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2013
J. L. Taín (Instituto de Física Corpuscular, CSIC-Univ. Valencia)
Charge particle radiative capture reactions (X,γ) occurring at energies well below the Coulomb barrier are key reactions in a number of astrophysical scenarios such as novae, supernovae type Ia and AGB stars. They have been proposed as scientific goals of the project for the construction of a Nuclear Astrophysics Facility at the Canfranc Underground Laboratory (LSC) [1]. One difficulty of such measurements is the very low cross-section, which requires a strong minimization of the background, such as the one achieved in an underground lab. Another difficulty, affecting the accuracy of the measurement, is the need to detect a γ-ray cascade of, in general, unknown characteristics. We propose to use a segmented highly efficient Total Absorption Spectrometer (TAS), to measure energy and multiplicity of the cascade, as the optimum approach to this problem. A test measurement using a compact BaF2 TAS at JYFL (Finland) is planned and will serve to study a number of issues, including the beam induced background. These ideas will be developed in the talk.
[1] L. M. Fraile et al., A NUCLEAR ASTROPHYSICS FACILITY FOR LSC: THE SOURCES OF NEUTRONS IN THE STARS AND OTHER REACTIONS OF ASTROPHYSICAL INTEREST, October 2012. .
[1] L. M. Fraile et al., A NUCLEAR ASTROPHYSICS FACILITY FOR LSC: THE SOURCES OF NEUTRONS IN THE STARS AND OTHER REACTIONS OF ASTROPHYSICAL INTEREST, October 2012. .
F. Delaunay (Nuclear Structure Group, LPC Caen, France
The Nuclear Structure Group of LPC Caen is developing a new neutron time-of-flight detector array for structure studies. Our main physics interest is the investigation of beta-delayed neutron emission from neutron-rich nuclei, including the most exotic cases for which two or more neutrons are emitted. The detection of these multiple delayed neutrons requires an array with significantly improved performance compared to existing arrays, in particular a strong background reduction capability. Our main development strategies towards such an improved array involve the use of modules of scintillator with neutron-gamma discrimination properties, digital acquisition and signal processing, and a detailed characterisation of the response of individual modules (intrinsic efficiency, cross-talk probability). In this talk the status of this development will be presented.
2012
S. Beceiro (NSCL-Michigan US)
The Active-Target Time Projection Chamber (AT-TPC) is a next generation tracking detector being developed for studying low-energy reactions with high resolution and efficiency. In order to take full advantage of the capabilities of the detector, a robust and efficient tracking algorithm needs to be developed to reconstruct reaction tracks and obtain all kinematic observables of interest such as energy and scattering angle.We have developed a simulation to perform the track reconstruction in the AT-TPC based on modeling the ionization track and the corresponding drift electrons through the detector and it will be presented. The detector is already being build to start running next year at NSCL (MSU). In the mean while a half-size prototype was build and tested in the tandem accelerator of Notre Dame University (Indiana) showing promising results.
K.-H. Schmidt (GSI, Germany, Spain) (Work performed in collaborastion with B. Jurado at CENBG, CNRS/IN2P3, Chemin du Solarium B.P. 120, 33175 Gradignan, France)
Even in low-energy fission, the fission fragments carry a considerable amount of excitation energy. This leads to the emission of several prompt neutrons and gamma rays. In particular the prompt-neutron multiplicity has been studied in several experiments due to its importance for the design and the operation of fission reactors. The surprising result of several high-precision experiments was that an increase of the initial excitation energy of the fissioning nucleus enhances the number of neutrons emitted by the heavy fragment, only. It will be shown that the fissioning nucleus before scission forms a very peculiar system of two thermostats in contact. They undergo a process of energy sorting that is reminiscent of Maxwell's demon. At the end of the energy sorting, the production of even-Z light fragments is enhanced due to the even-odd fluctuations in nuclear binding energy. It will be argued that the magnitude of the even-odd effect in Z yields can be exploited as a new kind of nuclear clock that measures the saddle-to-scission time in comparison with the speed of the heat transfer between the fragments.
*) This work was supported by the European Commission within the Sixth Framework Programme through EFNUDAT (project no. 036434) and within the Seventh Framework Programme through Fission-2010-ERINDA (project no.269499) and by the OECD Nuclear-Energy Agency.
