Misura della reazione 3He(4He, )7Be a LUNA

LUNA at LNGS
Alessandra Guglielmetti
Universita’ degli Studi di Milano and
INFN, Milano, ITALY
Outline:
-Nuclear Fusion reactions in stars
-Why going underground
-The Luna Experiment
-Future perspective
Laboratory
Underground
Nuclear
Astrophysics
Hydrogen burning
Produces energy for most of the life of the stars
pp chain
p + p  d + e+ + n e
d + p  3He + g
84.7 %
3He
13.8 %
+3He  a + 2p
3He
+4He  7Be + g
0.02 %
13.78 %
7Be+e- 7Li
7Li
+ g +ne
+p a+ a
7Be
8B
+ p  8B + g
2a + e++ ne
4p  4He + 2e+ + 2ne + 26.73 MeV
Nuclear reactions in stars
Sun:
T= 1.5 107 K
kT = 1 keV<< EC (0.5-2 MeV)
Reaction
3He(3He,2p)4He
E0
21 keV
d(p,g)3He
6 keV
14N(p,g)15O
27 keV
3He(4He,g)7Be
22 keV
Cross section and astrophysical S factor
1
 (E)  exp(- 31.29Z1Z 2 /E ) S(E)
E
Astrophysical
Gamow energy region
Gamow factor EG
factor
Cross section of
the order of pb!
S factor can be extrapolated
to zero energy but if resonances
are present?
Sub-Thr
resonance
Extrapol.
Mesurements
Tail of a broad
resonance
Narrow
resonance
Non resonant process
Danger in extrapolations!
Sun
Luminosity (irradiated energy per time) = 2 ·1039 MeV/s
Q-value (energy for each reaction) = 26.73 MeV

Reaction rate = 1038 s-1
Rlab= ··Ip··Nav/A
Laboratory
 ~ 10 %
IP ~ mA
 ~ g/cm2
pb <  < nb
event/month < Rlab < event/day

Underground Laboratory
Cross section measurement requirements
Environmental radioactivity
has to be considered
underground  shielding
Rlab > Bcosm+ Benv + Bbeam induced
Beam induced bck from
impurities in beam & targets 
high purity
3MeV < Eg < 8MeV:
0.5 Counts/s
1,00E+00
HpGe
1,00E+00
GOING
UNDERGROUND
1,00E-01
1,00E-02
1,00E-03
1,00E-01
1,00E-02
counts
counts
3MeV < Eg < 8MeV
0.0002 Counts/s
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
10-6
10-3
Laboratory for Underground Nuclear
Astrophysics
400 kV Accelerator :
I
max
 500 A protons I
Energy spread  70 eV
E beam  50 – 400 keV
max
 250 A alphas
Long term stability  5eV/h
LUNA "non solar phase" 2006-ongoing
(p,g) reactions on :
Nitrogen, Oxygen, Neon, Sodium and Magnesium isotopes
belonging to:
CNO, NeNa and MgAl cycles of Hydrogen burning
Important for second generation stars with temperature
and mass higher than those of our Sun
Seeds of the reactions already present
Higher Coulomb barrier: these cycles are unimportant for
energy generation but essential for nucleosynthesis of
elements with A>20
D(4He,g)6Li
6Li
detected in metal poor stars is
unexpectedly large compared to BBN
predictions.
D(4He,g)6Li is the main reaction for 6Li
production
No direct measurements for Ecm<650 keV
Theoretical calculations for the S-factor
differ by more than one order of
magnitude
data taking concluded
reaction
CNO cycle
In progress
Ne-Na cycle
BBN
Q-value
(MeV)
Gamow
energy (keV)
12.13
10-300
130
50
17O(p,g)18F
5.6
35-260
300
65
18O(p,g)19F
8.0
50-200
143
89
23Na(p,g)24Mg
11.7
100-200
240
138
22Ne(p,g)23Na
8.8
50-300
250
68
1.47
50-300
700(direct)
50(indirect)
50
15N(p,g)16O
D(a,g)6Li
Lowest meas.
Energy (keV)
In progress
proposal approved by LNGS SC in 2007
LUNA
limit
LOI to LNGS for a new accelerator for He-burning key reactions
3.5 MeV accelerator
Reaction rate
Estimate
At LUNA
12C(a,g)16
O
The “Holy Grail”
Reaction rate
Estimate
At LUNA
13C(a,n)16
O
Reaction rate
Estimate
At LUNA
22Ne(a,n)25M
g
Recoil mass separator approach
A+aC+g
A
Cn+
a
detection
A/C>1015
g
A
detection
separation
- low induced background
- high detection efficiency
- measurement of tot
- low background g-ray spectra
coincidence
European Recoil-separator for Nuclear Astrophysics
ion source
tandem
accelerator
ion beam
purification:
velocity
and momentum
filter
beam
preparation
g detection
setup
recoil
focusing
magnetic
quadrupole
multiplets
ion beam
emittance
control
4He gas
target
recoils
separation
Wien
filter
(velocity)
60° magnet
(momentum)
Wien filter
TOF/DE-E
(velocity)
detector
ERNA experimental program
Hydrogen burning and neutrino flux from 8B
3He(a,g)7Be measured in Bochum
7Be(p,g)8B
Helium burning and synthesis of Oxygen and Fluorine
12C(a,g)16O measured in Bochum down to ~2 MeV CM
14N(a,g)18F(b+)18O
15N(a,g)19F
LUNA COLLABORATION
Laboratori Nazionali del Gran Sasso, INFN, ASSERGI:
A.Formicola, C.Gustavino, M.Junker
Forschungszentrum Dresden-Rossendorf, Germany
D. Bemmerer, M.Marta
INFN, Padova, Italy
C. Broggini, A. Caciolli, M. Erhard, R.Menegazzo, C. Rossi Alvarez
Institute of Nuclear Research (ATOMKI), Debrecen, Hungary
Z.Elekes, Zs.Fülöp, Gy. Gyurky, E.Somorjai
Osservatorio Astronomico di Collurania, Teramo, and INFN, Napoli, Italy
O. Straniero
Ruhr-Universität Bochum, Bochum, Germany
C.Rolfs, F.Strieder, H.P.Trautvetter
Seconda Università di Napoli, Caserta, and INFN, Napoli, Italy
F.Terrasi
Università di Genova and INFN, Genova, Italy
F. Confortola, P.Corvisiero, H. Costantini, A. Lemut, P.Prati
Università di Milano and INFN, Milano, Italy
V. Capogrosso, A.Guglielmetti, C. Mazzocchi
Università di Napoli ''Federico II'', and INFN, Napoli, Italy
G.Imbriani,B. Limata, V.Roca
Università di Torino and INFN, Torino, Italy
G.Gervino
ERNA COLLABORATION
INFN, Napoli, Italy
M. De Cesare, N. De Cesare, A. Di Leva, A. D'Onofrio, L. Gialanella, G.
Imbriani, B. Limata, M. Romano, D. Schuermann, F.Terrasi, S. Cristallo, L.
Piersanti
INFN, Napoli, Italy
M. Busso, R. Guandalini, M. Nucci, S. Palmerini. A. Salterelli
Ruhr-Universität Bochum, Bochum, Germany
D. Rogalla, C.Rolfs, F.Strieder
Institute of Nuclear Research (ATOMKI), Debrecen, Hungary
University of Connecticut, USA
CNRS Orsay, France
University of Jerusalem, Israel