1. Zs. Fülöp ATOMKI, Debrecen, Hungary
Nuclear astrophysics underground
Zs. Fülöp ATOMKI, Debrecen, Hungary
Interdisciplinary aspects
instruments
networks
Source: EUROGenesis network

2. Nuclear astrophysics in a nutshell
Astrophysical initiatives (mass range, reaction, precision)
Temperature – collision energy
Timeline – nuclear decay properties
+ stellar effects at high temperatures
thermally excited target
+ atomic effects at low temperatures
electron screening
+ high density environment

3. Nuclear physics

4. Nuclear physics + astro

5. Nuclear physics + astro + EU-funding
Source: R. Hirschi

6. Temperature - reaction rate
Nonexplosive scenario:
Low energy
Small cross sections
Extrapolation needed (S-factor)
→ indirect methods
Explosive scenario:
Higher energies
High cross sections
Exotic nuclei (low intensities)
→ RIB
Charged particle reaction cross sections are difficult to measure at astrophysical energies

7. Precision data for solar models
+ CNO
E0 = 21 keV, σ = 7 ·10-13 barn
E0 = 22 keV, σ = 9 ·10-18 barn
Adelberger et al.
Rev.Mod.Phys
1998 → 2011

8. Two approaches to stellar energies
Direct Measurement:
• Low laboratory background
• Low ion beam induced background
• High beam intensity
• High detection efficiency
Direct data for the total cross section at astrophysical energies
Extrapolations:
• Measure level gamma widths
• Measure asymptotic normalization constants (ANCs)
• Measure cross sections at high energies
• R-matrix fit for each transition
Extrapolations for each transition are summed to give the total extrapolated cross section at astrophysical energies

9. Improving the figure of merit
Increase the number of counts in the peak:
Increase the beam current
Increase the target thickness
Increase the detector efficiency
Reduce the background:
Use Compton reduction
Use coincidence technique
Use shielding
Minimum detection limit:
The cross section of a (p,g) reaction, is proportional for the yield of the emitted gammas, and in this cease for the peak area.
From the mathematical statistic, we know. The peak was detected significantly, if its area are more then three times the square root of the background counts under it.
In the nuclear astrophysics we would like to measure small cross sections. An then start the fight with the background.
If you don't have a significant peak, you have to ways to increase the sensitivity.
Increase the peak are, this can be done in an in-beam measurement, with increased current or use a thicker target, or increase the detector efficiency.
The other way is to decrease the background, for example we can go underground. N

10. A unique approach: LUNA @LNGS
Neutrino detection: shield+detector
Nuclear physics: shield+detector+source
Laboratory for Underground Nuclear Astrophysics
50 kV :
( )
400 kV:
(2000…)
d(p,)3He
3He(3He,2p)4He
14N(p,)15O

11. Long term stability  5 eV/h
LUNA aims, tools
1. Direct experiment in Gamow window
2. Reach lower energies with competitive accuracy
3. Improve accuracy at already
reached energies
Preserve excellent background conditions → beam induced bg control
U = 50 – 400 kV
I  500 A for p  250 A for α
Energy spread  70eV
Long term stability  5 eV/h

13. HPGe detector underground

15. Solar Fusion Cross Sections
1998
2011
Adelberger et al, Rev.Mod.Phys % → 5.3% error

16. Underground laboratories: cons
Highly specialized
Long experiments (24/24), overbooked beamtime
Concerns about produced radiation
Limited energy range
Accessibility → manpower
A network of satellite overground labs is needed

17. Overground contribution
Same experiments at higher energies eg 15N(p,γ)
Different experiments at higher energies eg 14N(p,γ)
Feasibility studies (target properties)
Auxiliary experiments (half-lives, stopping power)

18. Experiments at LNGS/LUNA

19. Reaction types → experimental approaches
Radiative capture vs transfer reaction
Gamma detection vs charged particle detection
Low bombarding energy: → Reaction Q-value is dominant in gamma energies

20. First successes at the 50kV machine
d(p,γ)3He, Q=5.5MeV
Gamow-peak

21. Example: the 14N(p,γ)15O reaction
Key reaction of CNO cycle
Neutrino detection by Borexino detector
Age of globular clusters
High Q-value →
cosmic ray induced bg dominant

22. CNO as a source of neutrinos

23. 14N(p,γ)15O: Age of globular clusters

24. Ambiguous extrapolations: 14N(p,)15O
Angulo, Descouvement (2001),
Nucl. Phys A
Schröder et al. (1987)
S(0) = 1.55 ± 0.34 keV-b (Schröder)
R/DC  0
S(0) = 0.08 ±0.06 keV-b (Angulo)

