Stars, Accelerators and Underground Laboratories

1. Stars, Accelerators and Underground Laboratories Marialuisa Aliotta School of Physics University of Edinburgh Scottish Universities Physics Alliance • nuclear astrophysics nuclear reactions in stars experimental approach • underground studies why underground LUNA – pioneering project • future facilities perspectives at Boulby John Adams Institute, Oxford, June 14th 2007

2. Courtesy: M. Arnould (EXPERIMENTAL) NUCLEAR ASTROPHYSICS • study energy generation processes in stars • study nucleosynthesis of the elements MACRO-COSMOS intimately related to MICRO-COSMOS NUCLEAR PHYSICS KEY to understand Universe at large

3. Greek philosophers 4 building blocks earth air water fire 1896 Mendeleev 92 building blocks (chemical elements) In search of the building blocks of the Universe… What are we made of? questions: how, where and when have the elements been made?

4. thermonuclear reactions mixing of interstellar gas • energy production • stability against collapse • synthesis of “metals” abundance distribution Overview BIRTH gravitational contraction Interstellar gas Stars explosion ejection DEATH

5. Stellar nucleosynthesis elements synthesised inside the stars nuclear processes well defined stages of stellar evolution courtesy: M. Wiescher, JINA lectures on Nuclear Astrophysics Burbidge, Burbidge, Fowler, Hoyle (B2FH, 1957) 1983 Nobel Prize "for his theoretical and experimental studies of the nuclear reactions of importance in the formation of the chemical elements in the universe"

6. Nuclear processes in stars charged-particle induced reaction mainly neutron capture reaction during quiescent stages of stellar evolution mainly during explosive stages of stellar evolution involve mainly STABLE NUCLEI involve mainly UNSTABLE NUCLEI

7. stellar reactions on earth Experimental Approach Laboratory requirements and techniques

8. Coulomb potential V Ecoul ~ Z1Z2 (MeV) Ekin ~ kT (keV) r0 r nuclear well (E) = exp(-2) S(E) nuclear fingerprint Reactions between charged particles In stellar plasmas: available kinetic energy from thermal motion at temperature T Average kinetic energy: kT ~ 8.6 x 10-8 T[K] keV T ~ 15x106 K (e.g. our Sun)  kT ~ 1 keV T ~ 1010 K (Big Bang)  kT ~ 2 MeV during quiescent burnings: kT << Ec reactions occur through TUNNEL EFFECT tunneling probability P  exp(-2) reaction cross section: determines exponential drop in abundance curve!

9. Maxwell-Boltzmann distribution  exp(-E/kT) tunnelling through Coulomb barrier  exp(- ) Gamow peak relative probability E0 energy kT E0 nuclear fingerprint Relevant energy: the Gamow peak most effective energy region for thermonuclear reactions convolution between MB distribution and tunnel probability Gamow peakE0 = f(Z1, Z2, T) Example: T ~ 15x106 K (T6 = 15) STRONG sensitivity to Coulomb barrier H-burning discrete stages of nuclear burning: He-burning C/O-burning …

10. (E) resonance LOG SCALE non-resonant (E) = exp(-2) S(E) direct measurements  S(E) E0 Ecoul extrapolation low-energy tail of broad resonance direct measurement LINEAR SCALE Coulomb barrier extrapolation needed ! sub-threshold resonance non resonant process -Er Er DANGER OF EXTRAPOLATION ! 0 interaction energy E Experimental approach Gamow peak: energy window where information on nuclear processes must be obtained BUT kT << E0 << Ecoul 10-18 barn <  < 10-9 barn major experimental difficulties Procedure: measure (E) over as wide a range as possible, then extrapolate down to E0! CROSS SECTION S-FACTOR S(E) = E(E) exp(2)

11. Going underground: a possible solution to the extrapolation procedure! reduce background (mainly from cosmic rays) improve signal-to-noise ratio for reaction of interest “Some people are so crazy that they actually venture into deep mines to observe the stars in the sky" Naturalis Historia – Pliny, 44 A.D.