References:
"Entropy-driven excitation-energy sorting in superfluid fission dynamics" K.-H. Schmidt, B. Jurado, Phys. Rev. Lett. 104 (2010) 212501
"Thermodynamics of nuclei in thermal contact" K.-H. Schmidt, B. Jurado, Phys. Rev. C 83 (2011) 014607
"Final excitation energy of fission fragments" K.-H. Schmidt, B. Jurado, Phys. Rev. C 83 (2011) 061601(R)
*) This work was supported by the European Commission within the Sixth Framework Programme through EFNUDAT (project no. 036434) and within the Seventh Framework Programme through Fission-2010-ERINDA (project no.269499) and by the OECD Nuclear-Energy Agency.
References:
"Entropy-driven excitation-energy sorting in superfluid fission dynamics" K.-H. Schmidt, B. Jurado, Phys. Rev. Lett. 104 (2010) 212501
"Thermodynamics of nuclei in thermal contact" K.-H. Schmidt, B. Jurado, Phys. Rev. C 83 (2011) 014607
"Final excitation energy of fission fragments" K.-H. Schmidt, B. Jurado, Phys. Rev. C 83 (2011) 061601(R)
M. Gascon (Univ. Standford, California, US)
D. Rodríguez (Univ. Grananda, Granada, Spain)
The mass of a composite quantum mechanical system such as an atom is the sum of its building blocks minus the binding energy. This energy reflects all physical forces acting in such a quantum system and can be determined in many cases, and with very high accuracy, by storing an atomic ion in a Penning trap. However, the most highly developed type of Penning-trap mass spectrometer presently at hands needs a drastic improvement in sensitivity and accuracy to address interesting topics in modern physics, for instance, to make practicable mass measurements on Superheavy Elements (Z>104) produced in fusion-evaporation reactions with minute production rates, or to measure the masses of the pair 187Re-187Os with an accuracy better than 10-11 relevant for the determination of the mass of the electron antineutrino. In order to reach these aims, we are building up at the University of Granada a novel device called quantum sensor consisting of a single 40Ca+ ion stored in a Penning trap and lasercooled to mK temperatures. The mass measurement is based on monitoring the fluorescence photons and not on electronic detection. The project has been recently started and is funded by the European Research Council (StG-ERC-2011). In this talk, the physics motivation and a detailed description of the device together with its expected performance will be presented.
A. Algora (IFIC (CSIC-Univ. Valencia), Valencia, Spain-IFIC)
In this talk first we will introduce the so-called “Pandemonium effect” [1] and explain how this experimental difficulty can be avoided using the total absorption technique (TAS) in beta decay studies. Then, we will present how this technique can be used to address different questions in nuclear structure and applications ranging from the determination of the shape of a nucleus in its ground state to possible applications in neutrino physics. Among the practical applications we will present the impact of recent measurements using this technique, that have contributed to a better prediction of the decay heat in reactors using the summation calculation method [2]. Future plans using this technique in different facilities will be also discussed.
[1] J. Hardy et al., Phys. Lett . B 71 (1977) 307
[2] A. Algora et al., Physical Review Letters 105 (2010) 202501, D. Jordan et al. in preparation.
[1] J. Hardy et al., Phys. Lett . B 71 (1977) 307
[2] A. Algora et al., Physical Review Letters 105 (2010) 202501, D. Jordan et al. in preparation.
M. J. García-Borge (Spanish representative of CERN-ISOLDE, CSIC-IEM)
Walking on the drip lines The atomic nucleus is a many body system consisting of primarily protons and neutrons whose interactions are determined by 3 of the 4 forces in nature: strong, weak and electromagnetic forces. Often the key nuclei are either very neutron or proton rich. Such a exotic systems of extreme isospin number allow to isolate and amplify specific aspects to nucleonic interactions. At the drip lines, the proximity to unbound systems requires that the coupling to the continuum has to be considered in order to describe the dynamics of these systems. The study of some of these nuclei has been the subject of our research program. In this seminar I will introduce the different research lines of the Nuclear Physics group at IEM-CSIC mainly interested on the study of exotic nuclei their structure and dynamics. To illustrate our work I will present two examples: 1. The effects of dipole polarizability and coupling to the continuum in the scattering of the halo nucleus 11Li on lead near the Coulomb barrier. 2. The study of the beta-decay of the lightest Ar isotopes, as example of comparison with state of art shell model calculation and determination of the quenching of the axial-vector coupling constant. Finally the last part will be dedicated to introduce the ISOLDE facility and its upgrade HIE-ISOLDE.
