Colloquium: Beta delayed fission of atomic nuclei

This Colloquium reviews the studies of exotic type of low-energy nuclear fission, the beta-delayed fission (bDF). Emphasis is made on the new data from very neutron-deficient nuclei in the lead region, previously scarcely studied as far as fission is concerned. These data establish the new region of asymmetric fission in addition to the previously known one in the transuranium nuclei. New production and identification techniques, which emerged in the last two decades, such as the wider use of electromagnetic separators and the application of selective laser ionization to produce intense isotopically or even isomerically pure radioactive beams are highlighted. A critical analysis of presently available DF data is presented and the importance of detailed quantitative DF studies, which become possible now, is stressed, along with the recent theory efforts in the domain of low-energy fission

Human schistosomiasis in the post Mass Drug Administration (MDA) era

Summary: Profound changes are occurring in the epidemiology of schistosomiasis, a neglected tropical disease caused by a chronic infection with parasitic helminths of the genus Schistosoma. Schistosomiasis currently affects 240 million people worldwide, mostly in sub-Saharan Africa. The advent and proliferation of mass drug administration (MDA) programmes using the drug praziquantel is resulting in substantial increases in the number of people, mainly children aged 6–14 years, being effectively treated, approaching the point where most people in endemic areas will receive one or more treatments during their lifetimes. Praziquantel treatment not only cures infection but also frees the host from the powerful immunomodulatory action of the parasites. The treatment simultaneously enhances exposure to key parasite antigens, accelerating the development of protective acquired immunity, which would take many years to develop naturally. At a population level, these changes constitute a substantial alteration to schistosome ecology in that the parasites are more likely to be exposed not only to praziquantel directly but also to hosts with altered immune phenotypes. Here, we consider the consequences of this for schistosome biology, immunoepidemiology, and public health. We anticipate that there could be substantial effects on chronic pathology, natural immunity, vaccine development strategies, immune disorders, and drug efficacy. This makes for a complex picture that will only become apparent over decades. We recommend careful monitoring and assessment to accompany the roll-out of MDA programmes to ensure that the considerable health benefits to populations are achieved and sustained

Shape staggering of midshell mercury isotopes from in-source laser spectroscopy compared with density-functional-theory and Monte Carlo shell-model calculations

Neutron-deficient 177−185Hg isotopes were studied using in-source laser resonance-ionization spectroscopy at the CERN-ISOLDE radioactive ion-beam facility in an experiment combining different detection methods tailored to the studied isotopes. These include either α-decay tagging or multireflection time-of-flight gating for isotope identification. The endpoint of the odd-even nuclear shape staggering in mercury was observed directly by measuring for the first time the isotope shifts and hyperfine structures of 177−180Hg. Changes in the mean-square charge radii for all mentioned isotopes, magnetic dipole, and electric quadrupole moments of the odd-A isotopes and arguments in favor of I=7/2 spin assignment for 177,179Hg were deduced. Experimental results are compared with density functional theory (DFT) and Monte Carlo shell model (MCSM) calculations. DFT calculations using Skyrme parametrizations predict a jump in the charge radius around the neutron N=104 midshell, with an odd-even staggering pattern related to the coexistence of nearly degenerate oblate and prolate minima. This near-degeneracy is highly sensitive to many aspects of the effective interaction, a fact that renders perfect agreement with experiments out of reach for current functionals. Despite this inherent difficulty, the SLy5s1 and a modified UNEDF1SO parametrization predict a qualitatively correct staggering that is off by two neutron numbers. MCSM calculations of states with the experimental spins and parities show good agreement for both electromagnetic moments and the observed charge radii. A clear mechanism for the origin of shape staggering within this context is identified: a substantial change in occupancy of the proton πh9/2 and neutron νi13/2 orbitals

A rich revenue from the use of radioactive beams and radioactive targets: recent highlights from the nTOF and ISOLDE facilities (1/2)

The On-Line Isotope Mass Separator ISOLDE is a facility dedicated to the production of a large variety of radioactive ion beams for a great number of different experiments, e.g. in the field of nuclear and atomic physics, solid-state physics, life sciences and material science. At ISOLDE, radioactive nuclides are produced in thick high-temperature targets via spallation, fission or fragmentation reactions. The targets are placed in the external proton beam of the PSB, which has an energy of 1.0 or 1.4 GeV and an intensity of about 2 microA. The target and ion-source together represent a small chemical factory for converting the nuclear reaction products into a radioactive ion beam. An electric field accelerates the ions, which are mass separated and steered to the experiments. Until now more than 600 isotopes of more than 60 elements (Z=2 to 88) have been produced with half-lives down to milliseconds and intensities up to 1011 ions per second. Through the advent of post-accelerated beams with the REX-ISOLDE charge breeder and linear accelerator, probing nuclear properties using transfer reactions and Coulomb excitation of exotic nuclear species is now possible. The neutron time-of-flight facility, nTOF, is a neutron source that has been operating at CERN since 2001 using the 20 GeV proton beam from the Proton Synchrotron PS. The concept of the nTOF neutron beam makes use of both the specifically high flux of neutrons attainable using the spallation process of 20 GeV protons on an extended lead target. The high neutron flux, the low repetition rates and the excellent energy resolution has opened new possibilities to high precision cross section measurements in the energy range from 1 eV to 250 MeV, for stable and, moreover, for radioactive targets. This first lecture will deal with recent highlights of the two facilities. The results obtained at ISOLDE have implications for the basic understanding of the atomic nucleus, but also for related fields like astrophysics and weak-interaction physics. The possibility of pure radioactive implants opens access to the investigation of problems in solid-state physics, in particular concerning impurities and defects in semiconductors. Biomedical studies using radioactive isotopes for diagnosis and therapy have introduced life-science into the research program. The nTOF facility allows precise measurements of neutron related processes that are relevant for several fields. One example is nuclear astrophysics where data produced by n_TOF are used to study the ordinary stellar evolution as well as supernovae. Intense neutron beams are also critical in the studies of processes of incineration of radioactive nuclear waste and for a better understanding of the effects of radiation in the treatment of tumors with beams of hadrons