12. The LUNA facility LUNA (Laboratory Undergroundfor Nuclear Astrophysics) Laboratori Nazionali del Gran Sasso Gran Sasso - Italy (1400 m rock -> 106 shielding factor) LUNA 400kV The (present) LUNA Collaboration Italy (INFN Gran Sasso, Napoli, Genova, Padova, Milano, Torino, Legnaro) Germany (Ruhr-Universität Bochum) Hungary (Atomki Debrecen)

13. HP Ge-Detector 3 MeV < Eg < 8 MeV earth’s surface  0.5 cts/s LNGS underground  0.0002 cts/s 4 BGO summing detector

14. R. Bonetti et al.: Phys. Rev. Lett. 82 (1999) 5205 C. Casella et al.: Nucl. Phys. A706 (2002) 203-216 d(p,g)3He 3He(3He,2p)4He LUNA (use the Moon to study the Sun) LUNA – Phase I: 50 kV accelerator (1992-2001) investigate reactions in solar pp chain @ lowest energy:  ~ 20 fb  1 count/month @ lowest energy:  ~ 9 pb  50 counts/day

15. Lemut et al Phys Lett B634 (2006) 483 astrophysical S-factor lowest measured s = 0.24x10-12 barn 15 O 13 14 15 N C reaction rate ~ factor 2 lower than NACRE 12 13 6 7 8 LUNA LUNA – Phase II: 400 kV accelerator (2002-2006) 14N(p,g)15O slowest reaction in CNO cycle

16. 14N(p,g)15O: bottleneck of CNO cycle Imbriani et al A&A 420 (2004) 625 CNO pp-chain major astrophysical implications: • age of globular clusters increased by 1Gy increase in age of Universe (in better agreement with other determinations) • solar neutrino flux from CNO reduced by factor 2 implications for Borexino detector • delay in onset of CNO cycle for massive stars so far:only threereactions studied directly at Gamow peak !! new/upgraded underground facilities are very much needed !!

17. LUNA is the only underground accelerator in the world for low-energy NA • current LUNA capabilities • (400 kV machine) • limited to acceleration of H and He beams • only direct kinematics studies are possible • (beam-induced background on target impurities) • reactions producing neutrons not allowed an upgrade of current facility seems unlikely because of severe space constraints at LNGS

18. Open Problems: • carbon burning in advanced stages of stellar evolution • neutron sources for s-process • Ne, Na, Mg and Al nucleosynthesis in AGB stars • isotopic composition of Novae ejecta • …

19. The Boulby Mine: An opportunity for the UK

20. Middlesborough Staithes Whitby York Boulby Mine • a working potash and salt mine • Cleveland - North East England • the deepest mine in Britain • (850m to 1.3km deep) courtesy: S. Paling

21. Heliminer Mine Shafts Dark Matter Research Areas Map of excavations • roadways & cavern excavated in Potash & Rock salt layer • over 40 km of tunnel dug each year (now > 1000 km in total) courtesy: S. Paling

22. Surface facilities The John Barton Building Surface facilities ~200m2: Admin & support facility: Office space, computing facilities, workshop, loading bay, showers, kitchen, laundry, conference room, remote monitoring of underground courtesy: S. Paling

23. CPL support & facilities Cleveland Potash Facilities • Shaft and Tunnel Maintenance • Ventilation • Health and Safety • Emergency rescue • Surface & Underground transport • Mechanical / Electrical workshops • Clean rooms • Chemical handling facilities • Electrical Supply courtesy: S. Paling

24. Requirements for an underground lab... 1.1 km (2805 mwe) CR muons attenuated by ~106 • Low Backgrounds • Deep (to shield from cosmic rays) • Low background rock/lab • (and/or adequate shielding) • Plenty of Laboratory space • Easy access for equipment • Proximity of services • Good infrastructure + facilities Salt = low in Uranium /Thorium (~ 67 / 125 ppb)  Low neutron background ~1000 m2, Potential for expansion Via mine shaft (2.0m3 cage) + Transport underground 20min  Whitby, Saltburn 1hr  York, Leeds, Middleborough < 5hrs  London, Manchester etc. • JIF Surface facility • JIF Underground facilities • Cleveland Potash Support Why is Boulby Special? courtesy: S. Paling

