Ness 2002 LUNA II facility INFN underground Gran Sasso Laboratories P. Corvisiero INFN - Italy
the pp chain p + p d + e + + + ν e e d + p 3 3 He He + γγ 84.7 % 13.8 % 3 3 He He + 3 3 He He α + 2p 3 2p 3 He He + 4 4 He He 7 7 Be Be + γγ 13.78 % 0.02 % 7 7 7 Be+e Be+e - - 7 7 Li Li + γ γ +ν 7 Be +ν e Be + p 8 8 B+γ B+γ e 7 7 Li Li + p α α + α 8 8 B B 2α 2α + e + + ν e e 4p 4 He + 2e + + 2ν e + 26.73 MeV
Tunnel & gamow T sun 16 10 6 k E MB 1.3keV Exponential drop of cross section in the energy range of the sun The Gamow Peak: Energy window in which non resonant reactions take place in stellar environment. Examples: E c /kev E 0 /kev σ (E 0 )/barn E min /kev 3 He( 3 He,2p) 4 He 1540 21 7 10-13 16.5 3 He(α,γ) 7 Be 1540 22 9 10-18 107 14 N(p,γ) 15 O 2270 26 4 10-21 200
The astrophysical S-factor σ(e) = S(E) exp(-2πη) /E S(E) = E σ(e) exp(2πη)? 2πη = 31.29 Z 1 Z 2 (µ/e) 0.5
Reaction rates inside the sun: Luminosity Q-value reaction rates L =2. 10 39 MeV/s Q=26.73 MeV L R = Q = 10 38 s -1 in the Lab: ε ~ 10 % I P ~ ma τ ~ µg/cm 2 pb < σ < nb R lab = σ ε I p τ N av /A??? event/month < R lab < event/day signal rate background rate cosmic ray flux at the sea level 2 10-2 cm -2 s -1 on a 10 cm 2 detector 2000 events/day!!!
Shower on LNGS Background reduction in LNGS (shielding 4000 m w.e.) Cosmic shower Radiation Muons Neutrons Photons LNGS/surface 10-6 10-3 10-1 Gran Sasso underground halls
Luna goal LUNA the first worldwide underground accelerator facility goal: technique: Provide a direct measurement of the most relevant fusion reactions of astrophysical interest taking advantage of the very low background of Gran Sasso underground Laboratories
LUNA site LUNA underground Laboratories LUNA 50kV LUNA 400kV
Luna 50 kv LUNA facility LUNA1 50 kv accelerator En. range: 3 50 kev En. stability: < 10-4 current intensity: 50-500 µa windowless gas target 0.3 1 mbar 3 He( 3 He,2p) 4 He D(p,γ) 3 He Gamow peak fully explored D( 3 He,p) 4 He electron screening
Foto 50 kv
Luna 400 kv LUNA2 400 kv accelerator En. range: 50 400 kev current intensity: 200-1000 µa Two different beam lines (2003) for solid and/or 0.5 10 mbar gas target En. calibrated to < 0.3 kev at E p = 130 400 kev Capture γ-rays from 12 C(p,γ) 13 N reaction; Resonances: 23 Na(p,γ) 24 Mg (E p = 308.9 kev) 26 Mg(p,γ) 27 Al (E p = 338.1 kev) 25 Mg(p,γ) 26 Al (E p = 389.2 kev) Present and future activity: 14 N(p,γ) 15 O 4 He( 3 He,γ) 7 Be in progress scheduled in 2004
LUNA phase 2LUNA II foto New 400 kv accelerator
U max = 50-400 kv LUNA 400 kv at LNGS: I LUNA II max = 650 µa Foto = 0.07 kev E max allowed beams : protons, alphas
