Underground Nuclear Astrophysics Pos(NIC-IX)003 He

PoS(NIC-IX)003 http://pos.sissa.it/ O reaction and the status of the ongoing 15 ) γ N(p, 14 ∗ [email protected] Speaker. Cross section measurements for quiescent stellartremely H low and counting He burning rate are andphase hampered cosmic mainly have by background. been ex- measured Some atphysics) of the taking the LUNA advantage main facility of reactions (Laboratory theSasso of for National very H-burning Laboratory Underground low in Nuclear background Italy. Astro- An environmentgiven overview of together of with the the the adopted Underground experimental latest Gran techniques results will on be the experiments. ∗ Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. c ° International Symposium on Nuclear Astrophysics -25-30 Nuclei June in 2006 the Cosmos -CERN IX Heide Costantini INFN Genova (IT) University ofE-mail: Notre Dame (USA) for the LUNA collaboration Underground nuclear astrophysics PoS(NIC-IX)003 He. At Be pro- 3 8 He nucleus and Heide Costantini 4 ν ν νν ν ν νν γ + ν ν νν ν ν νν + MeV MeV B + 8 + He B , which decays to + 4 K, the proton proton reaction → 8 2 γ 6 Be + e Be + = 28.3% = 28.3% 8 Be, which decays producing two = 19.17 = 19.17 → H + e H + 8 loss loss 10 2 ν ν νν ν → ν νν eff eff E E 0.11% 0.11% Be + Be × MeV B Be Be + p Be 7 → p 8 8 7 . 6 1 73 → ≈ γ + . 15 MeV), and two helium nuclei (chain He reaction produces a + p ν ν νν Li and a neutrino of either 0.38 MeV or 3 p + ≤ He 7 - 26 4 14% 0.25% 14% 0.25% He MeV Q MeV Q ν + 4 + Be Li + Be E He+ 7 2 8 99.89% ν 99.89% 7 3 p + e He + He 3 γ 2 ≤ → → → 4 → = 4% = 4% - + 2 = 25.66 = 25.66 Be → loss 8 loss + ν ν ν νν ν νν He + + He eff eff 3 He E E e 4 2 Li + p Li Be + e → He 7 7 + 3 + + He p-p CHAIN p-p He H + p 3 2 4 He ν ν νν ν ν νν + 2p 3 MeV MeV Q MeV MeV Q → + He + p 4 4 particle: 86% 86% → = 2% = 2% α = 26.20 H + e = 26.20 2 He loss loss 99.75% 99.75% 3 CHAIN I CHAIN II CHAIN III ν ν νν ν CHAIN I CHAIN II CHAIN III ν νν E eff E eff → Q Q Li nucleus captures a proton producing 7 He + 3 p + p Scheme of the p-p nuclear reactions chain. The reactions are divided in three chains and the final Be electron capture competes with proton capture producing Be is unstable and decays via electron capture to 7 7 When the center of a star reaches a temperature of T The fusion of hydrogen into helium represents the greater part of the stars life (main sequence helium nuclei (chain II). ducing a positron, a high energy neutrino (0 MeV 0.86 MeV. Finally the rate becomes significant. Thethis deuterium point produced three reacts different branches with are thetwo possible. protons proton The (chain sea I): producing An alternative is to catch an Figure 1: result is the transformation of four protons into a helium nucleus. III). Underground nuclear astrophysics 1. H-burning in stars stars) and is responsible for the prodigiousburning luminosity is: of those stars. The basic concept of hydrogen This transformation can occur throughThe two sequence different of processes: reactions the for p-p the p-p chain chain and is the shown CNO in cycle. fig PoS(NIC-IX)003 N, 13 (1.5) (1.2) (1.4) (1.3) , at the end 1.1 Heide Costantini dE KT / 99% 1% E − ν ν e + + πη 2 + + 4 γ γ e γ γ − πµ is the Maxwell-Boltzmann energy dis- e α 18 T e σ T + + + + + ) + + πη KT 2 E / N O N O N C C E CNO ( − E CNO Z 14 13 15 15 12 16 13 S e − 2 ) e ∞ X XZ 0 E → → → → → → → E ρ ∝ ( ρ Z 3 S p p ) 2 p p / E 3 + + ) = ) = + + ( ) p 1 ) = φ N N O N C C E − KT 13 13 14 15 15 12 ( ( p CNO keV) is much smaller than the Coulomb barrier, nuclear ( (                        ε ε n ≈ n 8 K H-burning occurs mainly through the CNO cycle. 