25. LUNA Experiment: lower energies →
better extrapolation
LUNA result
Schröder corrected values
S0gs = 0.25  0.06 keV b

26. Age of globular clusters is longer: +0.7-1 Gyr
Schröder(‘87) [kev-b]
Angulo (’01) [kev-b]
3.2 ± 0.5
1.8 ± 0.2
S0tot = 1.7 ± 0.1 keV b
Phys. Lett. B591 (2004) 61.
Astron. Astrophys. 420 (2004) 625.
Age of globular clusters is longer: Gyr
CNO neutrino flux is smaller (50%)
Science: Contradiction between the age of globular clusters and the universe?
→ more precise observations are needed!! (GAIA)

27. Summing effect 17cm 1 cm Summing peak Simulation R/dc6.79 100%

28. Clover detector underground
High intrinsic background: no problem at high γ energies
Segmentation: reduces summing (43% → 7%)
addback
singles
PHYS. REV. C 78, (R) (2008)
PHYS. REV. C 83, (2011)

29. Total S-factor 14N(p,)15O Ground state transition
- LUNA data
- R-matrix fits
- LENA/TUNL data
- Indirect methods
Effect of the subtreshold resonance lifetime

30. 15O: present status Group Method 6.79 [fs] S(0)GS [keVb] Oxford 1968
DSAM d(14N,n)15O*(6.79)
< 28
n.g.
TUNL 2001
DSAM 14N(p,)15O*(6.79)
1.60.7
LUNA 2004
Cross sect + R-matrix
1.10.5
0.250.06
TUNL 2005
0.30.1
0.490.08
Bochum 2008
< 0.77
LUNA 2008
0.750.2
0.200.05

31. Lifetime of the 6.792 MeV level in 15O studied at AGATA demonstrator by DSAM
14N(p,γ)15O: CNO relevance
Subthreshold level populated in 14N(d,n)15O
Upper limit for lifetime in the fs range
C. Michelagnoli et al, submitted to PRL
Source: D. Bemmerer

32. New challenges Gaia mission (ESA) Improving neutrino statistics
14N(p,)15O: 5% error required!!
S(0)gs 0.06 keV barn

33. 3He(α,γ)7Be and the pp-chain
E0 = 21 keV, σ = 7 ·10-13 barn
E0 = 22 keV, σ = 9 ·10-18 barn

34. 3He(a,g)7Be 7Be7Li*(g) Online: Eγ =1585 keV + Ecm (DC0)
Eγ =1157 keV + Ecm (C0.429)
Eγ = 429 keV
Offline:
Eγ = 478 keV, T1/2=53 d
Low energy laboratory background:
Well shielded detector with low intrinsic background is necessary!!!

35. Low energy 3He(α,γ)7Be activation
Activation vs. in beam approach:
Partly independent (irradiation + off-line γ)
Inherent 4π cross section (no angular effects)
Off-line part can be repeated (long half-life)
Well-known background (no beam induced bg)
No summing problems
Cannot reach “low” energy
A good tool to investigate systematic errors !!! 1 1

36. Complementary Measurements at ATOMKI
Catcher purity investigation overground:
possible DH2+ or DD+ parasitic beam along with 6Li or 10B impurity in beam stop:
6Li(p,)7Be:  = EDH2+=233 keV
6Li(d,n)7Be:  = EDH2+=233 keV
10B(p,)7Be:  = EDH2+=233 keV
 beam and beam stop purity is crucial

38. Result: Before LUNA
Lowest energy (on-line) measurement: Ec.m. = 107 keV (with 17% error)
Lowest energy activation measurement: Ec.m. = 420 keV (with 8% error)
Lowest energy activation

39. After LUNA
LUNA activation: Ec.m. = keV, <5 % precision
LUNA: PRL 97, (2006)

40. ERNA results + advances in theory
Theory: T. Neff: PRL 106, (2011)
ERNA: PRL 102, (2009)

41. The LUNA-MV project LUNA-MV underground accelerator in LNGS
MV single ended
H,He,C
High current
n-shield

42. LUNA-MV timeline
Source: M. Junker

43. Underground movements around the world
China
USA
Source: P.Prati

44. Summary/outlook
Accelerator based nuclear astrophysics is a promising application of nuclear physics
A large variety of nuclear experiments is needed from low to high energy, from stable to radioactive beams, from structure to reactions.
NuPECC recommendation: new accelerator underground (higher energy, heavy ions)
This standalone underground facility should be complemented by overground labs.

45. LUNA members
Laboratori Nazionali del Gran Sasso, INFN, Assergi, Italy: 
Gran Sasso Science Institute, Italy
Osservatorio Astronomico di Collurania, Teramo, Italy
INFN, Padova, Italy
INFN, Roma La Sapienza, Italy
Università di Genova and INFN, Genova, Italy
Università di Milano and INFN, Milano, Italy
Università di Napoli ''Federico II'', Italy
INFN, Napoli, Italy
Università di Torino and INFN, Torino, Italy
The University of Edinburgh, UK
ATOMKI, Debrecen, Hungary
Helmholtz-Zentrum Dresden-Rossendorf, Germany