1. (Some) Current Topics in Nuclear Astrophysics
XLIX International Winter Meeting on Nuclear Physics, Bormio, Italy
January, 2011
R.E. Tribble
Texas A&M University

3. The Origin of the Elements
Observations provide picture of elemental abundance over time
Baryon to Photon ratio fixes BBN – Li is an anomoly

4. Fate of Massive Pop III Stars
White Dwarf G
Collapse H G
pp-I,II,III
Black Hole H G
CNO, rp 3a
3a->sufficient 12C??
Critical Mass Fraction of C
1E-9 (A. Heger et al. )
1E-10 (Weiss et al. 2000)
1E-12 (Siess et al. 2002)
Explode

5. Updated Reaction Sequences in Pop III Stars
(p,g) rates known;
need (a,g) rates
Rap-I,II and III, substitution
for 3a and CNO!
(Wiescher et al., 1989)

6. The Origin of the Elements
Observations provide picture of elemental abundance over time
Quasars among
oldest stars seen
in universe
Baryon to Photon ratio fixes BBN – Li is an anomoly

7. The Origin of the Elements
Observations provide picture of elemental abundance over time
Must understand nucleosynthesis sites and events to explain the abundances

8. The (radio) active Universe
[22Na decay?]
1 MeV-30 MeV
g-Radiation in Galactic Survey
(26Al Half life: 700,0000 years)
44Ti in Supernova Cas-A Location
(Half life: 60 years)

9. Nucleosynthesis: a multitude of mechanisms: p-p chain reactions, CNO cycle, ...
12C(p,g)13N(b+)13C
13C(a,n) H
p-process
s-process
Capture reactions of charged particles
Capture reactions of neutrons
Fusion reactions between light particles
Photo-dissociation reactions
Radioactive decay processes
electron and neutrino induced reactions
at stellar temperature & density conditions!

10. Radiative p (a) capture at stellar energies
Classical barrier penetration problem
Direct radiative capture
low energies Þ capture at large radii
very small cross sections
define astrophysical S factor:

11. Direct Radiative proton capture
M is:
Integrate over ξ:
ANC Þ amplitude for tail of
overlap function
Low B.E.:
Find:

12. Radiative [p(a)] Capture with resonant and subthreshold states: ANCs
Capture through resonance
resonance
Direct capture
subthreshold state
Capture to ground state
through subthreshold state
Interference effects

13. Techniques to obtain reaction rates in Nuclear Astrophysics
Direct Measurements (LUNA, LENA, DRAGON, . . .)
Radiative widths for resonance rates*
- populate resonance state and measure decay
Coulomb dissociation; Knockout reactions
- applications with RIBs from fragmentation
Trojan Horse Method**
- unique way to understand screening
Asymptotic Normalization Coefficients*
- stable and radioactive beams

14. rp-process nucleosynthesis
Material accreted in binary builds up and eventually undergoes r-p process nucleosynthesis
Pulsar distribution of gamma rays from r-p processing
97-98
2000

15. Explosive H-burning in novae: “22Na puzzle”
- novae: explosive H-burning of accreting material in binaries star-WD. ~ 30/yr.
-  rays from the decay of long-lived isotopes like 26Al have been detected
- E=1.275 MeV  ray following the decay of 22Na predicted, but not observed by space gamma-ray telescopes
NeNa cycle
22Na depletion in novae: how does it happen?
what are the stellar reaction rates for the 22Mg(p,)23Al and 22Na(p,)23Mg?

16. 22Mg(p,g)23Al Reaction Rate S(E) – Direct Capture reaction rate
Mirror Symmetry Þ
S -factor [KeV b]
Reaction Rate (cm3/mole/s)
EC.M [MeV]
T9 (109 K)
r=106 gm/cm3, T9=0.4
22Mg(p,g)23Al competes with b+ rate
but photodisintegration is issue
S(E) – Direct Capture reaction rate

17. E=207 keV => DE=16 keV 5/2+ β+ 22Mg(p,g)23Al β+ p 22Na(p,g)23Mg
Tighe ea, LBL 1995
Perajarvi ea, JYFL 2000
5/2+
23Al (4)s
Qec=12240keV
Proton br. total=?!% β+
22Mg(p,g)23Al β+
?!%
9548
8456
8164
8003
7877 p
IAS: ft=2140 s +/-5%
7803 IAS 5/2+, T=3/2
7787 (7/2)+
6985 5/2+
6575 5/2+
2905 (3,5/2)+
2359 1/2+ NO!
2051 7/2+
450 5/2+
/2+
E=207 keV => DE=16 keV
22Na
Sp=7580 keV
It turned out Tighe et al are wrong! Just noise!
Our exp: first time the two states 7803 and 7787 keV seen in the same experiment. How is the proton decay?
22Na(p,g)23Mg
resonances
Most important:
wg7787=__._? meV
VE Iacob, et al., PRC 74, Oct. 2006
& Y Zhai thesis
23Mg 17

