Download Broggini

The scientific program for the first five
years of LUNA-MV
High current H+ (1 mA), 4He+ , 12C+ (150 μA) and 12C++
(100 eμA) beams in the energy range: 0.3-3.5 (7) MeV
deep underground @LNGS.
From hydrogen burning to helium and carbon
burning
Carlo Broggini
INFN-Padova
Nucleosynthesis: from p-p chain, CNO, NeNa and MgAl cycles to
the region beyond Fe
Stellar evolution: from Main Sequence stars to thermonuclear
supernovae and core collapse supernovae
14N(p,
g)15O
278
7297
14N+p
(p,g)
13C
14N
(p,g)
b+
13N
- 504
15O
1/2
+
7276
7/2
+
6859
6793
5/2
+
3/2
+
6176
3/2
-
5241
5/2
+
1/2
+
5183
b+
(p,g)
12C
-21
7556
(p,a)
15N
The bottleneck reaction of
the CNO cycle already studied
by LUNA (2004-11)
1)
“High” energy: solid target + HpGe,
excellent energy resolution but small
efficiency. Study of the 5 different
radiative captures.
2)
Low energy: gas target + BGO,
bad energy resolution but excellent
efficiency. Study of the total
cross section. s(70 keV)=200 fb,
11 events/day
(p,g)
16O
15O
0
1/2
-
3) Measurement with a clover detector
in the energy region above the
259 keV resonance
LUNA: St(0)=1.57±0.13 keV b
Sgs(0)=0.20±0.05 keV b
Adelberger et al. 2011 : St(0)=1.66±0.12 keV b
Sgs(0)=0.27±0.05 keV b
Q. Li et al. 2016, study over a wide energy
region of 6.79 MeV and g.s. transitions:
Sgs(0)=0.42±0.04 +009 -0.19 keV b
It is mandatory to have a low background
measurement over a wide energy region
The solar abundance problem
new spectroscopic determination of the solar photosphere, in
particular C, N and O: 30-40% lower than before
SSM predictions disagree with heliosysmology results
Physical conditions in the solar core are determined
by pp-chain, in particular the temperature profile,
CNO luminosity ~1%
cno = LF(S1,14,C+Ncore)
probe of the (C+N) abundance
in the Sun core
Borexino:
cno< 7.7*108 cm-2s-1
From A.Serenelli, Topical Issue on
underground nuclear astrophysics and
solar neutrinos EPJA 52(2016):
Intrinsic error on the (C+N) determination of 11%, 2.6% from heavy element settling
and 10.6% from nuclear cross sections (S17 and S114, ~7.5% each).
CNO neutrino flux with 10% uncertainty
C+N abundance in the Sun core
with ~15% uncertainty
14N(p,
g)15O @LUNA MV: day zero experiment to verify accelerator
and solid target set-up + to reduce the error on S114
Set-up: several gamma ray detectors (if necessary, there is space for
an array).
Expected beam time: ~6 months
12C+ 12C
the trigger of Carbon burning
* The lower stellar mass bound Mup for the Carbon ignition:
C-O white dwarf (+Nova or thermonuclear supernova)
or
massive O-Ne WD or core collapse supernova (+neutron star or
black hole)
* Protons and alpha injection for nucleosynthesis in massive stars
Coulomb barrier: EC= 6.7 MeV
12C+12C 20Ne
+ a
12C+12C 23Na
+ p
12C+12C 24Mg
+ g
12C+12C 23Mg + n
12C+12C 16O + 2a
12C+12C 16O + 8Be
Q=4.62 MeV
Q=2.24 MeV
Q=13.93 MeV negligible
Q=-2.62 MeV endothermic
Q=-0.12 MeV three particles
Q=-0.21 MeV higher Coulomb barrier
Energy (CM) region of
interest:
0.9-3.4 MeV
explosive C-burning from
0.7 MeV
Relevant energy range in stars
Eg = 440 keV
Eg = 1634 keV
12C+12C 20Ne
+ ai + gi
12C+12C 23Na
+ pi +
gi
Detection: particles (Silicon
detectors, ΔE-E telescopes,
ionization chambers)
and gammas (from the first
excited state, Ge detectors)
Main advantage deep
underground @LNGS: gamma
ray suppression in a shielded
detector (~5 orders of
magnitude)
T. Spillane et al., Phys Rev Lett. 98 (2007) 122501
Several resonances spaced by 300-500 keV,
typical width G≈10 keV
Improvements @LNGS:
With a shielded Ge detector bck of 52 cpd
425-455 keV and 1 cpd 1619-1649 keV
Minimum energy 1955 for the proton channel
(bck limited) and 1605 keV for the alpha
channel (time limited). All this with 1mm thick
carbon target, 5 keV spacing and 30% stat.
