Transcript Document 7698713

ALNA- Accelerator Laboratory for Nuclear
Astrophysics Underground
Heide Costantini
University of Notre Dame, IN, USA
INFN, Genova, Italy
Outline:
• Nuclear astrophysics:
- main reactions
- experimental problems
• LUNA:
- an example of experimental nuclear astrophysics
laboratory UNDERGROUND
• ALNA:
- goal
- methods
- experimental techniques
the abundance of the elements in the Universe
1010
Charged particles
Fusion reactions
relative abundance
108
106
the ambitious task of
Nuclear Astrophysics
is to explain the origin
and relative abundance
of the elements
in the Universe
104
n-capture, -decay,…
N-ToF, RIA
102
1
Fe
10-2
0
10
20
30
40
50
60
70
Atomic number
80
90
elements are produced inside stars during their life
Hydrogen burning
produces energy for most of the life of the stars
pp chain
p + p d +
e+
CNO cycle
+ ne
3He
13.8 %
+3He  a + 2p
3He
0.02 %
13.78 %
7Be+e- 7Li
7Li
+ g +ne
+p a+ a
15N
+4He  7Be + g
7Be
8B
+ p  8B + g
13C
p,g
+
15O
13N
-
p,a
d + p  3He + g
84.7 %
p,g
12C
p,g
2a + e++ ne
4p  4He + 2e+ + 2ne + 26.73 MeV
14N
Helium burning
4He
4He
Triple a
12C(a,g)16O
4He
12C
16O
16O(a,g)20Ne
20Ne
Two questions remain relevant: Energy production and timescale:
4He(2a,g)12C(a,g)16O(a,g)20Ne
Neutron production for weak s-process:
14N(a,g)18F(+n)18O(a,g)22Ne(a,n)
22Ne(a,g)
Neutron production for fast s-process:
13C(a,n)
The extrapolation problem
(E) = S(E)·exp(-2) /E
S(E) = E·(E)·exp(2)
2 = 31.29 Z1 Z2 (/E)0.5
?
S(E) factor
extrapolation is
needed….
??
sometimes extrapolation fails !!
Cross section measurement requirements
Environmental radioactivity
has to be considered
underground (shielding) and
intrinsic detector bck
Rlab > Bcosm+ Benv + Bbeam induced
Beam induced bck from
impurities in beam & targets 
high purity and detector
techniques (coincidence)
3MeV < Eg < 8MeV:
3MeV < Eg < 8MeV 0.0002 Counts/s
0.5 Counts/s
HpGe
1,00E+00
1,00E+00
GOING
UNDERGROUND
1,00E-01
1,00E-03
1,00E-02
counts
counts
1,00E-02
1,00E-01
1,00E-04
1,00E-03
1,00E-04
1,00E-05
1,00E-05
1,00E-06
1,00E-06
0
2000
4000
6000
Eg [keV]
8000
10000
0
2000
4000
Eg[keV]
6000
8000
10000
Laboratory for Underground
Nuclear Astrophysics
LUNA site
LNGS
(shielding  4000 m w.e.)
LUNA 1
(1992-2001)
50 kV
LUNA 2
(2000…)
400 kV
Radiation
LNGS/surface
Muons
Neutrons
Photons
10-6
10-3
10-1
Measurements @ LUNA
pp chain
CNO cycle
d + p
3He
3He
13.8 %
+3He  a + 2p
3He
15N
+4He  7Be + g
0.02 %
13.78 %
7Be+e- 7Li
7Li
+ g +ne
+p a+ a
3He(3He,2p)4He
7Be
8B
+ p  8B + g
13C
p,g
+
15O
13N
-
p,a
+ g
84.7 %
p,g
12C
p + p  d + e+ + n e
p,g
14N
2a + e++ ne
3He(4He,g)7Be
d(p,g)3He
14N(p,g)15O
LUNA II
U = 50 – 400 kV
I  500 A for protons
I  250 A for alphas
Energy spread  70eV
Long term stability: 5 eV/h
14N+p
278
7297
7556
1/2
7/2
+
5/2
+
6793
3/2
+
6176
3/2
-
5241
5/2
+
5183
1/2
+
7276
6859
-21
- 504
14N(p,g)15O
Q = 7.3 MeV
+
gas target
beam
15O 0
1/2
-
BGO summing
crystal
Spectrum 70 keV
t = 49.12 days
Q = 9277 C
Reaction Rate = 10.95  0.83 c/d
Background rate = 21.14  0.75 c/d
14N(p,g)15O
LUNA main results
3He(3He,2p)4He
• Lowest energy: 2cts/month
• Lowest cross section: 0.02 pbarn
• Background < 4*10-2 cts/d in ROI
Low cosmic background
High beam current
High efficiency detector
Pure gas target
Event identification
full advantage
Underground lab
Goal at ALNA:
• systematic study of reactions relevant for the
understanding of He-burning and C-burning in
red giants, AGB stars and late evolutionary
stages
Accelerators:
•1st phase:
•2nd phase:
installation of a small (2 MV terminal
Voltage) accelerator to study (a,n) and
(a,g) reactions in forward kinematics
heavy ion accelerator for inverse
kinematics studies (M. Couder’s talk)
1st phase
Accelerator Requirements
• energy calibration:
< 0.1%
• Energy resolution:
< 0.1%
• long-term stability:
> days to months
• beam intensity:
I > 100 A
• Energy range:
100kV-2MV
• Beam:
• Count rate limitation
of 1 ev/day
p, a
> 0.2 nbarn
1st phase
Detector facility requirements
• high efficiency
 increase counting rate
• Low intrinsic activity
decrease environmental background
• Passive shielding
• event identification
decrease beam-induced background
• active shielding
counts
counts
Example: 19F(p,a-g)16O background reduction by Q-value gating for 19F(p,g)20Ne
Eg
Eg
Facility requirements
• Depth shielding
• Space
 4000 (mwe)
15X10X5 (m3) accelerator
15x10x5 (m3) (target room 1st phase)
15X20X5 (m3) (target room 2nd phase)
• Electrical power
50 kW (1st phase)
200 kW (2nd phase)
•Additional facilities
machine 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