detectors Detectors 50x50 mm 2 Si detectors (1 mm thick) 50x50 mm 2 E- E Sitelescopes 3 He( 3 He,2p) 4 He D( 3 He,p) 4 He BGO 28cmx8cm 4π D(p,γ) 3 He 14 N(p,γ) 15 O four high eff. HpGe (140%, 120%, 2x100%) 14 N(p,γ) 15 O 4 He( 3 He,γ) 7 Be
30 10 BGO detector BGO 50 2000 Channels 20000 seeds 0 2000 4000 6000 Energy / kev 14 N(p,γ) 15 O Simulation 8000 10 6 10 4 10 2 10 0 4096 Channels 12.5 days Background Spectrum Measured Underground E>5.5 MeV: 4.4 cts/mev/day 2000 4000 6000 8000 Energy / kev
BGO & gastarget Bgo BGO and gas target and gas target pumping stages target calorimeter beam
background Silicon array: Background Less than 4*10-2 counts per day in ROI BGO: See spectrum HpGe: See spectrum
BGO spectrum numebr of events above E = 5 MeV: < 4 counts/mev/day Excellent for reactions with a Q-value > 5 MeV total Energy (MeV)
HpGe spectrum 0.511 40 K 214 Bi 208 Tl LNGS background HpGe 120 % t meas = 3.5 days above E = 5 MeV: < 2 10-3 counts/kev/day
P + N14 LUNA results 3 He( 3 He,2p) 4 He D(p,γ) 3 He 14 N(p, γ) 15 O
He3 + He3 Lowest energy: 2cts/month Lowest cross section: 0.02 pbarn Background < 4*10-2 cts/d in ROI
P + d test D(p,γ) 3 He The second reaction mesured below the Gamow peak Test for: detector, gas target, electronics Detector: BGO ( r int =3 cm, r ext =10 cm, L=28cm) Target: Gas target (p= 1 mbar, L targ = 10 cm) Eγ: 5.5 MeV `
P + d previous D(p,γ) 3 He: Physics case important reaction in protostars cosmogenic d is present in the gas cloud Griffiths et al 1963 Schmid et al 1997 no p+p bottleneck time evolution is governed by the S 1 2 factor Existing data are inconsistent
D(p,g) P + d 10 kev D(p,γ) 3 He LUNA data E cm = 10 kev
P + d 6 kev D(p,γ) 3 He below the Gamow peak E cm = 6 kev σ = 0.01 pbarn Viviani et al. PRC61 (2000)
CNO cycle p,γ 12 C 13 N p,α β - 14 N(p,γ) 15 O Bottle neck of CNO cycle 15 N 13 C 15 O β + p,γ p,γ 14 N Determination of CNO neutrino fluxes Slowest reaction
P+ 14 N and g.c.age P + N14 glob. clusters 14 N(p,γ) 15 O Chronometer of The Universe age S 14,1 /5 S 14,1 x5 Standard CF88
P + N14 Exc st 14 N(p,γ) 15 O E p = 250 kev Q = 41.2 C t = 20 h I =570 µa E target = 45 kev
P + N14 250 kev 14 N(p,γ) 15 O E p = 250 kev Q = 41.2 C t = 20 h I =570 µa E target = 45 kev
P + N14 g.s. 14 N(p,γ) 15 O E p = 250 kev Q = 41.2 C t = 20 h I =570 µa (p,γ 0 ) direct capture to g.s. E target = 45 kev
P + N14 Exc st 14 N(p,γ) 15 O E p = 250 kev Q = 41.2 C t = 20 h I =570 µa 6.79 6.18 (p,γ x ) capture to exc. states 5.18 E target = 45 kev
P + N14 200 kev 14 N(p,γ) 15 O Direct capture ground state transition in the 14 N(p,γ) 15 O reaction at a c.m. energy of 200 kev.
P + N1 4 rate 14 N(p,γ) 15 O Counting rate: 10 6 10 5 p=1 mbar; η=50%; I beam= 250 µa 10 4 10 3 10 2 10 1 back 1σ 10 0 10-1 10-2 50 70 90 110 130 150 170 190 E beam (kev)