Low-energy Nuclear Astrophysics Research Articles

Editorial of Low Energy Nuclear Astrophysics and Sterile Neutrinos as Dark Matter

This is an editorial on low energy nuclear astrophysics and sterile neutrinos as dark matter. First, the symmetric cosmic microwave background radiation and the the symmetric evolution of the Universe are editorialized. Then, low energy astrophysics with the evolution of the Sun, supernovae, and the Galaxy’s rotation are editorialized. In the final section, sterile neutrinos as dark matter is editorialized.

Advances in radiative capture studies at LUNA with a segmented BGO detector

Studies of charged-particle reactions for low-energy nuclear astrophysics require high sensitivity, which can be achieved by means of detection setups with high efficiency and low backgrounds, to obtain precise measurements in the energy region of interest for stellar scenarios. High-efficiency total absorption spectroscopy is an established and powerful tool for studying radiative capture reactions, particularly if combined with the cosmic background reduction by several orders of magnitude obtained at the Laboratory for Underground Nuclear Astrophysics (LUNA). We present recent improvements in the detection setup with the Bismuth Germanium Oxide (BGO) detector at LUNA, aiming to reduce high-energy backgrounds and increase the summing detection efficiency. The new design results in enhanced sensitivity of the BGO setup, as we demonstrate and discuss in the context of the first direct measurement of the 65 keV resonance (E x = 5672 keV) of the 17O(p,γ)18F reaction. Moreover, we show two applications of the BGO detector, which exploit its segmentation. In the case of complex γ-ray cascades, e.g. the de-excitation of E x = 5672 keV in 18F, the BGO segmentation allows to identify and suppress the beam-induced background signals that mimic the sum peak of interest. We demonstrate another new application for such a detector in form of in situ activation measurements of a reaction with β + unstable product nuclei, e.g. the 14N(p,γ)15O reaction.

Review of low energy nuclear astrophysics

In this review of Low Energy Nuclear Astrophysics, we review the nuclear energy and evolution of the sun. Then we review the estimate of dark matter from galaxy rotation. Next, we discuss neutron star formation from the gravitational collapse of massive stars which produces neutron stars and their velocity. Then the origin of supernovae, the estimate of dark energy from supernovae acceleration, and experiments related to low energy nuclear astrophysics are reviewed.

Stable beam experiments in wide energy ranges serving low energy nuclear astrophysics

In experimental nuclear astrophysics it is common knowledge that reaction cross sections must be measured in the astrophysically relevant, low energy ranges or at least as close to them as possible. In most of the cases, however, it is impossible to reach such low energies. The reactions must therefore be studied at higher energies and the cross sections must be extrapolated to lower ones. In this paper the importance of cross section measurements in wide energy ranges are emphasized and a few examples are shown from the areas of hydrogen burning processes and heavy element nucleosynthesis.

Experimental challenges in low-energy nuclear astrophysics

Nuclear astrophysics is an interdisciplinary field at the border between nuclear physics and astrophysics. It aims at answering fundamental questions such as how and where are elements synthesised, how energy is generated in stars and how stars evolve and eventually die. Nuclear astrophysics experiments use Earth-bound facilities to investigate nuclear reactions and nuclear properties of interest in stellar scenarios. This review will focus in particular on thermonuclear reactions occurring in relatively low temperature scenarios (T < 1 GK) such as quiescent burning stars and classical novae. Because of the hindering effect of the Coulomb repulsion between nuclei, nuclear cross sections in these scenarios can be extremely small (10−12 barn and even lower) and the signals produced can be challenging to disentangle from the natural background on the Earth’s surface.Moving underground to reduce the background induced by cosmic rays is one possible solution to this problem. For more than 20 years, the LUNA experiment has studied nuclear reactions employing accelerators based deep underground in the Gran Sasso Laboratory in Italy. In this review, recent results obtained at LUNA, as well as future prospects at the new LUNA-MV accelerator, soon to be installed underground will be reviewed.Another possible approach is to employ indirect methods to probe nuclear properties of astrophysical interest. This review work will mention in particular the novel possibility of carrying out nuclear astrophysics experiments at the newly commissioned CRYRING storage ring in GSI, Germany.

