Astrofisica Nucleare: una sfida interdisciplinare per la comunità

italianaAlessandra GuglielmettiUniversità degli Studi di Milano e INFN Milano

• Perché occuparsi di astrofisica nucleare: gioie e dolori…

• L’esperimento LUNA ai Laboratori del Gran Sasso: perché misurare sottoterra

• Principali esperimenti attivi in Italia (cenni…)

• Alcuni dei risultati più significativi ottenuti a LUNA

• Il futuro: il progetto LUNA MV

Astrofisica nucleareL’astrofisica nucleare si prefigge di comprendere imeccanismi di produzione di energia nelle stelle, in tuttele fasi di evoluzione stellare, e di spiegare le abbondanzedi tutti gli isotopi degli elementi che osserviamo innatura.

Gli studi condotti durante il secolo scorso hannodimostrato che l’essere umano è parte dell’ Universo chelo circonda anche attraverso un patrimonio comune: glielementi chimici che compongono il suo corpo.Al termine dell’esistenza terrena quegli elementitorneranno a far parte dello spazio e potranno dar luogoad altri esseri viventi.

Astrofisica nucleare

Astrofisicanucleare

Fisicanucleare

Fisica delneutrino

CosmologiaAstronomiaosservativa

Modellistellari

Sezioni d’urto e modelli stellari

-Stars are powered by nuclear reactions

-Among the key parameters (chemical composition, opacity, ...) to model stars, reaction cross sections play an important role

- They determine the origin of the elements in the cosmos, stellar evolution and dynamic

- Many reactions ask for high precision data!!

1E-03

1E-02

1E-01

1E+00

1E+01

1E+02

1E+03

1E+04

1E+05

1E+06

1E+07

1E+08

1E+09

1E+10

1E+11

0 50 100 150 200 250

Ab

un

dan

ce r

ela

tive t

o 1

06

Si

Mass Number

1H

4He

12C16O

20Ne

40Ca

56Fe

118Sn 138Ba195Pt

208Pb

232Th238U

a-elements

Type II SN

Fe-peak

Type I SN

N=82

r -process peak

Type II SNN=126

r -process peak

Type II SN

1H

12C16O

20Ne

40Ca

56Fe

118Sn 138Ba195Pt

208Pb

232Th238U

a-elements

Type II SN

Fe-peak

Type I SN

N=82

r -process peak

Type II SNN=126

r -process peak

Type II SN

N=82

s-process peak

AGB stars

N=82

s-process peak

AGB stars N=126

s-process peak

AGB stars

N=126

s-process peak

AGB stars19F

Big Bang

H-burning &

He-burning

Nuclear Astrophysics ambitious task is to explain the origin and relativeabundance of the elements in the Universe

Abbondanza degli elementi nelSistema solare

La tavola periodica

p + p 2H + e+ + np + e- + p 2H + e+ + n

3He + p 4He + e+ + n7Be + e- 7Li + n8B 8Be + e+ + n13N 13C + e+ + n15O 15N + e+ + n17F 17O + e+ + n

p-p chain

CNO cycle

Produzione di neutrini nel Sole

Neutrino flux from the Sun can be used to study:• Solar interior composition metallicity• Neutrino propertiesonly if the cross sections of the involved reactions are known with enough accuracy

G. Bellini et al. PRD 2014

Nucleosintesi primordiale (BBN)Production of the lightest elements (D, 3He, 4He, 7Li, 6Li) in the first minutes after the Big Bang

The general concordance between predicted (BBN theory) and observed (stellar spectra) abundances gives a direct probe of the Universal baryon density

CMB anisotropy measurement (e.g. Planck satellite) gives an independent measurement of the Universal baryon density

The agreement of the two results has to be understood in terms of uncertainties in the BBN predictions

He3 He

4

Be7

Li7

HDp

n

2

1

3 4

2

8

9

6

7

11

12

10

35

Li6

13

1. n p + e- + n

2. p + n D + g

3. D + p 3He + g

4. D + D 3He + n

5. D + D 3H + p

6. 3H + D 4He + n

7. 3H + 4H 7Li + g

8. 3He + n 3H + p

9. 3He + D 4He + p

10. 3He + 4He 7Be + g

11. 7Li + p 4He + 4He

12. 7Be + n 7Li + p

13. 4He + D 6Li + g

BBN: il network di reazioni

Apart from 4He, uncertainties are dominated by systematic errorsin the nuclear cross sections

Rateo stellare e sezione d’urto (1)

The stellar reaction rate per particle pair at temperature T (cm3 s-1 mol-1) is given by:

