ALNA- Accelerator Laboratory for Nuclear Astrophysics Underground Heide Costantini University of Notre Dame, IN, USA INFN, Genova, Italy
Outline: LUNA: LUNA: - an example of experimental nuclear astrophysics laboratory UNDERGROUND ALNA: ALNA: - goal - methods - experimental techniques Nuclear astrophysics: Nuclear astrophysics: - main reactions - main reactions - experimental problems - experimental problems
the abundance of the elements in the Universe Atomic number relative abundance the ambitious task of Nuclear Astrophysics is to explain the origin and relative abundance of the elements in the Universe elements are produced inside stars during their life n-capture, -decay,… N-ToF, RIA Charged particles Fusion reactions Fe
p + p d + e + + e d + p 3 He + 3 He + 3 He + 2p 3 He + 4 He 7 Be + 7 Be+e - 7 Li + + e 7 Be + p 8 B + 7 Li + p + 8 B 2 + e + + e 84.7 %13.8 % % 0.02 % pp chain 12 C 13 N p, -- 13 C 14 N p, 15 O ++ 15 N p, p, CNO cycle produces energy for most of the life of the stars 4p 4He + 2e+ + 2 e MeV Hydrogen burning
Two questions remain relevant: Energy production and timescale: 4 He(2 , ) 12 C( , ) 16 O( , ) 20 Ne Neutron production for weak s-process: 14 N( , ) 18 F( + ) 18 O( , ) 22 Ne( ,n) 22 Ne( , ) Neutron production for fast s-process: 13 C( ,n) 12 C( , ) 16 O Triple 4 He 16 O 12 C 4 He 20 Ne 16 O( , ) 20 Ne 4 He Helium burning
The extrapolation problem ? extrapolation is needed…. ? ? S(E) factor S(E) = E· (E)·exp(2 ) (E) = S(E)·exp(-2 ) /E 2 = Z 1 Z 2 ( /E) 0.5 sometimes extrapolation fails !!
R lab > B cosm + B env + B beam induced Environmental radioactivity has to be considered underground (shielding) and intrinsic detector bck Beam induced bck from impurities in beam & targets high purity and detector techniques (coincidence) Cross section measurement requirements 3MeV < E < 8MeV: 0.5 Counts/s 3MeV < E < 8MeV 3MeV < E < 8MeV Counts/s GOING UNDERGROUND HpGe
LUNA site LUNA 1 ( ) 50 kV LUNA 2 (2000 …) 400 kV Laboratory for Underground Nuclear Astrophysics Nuclear Astrophysics RadiationLNGS/surface Muons Neutrons Photons LNGS (shielding 4000 m w.e.)
LUNA 12 C 13 N p, -- 13 C 14 N p, 15 O ++ 15 N p, p, CNO cycle p + p d + e + + e d + p 3 He + 3 He + 3 He + 2p 3 He + 4 He 7 Be + 7 Be+e - 7 Li + + e 7 Be + p 8 B + 7 Li + p + 8 B 2 + e + + e 84.7 %13.8 % % 0.02 % pp chain 3 He( 4 He, ) 7 Be 14 N(p, ) 15 O d(p, ) 3 He 3 He( 3 He,2p) 4 He
Energy spread 70eV Long term stability: 5 eV/h U = 50 – 400 kV I 500 A for protons I 250 A for alphas LUNA II
Q = 7.3 MeV N+p /2 + 7/2 + 5/2 + 3/2 + 3/2 - 5/2 + 1/2 + 1/ O 14 N(p, ) 15 O gas target beam Reaction Rate = 0.83 c/d Background rate = 0.75 c/d t = days Q = 927 7 C Spectrum 70 keV BGO summing crystal
LUNA main results High beam current Event identification High efficiency detector Pure gas target full advantage Underground lab Lowest energy: 2cts/month Lowest cross section: 0.02 pbarn Background < 4*10 -2 cts/d in ROI 3 He( 3 He,2p)4He 14 N(p, ) 15 O Low cosmic background
Goal at ALNA: He-burningC-burning systematic study of reactions relevant for the understanding of He-burning and C-burning in red giants, AGB stars and late evolutionary stages Accelerators: installation of a small (2 MV terminal Voltage) accelerator to study ( ,n) and ( , ) reactions in forward kinematics 1 st phase: (M. Couder’s talk) heavy ion accelerator for inverse kinematics studies (M. Couder’s talk) 2 nd phase:
energy calibration:< 0.1% Energy resolution:< 0.1% long-term stability: > days to months beam intensity: I > 100 A Energy range:100kV-2MV Beam: p, Count rate limitation of 1 ev/day > 0.2 nbarn Accelerator Requirements 1 st phase
high efficiency increase counting rate Low intrinsic activity Passive shielding event identification active shielding decrease beam-induced background decrease environmental background Detector facility requirements 1 st phase Example: 19 F(p, - ) 16 O background reduction by Q-value gating for 19 F(p, ) 20 Ne counts EE EE
Facility requirements Depth shielding 4000 (mwe) Space 15X10X5 (m 3 ) accelerator 15x10x5 (m 3 ) (target room 1 st phase) 15X20X5 (m 3 ) (target room 2 nd phase) Electrical power 50 kW ( 1 st phase) 200 kW (2 nd phase) Additional facilitiesmachine shop power supply low level counting DI water system compressed air LN2 5 ton crane in target area
Contributors and collaborators: A. Champagne University of North Carolina R. Clark LBNL M. Couder University of Notre Dame M. Cromaz LBNL A. Garcia University of Washington J. Görres University of Notre Dame U. Greife Colorado School of Mines C. Iliadis University of North Carolina D. Leitner LBNL P. Parker Yale University K. Snover University of Washington P. Vetter LBNL M Wiescher University of Notre Dame
Main reactions: 3 12 C and 12 C( , ) 16 O 12 C/ 16 O abundance ratio in the Universe Determines conditions of Type II SN outcome of core collapse (n-star or black hole) Type Ia SN C-O fuel abundances outcome of the white dwarf material In particular 12 C( , ) 16 O Relevant energy region 300 keV BUT estimated (300 keV) barn!! 40 years of experimental effort with different experimental techniques Results implemented in R-matrix extrapolations but still large uncertainty Accurate low energy data could improve substantially R-matrix extrapolations
Neutron sources: 13 C( ,n) 16 O, 22 Ne( ,n) 25 Mg, 17 O( ,n) Slow neutron capture reactions (s-process) are responsible for the origin of approximately 50% of isotopes above iron Principal proposed site are AGB stars and stellar He and C- burning in massive stars The s-process rate depends on initial n-abundance reaction rate of n-sources reactions Gamow Energy: 13 C( ,n) 16 O: keV 22 Ne(a,n) 25 Mg: keV Low cross sections and cosmic rays major problems for measurements at surface laboratory 22 Ne( ,n) 25 Mg
d contamination was present in the gas target due to vacuum pumps oil 3 He(d,p) 4 He. Si detectors beam p p 4He4He 3 He gas target 3 He( 3 He,2p) 4 He Carefull analysis of the E-E Si detector spectra reduced in part beam induced bck. beam E-E p p 4He4He 3 He gas target Si detectors beam p p 4He4He 3 He gas target Coincidence requirement between two Si detectors 3 He(d,p) 4 He is completeley suppressed
LUNA’s accelerators 50 kV: LUNAI Energy spread: 20 eV keV/h 3 He( 3 He,2p) 4 He d( 3 He,p) 4 He d(p, ) 3 He