Development of a variable-energy, high-intensity, pulsed-mode ion source for low-energy nuclear astrophysics studies.

The primary challenge in directly measuring nuclear reaction rates near stellar energies is their small cross sections. The signal-to-background ratio in these complex experiments can be significantly improved by employing high-current (mA-range) beams and novel detection techniques. Therefore, the electron cyclotron resonance ion source at the Laboratory for Experimental Nuclear Astrophysics underwent a complete upgrade of its acceleration column and microwave system to obtain high-intensity, pulsed proton beams. The new column uses a compression design with O-ring seals for vacuum integrity. Its voltage gradient between electrode sections is produced by the parallel resistance of channels of chilled, deionized water. It also incorporates alternating, transverse magnetic fields for electron suppression and an axially adjustable beam extraction system. Following this upgrade, the operational bremsstrahlung radiation levels and high-voltage stability of the source were vastly improved, over 3.5 mA of target beam current was achieved, and an order-of-magnitude increase in normalized brightness was measured. Beam optics calculations, structural design, and further performance results for this source are presented.

Active Oxygen Target for Studies in Nuclear Astrophysics with Laser Compton Backscattered γ-ray Beams

An active target is being developed to be used in low-energy nuclear astrophysics experiments. It is a position- and time-sensitive detector system based on the low-pressure Multi Wire Proportional Chamber (MWPC) technique. Methylal ((OCH3)2CH2), at a pressure of a few Torr, serves as the working gas for MWPC operation, and in addition, the oxygen atoms of the methylal molecules serve as an experimental target. The main advantage of this new target detector system is that it has high sensitivity to the low-energy, highly-ionizing particles produced after photodisintegration of 16O and insensitivity to γ-rays and minimum ionizing particles. This allows users to detect only the products of the nuclear reaction of interest. The threshold energies for detection of α particles and 12C nuclei are about 50 keV and 100 keV, respectively. The main disadvantage of this detector is the small target thickness, which is around a few tens of μg/cm2. However, reasonable luminosity can be achieved by using a multimodule detector system and an intense, Laser Compton Backscattered (LCB) γ-ray beam. This paper summarizes the architecture of the active target and reports test results of the prototype detector. The tests investigated the timing and position resolutions of 30 × 30 mm2 low-pressure MWPC units using an α-particle source. The possibility of measuring the 16O(γ, α)12C cross-section in the 8–10 MeV energy region by using a LCB γ-ray beam is also discussed. A measurement of the 16O(γ, α)12C cross-section will enable the reaction rate of 12C(α, γ)16O to be determined with significantly improved precision compared to previous experiments.

Development of a variable-energy, high-intensity, pulsed-mode ion source for low-energy nuclear astrophysics studies

Development of a variable-energy, high-intensity, pulsed-mode ion source for low-energy nuclear astrophysics studies

Underground nuclear astrophysics studies with CASPAR

The drive of low-energy nuclear astrophysics laboratories is to study the reactions of importance to stellar burning processes and elemental production through stellar nucleosynthesis, over the energy range of astrophysical interest. As laboratory measurements approach the stellar burning window, the rapid drop off of cross-sections is a significant barrier and drives the need to lower background interference. The natural background suppression of underground accelerator facilities enables the extension of current experimental data to lower energies. An example of such reactions of interest are those thought to be sources of neutrons for the s-process, the major production mechanism for elements above the iron peak. The reactions 13 C(α,n)16 O and 22 Ne(α,n)25 Mg are the proposed initial focus of the new nuclear astrophysics accelerator laboratory (CASPAR) currently under construction at the Sanford Underground Research Facility, Lead, South Dakota

Bubble chambers for experiments in nuclear astrophysics

A bubble chamber has been developed to be used as an active target system for low energy nuclear astrophysics experiments. Adopting ideas from dark matter detection with superheated liquids, a detector system compatible with γ-ray beams has been developed. This detector alleviates some of the limitations encountered in standard measurements of the minute cross-sections of interest to stellar environments. While the astrophysically relevant nuclear reaction processes at hydrostatic burning temperatures are dominated by radiative captures, in this experimental scheme we measure the time-reversed processes. Such photodisintegrations allow us to compute the radiative capture cross-sections when transitions to excited states of the reaction products are negligible. Due to the transformation of phase space, the photodisintegration cross-sections are up to two orders of magnitude higher. The main advantage of the new target-detector system is a density several orders of magnitude higher than conventional gas targets. Also, the detector is virtually insensitive to the γ-ray beam itself, thus allowing us to detect only the products of the nuclear reaction of interest. The development and the operation as well as the advantages and disadvantages of the bubble chamber are discussed.