𝜎𝑣 =8

𝜋𝜇

1 2

𝑘𝑇 −3 2 0

∞

𝜎 𝐸 𝐸 exp −𝐸

𝑘𝑇𝑑𝐸

For charged particle induced non-resonant reactions the cross section

𝜎 𝐸 =1

𝐸𝑆 𝐸 𝑃(𝐸)

P(E) tunneling probability

S(E) astrophysical S-factor nuclear physics, smooth energy dependance

Rateo stellare e sezione d’urto (2)

When E<<EC (Coulomb barrier)

𝜎𝑣 =8

𝜋𝜇

1 2

𝑘𝑇 −3 2 0

∞

𝑆 𝐸 exp −𝐸

𝑘𝑇−

𝐸𝐺𝐸

𝑑𝐸

exp −𝐸

𝑘𝑇Maxwell Boltzmann distribution of the

velocities

exp −𝐸𝐺

𝐸tunneling probability

𝐸𝐺 = 𝑍1𝑍2 2𝜇 𝜋𝑒2/ℏ2

Most of the reactions occur at energy

𝐸0= 1.22 (𝜇𝑍12𝑍22𝑇62)1/3

keV

(maximum value of the integrand)

Rateo stellare e sezione d’urto (3)

In our Sun: T6 = 15 kT = 1 keV EC ≈ 0.5-2 MeV

3He(3He,2p)4He E0=21 keV

d(p,g)3He E0=6 keV

14N(p,g)15O E0=27 keV

3He(4He,g)7Be E0=22 keV

kT but also E0 << EC

Cross sections in the range of pb-fb at stellar energies!

When a resonance is present at energy ER

𝜎𝑣 =2𝜋

𝜇 𝐾𝑇

3 2ℏ2exp

−𝐸𝑅

𝑘𝑇𝜔𝛾 where 𝜔𝛾 is the resonance strength

Sole vs LaboratorioSun:Luminosity = 2 ·1039 MeV/s

Q-value (H burning) = 26.73 MeV Reaction rate Rsun = 1038 counts/s

Laboratory: Rlab= Np Nt s e

Np = number of projectile ions ≈ 1014 pps (100 mA q=1+)

Nt = number of target atoms ≈ 1019 at/cm2

s = cross section = 10-15 barn

e= efficiency ≈ 100% for charged particles 1% for gamma rays

Rlab ≈ 0.3-30 counts/year

Tipicamente in un laboratorio sulla Terra…

Gamow energy region

But…

R has to be compared with background B

Bbeam induced : reactions with impurities in the target, collimators,… secondary processes

Benv : natural radioactivity mainly from U and Th chains

Bcosmic : mainly muons

Fondo e segnale

LUNA site

LUNA 1(1992-2001)

50 kV

LUNA 2(2000…)

400 kV

Laboratory for Underground

Nuclear Astrophysics

Radiation LNGS/surface

Muons

Neutrons

10-6

10-3

LNGS (1400 m rock shielding 4000 m w.e.)

LUNA MV(2019...)

Cross section measurement requirements

1,00E-06

1,00E-05

1,00E-04

1,00E-03

1,00E-02

1,00E-01

1,00E+00

0 2000 4000 6000 8000 10000

Eg[keV]

coun

ts

1,00E-06

1,00E-05

1,00E-04

1,00E-03

1,00E-02

1,00E-01

1,00E+00

0 2000 4000 6000 8000 10000

Eg [keV]

coun

ts

Pb

Cu

mEg<3MeVpassive shielding Underground passive shielding is more effective since μ flux, that create secondary g’s in the shield, is suppressed. A reduction of 5 o.o.m. was obtained

LUNA: riduzione del fondo (g)Eg>3MeV: reduction of a factor 2000 simply going underground

HPGe HPGe

3MeV < Eg < 8MeV: 0.5 Counts/s

3MeV < Eg < 8MeV: 0.0002 Counts/s

m

LUNA: riduzione del fondo (a)With a Si detector:Underground+Pb vs. Overground: factor ~10-15 reduction in the range200 keV - 2.5 MeV

27 anni a LUNA: H burning

Ne-Na cycleMg-Al cycle

CNO cycle

He3 He

4

Be7

Li7

HDp

n

2

1

3 4

2

8

9

6

7

11

12

10

35

Li6

13

1. n p + e- + n

2. p + n D + g

3. D + p 3He + g

4. D + D 3He + n

5. D + D 3H + p

6. 3H + D 4He + n

7. 3H + 4H 7Li + g

8. 3He + n 3H + p

9. 3He + D 4He + p

10. 3He + 4He 7Be + g

11. 7Li + p 4He + 4He

12. 7Be + n 7Li + p

13. 4He + D 6Li + g

…e BBN

Principali esperimenti attivi in Italia-1ERNA: European Recoil mass separator for Nuclear Astrophysics(CIRCE laboratory in Caserta)Radiative capture reactions are measured in inverse kinematics by directly detetcting the recoils, after separating them from the beamions with a RMS. Possibility of using also radioactive beams (see e.g. recent results on 7Be(p,g)8B)

