General Description of Fission Observables: GEF Model Code

Some aspects of heavy-ion reactions close to the Coulomb barrier are reviewed in experiment and theory Fusion, complex reactions and quasi-elastic reactions are covered, both microscopic and macroscopic approaches to the theory are discussed A brief outlook is given

https://iopscience.iop.org/article/10.1088/0954-3899/20/9/004/pdf

Heavy-ion reactions close to the Coulomb barrier

In the last two decades, through technological, experimental and theoretical advances, the situation in experimental fission studies has changed dramatically. With the use of advanced production and detection techniques both much more detailed and precise information can now be obtained for the traditional regions of fission research and, crucially, new regions of nuclei have become routinely accessible for fission studies. This work first of all reviews the recent developments in experimental fission techniques, in particular the resurgence of transfer-induced fission reactions with light and heavy ions, the emerging use of inverse-kinematic approaches, both at Coulomb and relativistic energies, and of fission studies with radioactive beams. The emphasis on the fission-fragment mass and charge distributions will be made in this work, though some of the other fission observables, such as prompt neutron and γ-ray emission will also be reviewed. A particular attention will be given to the low-energy fission in the so far scarcely explored nuclei in the very neutron-deficient lead region. They recently became the focus for several complementary experimental studies, such as β-delayed fission with radioactive beams at ISOLDE(CERN), Coulex-induced fission of relativistic secondary beams at FRS(GSI), and several prompt fusion-fission studies. The synergy of these approaches allows a unique insight in the new region of asymmetric fission around 180Hg, recently discovered at ISOLDE. Recent extensive theoretical efforts in this region will also be outlined. The unprecedented high-quality data for fission fragments, completely identified in Z and A, by means of reactions in inverse kinematics at FRS(GSI) and VAMOS(GANIL) will be also reviewed. These experiments explored an extended range of mercury-to-californium elements, spanning from the neutron-deficient to neutron-rich nuclides, and covering both asymmetric, symmetric and transitional fission regions. Some aspects of heavy-ion induced fusion-fission and quasifission reactions will be also discussed, which reveal their dynamical features, such as the fission time scale. The crucial role of the multi-chance fission, probed by means of multinucleon-transfer induced fission reactions, will be highlighted. The review will conclude with the discussion of the new experimental fission facilities which are presently being brought into operation, along with promising 'next-generation' fission approaches, which might become available within the next decade.

/pdf/nuclear-fission-a-review-of-experimental-advances-and-1el0tcg7me.pdf

Nuclear fission: a review of experimental advances and phenomenology.

We present a review of the antineutrino spectra emitted from reactors. Knowledge of these spectra and their associated uncertainties is crucial for neutrino oscillation studies. The spectra used to date have been determined either by converting measured electron spectra to antineutrino spectra or by summing over all of the thousands of transitions that make up the spectra, using modern databases as input. The uncertainties in the subdominant corrections to β-decay plague both methods, and we provide estimates of these uncertainties. Improving on current knowledge of the antineutrino spectra from reactors will require new experiments. Such experiments would also address the so-called reactor neutrino anomaly and the possible origin of the shoulder observed in the antineutrino spectra measured in recent high-statistics reactor neutrino experiments.

Reactor Neutrino Spectra

Prompt fission neutron spectra of actinides

A twin ionization chamber for fission fragment detection is described. The detector permits measurement of the two fission fragment kinetic energies in an advantageous 2×2 π geometry with an energy resolution of

A twin ionization chamber for fission fragment detection

235U(n, f) Fragment mass-, kinetic energy- and angular distributions for incident neutron energies between thermal and 6 MeV

Fission mode fluctuations in the resonances of 235U(n,f)

A formula for the fission fragment yield area in the coordinate system of the fragment total kinetic energy and of the fragment mass is presented. It was deduced along the lines of the multiexit- channel model of fission elaborated by Brosa, Grossmann and Müller. This formula was fitted to the fragment mass-, average total kinetic energy-, and variance distributions of the thermal neutron induced fission of 235U. The obtained parameters are compared with the theoretical predictions. Further improvements of the fragment yield representation are discussed.

/pdf/three-exit-channels-in-the-fission-of-235u-n-f-2klmhoc3vn.pdf

H.-H. Knitter

Papers

A twin ionization chamber for fission fragment detection

235U(n, f) Fragment mass-, kinetic energy- and angular distributions for incident neutron energies between thermal and 6 MeV

Fission mode fluctuations in the resonances of 235U(n,f)

Three Exit Channels in the Fission of 235U(n, f)

The positive odd-even effects observed in cold fragmentation — are they real?