The Second-phase Development of the China JinPing Underground Laboratory

During 2013-2015 an expansion of the China JinPing underground Laboratory (CJPL) will be undertaken along a main branch of a bypass tunnel in the JinPing tunnel complex. This second phase of CJPL will increase laboratory space to approximately 96,000 m3, which can be compared to the existing CJPL-I volume of ∼ 4,000 m3. One design configuration has eight additional hall spaces, each over 60 m long and approximately12 m in width, with overburdens of about 2.4km of rock, oriented parallel to and away from the main water transport and auto traffic tunnels. There are additional possibilities for further expansions at a nearby second bypass tunnel and along the entrance and exit branches of both bypass tunnels, potentially leading to an expanded CJPL comparable in size to Gran Sasso. Concurrent with the excavation activities, planning is underway for dark matter and other rare-event detectors, as well as for geophysics/engineering and other coupled multi-disciplinary sensors. In the town meeting on 8 September, 2013 at Asilomar, CA, associated with the 13th International Conference on Topics in Astroparticle and Underground Physics (TAUP), presentations and panel discussions addressed plans for one-ton expansions of the current CJPL germanium detector array of the China Darkmatter EXperiment (CDEX) collaboration and of the duel-phase xenon detector of the Panda-X collaboration, as well as possible new detector initiatives for dark matter studies, low-energy solar neutrino detection, neutrinoless double beta searches, and geoneutrinos. JinPing was also discussed as a site for a low-energy nuclear astrophysics accelerator. Geophysics/engineering opportunities include acoustic and micro-seismic monitoring of rock bursts during and after excavation, coupled-process in situ measurements, local, regional, and global monitoring of seismically induced radon emission, and electromagnetic signals. Additional ideas and projects will likely be developed in the next few years, driven by China's domestic needs and by international experiments requiring access to very great depths.

A new experimental setup established for low-energy nuclear astrophysics studies

An experimental setup for low-energy nuclear astrophysics studies has been recently established at the Institute of Modern Physics (IMP), Lanzhou, China. The driver machine is a 320kV high voltage platform, which can provide intense currents of proton, alpha and many heavy ion beams. The energy of a proton beam was calibrated against the nominal platform high voltage by using a well-known resonant reaction of 11B(p,γ)12C and a non-resonant reaction 12C(p,γ)13N. The accuracy was achieved to be better than ±0.5keV. The detection system consists of a Clover-type high-purity germanium detector, a silicon detector and a plastic scintillator. The performance of the detectors was tested by several experiments. The astrophysical S-factors of the 7Li(p,γ)8Be and 7Li(p,α)3He reactions were measured with this new setup, and our data agree with the values found in the literature. In addition, the upgrade of our driver machine and experimental setup has been discussed. As a future goal, a fascinating National Deep Underground Laboratory in China, the deepest underground laboratory all over the world, is prospected.

Low-energy nuclear astrophysics - the fascinating region of A=7

Low-energy nuclear astrophysics - the fascinating region of A=7

Low-energy nuclear astrophysics - the fascinating region of A=7

Abstract We discuss results and future plans for low-energy reactions that play an important role in current nuclear astrophysics research and that happen to concentrate around the region of A = 7 . The 7 Be(p,γ) 8 B and the 3 He( 4 He,γ) 7 Be reactions are crucial for understanding the solar-neutrino oscillation phenomenon and the latter one plays a central role in the issue of cosmic 7 Li abundance and big-bang nucleosynthesis. We also present results regarding the host dependence of the half-life of the electron-capture 7 Be radio-nuclide.