1. Experiments in Explosive Nuclear Astrophysics
PJ Woods, University of Edinburgh

2. Puzzle of the origin of heavy ‘p-nuclei’ – abundant proton-rich isotopes eg 92Mo and 96Ru
Supernova shock
passing through
O-Ne layers of
progenitor star

3. Predicted p-process abundances relative to observed abundances
Arnould & Goriely Phys. Rep. 384,1 (2003)

4. Reaction peak observed!
Study of 96Ru(p,γ) reaction using decelerated beams on ESR at GSI (M Heil, R Reifarth)
Reaction peak observed!
σ(p,γ)= 3.6(5) mb
Edinburgh DSSD strip detectors measure recoiling reaction products:
will use technique next year with detectors inside ESR vacuum
ultimate goal to use RIB on NESR for next phase of FAIR

5. …..with injection of RIBs from an ISOL the deceleration phase can be avoided and reactions performed directly at astrophysical energies

6. Galactic abundance distribution of the cosmic
γ-ray emitter 26Al
INTEGRAL Measured abundance 2.8(8) Solar Masses
[R. Diehl, Nature 439, 45(2006)]

7. Supernova Cycle

8. Main Origin of 26Al in massive stars
3 Mechanisms:
convective hydrogen burning in Wolf-Rayet stars followed by ejection by stellar wind
convective Carbon shell burning followed by ejection from core collapse supernova
explosive Ne/C burning in core collapse phase of supernova

9. 25Al(p,g)26Si: E922 (A.Chen) DRAGON
MgAl cycle
26gAl(p,g)27Si, 26mAl(p,g)27Si: E989,E990 (C. Ruiz and A. Murphy) DRAGON and TUDA
25Al(p,g)26Si: E922 (A.Chen) DRAGON 26 27 28 Si Si Si
2.21s
4.16s 25 26 27 Al Al Al
7.18s
0.717Myr
6.35s 24 25 26 Mg Mg Mg
1.809 MeV

10. H fusion reactions at stellar energies
Gamow peak
tunnelling through
Coulomb barrier
 exp( )
Maxwell-Boltzmann
distribution
 exp(-E/kT)
relative probability
energy kT E0
E0
Reaction rates dominated by a few low energy
resonances in Gamow burning window

11. Direct measurement of 26gAl(p,γ)27Si reaction on
MD1
ED1
Direct measurement of 26gAl(p,γ)27Si reaction on
189 keV resonance PRL
Lower energy resonances key for dominant
sources of 26gAl eg Wolf-Rayet stars

12. Identification of key low energy resonances in 27Si for the 26Al(p,γ) reaction using Gammasphere Ge-array at Argonne 16O + 12C  27Si + n + γ’s

13. Identification of key low energy resonances for 26gAl(p,γ)27Si burning in Wolf-Rayet Stars G.J.Lotay et al., PRL 102, (2009)

14. Vast reduction in uncertainty (~105) in 26gAl(p,γ)27Si reaction rate

15. C Illiadis et al. , Ast. J. Supp
C Illiadis et al., Ast. J. Supp. 193, 16 (2011) Sensitivity study of 26Al abundance in Massive stars
 26Al(n,p) and 26Al(n,α) reaction rates represent
critical uncertainties for 26Al material processed by explosive and convective burning in massive stars
and ejected into the ISM by core collapse supernovae

16. 26Al(n, p) 26Mg reaction

17. First direct study of 26Al(n,p)26Mg reaction HP Trautvetter and F Käppeler, ZPA 381, 121 (1984)

18. HP Trautvetter et al., ZPA 323, 1 (1986)

19. Use of ΔE – E silicon detection system

20. Important discrepancies in σ-values for 26Al(n,p) reaction  Illiadis et al. emphasise need for new measurement particularly at high energies/T relevant for CCSN

21. A measurement could be performed at n_TOF facility using a radioactive 26Al target produced in collaboration with PSI
Experimental area for n-capture expts
BaF2
C6D6
C6D6
neutrons

22. November test expt at n_TOF using double-sided silicon strip detectors for 6Li + n  α + t reaction
DSSDs
6Li target
neutron beam
PJW, Franz Kaeppeler,
Claudia Lederer

23. The Hot CNO Cycles

24. 14O(α,p)17F
Rate dominated by a single 1- resonance at MeV in 18Ne
 Main uncertainty in branch to 1st excited state in 17F ?
14O + α
17F + p
18Ne
6.15
Eγ=495 keV
I(17F)~103 pps
on CH2 target
 17F(p,p’) reaction study on REX-ISOLDE accelerator CERN Miniball Ge-array + Edinburgh CD system in coincidence

25. First look for γ-decays in coincidences with p’s….

26. Inelastic channel comparable to 14O(α,p)17Fgs reaction rate
J J He et. al PRC (R) (2009)
Resonance observed for inelastic branch
Inelastic channel comparable to 14O(α,p)17Fgs reaction rate

27. New observations of Elemental Abundances in metal poor stars:
 Evidence for robust r-process mechanisms
(C. Sneden, J.J. Cowan, et al.)

28. r-process path (n, g) ↔ (g, n) equilibrium
freeze-out, waiting points and b-decay
new isotopic chain, increase of Sn
Towards valley
of stability

29. Sites of the r-process R-process related to environments with
high-neutron density and high temperature.
Type II supernovae prime suspects…
Neutron star mergers and accretion disks in g-ray bursts promising alternatives.
Not enough is known at
present about the physics
to create realistic models

30. Imprints of shell effects in r-process?
R - abundances
Details of nuclear properties
130Cd
“..the calculated r-abundance ‘hole‘ in the A  120 region reflects ... the weakening of the shell strength ... below 132Sn “ K-L Kratz
bottleneck at N=82 waiting point
near stability?

31. NUSTAR@FAIR – an r-process Laboratory
Fragmentation/fission beams selected by Super FRS.
DeSpec :decay spec
R3B: (γ,n)
NESR: mass measurements
(p,γ) reactions for p-process

32. r-process nuclei synthesised by fast-fission of 1 GeV/u 238U ions at FAIR
Advanced Implantation Detection Array (AIDA)
ASIC instrumented Double-sided Silicon Strip Detectors
238U fission fragments
from new super-FRS

33. AIDA: DSSD Array for (Super) FRS
Edinburgh, Liverpool, STFC Daresbury and Rutherford Lab. collaboration
ASIC instrumentation, 128 * 128 strips per wafer, strip pitch 625mm

34. AIDA Implantation DSSD Configurations
Two configurations proposed:
8cm x 24cm
“cocktail” mode
many isotopes measured simultaneously
b) 8cm x 8cm
concentrate on particular isotope(s)
high efficiency mode using:
total absorption spectrometer
moderated neutron detector array

35. First in-beam test of AIDA@GSI last month!

36. Implantation and decay setup: AIDA + RISING

37. Conclusions
Increasingly strong and fruitful interplay between studies of
the structure and reactions of unstable nuclei, and
explosive nuclear astrophysics.
An exciting burgeoning field which needs to utilise and
develop a whole range of experimental techniques and
instrumentation, particularly at new generation RIB facilities

38. Successful collaboration between nuclear astrophysics and astronomy, Dead Sea , PANIC meeting Eilat