Principali esperimenti attivi in Italia-2ASFIN: AStroFIsica Nucleare (LNS and many other laboratoriesworldwide)

Use of the indirect method «Trojan Horse» to obtain the cross section of the two body reaction a + b c + d using a three body reaction a + x c + d + s where x is given by a b s cluster and s acts as spectator. If the beam energy is larger than the Coulomb barrier the TH nucleus x can be brought into the nuclear field of the nucleus a and b induces the virtual reaction. No Coulomb barrier suppression and no electron screening effects. Recent results on 12C+12C (see later). Direct data are needed for normalization

x

a

b

break-up

s

d

c

Principali esperimenti attivi in Italia-3NTOF: Neutron Time Of Flight (CERN)A pulsed neutron source coupled to a 185 m flight pathallows to obtain neutrons of 25 meV < En < 1 GeV; very high istantaneous intensity (105 n/cm2 per bunch) and precise energy resolution (DE/E = 10-4). Many different applications. For nuclear astrophysics: study of neutron induced reactions responsible of the heavy elements nucleosynthesis and study of reactionsrelevant for BBN (e.g. n+7Be)

La comunità italiana è già ben organizzata…

Acceleratore LUNA 1 (50 kV)

Energy spread:20 eV

keV/h

3He(3He,2p)4He e il puzzle dei neutrini solari

Weak interaction: σpp≈10-51 cm2

Determines the velocity of the cycle

Other reactions are governed by the strong interaction

(σ ≈ 10-36 ÷ 10-33cm2)

p + p d + e+ + ne

d + p 3He + g

3He +3He a + 2p 3He +4He 7Be + g

7Be+e- 7Li + g +ne7Be + p 8B + g

7Li + p a + a 8B 2a + e++ ne

84.7 % 13.8 %

13.78 % 0.02 %

pp chain

solar neutrino puzzle?

3He(3He,2p)4He

3He beam on 3He “windowless gas target”. Silicon detectors

Beam induced background from the 3He(d,p)4He reaction (beam impurity HD)coincidence between 2 silicon detectors

0

0.0004

0.0008

0.0012

0.0016

0.002

co

un

ts p

er

se

co

nd

1000 104

300 Energy (keV)

LNGS

Bochum

Cosmic background suppressionin a silicon detector

La misura 3He(3He,2p)4He a LUNA 1

3He(3He,2p)4He e il puzzle dei neutrini solari

•Fundamental reaction of the p-p cycle•Measured down to the lower edge of the solar Gamow peak•No resonances no nuclear explanation for the solar neutrino puzzle•Screening effect

R. Bonetti et al., PRL (1999)

E beam 50 – 400 keV

I max 500 mA protons I max 250 mA alphas

Energy spread 70 eV Long term stability 5eV/h

Acceleratore LUNA 2 (400kV)

S 14,1 /5

S 14,1 x5

Standard CF88

Influences: • CNO neutrino flux Solar metallicity

• Globular cluster age

14N(p,g)15O: neutrini CNO e…

factor 10 !

Angulo

Schröder

14N(p,g)15O: stato dell’arte pre-LUNA

Transition

(MeV)

Schröder et al.

(Nucl.Phys.A 1987)

Angulo et al.

(Nucl.Phys.A2001)

RC / 0 1.55 ± 0.34 0.08 ± 0.06

S(0) [keV-b] 3.20 ± 0.54 1.77 ± 0.20

factor 20 !

Solid target + HPGe detector: high resolution

single g transitions Energy range 119-367 keV

Gas target+ BGO detector: high efficiency

total cross section Energy range 70-230 keV

S0(LUNA) = 1.61 ± 0.08 keV b

La misura 14N(p,g)15O a LUNA 2

CNO neutrino flux decreases of a factor 2 Globular Cluster age increases of 0.7 – 1 Gyr: new lower limit on the Age of the Universe T>14 Gy

G. Imbriani et al., EPJ (2005); G. Imbriani et al., A&A (2004)

17O(p,g)18F : nucleosintesi

17O+p is very important for hydrogen burning in different stellar environments:- Red giants- Massive stars- AGB- Novae