6 s 10 = × > ]. v 1 σ ICNO K, carbon present in the star can react with the proton sea producing < 6 10 C which, in turn, captures another proton. As shown in equation × 13 15 ≈ where T is the stellar temperature and where the exponential term takes into account the tunnelling probability and the S-factor, S(E), The reaction rate can thus be expressed as: Nuclear reactions during H-burning occur between charged particles and since the typical If in addition to hydrogen and helium, heavier elements are present in the star’s interior, a smoothly varying function withproperties the of the energy reaction for [ non resonant reactions, includes all the nuclear (1.1) The CNO cycle energy production rate increasesrate. faster with temperature than the p-p chain reaction reactions occur through tunnelling effect.define the For cross charged section particle as: reaction it is therefore possible to tribution that determines the velocity distributionof of non-degenerate the matter nuclei like inside in the quiescent stellar H-burning. plasma in the case energy of the interacting nuclei (KT of this first part of thein CNO-I the cycle, four p-p protons chain are and transformed with in the one same helium Q-value: nucleus, exactly as where X is thestellar hydrogen temperature abundance exceeds and 15 Z is the metal abundance. Therefore when the central Underground nuclear astrophysics second possibility for the conversion of hydrogengated into in helium 1938 is by offered H. by Bethe aincreases and reaction to C.F. cycle T Von investi- Weiszäker: the CNO-cycle. When the central temperature which decays to PoS(NIC-IX)003 He 4 He,2p) 3 Heide Costantini He( 3 A for protons and 250 µ A becomes a fundamental require- µ He nuclear reaction has been studied using 4 He). 4 4 He,2p) 3 He,2p) He( 3 3 He( 3 ]). However extrapolations can sometimes fail, for example in the case of 2 ), an uncertainty of few per cent in the energy brings a very large error in the ]. barn corresponding to experimental counting rate ranging from few events per 3 1.4 O and 22 keV for 12 15 − ) γ -10 9 − N(p, . Measurements generally last several weeks and months and therefore long term energy 14 α During the first phase of LUNA, the Since the main feature of an underground nuclear reaction measurement is the extremely low One of the goal of experimental nuclear astrophysics is to measure nuclear reactions at the Therefore experimentalists measure nuclear reactions at higher energies, transform the cross The Laboratory for Underground Nuclear Astrophysics (LUNA) has been designed to measure The product of the two exponentialFor terms a leads given to stellar a temperature well T, defined nuclear peak reactions (the are Gamow taking peak). place mainly inside the Gamow A for µ ment. The LUNA facilityHelium operates and a proton 50 beams kV are operated and at a currents 400 of kV approximately low 500 energy electrostatic accelerators. the home-made 50 kV accelerator. The presence of a low energy resonance in the 2.2 Main nuclear reaction studied at LUNA: experimental techniques and challenges. cross section determination. ThereforekV a accelerator good a energy beam energy resolution stability isthe of required. order 5 of eV/hour For has 70 been eV the measured LUNA and [ 400 the energy spread is of cross section, high beam current up to several hundreds of 2.1 Accelerators energies at which they take placeorder inside of stars. 10 Cross sections at the Gamow peak energy are of the section into S-factor and then extrapolate the S-factorthe by R-matrix means of method different techniques [ (for example 2. The LUNA project nuclear reactions mainly of H-burningpossible to both the of Gamow p-p peak. chainSasso It (LNGS) and is in located CNO Italy. deep The cycle Gran underground atthick) Sasso in equivalent energies site the to is as Laboratori 3800 protected Nazionali m close from water, del cosmic as of suppressing Gran rays magnitude the by flux and a of the rock cosmic neutron cover ray flux (1400 induced by m muons three by orders six of orders magnitude. day to few events per monththese reaction with measurements typical at laboratory surface conditions. laboratory isby The that cosmic main the rays, detectors problem that are in continuously interacting