error)
Expected beam time: ~2.5 years
Beam induced bck: 1H and 2H in the target
Gamma detection: 2H(12C,p1 γ)13C
and 1H(12C,γ )13N
Particle detection (at backward
angles): 2H(12C,2H)12C + 12C(d,p)13C
Heating at high temperature
is able to reduce the contamination
D
educe
The neutrons for the s-process: nucleosynthesis of half of all elements
heavier than Fe (e.g. W, Pd, La, Nd)
Two components were identified and connected to stellar sites:
Main s-process ~90<A<210
Weak s-process A<~90
TP-AGB stars
massive stars > 10 M⊙
shell He-burning
T9 ~ 0.1 K
107-108 cm-3
He-flash
0.25 ≤ T9 ~ 0.4 K
1010-1011 cm-3
13C(a,n)16O
22Ne(a,n)25Mg
13C(a,n)
22Ne(a,n)
core He-burning
3-3.5·108 K
106 cm-3
shell C-burning
~109 K
1011-1012 cm-3
22Ne(a,n)25Mg
13C(a,n)16O
S [MeV b ]
Energy region of interest: 140-230 keV (T = 90 · 106 K)
´ 106
6
5
• large statistical uncertainties at low
energies
• large scatter in absolute values
(normalization problem)
• unknown systematic uncertainties
• uncertainties in detection
efficiencies
• contribution from sub-threshold
state (E=6.356 MeV in 17O)
• contribution from electron
screening
Davids1968
Bair1973
Kellogg1989
Drotleff1993
Harrissopulos2005
Heil2008
4
3
fits/theory
Hale1987
Kubono2003
Heil2008
2
1
0
0.1 0.2 0.3
LUNA400 range
0.4
0.5
0.6
0.7
0.8
0.9
1.0 1.1
Ec.m.[MeV]
No data at low energy because of high neutron background in surface laboratories.
Extrapolations differ by a factor ~4 (10% accuracy and precision would be required).
Direct Kinematics
energy range Ecm = 210 – 300 keV (Ebeam ~ 275 – 400 keV) at LUNA-400
energy range Ecm = 240 – 1060 keV (Ebeam ~ 0.3 – 1.4 MeV) at LUNA-MV
4He beam
13CH gas target (drawbacks: limit on the density, possible molecule cracking)
4
P = 1 mbar
2.5 1017 atoms/cm2
L = 10 cm
13C-enriched solid target (drawbacks: degradation and possible carbon deposition)
density 2·1017-1018 at/cm2
(electron gun evaporation, implantation on Au/ Ta, synthetic diamonds……)
beam induced background (α,n) reactions on target impurities or along the beam line
( 10B, 11B, 17O, 18O)
neutron energy range: En = 2 – 3.5 MeV
Inverse Kinematics (different systematics)
13C
beam (only possible at LUNA-MV)
4He gas target
P = 1 mbar
2.5 1017 atoms/cm2
L = 10 cm
beam induced background: 13C reaction on 2H, 6Li, 7Li, 10B, 11B,
neutron energy range: En = 2 – 5 MeV
16O, 19F
10
Both solid target and gas target solutions are tested @ LNL and LNGS: R&D+first
measurement @LUNA400
Reaction rate with enriched 13C target (99%)
and Ia = 200 μA
Elab
[keV]
Ecm
[keV]
Rate
[neutr/h]
Nt = 1018
at/cm2
1200
918
2 105
Ia = 1 mA
1000
764
4 106
800
612
2 107
400
306
339
Lower beam current at high energy to
reduce the neutron production (maximum
acceptable rate: 2000 neutrons/s).
