar power:
Thanks to substantial efforts in experiment, theory & evaluation
5%
5%
7%
7%
13%
5-10%
log (abundance)
Act I
Act II: Stars and their
catastrophic deaths
Mass