395 research outputs found
LUNA: Status and Prospects
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 C+C and of the two
reactions which generate free neutrons inside stars:
C(,n)O and Ne(,n)Mg.Comment: To be published in Progress in Particle and Nuclear Physics 98C
(2018) pp. 55-8
Constraining Big Bang lithium production with recent solar neutrino data
The 3He({\alpha},{\gamma})7Be reaction affects not only the production of 7Li
in Big Bang nucleosynthesis, but also the fluxes of 7Be and 8B neutrinos from
the Sun. This double role is exploited here to constrain the former by the
latter. A number of recent experiments on 3He({\alpha},{\gamma})7Be provide
precise cross section data at E = 0.5-1.0 MeV center-of-mass energy. However,
there is a scarcity of precise data at Big Bang energies, 0.1-0.5 MeV, and
below. This problem can be alleviated, based on precisely calibrated 7Be and 8B
neutrino fluxes from the Sun that are now available, assuming the neutrino
flavour oscillation framework to be correct. These fluxes and the standard
solar model are used here to determine the 3He(alpha,gamma)7Be astrophysical
S-factor at the solar Gamow peak, S(23+6-5 keV) = 0.548+/-0.054 keVb. This new
data point is then included in a re-evaluation of the 3He({\alpha},{\gamma})7Be
S-factor at Big Bang energies, following an approach recently developed for
this reaction in the context of solar fusion studies. The re-evaluated S-factor
curve is then used to re-determine the 3He({\alpha},{\gamma})7Be thermonuclear
reaction rate at Big Bang energies. The predicted primordial lithium abundance
is 7Li/H = 5.0e-10, far higher than the Spite plateau.Comment: Final accepted version, some typos corrected, in the press at Phys.
Rev.
LUNA: Nuclear Astrophysics Deep Underground
Nuclear astrophysics strives for a comprehensive picture of the nuclear
reactions responsible for synthesizing the chemical elements and for powering
the stellar evolution engine. Deep underground in the Gran Sasso laboratory the
cross sections of the key reactions of the proton-proton chain and of the
Carbon-Nitrogen-Oxygen (CNO) cycle have been measured right down to the
energies of astrophysical interest. The salient features of underground nuclear
astrophysics are summarized here. The main results obtained by LUNA in the last
twenty years are reviewed, and their influence on the comprehension of the
properties of the neutrino, of the Sun and of the Universe itself are
discussed. Future directions of underground nuclear astrophysics towards the
study of helium and carbon burning and of stellar neutron sources in stars are
pointed out.Comment: Invited review, submitted to Annu. Rev. Nucl. Part. Scienc
Development of a jet gas target system for the Felsenkeller underground accelerator
For direct cross-section measurements in nuclear astrophysics, in addition to
suitable ion beams and detectors, also highly pure and stable targets are
needed. Here, using a gas jet as a target offers an attractive approach that
combines high stability even under significant beam load with excellent purity
and high localisation. Such a target is currently under construction at the
Felsenkeller underground ion accelerator lab for nuclear astrophysics in
Dresden, Germany. The target thickness will be measured by optical
interferometry, allowing an in-situ thickness determination including also
beam-induced effects. The contribution reports on the status of this new system
and outlines possible applications in nuclear astrophysics.Comment: Submitted to Nuclear Physics in Astrophysics - X conference
proceedin
Cosmic-ray induced background intercomparison with actively shielded HPGe detectors at underground locations
The main background above 3\,MeV for in-beam nuclear astrophysics studies
with -ray detectors is caused by cosmic-ray induced secondaries. The
two commonly used suppression methods, active and passive shielding, against
this kind of background were formerly considered only as alternatives in
nuclear astrophysics experiments. In this work the study of the effects of
active shielding against cosmic-ray induced events at a medium deep location is
performed. Background spectra were recorded with two actively shielded HPGe
detectors. The experiment was located at 148\,m below the surface of the Earth
in the Reiche Zeche mine in Freiberg, Germany. The results are compared to data
with the same detectors at the Earth's surface, and at depths of 45\,m and
1400\,m, respectively.Comment: Minor errors corrected; final versio
Precise nuclear physics for the Sun
For many centuries, the study of the Sun has been an important testbed for understanding stars that are further away. One of the first astronomical observations Galileo Galilei made in 1612 with the newly invented telescope concerned the sunspots, and in 1814, Joseph von Fraunhofer employed his new spectroscope to discover the absorption lines in the solar spectrum that are now named after him.
