- Published on 14 June 2017
In high-temperature field theory applied to nuclear physics, in particular to relativistic heavy-ion collisions, it is a longstanding question how hadrons precisely transform into a quark-gluon matter and back. The change in the effective number of degrees of freedom is rather gradual than sudden, despite the identification of a single deconfinement temperature. In order to gain an insight into this issue while considering the structure of the QGP we review the spectral function approach and its main consequences for the medium properties, including the shear viscosity. The figure plots a sample spectral density on the left and the effective number of degrees of freedom (energy density relative to the free Boltzmann gas) to the right. Two thin spectral lines result in a doubled Stefan-Boltzmann limit (SB), while any finite width reduces the result down to a single SB. When spectral lines become wide, their individual contributions to energy density and pressure drops. Continuum parts have negligible contribution. This causes the melting of hadrons like butter melts in the Sun, with no latent heat in this process.
- Published on 06 May 2017
New approach to analysing anomalies in collisions between atomic nuclei promises a new perspective on how they interact
Anomalies always catch the eye. They stand out from an otherwise well-understood order. Anomalies also occur at sub-atomic scale, as nuclei collide and scatter off into each other—an approach used to explore the properties of atomic nuclei. The most basic kind of scattering is called ‘elastic scattering,’ in which interacting particles emerge in the same state after they collide. Although we have the most precise experimental data about this type of scattering, Raymond Mackintosh from the Open University, UK, contends in a paper published in EPJ A that a new approach to analysing such data harbours potential new interpretations of fundamental information about atomic nuclei.
EPJ A Highlight - Open refereed paper reveals how to study unstable radioactive nuclei’s dual traits
- Published on 16 November 2016
HIE-ISOLDE acceleration of radioactive beams to peer into the dual state of matter unique to nuclei
Radioactive nuclides, found within an atom's core, all share a common feature: they have too many or too few neutrons to be stable. In a new review published in EPJ A, Maria Jose Borges and Karsten Riisager explain how overcoming technical difficulties in accelerating such radioactive nuclei beams can help push back the boundaries of nuclear physics research. This fascinating topic is the first EPJ A paper to be subjected to an open referee process, whereby the referee's comments are included.
- Published on 12 October 2016
Pursuing a detective's approach to carbon atom breakup yields clues relevant to fusion reactions and astrophysics phenomena
Regardless of the scenario, breaking up is dramatic. Take for example the case of carbon (12C) splitting into three nuclei of helium. Until now, due to the poor quality of data and limited detection capabilities, physicists did not know whether the helium fragments were the object of a direct breakup in multiple fragments up front or were formed in a sequence of successive fragmentations. The question has been puzzling physicists for some time. Now, scientists from Denmark's Aarhus University have used a state-of-the-art detector capable of measuring, for the first time, the precise disintegration of the 12C into three helium nuclei. Their findings, released in a study published in EPJ A, reveal a sequence of fragmentations, relevant to developing a specific kind of fusion reactions and in astrophysics.
- Published on 21 June 2016
High purity germanium detectors have grown into the most popular devices within the field of gamma ray spectroscopy. The sensitive part of these detectors consist of the largest, purest and monocrystalline semi-conductors used on earth. In the past Ge, detectors were famous for their outstanding energy resolution and timing information for electromagnetic radiation, especially in the field of nuclear physics and nuclear astrophysics. Recently the introduction of digital data acquisition systems and the segmentation of the Ge crystals opened up new opportunities. The interaction position of the gamma rays inside the detector volume provides new additional information by means of the pulse shape of the various signals. In this way, the Ge detector becomes a position sensitive device and allows for a novel detection method called gamma-ray tracking.
- Published on 01 June 2016
Use of relative coordinates in nuclear structure calculations helps reduce the amount of computational power required
The atomic nucleus is highly complex. This complexity partly stems from the nuclear interactions in atomic nuclei, which induce strong correlations between the elementary particles, or nucleons, that constitute the heart of the atom. The trouble is that understanding this complexity often requires a tremendous amount of computational power. In a new study published in EPJ A, Susanna Liebig from Forschungszentrum Jülich, Germany, and colleagues propose a new approach to nuclear structure calculations. The results are freely available to the nuclear physicists’ community so that other groups can perform their own nuclear structure calculations, even if they have only limited computational resources.
- Published on 25 May 2016
The Nuclear Physics Division of the EPS awards the prestigious Lise Meitner Prize every alternate year to one or several individuals for outstanding work in the fields of experimental, theoretical or applied nuclear science. Professor Ulf-G.Meißner, Universität Bonn and Forschungszentrum Jülich, Germany, Managing Editor for Reviews and former Editor-in-Chief of EPJ A, receives the 2016 Lise Meitner Prize “for his developments and applications of effective field theories in hadron and nuclear physics, that allowed for systematic and precise investigations of the structure and dynamics of nucleons and nuclei based on Quantum Chromodynamics”.
- Published on 10 May 2016
Theoretical nuclear physics could yield unique insights by extending methods and observations from other research fields
The theoretical view of the structure of the atom nucleus is not carved in stone. Particularly, nuclear physics research could benefit from approaches found in other fields of physics. Reflections on these aspects were just released in a new type of rapid publications in the new Letters section of EPJ A, which provides a forum for the concise expression of more personal opinions on important scientific matters in the field. In a Letter to the EPJ A Editor, Pier Francesco Bortignon and Ricardo A. Broglia from the University of Milan, Italy, use, among others, the example of superconductivity to explain how nuclear physics can extend physical concepts originally developed in solid state physics.
- Published on 25 April 2016
This paper presents a number of novel and alternative analysis techniques to extract transition strengths and quadrupole moments from Coulomb excitation data with Radioactive Ion Beams (RIBs) using the GOSIA code. It is anticipated that related approaches and techniques will gain an even greater importance as a wider range of post-accelerated RIBs becomes available at the next generation of ISOL facilities.
- Published on 22 April 2016
60Ge, with its 28 neutrons and 32 protons, is an extremely exotic nucleus, discovered about 10 years ago when only three ions were produced. Its decay properties were measured for the first time in this work. In this experiment, performed at the National Superconducting Cyclotron Laboratory (MSU, USA), the
60Ge ions were produced in 78Kr beam fragmentation reactions and separated from the other reaction products in the A1900 separator. The ions were detected in the active volume of the gaseous time-projection chamber with optical readout (OTPC), where they later decayed. This detector allows exotic decay modes to be identified, even with very small statistics present. The decay of about 20
60Ge ions was observed by β-delayed proton emission yielding a branching ratio of ~100% and a half-life of 20+7-5 ms. This value agrees well with theoretical predictions.