performing bombarded background with in the the detectors. detector, the The cosmic target backgroundrate and rate at the is the generally surrounding Gamow much materials, peak. larger than create the reaction an unpredicted narrow resonance at low energiesstate. or in One the case solution of to contributions from overcomeunderground a this laboratory subthreshold problems where the is cosmic to flux perform is nuclear reduced reaction by measurements several orders in of an magnitude. Underground nuclear astrophysics peak. In the casekeV of for H-burning typical energies are of the order of tens of keV (for example 27 stability becomes very important. Furthermore sincethe the energy (see cross eq. section depends exponentially from PoS(NIC-IX)003 He 4 ], is 1 ]. Thus, 8 He,2p) ], there are 3 8 Heide Costantini He( He reaction was 3 4 He(d,p) 3 ). The latter process is enhanced 2 O nucleus. ]. The capture cross section needs to be 15 7 , 6 O (see fig. 15 5 O reaction. 15 ) γ Level scheme of the O, the slowest process in the H-burning CNO cycle [ 15 N(p, ) γ 14 Figure 2: N(p, 14 ]. 4 -ray measurements, i.e. the center-of-mass energy E=240 keV [ γ He reaction cross section. To distinguish between the protons coming from 4 ] and the solar neutrino spectrum [ =30 keV (the Gamow peak in core H-burning stars), which is far below the low- 5 He reaction and the protons from the contaminant reaction, a coincidence be- 0 4 He reaction. Thanks two this technique the background 4 He(d,p) 3 He,2p) 3 He,2p) He( 3 The capture reaction The cross section was measured down to about 15 keV covering all theAfter solar the success Gamow of peak this first experiment, a new 400KV accelerator was installed and the first A windowless gas target was used and the protons coming out from the reaction were de- O and the capture to the ground state (gs) in 3 He deuterium contamination in the gas target produced a very high background signal due to 15 3 He( of high astrophysical interestglobular as clusters its [ reaction rate influences sensitively the age determination of two major and nearly equalin contributions to S(0): the direct capture (DC) to the 6.79 MeV state completely suppressed [ the data had to beastrophysical extrapolated over S-factor a at large zero energy gap energy, leading S(0). to a According substantial to uncertainty for the the data and analysis of [ tween two silicon detectors was3 required as a signature of the emission of the two protons from the the a the strong known down to E energy limit of direct and excluding the existence of any resonance.Solar Neutrino This Problem important was result showed not that in the the solution uncertainty of of the the Standardmeasurement Solar performed Model. was the Underground nuclear astrophysics was invoked, before the SNO andNeutrino Problem. Kamland results, as a possible nuclear explanation of thetected Solar with Si-detectors. Sincebeam cosmic induced background background is canlevel suppressed become in a in target critical an and issue underground beampresent and laboratory, purity. due has Gas for to targets examples are be to generally vacuum avoided pumps favored by oil although keeping contamination. impurities a can In high still the be case of the PoS(NIC-IX)003 ]. 14 =180 keV. It , ] using an R- p 9 Heide Costantini 13 , 12 energies below 3 MeV, the γ has been taken a E 4 ] were reanalyzed by [ 8 -transitions and in particular the ground γ ). In this energy region the dominant back- ]. The LUNA collaboration started in 2001 a ] for capture to the ground state, they reported 8 2.2 11 6 -decays. The ground state transition energy is close γ O reaction is particularly well suited for an underground radiation coming from environmental radioactive isotopes ). In order to lower beam induced background, a careful 15 γ ) =-507 keV, the width of which was taken as a free parameter 2.2 γ R N(p, 14 -detectors, the advantage of an underground laboratory is particularly O