18. 23Al b-delayed p-decay sp – after bkg subtraction
Resonances for 22Na(p,g)23Mg
Gamow window
848
566
263
206
303
1175
344
394
440
E=223 keV IAS
Antti Saastamoinen et al., submitted to PRC
“world record”

19. = studied at TAMU 32Ar 31Ar 33Ar 35Ar 34Ar 36Ar 31Cl 30Cl 32Cl 34Cl
also 38Ca, 46V, 57Cu, 62Ga, …
32Ar
31Ar
33Ar
35Ar
34Ar
36Ar
= studied at TAMU
31Cl
30Cl
32Cl
34Cl
33Cl
35Cl
28S
27S
29S
31S
30S
32S
33S
34S
= planned
25P
27P
26P
28P
30P
29P
31P
23Si
25Si
24Si
26Si
28Si
27Si
29Si
30Si
21Al
22Al
24Al
23Al
25Al
26Al
27Al
24Mg
23Mg
22Mg
21Mg
20Mg
25Mg
26Mg
19Na
20Na
21Na
22Na
23Na
16Ne
17Ne
18Ne
19Ne
20Ne
21Ne
22Ne
14F
15F
16F
17F
18F
19F
Prospects with MARS
stable
12O
13O
14O
15O
16O
17O
18O
used at TAMU
11N
12N
13N
14N
15N
(p,n) possible 9C
10C
11C
12C
13C
14C
15C
(p,2n) possible 8B 9B
10B
11B
7Be
8Be
9Be 19

20. r-Process Nucleosynthesis
Site?? Mechanisms??
Neutrino-driven wind model
Merging neutron star model
(n,)-(,n) equilibrium (binding-energy)
-decay properties (T1/2, Pn values)
Freeze-out (neutron capture)
Issues: neutron source(s); nuclear properties

21. Origin of seed and fuel Hydrogen Burning: 4He, 14N
Helium Burning: 12C, 16O, 22Ne, n, s-nuclei
Carbon Burning: 16O, 20Ne, 24Mg ... s-nuclei

22. 22Ne(α,n) as a neutron source
NACRE lower limit
NACRE upper limit
Present uncertainty
translates into large uncertainty
in s-process element production with
broad consequences for explosive scenarios
of nucleosynthesis such as p-process and r-process

23. To Do Better  underground?
Environmental Radioactivity
Cosmic Rays
background
Requires multi-MeV accelerator
underground – plus shielding

24. Neutron Induced Processes [General Considerations]
Recent focus on observations in metal
poor stars (early generation stars)
Evidence for anamolies in nuclear
synthesis versus conventional models
Expect a lot of interest here in future
Need new ways to obtain information for
(n,2n), (n,g), ...

25. Properties of r-process nuclei
(n,)-(,n) equilibrium (binding-energy)  masses
-decay properties (T1/2, Pn values)
Need to produce these nuclei
in the laboratory!

26. (Operating or Under Construction)
RIB Facilities
(Operating or Under Construction)
Fragmentation: the path to r-process nuclei?

27. RIKEN RI Beam Factory (RIBF)
Experiment facility
To be funded
In phase II
Old facility
Accelerator
SHE
(eg. Z=113)
RIPS
GARIS
SCRIT
60~100 MeV/nucleon
~5 MeV/nucleon
RILAC
AVF
ZeroDegree
SAMURAI
fRC
RRC
SRC
SLOWRI
IRC
RI-ring
CRIB (CNS)
SHARAQ (CNS)
BigRIPS
<10 MeV/nucleon
MeV/nucleon
New facility
Intense (80 kW max.) H.I. beams (up to U) of 345AMeV at SRC
Fast RI beams by projectile fragmentation and U-fission at BigRIPS
Operation since 2007

28. Helmholtzzentrum GmbH
Modular Version
Helmholtzzentrum GmbH
CBM
APPA

29. NSCL to FRIB Project Manager: Thomas Glasmacher
Director: Konrad Gelbke
TPC estimate $614M
CD-4 Range

30. T-REX
[TAMU Reaccelerated Exotics]

31. New facilities in the U. S
New facilities in the U.S. and around the world: a bright future for nuclear astrophysics!

32. Hot CNO Cycle and 13N(p,g)14ONa Ne F O N C 3 4 5 6 7 8 9 10
CNO
Hot CNO (T9=0.2)
Hot CNO (T9=0.4)
Breakout
Reactions
Discuss after POP III
[Precursor to rp process]

33. The nuclear trigger of X-ray bursts 15O(,)19Ne, 18Ne(,p)21Na
Reaction rate determined by single resonance
upper limit lower limit He O C Be Mg Ne 2 8 10 6 4 14 12 18 16
15O(,)19Ne as switch for XRB pattern

34. 22Mg(p,g)23Al from 22Ne + n « 23Ne and mirror symmetry
ANCs for 13C(22Ne,23Ne)12C
p1/2d5/2
=0.849 ± fm-1
p1/2s1/2
=19.2 ± 1.6 fm-1