B. Gomez-Hornillos(UPC, Spain)
This talk will summarise the work performed at UPC to design and build a 3He neutron detector and the measurements performed with it related to beta delayed neutrons. The neutron detector has been designed based on MonteCarlo simulations with the MCNPX and GEANT4 codes in order to obtain the highest detection efficiency while keeping it constant in the range of neutron energies from 1keV to 1MeV. Based on the results of the simulations the detector has been built at the workshop at UPC, it consists of 20 3He counters embedded in a polyethylene matrix. The results of the simulations have been validated with a 252Cf source in the lab at UPC. The first experiments with this detector was carried out in the accelerator at the University of Jyväskylä, Finland, with the collaboration of IFIC (Valencia) and CIEMAT (Madrid) where the beta delayed neutron emission of ions of technological interest were measured. Two more experiments were performed at GSI in Sep 2011 to measure ions of astrophysical interest related to the r-process.
2011
New techniques for the exploration of the nuclear fission process: Multi-nucleon-transfer induced fission using inverse kinematics.
F. Farget (GANIL, France)
Nuclear fission is the most extreme manifestation of the collective motion of the nucleus constituents, resulting in the division in two parts of the atomic nucleus. The main features of the distributions of fission fragments are governed by the properties of individual nucleons, as pairing interaction and shell structure. For 70 years, fission has generated enthusiasm of physicists, which led to the construction of sophisticated equipment dedicated to its study, which results in a general vision of the process more or less accepted by the scientific community. In a first part, we will point out some failures and inaccuracies that exist in the general model, and demonstrate that the sources are the limitations of experimental techniques. We will then show that new techniques based on inverse kinematics coupled with a spectrometer are very promising. This will be illustrated by the results obtained in an experiment at GANIL which aims to study the characteristics of the isotopic distributions of fission products as a function on the fissioning system and the excitation energy.
K. Summerer (GSI, Germany)
Laboratory experiments to determine low-energy cross sections between light nuclei have provided insight into fundamental astrophysical processes such as Big-Bang Nucleosynthesis or fusion reactions within the pp-chain of main-sequence stars like our Sun. In some cases, the reaction cross sections can also (or even only) be determined by an indirect method, Coulomb Dissociation, performed at high-energy accelerators like GSI at Darmstadt, Germany. Two examples will be discussed in detail: (1) The D(a,g)6Li reaction relevant in the context with the claimed observation of primordial 6Li in the atmospheres of old halo stars. (2) The 7Be(p,g)8B reaction as an important ingredient in the calculation of the high-energy neutrino flux from the Sun. Both cases are related to fundamental aspects of our physical understanding of the Universe.
B. Fernández-Domínguez.(Univ. Santiago de Compostela)
The single-particle structure of exotic nuclei evolves with the isospin. The well-stablished sequence of magic numbers is modified as we move away from the line of stability. As drip-lines are approached most of the levels of interest are unbound which poses a great experimental challenge.
One-nucleon transfer reactions selectively and directly probe the single-particle nature of nuclear levels. A campaign of experiments performed in GANIL with the TIARA+MUST2+VAMOS+EXOGAM set-up aimed to study the structure of light neutron-rich nuclei in the sd-fp region.The complete set-up allowed the study of transfer to bound and unbound states with full channel identification.
One-nucleon transfer reactions selectively and directly probe the single-particle nature of nuclear levels. A campaign of experiments performed in GANIL with the TIARA+MUST2+VAMOS+EXOGAM set-up aimed to study the structure of light neutron-rich nuclei in the sd-fp region.The complete set-up allowed the study of transfer to bound and unbound states with full channel identification.
Recent results of neutron transfer reactions induced by radioactive beams will be presented. Special emphasis will be given to the technical and theoretical challenges associated with the characterisation of unbound states, highlighting the interplay between structure and reaction mechanism in the transfer to states in the continuum. In addition, the present results pose a challenge to the interactions used to describe the evolution of nuclear structure in this region.
- Luis Roso, May 2011
- Joakim Cederkall, April 2011
- Benjamin Pietras, March 2011
- Jose
- Isaac Vidaña
2009
- Coulom Dissociation of 8B and the solar neutrino problem, K. Suemmerer
- Nuclear Data and Reactor Physics, L. Tassan-Got
- Epax: an empiric parametization of fragmentation cross-section, K. Suemmerer
2006
- Production of the core fragments and excited states in neutron removal from the sd-shell nuclei (21-13O, 18-20N, 22F, 17Ne), Y. Parfenova
- Production of the core fragments and excited states in neutron removal from 14,15,17C isotopes, Y. Parfenova
- Study of proton-induced fission of actinides based on the measurement of fission fragment's characteristics with Multi Wire Proportional gas Counters (MWPC). S. Isaev