375
287
103
350
268
28
300
229
1.3
275
210
0.2
250
191
0.02
≈ 1-2 months beam time with
bck = 0
Work in progress to optimize the neutron detector efficiency for the measurement
@LUNA400: 3He proportional counters inside a polyethylene cube
• 3He tubes in two concentric ring: r1 inner
radius, r2 outer radius
• Polyethylene cube of L ~ 40 cm
• 18 stainless tubes (1 inch diameter,
• 25 or 40 cm long, P = 10 atm)
• Expected efficiency @ 2 MeV › 30%
r2
r1
A different neutron detector might be developed for LUNA-MV in addition to
3He counters: panels of 6Li loaded plastic scintillator surrounding a polyethylenegraphyte moderator
22Ne(a,n)25Mg
Eth= 0.57 MeV
- Very complex level scheme of 26Mg
- The lowest well studied resonance at Eα=832 keV
dominates the rate
- The influence of a possible resonance at 635 keV has
been ruled out because of parity conservation
- Only upper limits at: 570<Eα<800 keV (~10 pb), the
energy region of interest for AGB stars.
Extrapolations may be affected by unknown
resonances
@T9 < 0.18 the competing reaction 22Ne(α,γ)26Mg (Q=10.6
MeV) should become dominant (400 kV accelerator).
For the measurement @LUNA: 22Ne windowless
gas target + 3He counters inside moderator.
To fully exploit LNGS low background we need:
shielded detector, selected tubes, pulse shape
discrimination, remove 11B (because of
11B(a,n)14N)… to reach the level of ~10 n/day.
Scientific program of LUNA-MV (first run January 2019) ˃ 10 years mainly
devoted to the study of helium and carbon burning
First 5 years:
14N(p,g)15O: the bottleneck reaction of the CNO cycle in connection
with the solar abundance problem
12C
+ 12C:
the trigger of carbon burning in star, White Dwarf (+Nova or
thermonuclear SN) or O-Ne WD or core collapse SN (+neutron star or black
hole)
Sources of the neutrons responsible for the S-process: 50% of the
elements beyond Iron (neutron capture followed by beta decay):
13C(a,n)16O: isotopes with A≥90 during helium burning shell in low mass
AGB stars (4 solar masses)
22Ne(a,n)25Mg: isotopes with A‹90 during He burning in high mass AGB
stars and during He and C burning in massive stars
12C(a,g)16O: the flagship reaction of the next 5 year plan
1979 proposed by A. Zichichi , 1989 MACRO experiment ON
1400 m of dolomite rock, CaMg(CO3)2, (~3800 m w.e.)
Surf.: 17 800 m2, Vol.: 180 000 m3, Ventilation: 1 vol / 3.5 hours
(Rn in air 20-80 Bq m-3)
Muon flux: 1.1 m-2h-1, 6 orders of magnitude reduction
Neutron flux, mainly from (a,n): 2.92 10-6 cm-2s-1 (0-1 keV),
0.86 10-6 cm-2s-1 (> 1 keV), 3 orders of magnitude reduction
Gamma rays: only 1 order of magnitude reduction, but with thick
shield about 5 orders of magnitude in the region of natural
radioactivity and 4-5 orders above 3.2 MeV without any shield
Alpha particles: factor ~15 below 3 MeV (shielded Si detector)
≥ 1 month
≥ 308 day
- Terminal voltage Ripple (Rms): 20 -80 V
Underground accelerators
LUNA
JUNA
Bck.
Acceler.
Beam
intensity
Program
Expected
start
Notes
LNGS
LUNA
400
~300 mA
13C(a,n)
2017
Solid +
gas target
400 kV –
ECR
10 mA !
~ 2 OoM
better
et al.,
25Mg(p,g)
13C(a,n)
Mid 2016
2019
12C(a,g)
CASPAR
~ LUNA
Old 1 MV
150 mA
14N(p,g)
?
13C(a,n)
22Ne(a,n)
LUNA MV
LNGS
3.5 MV +
ECR
1 mA
14N(p,g)
+ 12C
13C(a,n)
22Ne(a,n)
12C(a,g)
12C
Mid 2016
?
?
2019
?
?
?
?
Gas
target +
3He tubes
in liq.
Scint.
Gas
target +
3He tubes