studying this reactions in two different phases [ γ 15 ) γ N(p, 14 -energies above 3 MeV (see fig. γ Bi etc.) that are always present in the rocks surrounding the laboratory. Radiative re- 214 ]. Subsequently, the data of Schröder et al [ 8 Background spectra taken with the 126% high purity germanium detector at surface (top spectrum) Tl, 208 The goal of the first phase was to study the single The measurement of the As a matter of fact for ] and by a Coulomb excitation measurement [ K, 40 10 background spectrum is dominated by and underground with a 5 cmspectra lead and shielding the (bottom counts spectrum). are The expressed measurement in time arbitrary is units. the same for both study of different solidon targets a and Ta backing backing materials were was finally performed chosen. and The TiN spectrum sputtered of targets fig. Figure 3: state transition. Therefore aand solid it target was coupled possible with toto a distinguish the high the Q-value resolution single of the HpGe-detector reaction was andenergy so used spectra a around clean signal 7 could MeV be detected (fig. thanks to the background free a negligible contribution duewidth to of a the smaller 6.79 total MeV[ width state of was the supported by subthresholdreinvestigation a resonance. of lifetime measurement A via smaller Doppler-shift method ground source are cosmic raysreduced by and more by than three bringing orders the of detector magnitude. On underground the the other background hand( at rate is action measurements are consequently favored underground especially for high Q-value reactions. appreciated at experiment since the Q-value of the reaction is 7.3 MeV. Underground nuclear astrophysics due to a subthreshold resonance at E in the fit [ matrix approach. Contrary to the extrapolation by [ PoS(NIC-IX)003 =4.4 and =150. In γ 6 O reaction 15 ) γ -cascades are =80 keV) the b γ Heide Costantini N(p, ] above T 14 19 C reaction at E 1 Gyears depending by 12 ± ) γ B(p, 11 ) reactions from neutrons produced γ A), the gas target local density along the N spectra. Again beam induced background µ 14 ] that the rate has to be reduced by nearly a 9 BGO summing crystal. All the ]. In the gas target experiment the main source =500 7 p π 16 =140-400 keV. b around 7 MeV where the detection efficiency is about ). cm He gas, beam induced background measurements could be 5 4 =180 keV. The secondary transitions from the p =Q+E γ ]. A careful study of beam heating effect was performed and the results 15 ,n) from natural radioactivity or residual cosmic muons. C due to Boron contaminant in Ta backing. Cross section measurements with solid target α HpGe spectrum taken at E ]. Due to the intense beam current (I 12 ) ] but differed in the weight of the contributions from the various transitions. The extracted 14 γ In the case of low Q-value reactions, the advantage of an underground laboratory is not evident The two different approaches were complementary and both took extreme advantage of the Beam induced background was mainly disturbing the measurements at intermediate energies, The weak side of using a high resolution germanium detector is the relatively low detection The final results from both experiments were in good agreement with new measurement by 18 , B(p, 17 main background source in the ROI was coming from (n, conclusion, with the present determination of theis reaction the rates age the increase main astrophysical of consequence thethe Globular metallicity Clusters of by about the 1 Globular Gyear, Cluster i.e and about the 14 reduction of a factor 2 of solar CNO neutrinos. was a major problem at intermediate energies. Ateither the by lowest ( measured energy (E stellar reaction rate confirmedfactor the of conclusion two at of low [ temperatures, but it is in good agreement with NACRE [ were implemented in the final data analysis [ low background laboratory (see figure beam path is decreased [ performed and the obtained spectra subtracted to