Nuclear fission is accompanied by the prompt emission of neutrons, gamma rays and x-rays. It has been known since the sixties that fission prompt x-rays originate essentially as a consequence of the internal conversions occurring in the prompt gamma deexcitation cascades of fission fragments.
This work presents for the first time a measurement of the prompt fission x-ray yields in 238U(n,f) for average incident neutron energies ranging from 3 to 200 MeV. These results provide new information on fission fragment deexcitation and allow testing the current knowledge of fission fragment nuclear structure. These results provide also a means to investigate the evolution, as a function of incident neutron energy, of fission fragment charge yields and elemental prompt x-ray emission probabilities.
The electromagnetic polarisabilities of the nucleons characterise their responses to external fields. The simplest are the electric and magnetic polarisabilities that describe the induced dipole moments. For spin-1/2 particles there are also four spin polarisabilities, analogous to rotations of the polarisation of light by optically active media. The best experimental window on them is Compton scattering of photons, which has provided good determinations of the electric and magnetic polarisabilities of the proton. Future experiments with polarised protons will give access to its spin polarisabilities. In contrast, much less is known of about the neutron since it does not exist as a stable target. Nonetheless, its properties can be obtained from Compton scattering on light nuclei, most notably the deuteron -- a weakly bound proton and neutron. A new generation of experiments is planned to provide beams of polarised photons on targets of polarised deuterons. If the spins of the final particles are not observed, there are 18 independent observables. This work provides, for the first time, the complete set of these, which will be needed for the experimental analyses. More importantly, it also examines their sensitivities to the various polarisabilities, which will be crucial for the design of the experiments.
From January 2013 Nicolas Alamanos succeeds Enzo De Sanctis as Editor in Chief of EPJ A for the experimental physics section.
Professor Alamanos is Deputy Director of the Institute of Research into the Fundamental Laws of the Universe (IRFU) and Research Director at CEA Saclay working in the domain of fundamental research in Nuclear Physics. During his long scientific career, he has served on many scientific and program advisory committees and has occupied different managerial positions. Most notably he has been president of GANIL’s scientific council and director of Saclay Nuclear Physics Division. He is a member or evaluator of many national committees – ARISTEIA (GRECE), FRS-FNRS (Belgium), ANR (France). He is currently a member of the GANIL/SPIRAL2 scientific council, of GANIL’s program advisory committee, and scientific counselor of the European program “CEA-Euro talents” in the domain of high energy physics and physics of the universe.
In addition to his various scientific and administrative duties, Professor Alamanos has always been very active editorially: beyond having been a member of the editorial board of EPJ A for many years, he is the Editor of the Scholarpedia Encyclopedia of Nuclear Physics.
Dr. Eric Bauge et al describe a body of work accomplished by the CEA/DAM. Their goal is to determine accurate nuclear reaction cross sections for use in neutron transport codes. This work integrates theory and modeling, experiment, computer simulation, and statistical analysis. It involves researchers who thrive on multidisciplinary work, and who are motivated to achieve realistic simulation predictions in nuclear technology applications. Not only has the group succeeded in creating databases of accurate cross sections, but in every aspect of the work significant progress has been made in advancing our understanding of the underlying nuclear physics.
Quarks and gluons are the fundamental constituents of most of the matter in the visible Universe; Quantum Chromodynamics (QCD), a relativistic quantum field theory based on color gauge symmetry, describes their strong interactions. The understanding of the static and dynamical properties of the visible strongly interacting particles - hadrons - in terms of quarks and gluons is one of the most fascinating issues in hadron physics and QCD. In particular the exploration of the internal structure of protons and neutrons is one of the outstanding questions in experimental and theoretical nuclear and hadron physics. Impressive progress has been achieved recently.
The synthesis of a superheavy element with the proton number Z=116 has been studied at the velocity filter SHIP of GSI in Darmstadt using a 48Ca beam on radioactive 248Cm targets. At excitation energies of the compound nuclei of 40.9 MeV, four decay chains were measured, which were assigned to the isotope 292116 produced in 4n channel, and one chain, which was assigned to 293116 produced in 3n channel. All chains are terminated by spontaneous fission decays of either 277Hs or 284Cn isotopes on the shoreline of the neutron-rich superheavy island.
The accurate knowledge of (n,gamma) neutron-capture cross-sections for fissile isotopes is highly relevant for next-generation applications of nuclear technology. However, accurate measurements are difficult due to the gamma-ray background generated in competing (n,f) fission reactions. Scientists at the n_TOF facility at CERN have developed a new experimental setup that is capable of simultaneously measuring and identifying the capture and fission reactions.
Vacuum polarisation, the modification of the photon propagator due to virtual electron-positron pairs, is one of the first quantum loop corrections encountered in field theory. In both QED and QCD it causes the running of the appropriate fine structure constant as the physical scale is varied, and also corrects the magnetic moments of electrons and muons from the value 2 predicted by the Dirac equation.
One important message that has emerged from developments of effective field theories and effective Hamiltonians for nuclear physics is that many-body forces are inevitable whenever degrees of freedom are eliminated. At the same time, first-principles calculations have shown that two-body forces alone are not able to give an accurate account of the energies of light nuclei and the saturation of nuclear matter. Three- (and possibly more-) body forces are thus essential in low-energy nuclear physics.
A key to our understanding of Quantum Chromodynamics (QCD) in the strong regime is our ability to
reproduce the hadronic excitation spectrum. Up to now, and due to their limited predictive power, quark
models forecast of this spectrum at high excitation energies is unsatisfactory and is dubbed ``the missing
resonances problem”. To explore the high excitation energies in the hadron spectrum production or scattering
of heavier mesons from a nucleon target is essential.
We are grateful to the referees for their very detailed review of our manuscript and for the important remarks and corrections. The referees are very nice experts of the subject of the paper. The manuscript has been revised with our pleasure. Thank you very much for the choice of the referees who were high level experts and kind scientists.
Avazbek Nasirov, Joint Institute for Nuclear Research, Moscow Region, Russian Federation