25. Advantage of salt mine: extremely low g background at Eg < 2-3 MeV

26. The facility a complementary facility to LUNA ideal to study reactions otherwise not feasible high voltage machine + appropriate ion source for production & acceleration of heavy nuclei inverse kinematics studies

27. What facility? the accelerator beams • 3 MV single-ended machine (e.g. NEC, Pelletron) • ECR source (e.g. for high intensity (~500 mA) 12C beam at high charge states) • Beam-lines + detection systems (gamma, neutron, charged particles) studies possible both in direct and inverse kinematics estimated cost for accelerator + ECR source: ~2.5 M€ = 1.7 M£

28. the Physics

29. Crab Nebula SN 1054 Aguilera et al. PRC 73 (2006) 64601 Spillane et al PRL 98 (2007) 122501 a channel p channel importance: evolution of massive stars Gamow region: 1 – 3 MeV min. measured E: 2.1 MeV (by g-ray spectroscopy) passive lead & concrete shielding 12C+12C 12C(12C,a)20Ne and12C(12C,p)23Na channels further measurements currently in progress in Bochum (Germany) however: major improvements expected for measurementsunderground!

30. M. Heil, PhD Thesis - Karlsruhe, 2002 Courtesy: F. Strieder 13C(,n)16O importance: s-process in AGB stars Gamow region: 130 - 250 keV min. measured E: 270 keV contributions from sub-threshold states? mainly hampered by cosmic background  good case for underground investigation

31. Jaeger PRL 87 (2001) 202501 importance: s-process in AGB stars Gamow region: 400 - 700 keV min. measured E: ~550 keV 22Ne(,n)25Mg mainly hampered by cosmic background  good case for underground investigation reaction rate still uncertain by orders of magnitude uncertain nucleosynthesis predictions similar considerations apply also to 22Ne(a,g)25Mg reaction Karakas et al ApJ 643 (2006) 471

32. Other examples abundances of Ne, Na, Mg, Al, … in AGB stars and nova ejecta affected by many (p,g) and (p,a) reactions shaded areas indicate current estimate of reaction rate uncertainties Iliadis et al. ApJ S134 (2001) 151; S142 (2002) 105; Izzard et al A&A (2007) submitted !! new measurements undergroundare very much needed !!

33. The proposal Experimental Low-Energy Nuclear Astrophysics

34. Stage 1: Feasibility Study • (duration: ~18 months, cost: ~ € 300k) • neutron & gamma-ray background measurements  best location within mine • infrastructure design (by engineering company) • accelerator and beam tests (at Saclay) • Stage 2: Construction, Commissioning, Exploitation • (duration: ~24+12 months, cost: ~ €3-5M) • construction of infrastructure • commissioning of facility • initial exploitation Statement of Interest already submitted to Science and Technology Facilities Council full proposal in preparation

35. ERC Start Grant submitted budget: €1.9M overall duration: 5 years aim: team of people for development of state-of-the-art equipment team: PI + 2 senior PDRAs • tasks: • background measurements • requirements for infrastructure • beam and accelerator tests (e.g. Saclay) • oversee design and construction of infrastructure • equipment (gamma-ray array, neutron detector, gas target,…) • exploitation of equipment first at surface facilities and then underground Stage 2 submission deadline (if Stage 1 successful): September 17th 2007

36. Summary Experimental Nuclear Astrophysics:very lively research field quiescent evolution: generally well understood • direct measurements at relevant astrophysical energies severely hampered by cosmic-background • only few reactions measured so far • new/upgraded underground facilities needed

37. Middlesborough Staithes Whitby York future opportunities Boulby salt mine: an ideal location in the UK depth ~ 1100 m • background level ~ factor 10-30 lower than at GS • no space constraints (no interference with other experiments) • existing support and safety facilities • opportunitiesfor involvement at various level

39. The End if interested please get in touch: m.aliotta@ed.ac.uk