the since by decreasing the beamtion energy, the of Coulomb the parasitic barrier reactions. was sensitively affecting the cross sec- efficiency. Therefore to push the cross sectionof measurements the toward lower experiment energies a was second started phase using a nearly 4 [ Figure 4: are visible together with the primary and secondary transitions from the 65% [ of beam induced background wasBy coming replacing the from N impurities gas in with the the collimators inert and the beam stop. setup were performed in the energy range E Underground nuclear astrophysics clearly shows the contribution of11 both the studied reaction and of the parasitic background reaction summed together to a peak at E 11.6 MeV. PoS(NIC-IX)003 Li 7 =3%. ]. The ) 6 B ( Φ He window- / 3 ] reduces the =7% [ )) ) Heide Costantini 21 B B ( ( Φ Φ ( / ∆ is reduced to a corre- )) B 34 ( = 478 keV), coming from γ Φ ( ∆ s (E s below 2 MeV is of five orders γ γ 1.6 and 1.2 MeV), coming from ≈ γ solid target tot gas-target B neutrino data. 8 -rays (E γ 8 E (keV) result. A recent activation study [ γ reaction. O 15 ) γ , p ( of Lead and Copper) and placed at close distance to a 3 N 0 50 100 150 200 250 300 350 400 14 -rays are measured with an ultra-low 135% background germanium de-

γ 1E+03 1E+02 1E+01 1E+00 S-factor (keVb) S-factor Be has a Q-value of 1.6 MeV. This reaction is presently under study at LUNA. 7 ) γ Be reaction is one of the major source of uncertainty in determing the Boron solar He, ]. Past measurements, that go back to twenty years ago, have been performed using 7 4 ) 20 γ , He( Comparison between the astrophysical factor obtained with the LUNA high resolution and high α 3 -capture, are detected, while in the second one the delayed α He( The goal of the experiment at LUNA is to measure the cross sectionThe of prompt the capture reaction using both A global analysis indicates that the extrapolated S(0) obtained with the activation method is The 3 Be decay through electron capture, are counted. techniques at the same time reducing the error on the astrophysical factor S(3,4) to 4%. discrepancy to 9% still not at the precision level of the less gas target. The suppression factor obtained with the shield for tector heavily shielded (0.3 m neutrino Flux and dominates over the presentforeseeable observational accuracy accuracy of the new generation solar neutrino experiments is direct two different methods. In the first method prompt The at first sight. Environmentalpassively background with is proper also Lead and present Copper underground.underground shield laboratory. as Detectors In on a can surface. surface be However laboratory therebut shielded passive is shielding above a can big a be advantage certain built in aroundmaterial a thickness the since the detectors cosmic muons shield interact with efficiency thein cannot shielding the material be detector. and Obviously can increased this create by background problem signals is adding dramatically further reduced shield in an underground laboratory. Figure 5: efficiency experiments for the This result could illuminate about solar physics if the uncertainty on S Underground nuclear astrophysics abundance [ sponding level. Moreover this reaction plays an important role in understanding the primordial 7 sistematically 13% higher than the prompt- PoS(NIC-IX)003 Al 26 ) γ A and Mg(p, ]. The µ 25 Mg solid 22 25 Heide Costantini =400 keV obtained α to the excited state gs -astronomy [ γ Al 26 decay of + β 9 Al reaction is finished, LUNA will end the current BGO summing crystal with a high purity 26 ) π γ Mg(p, 25 -ray, one of the most important line for γ Be nuclei are collected on the beam stop and are counted off-line by 7 Be reaction measurement is finished, LUNA will start to study the 7 ). ) 6 γ , α Al is very complicated and a lot of resonances of low intensities are present in -Rutherford scattering cross section with a silicon detector positioned inside the 26 He( α 3 Comparison between the background spectrum and the reaction spectrum at E Mg gives rise to a 1.8 MeV When the measurement of the When the Besides from the rocks, environmental background can come also from all the materials sur- In September 2005 a working group has been formed inside the LUNA collaboration with the At the same time a new idea of an underground accelerator facility to be installed inside the 26 therefore to avoid systematic uncertaintiessured due through to beam heating effects the target density is mea- 3. Outlook a 125% HpGe detector, completelypositioned shielded in by the 15 low cm activity of laboratory lead at and LNGS. 10 The cm typical of beam copper current on is about each 250 side, target chamber. the astrophysical energy region. The measurementformed of at the LUNA weak coupling a low energy high resonances efficient 4 will be per- rounding the detector and fromclose the to detector the itself. detector Therefore werechamber the made assembling. target of chamber The and OFC all copper the and setup no welding materials have been used in the reaction. It’s the slowest reaction of the Mg-Al cycle. The level scheme of target. First test of target purity and stability has been performed. Figure 6: goal to determine a listaccelerator of and reaction for of which astrophysical an relevance undergroundthe approach that working represents could group a is be clear to studied advantage. investigate at theenergy An the importance accelerator other and that 400 goal the could kV of possibility be of used the for installation the of study a of higher He-burning keyfuture nuclear DUSEL reactions. underground laboratory is developing in the United States nuclear astrophysics co- scientific approved program. Underground nuclear astrophysics of magnitude (see fig. of with the ultra low background 135%of HpGe the detector. natural The environmental suppression radioactivity factor is due of to five the orders passive of Pb-Cu magnitude. shield PoS(NIC-IX)003 Heide Costantini 10 capture reactions in inverse kinematics using the recoil α ) reactions in forward kinematics, and in a second phase a higher energy γ , α ,n) and ( α [7] S. Degl’Innocenti et al., Phys. Lett.[8] B 590(2004)13 U. Schröder et al, Nucl. Phys.[9] A 467(1987)240 C. Angulo and P. Descouvemont, 2001, Nucl. Phys. A 690(2001)755 [2] A.N. Lane and R.G. Thomas, Rev.[3] Mod. Phys. 30(1958)257 A. Formicola et al., Nucl. Inst.[4] Meth. A, R. 507(2003)609 Bonetti et al.,Phys. Rev. Lett.[5] 82(1999)5205 G. Imbriani et al, A&A, 420(2004)625 [6] J. N. Bahcall and M. H. Pinsonneault, Phys. Rev. Lett. 92(2004)121301 [1] C. Rolfs and W.S. Rodney: Cauldrons in the cosmos, University of Chicago Press (1988) [19] C. Angulo et al, Nucl. Phys.[20] A 656(1999)3 A. Coc et al., Astrophys. J.[21] 600(2004)544 B.S. Nara Singh et al., Phys.[22] Rev. Let. 93(2004)262503 R. Diehl et al. A&A, 298(1995)445. [15] J. Görres et al., Nucl. Inst.[16] Meth. A, D. 177(1980)295 Bemmerer et al., submitted to[17] Nucl. Phys. A.M. A Mukhamedzhanov et al, Phys. Rev.[18] C 67(2003)065804 R.C. Runkle et al.,Phys. Rev. Lett. 94(2005)082503 [11] K. Yamada et al, Phys. Lett.[12] B 579(2004)265 A. Formicola et al, Phys.Lett.B, 591(2004)61-68 [13] G. Imbriani et al, Eur.Phys.Journal A,[14] 25(2005)455-466 A. Lemut et al., Phys. Lett. B 634(2006)483-487 [10] P.F. Bertone et al, Phys. Rev. Lett. 87(2001)152501 separator technique. References heavy ion machine to study proton and Underground nuclear astrophysics munity. The new facility (ALNA: Acceleratorshould Laboratory be for Nuclear mainly Astrophysics focused Underground) onple the the study low of background He-burning environmenttechniques and of aimed C-burning an reactions. to underground maximum laboratory ALNA detection withactive will background efficiency state cou- reduction. and of The unique the idea event art isto identification detection to study capability install ( for in a first phase a small accelerator for light ions