- light nuclei (17O/18O/18F …) abundances- observation of 18F g-ray signal (b+ decay, annihilation with e-, 511 keVgamma)

Classical novae T=0.1-0.4 GK => EGamow = 100 – 260 keVFor 17O(p,γ)18F: resonance at Ep = 183 keV and non resonant contribution

La misura 17O(p,g)18F a LUNA 2183 keV resonance and direct capture component for E=160-370 keV measured with prompt gammas and activation Gamow window for Novae region explored with the highest precision to-date

Enriched (70%) 17O targets on tantalum backings (anodization process)

La misura 17O(p,g)18F a LUNA 2183 keV resonance: wg=1.67±0.12 meV (weighted average of prompt and activation)Several new transitions identified and branching ratios determined

17O(p,g)18F : risultati e loro impatto

The new reaction rate allows to calculate abundances of 18O, 18F, 19F and 15N using nova models with 10% precision

D. Scott et al., PRL (2012) A. Di Leva et al., PRC (2014)

He3 He

4

Be7

Li7

HDp

n

2

1

3 4

2

8

9

6

7

11

12

10

35

Li6

13

1. n p + e- + n

2. p + n D + g

3. D + p 3He + g

4. D + D 3He + n

5. D + D 3H + p

6. 3H + D 4He + n

7. 3H + 4H 7Li + g

8. 3He + n 3H + p

9. 3He + D 4He + p

10. 3He + 4He 7Be + g

11. 7Li + p 4He + 4He

12. 7Be + n 7Li + p

13. 4He + D 6Li + g

2H(a,g)6Li: il 6Li primordiale astronomia osservativa e cosmologia

I due problemi del Litio

1) The BBN 7Li predictions are a factor 2-4 higher than observations: a nuclear physics solution is highly improbable

(e.g. 3He(4He,g)7Be measurement at LUNA)

2) The amount of 6Li predicted by the BBN is about 3 oom lower than the observed one in metal poor stars (debated but still «true» for a few

metal poor stars)

BBN predicts 6Li/7Li= 2 * 10-5 much below the detected levels of about 6Li/7Li= 5 * 10-2

Necessary to constrain nuclear physics input: 2H(a,g)6Li

2H(a,g)6Li: stato dell’arte pre-LUNA

No data in the BBN energy range!

Upper limits (indirect meas)

La misura 2H(a,g)6Li a LUNA 2

Strong beam induced background due to:1) Rutherford scattering of 4He beam on 2H target2) 2H(d,n)3He reaction3) Inelastic neutron scattering on different materials (Cu, Pb, Ge,…)

g background in the 2H(a,g)6Li RoI

The beam induced background weakly depends on the beam energy

La misura 2H(a,g)6Li a LUNA 2

An irradiation at one given beam energy can be used as a background monitor for an irradiation at a different beam energy, if the two ROIs do not overlap

Natural background subtracted

400 keV data (grey filled)

280 keV data (red empty) rescaled to take into account

the weak energy dependence of the beam induced background

New LUNA data

From the new data on the 2H(a,g)6Li reaction: 6Li/7Li = (1.5 ± 0.3) * 10-5

2H(a,g)6Li : risultati

Standard BBN production as a possible explanation for the reported 6Li detections is ruled out. “Non standard” physics solutions?

M. Anders et al., PRL (2014)

02/10/2018 52

Nuclear reactions involving few-nucleon systems represent an “ideal laboratory” where theoretical predictions can be compared with experimental data. Recently, a reliable ab initio nuclear theory calculation of the 2H(p,g)3He cross section has been performed (Marcucci 2016) and the S-factor has been determined in the BBN energy range However, the theoretical result is systematically larger than the best-fit value derived from the experimental data in the BBN energy range.

2H(p,g)3He : fisica nucleare teorica

At LUNA:-Cross section measurement at30keV<Ecm<300keV with high accuracy-Differential cross sectionmeasurementData analysis ongoing

Il progetto premiale MIUR LUNA MVA new 3.5 MV accelerator will be installed in April 2019 in the north part of Hall B at Gran Sasso. The accelerator is ready at HVEE and will be tested this winter

He and C burning key reactions will be measured

L’acceleratore LUNA MVIn-line Cockcroft Walton accelerator

In the energy range0.3-3.5 MeV

H+ beam:500-1000 emA

He+ beam:300-500 emA

C+ beam:100-150 emA

C++ beam:100 emA

Beam energy reproducibility : 10-4 * TV or 50 VThe accelerator hall will be shielded by 80 cm thick concrete walls: no perturbation of the LNGS natural neutron flux

Programma scientifico a LUNA MV (2019-2024)

14N(p,g)15O: the bottleneck reaction of the CNO cycle in connection with the solar abundance problem. Also commissioning measurement for the LUNA MV facility

12C+12C: energy production and nucleosynthesis in Carbon burning. Global chemical evolution of the Universe

13C(a,n)16O and 22Ne(a,n)25Mg : neutron sources for the s-process (nucleosynthesis beyond Fe)

Later on…

12C(a,g)16O: key reaction of Helium burning: determines C/O ratio and stellar evolution…..