The fifth decade of ISOLDE: HIE-ISOLDE. (2/2)

The On-Line Isotope Mass Separator ISOLDE is a facility dedicated to the production of a large variety of radioactive ion beams for a great number of different experiments, e.g. in the field of nuclear and atomic physics, solid-state physics, life sciences and material science. At ISOLDE, radioactive nuclides are produced in thick high-temperature targets via spallation, fission or fragmentation reactions. The targets are placed in the external proton beam of the PSB, which has an energy of 1.0 or 1.4 GeV and an intensity of about 2 microA. The target and ion-source together represent a small chemical factory for converting the nuclear reaction products into a radioactive ion beam. An electric field accelerates the ions, which are mass separated and steered to the experiments. Until now more than 600 isotopes of more than 60 elements (Z=2 to 88) have been produced with half-lives down to milliseconds and intensities up to 1011 ions per second. Through the advent of post-accelerated beams with the REX-ISOLDE charge breeder and linear accelerator, probing nuclear properties using transfer reactions and Coulomb excitation of exotic nuclear species is now possible. The neutron time-of-flight facility, nTOF, is a neutron source that has been operating at CERN since 2001 using the 20 GeV proton beam from the Proton Synchrotron PS. The concept of the nTOF neutron beam makes use of both the specifically high flux of neutrons attainable using the spallation process of 20 GeV protons on an extended lead target. The high neutron flux, the low repetition rates and the excellent energy resolution has opened new possibilities to high precision cross section measurements in the energy range from 1 eV to 250 MeV, for stable and, moreover, for radioactive targets. This second lecture will deal with the new possibilities arising from a major upgrade of the facility, called HIE-ISOLDE. This upgrade program will be placed in the context of the international effort to explore the nuclear chart through the use of radioactive ion beams

The Institute for Nuclear and Radiation Physics at the University of Leuven

Last year some two hundred present and former collaborators came to Leuven to celebrate the fiftieth anniversary of the Instituut voor Kern- en Stralingsfysica (IKS; Institute for Nuclear and Radiation Physics). The institute originated in the slipstream of the separation of the Catholic University of Leuven into two parts: the Flemish KU Leuven, remaining in the city of Leuven and the French Université Catholique de Louvain, situated in the new town of Louvain-la-Neuve. The IKS started in 1967 with two professors, two Ph.D. students, and three technicians. Its physics program was influenced by the work of Professor Erwin Bodenstedt at the Institut für Strahlen-und Kernphysik of the Universität Bonn. It concentrated on the measurement of magnetic moments of excited nuclei using radioactive ion implantation and hyperfine techniques such as perturbed angular correlation, Mössbauer spectroscopy, and nuclear orientation. Although in the beginning solid-state physics issues related to implantation were treated as secondary but necessary input for the nuclear physics questions, it developed soon as an independent, complementary research line.status: publishe

The first record of polystomes (Monogenea: Polystomatidae) from caecilian hosts (Amphibia: Gymnophiona), with the description of a new genus and two new species

http://dx.doi.org/10.1007/s11230-007-9120-

On the validity of the Geiger–Nuttall alpha-decay law and its microscopic basis

The Geiger–Nuttall (GN) law relates the partial α-decay half-life with the energy of the escaping αparticle and contains for every isotopic chain two experimentally determined coefficients. The expression is supported by several phenomenological approaches, however its coefficients lack a fully microscopic basis. In this paper we will show that: (1)the empirical coefficients that appear in the GN law have a deep physical meaning, and(2)the GN law is successful within the restricted experimental data sets available so far, but is not valid in general. We will show that, when the dependence of logarithm values of the αformation probability on the neutron number is not linear or constant, the GN law is broken. For the αdecay of neutron-deficient nucleus 186Po, the difference between the experimental half-life and that predicted by the GN lawis as large as one order of magnitude.publisher: Elsevier articletitle: On the validity of the Geiger–Nuttall alpha-decay law and its microscopic basis journaltitle: Physics Letters B articlelink: http://dx.doi.org/10.1016/j.physletb.2014.05.066 content_type: article copyright: Copyright © 2014 The Authors. Published by Elsevier B.V.status: publishe