Even though more refined and new modes of observation are now available than in the days of Galileo and Fraunhofer, the study of the Sun is still high on the agenda of contemporary science, due to three guiding interests.
The first is connected to the ages-old human striving to understand the structure of the larger world surrounding us. Modern telescopes, some of them even based outside the Earth’s atmosphere in space, have succeeded in observing astronomical objects that are billions of light- years away. However, for practical reasons precision data that are important for understanding stars can still only be gained from the Sun. In a sense, the observations of far-away astronomical objects thus call for a more precise study of the closeby, of the Sun, for their interpretation.
The second interest stems from the human desire to understand the essence of the world, in particular the elementary particles of which it consists. Large accelerators have been constructed to produce and collide these particles. However, man-made machines can never be as luminous as the Sun when it comes to producing particles. Solar neutrinos have thus served not only as an astronomical tool to understand the Sun’s inner workings, but their behavior on the way from the Sun to the Earth is also being studied with the aim to understand their nature and interactions.
The third interest is strictly connected to life on Earth. A multitude of research has shown that even relatively slight changes in the Earth’s climate may strongly affect the living conditions in a number of densely populated areas, mainly near the ocean shore and in arid regions. Thus, great effort is expended on the study of greenhouse gases in the Earth’s atmosphere. Also the Sun, via the solar irradiance and via the effects of the so-called solar wind of magnetic particles on the Earth’s atmosphere, may affect the climate. There is no proof linking solar effects to short-term changes in the Earth’s climate. However, such effects cannot be excluded, either, making it necessary to study the Sun.
The experiments summarized in the present work contribute to the present-day study of our Sun by repeating, in the laboratory, some of the nuclear processes that take place in the core of the Sun. They aim to improve the precision of the nuclear cross section data that lay the foundation of the model of the nuclear reactions generating energy and producing neutrinos in the Sun.
In order to reach this goal, low-energy nuclear physics experiments are performed. Wherever possible, the data are taken in a low-background, underground environment. There is only one underground accelerator facility in the world, the Laboratory Underground for Nuclear Astro- physics (LUNA) 0.4 MV accelerator in the Gran Sasso laboratory in Italy. Much of the research described here is based on experiments at LUNA. Background and feasibility studies shown here lay the base for future, higher-energy underground accelerators. Finally, it is shown that such a device can even be placed in a shallow-underground facility such as the Dresden Felsenkeller without great loss of sensitivity
Primordial nucleosynthesis
Big Bang nucleosynthesis (BBN) describes the production of light nuclei in the early phases of the Universe. For this, precise knowledge of the cosmological parameters, such as the baryon density, as well as the cross section of the fusion reactions involved are needed. In general, the energies of interest for BBN are so low (E < 1MeV) that nuclear cross section measurements are practically unfeasible at the Earth’s surface. As of today, LUNA (Laboratory for Underground Nuclear Astrophysics) has been the only facility in the world available to perform direct measurements of small cross section in a very low background radiation. Owing to the background suppression provided by about 1400 meters of rock at the Laboratori Nazionali del Gran Sasso (LNGS), Italy, and to the high current offered by the LUNA accelerator, it has been possible to investigate cross sections at energies of interest for Big Bang nucleosynthesis using protons, 3He and alpha particles as projectiles. The main reaction studied in the past at LUNA is the 2H(4He, (Formula presented.))6Li. Its cross section was measured directly, for the first time, in the BBN energy range. Other processes like 2H(p, (Formula presented.))3He , 3He(2H, p)4He and 3He(4He, (Formula presented.))7Be were also studied at LUNA, thus enabling to reduce the uncertainty on the overall reaction rate and consequently on the determination of primordial abundances. The improvements on BBN due to the LUNA experimental data will be discussed and a perspective of future measurements will be outlined. © 2016, SIF, Springer-Verlag Berlin Heidelberg
- …