La reazione 12C+12C: come e perchè

Its rate determines the value of “Mup”:

If Mstar>Mup: quiescent Carbon burning core-collapsesupernovae, neutron stars, stellar mass black holes

If Mstar<Mup: no Carbon burning white dwarfs, nova, type Ia supernovae

The reaction produces protons and alphas in a hot environmentnucleosynthesis in massive stars

12C+12C 20Ne + a Q = 4.62 MeV12C+12C 23Na + p Q = 2.24 MeV 12C+12C 24Mg + g Q = 13.93 MeV negligible12C+12C 23Mg + n Q = -2.62 MeV endothermic for low energies12C+12C 16O + 2a Q = -0.12 MeV three particles reduced prob.12C+12C 16O + 8Be Q= -0.21 MeV higher Coulomb barrier

La reazione 12C+12C: possibili strategie

Eg = 1634 keV

Eg = 440 keV

Quiescent carbon burning: 0.9 MeV<ECM<3.4 MeVType Ia supernovae: ECM ≥ 0.7 MeV

12C+12C 20Ne + ai + gi

12C+12C 23Na + pi + gi

ParticlesGammas

12C+12C: stato dell’arte

Several resonances spaced by 300-500 keV Typical width G≈ 10keV

T. Spillane et al, PRL (2007)

A. Tumino et al., Nature (2018)Trojan Horse Method (ASFIN)

12C+12C a LUNA MVC target: beam induced background due to H and 2H contamination in 12C targets:

Gammas: 2H(12C,pg)13C (Eg = 3089 keV) and 1H(12C,g)13N (Eg = 2365 keV). At low beam energies the Compton continuum may dominate the gamma spectrum

Particles: 2H(12C,pg)13C emits low energy protons;2-step process (2H in the target elastically scattered at forward angles by the C beam, then 2H(12C,p)13C reaction)

Possible strategy: heat targets at very high temperatures (up to 1200 °C) and measure residual contaminations with IBA techniques

Progetto Giovani CSN5 dell’INFN: HEAT e collaborazione con ERNA

12C+12C a LUNA MV1) Very well shielded HpGe detector: search for low energy resonances. At LUNA a 5 o.o.m. background reduction has already been obtained for low energy gammas (< 3 MeV)

2) particle detection with a less efficient apparatus (only higher energies) but total cross section. Collaboration with ERNA

Direct measurements at energies 1.5 MeV<ECM<2.5 MeV (same energy range as THM data)

La collaborazione LUNA

• F. Amodio, G.F. Ciani*, L. Csedreki, L. Di Paolo, A. Formicola, M. Junker, A. Razeto| INFN LNGS /*GSSI, Italy

• D. Bemmerer, K. Stoeckel, M. Takacs, | HZDR Dresden, Germany• C. Broggini, A. Caciolli, R. Depalo, P. Marigo, R. Menegazzo, D. Piatti | Università di

Padova and INFN Padova, Italy• C. Gustavino | INFN Roma1, Italy• Z. Elekes, Zs. Fülöp, Gy. Gyurky,T. Szucs | MTA-ATOMKI Debrecen, Hungary• M. Lugaro | Konkoly Observatory, Hungarian Academy of Sciences, Budapest, Hungary• O. Straniero | INAF Osservatorio Astronomico di Collurania, Teramo, Italy• F. Cavanna, P. Corvisiero, F. Ferraro, P. Prati, S. Zavatarelli | Università di Genova and

INFN Genova, Italy• A. Guglielmetti| Università di Milano and INFN Milano, Italy• J. Balibrea, A. Best, A. Di Leva, G. Imbriani, | Università di Napoli and INFN Napoli,

Italy• G. Gervino | Università di Torino and INFN Torino, Italy• M. Aliotta, C. Bruno, T. Chillery, T. Davinson | University of Edinburgh, United Kingdom• F. Barile, G. D’Erasmo, E.M. Fiore, V. Mossa, F. Pantaleo, V. Paticchio, R. Perrino*, L.

Schiavulli| Università di Bari and INFN Bari/*Lecce, Italy

LUNA is just 27-year old ….still a lot of energy for the future !!!