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

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

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

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)
"for his theoretical and experimental studies of the nuclear reactions
of importance in the formation of the chemical elements in the universe"
1983
Nobel Prize

6. during quiescent stages
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. determines exponential drop in abundance curve!
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
Ecoul ~ Z1Z2
(MeV)
nuclear
well
Coulomb potential V r r0
during quiescent burnings:
kT << Ec
Ekin ~ kT (keV)
reactions occur through TUNNEL EFFECT
tunneling probability P  exp(-2)
 (E) = exp(-2) S(E)
reaction cross section:
nuclear
fingerprint
determines exponential drop in abundance curve!

9. Relevant energy: the Gamow peak
most effective energy region
for thermonuclear reactions
Gamow peak
tunnelling through
Coulomb barrier
 exp( )
Maxwell-Boltzmann
distribution
 exp(-E/kT)
relative probability
energy kT E0
E0
convolution between MB distribution
and tunnel probability
Gamow peak E0 = f(Z1, Z2, T)
Example: T ~ 15x106 K (T6 = 15)
reaction
Coulomb
barrier (MeV) E0
(keV)
Reaction rate
(Gamow peak area)
p + p
0.55
5.9
7.0x10-6
 + 12C
3.43 56
5.9x10-56
16O + 16O
14.07
237
2.5x10-237
STRONG sensitivity
to Coulomb barrier
H-burning
discrete stages of nuclear burning: He-burning
C/O-burning …
nuclear
fingerprint

10. 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
 (E) = exp(-2) S(E)
S(E) = E (E) exp(2)
non resonant
process
interaction energy E
extrapolation
direct measurement
S(E)
LINEAR
SCALE
LOG
SCALE 
direct measurements E0
Ecoul
Coulomb
barrier
(E)
non-resonant
resonance
extrapolation
needed !
low-energy tail
of broad
resonance
-Er
sub-threshold
resonance
DANGER OF EXTRAPOLATION ! Er

11. a possible solution to the extrapolation procedure!
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 Underground for Nuclear Astrophysics)
Gran Sasso - Italy
Laboratori Nazionali del Gran Sasso
(1400 m rock -> 106 shielding factor)
Radiation
LNGS/surface
muons
neutrons
photons
10-6
10-3
10-1
LUNA 400kV
The (present) LUNA Collaboration
Italy (INFN Gran Sasso, Napoli, Genova, Padova, Milano, Torino, Legnaro)
Germany (Ruhr-Universität Bochum)
Hungary (Atomki Debrecen)

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

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

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

16. 14N(p,g)15O: bottleneck of CNO cycle
major astrophysical implications:
pp-chain
CNO
Imbriani et al A&A 420 (2004) 625
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 three reactions studied directly at Gamow peak
!! new/upgraded underground facilities are very much needed !!

17. current LUNA capabilities
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. An opportunity for the UK
The Boulby Mine:
An opportunity for the UK

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

21. roadways & cavern excavated in Potash & Rock salt layer
over 40 km of tunnel dug each
year (now > 1000 km in total)
Heliminer
Map of excavations
Mine Shafts
Dark Matter
Research Areas
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. Why is Boulby Special? Requirements for an underground lab...
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
1.1 km (2805 mwe)
CR muons attenuated by ~106
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
courtesy: S. Paling

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

26. inverse kinematics studies
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
Ion (charge state)
Particles per second H+
5.0x1014
He+
5.0x1013
He2+
1.0x1013
Xe17+
2.9x1012
Kr15+
4.1x1011
Ar11+
5.6x1011
Ne6+
1.0x1012
Fe11+
5.7x1011 (estimated)
Ni11+
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. 12C+12C importance: evolution of massive stars Gamow region: 1 – 3 MeV
min. measured E: 2.1 MeV (by g-ray spectroscopy)
passive lead & concrete shielding
Crab Nebula SN 1054
12C+12C
12C(12C,a)20Ne and 12C(12C,p)23Na channels
Spillane et al PRL 98 (2007)
a channel
p channel
Aguilera et al. PRC 73 (2006) 64601
further measurements currently in progress in Bochum (Germany)
however: major improvements expected for measurements underground!

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

31. 22Ne(,n)25Mg importance: s-process in AGB stars
Gamow region: keV
min. measured E: ~550 keV
22Ne(,n)25Mg
Jaeger PRL 87 (2001)
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 underground are very much needed !!

33. The proposal
Experimental Low-Energy Nuclear Astrophysics

34. Statement of Interest already submitted to
Science and Technology Facilities Council
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
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. future opportunities Boulby salt mine: an ideal location in the UK
Middlesborough
Whitby
Staithes
York
depth ~ 1100 m
background level ~ factor lower than at GS
no space constraints (no interference with other experiments)
existing support and safety facilities
opportunities for involvement at various level

39. if interested please get in touch:
The End
if interested please get in touch: