LUNA: Status and prospects

Abstract

The essential ingredients of nuclear astrophysics are the thermonuclear reactions which shape the life and death of stars and which are responsible for the synthesis of the chemical elements in the Universe. Deep underground in the Gran Sasso Laboratory the cross sections of the key reactions responsible for the hydrogen burning in stars have been measured with two accelerators of 50 and 400 kV voltage right down to the energies of astrophysical interest. As a matter of fact, the main advantage of the underground laboratory is the reduction of the background. Such a reduction has allowed, for the first time, to measure relevant cross sections at the Gamow energy. The qualifying features of underground nuclear astrophysics are exhaustively reviewed before discussing the current LUNA program which is mainly devoted to the study of the Big-Bang nucleosynthesis and of the synthesis of the light elements in AGB stars and classical novae. The main results obtained during the study of reactions relevant to the Sun are also reviewed and their influence on our understanding of the properties of the neutrino, of the Sun and of the Universe itself is discussed. Finally, the future of LUNA during the next decade is outlined. It will be mainly focused on the study of the nuclear burning stages after hydrogen burning: helium and carbon burning. All this will be accomplished thanks to a new 3.5 MV accelerator able to deliver high current beams of proton, helium and carbon which will start running under Gran Sasso in 2019. In particular, we will discuss the first phase of the scientific case of the 3.5 MV accelerator focused on the study of 12 C+ 12 C and of the two reactions which generate free neutrons inside stars: 13 C(α,n) 16 O and 22 Ne(α,n) 25 Mg. arXiv:1707.07952v4 [nucl-ex]

The muon intensity in the Felsenkeller shallow underground laboratory

“…Email address: d.bemmerer@hzdr.de (D. Bemmerer) Possible applications for such underground laboratories are ultra-low level γ-ray spectroscopy [14][15][16][17][18][19][20][21][22], ultra-pure material development [23], or nuclear astrophysics [24,25].…”

“…When the rock overburden exceeds 1000 m thickness, the muon intensity is suppressed by six orders of magnitude or more, so that it usually does not limit experiments any more. In these deep-underground settings, solar neutrino flux measurements [26][27][28], dark matter searches [29], and rare event studies [30] are possible, and also nuclear astrophysics greatly benefits [24,31].…”

Study of the 22Ne(α , γ)26Mg reaction at LUNA

“…The study of the 395 keV resonance of the 22 Ne(α, γ) 26 Mg reaction is already completed at LUNA 400 kV accelerator [8] installed in the underground Gran Sasso Laboratory, where the rock overburden of about 1400 m (3800 m water equivalent) reduces the muon component of the cosmic background by a factor of 10 6 and the neutron component by a factor of 10 3 [9]. The last component remains the most important source of background in the region of interest for the 22 Ne(α, γ) 26 Mg reaction.…”

Felsenkeller 5 MV underground accelerator: Towards the Holy Grail of Nuclear Astrophysics 12C(α, γ)16O

“…The Felsenkeller scientific program draws on many years of experience in nuclear astrophysics experiments at the overground HZDR 3 MV Tandetron accelerator [19][20][21][22][23][24] and on a long-standing involvement in the LUNA collaboration [10,11]. Complementary experiments studying the γ-widths of relevant levels [25,26] have been performed at the local bremsstrahlung facility [27] and are underway at the local neutron time-of-flight facility [28].…”

“…The most precise technique hitherto developed to address stable-ion nuclear reactions such as these is underground nuclear astrophysics, which has been pioneered by the LUNA collaboration working deep underground in the Gran Sasso laboratory, Italy [10]. There, in recent years a number of nuclear reactions important for Big Bang nucleosynthesis [11,12] and for stellar hydrogen burning [13-15, recent examples] have been studied using a 0.4 MV high-current accelerator.…”