J. Praena

Advanced nuclear energy systems and the need of accurate nuclear data: the n_TOF project at CERN

To satisfy the worlds constantly increasing demand for energy, a suitable mix of different energy sources has to be devised. In this scenario, an important role could be played by nuclear energy, provided that major safety, waste and proliferation issues affecting current nuclear reactors are satisfactorily addressed. To this purpose, a large effort has been under way for a few years towards the development of advanced nuclear systems with the aim of closing the fuel cycle. Generation IV reactors, with full or partial waste recycling capability, accelerator driven systems, as well as new fuel cycles are the main options being investigated. The design of advanced systems requires improvements in basic nuclear data, such as cross-sections for neutron-induced reactions on actinides. In this paper, the main concepts of advanced reactor systems are described, together with the related needs of new and accurate nuclear data. The present activity in this field at the neutron facility n_TOF at CERN is discussed.

Neutron capture cross section of unstable 63Ni: implications for stellar nucleosynthesis.

The 63Ni(n,γ) cross section has been measured for the first time at the neutron time-of-flight facility n_TOF at CERN from thermal neutron energies up to 200 keV. In total, capture kernels of 12 (new) resonances were determined. Maxwellian averaged cross sections were calculated for thermal energies from   kT=5-100  keV with uncertainties around 20%. Stellar model calculations for a 25M⊙ star show that the new data have a significant effect on the s-process production of 63Cu, 64Ni, and 64Zn in massive stars, allowing stronger constraints on the Cu yields from explosive nucleosynthesis in the subsequent supernova.

A Method to Obtain a Maxwell–Boltzmann Neutron Spectrum at kT = 30 keV for Nuclear Astrophysics Studies

A method to shape the neutron energy spectrum at low-energy accelerators is proposed by modification of the initial proton energy distribution. A first application to the superconductive RFQ of the SPES project at Laboratori Nazionali di Legnaro is investigated for the production of a Maxwell–Boltzmann neutron spectrum at kT = 30 keV via the 7Li(p, n)7Be reaction. Concept, solutions and calculations for a setup consisting of a proton energy shaper and a lithium target are presented. It is found that a power dentisity of 3 kW cm–2 could be sustained by the lithium target and a forward-directed neutron flux higher than 1010 s–1 at the sample position could be obtained. In the framework of the SPES project the construction of a LEgnaro NeutrOn Source (LENOS) for Astrophysics and for validation of integral nuclear data is proposed, suited for activation studies on stable and unstable isotopes.

Central Jastrow and linear state-dependent correlations in nuclei

Linearized state-dependent and central Jastrow correlated trial wavefunctions are used to study the ground state of spin-isospin saturated p-shell nuclei with V4-type forces. We extend the variational Monte Carlo method to incorporate this kind of operatorial correlation by introducing only minor changes with respect to the case of central correlations. Very good energies are obtained with this wavefunction for the nuclei studied. Finally, a discussion of the role of the different correlation mechanisms included in this trial wavefunction is performed in terms of both the momentum distribution and the one- and two-particle densities in position space.

33S as a cooperative capturer for BNCT

(33)S is a stable isotope of sulfur for which the emission of an α-particle is the dominant exit channel for neutron-induced reactions. In this work the enhancement of both the absorbed and the equivalent biologically weighted dose in a BNCT treatment with 13.5keV neutrons, due to the presence of (33)S, has been tested by means of Monte Carlo simulations. The kerma-fluence factors for the ICRU-4 tissue have been calculated using standard weighting factors. The simulations depend crucially on the scarce (33)S(n,α)(30)Si cross-section data. The presence of a high resonance at 13.5keV was established by previous authors providing discrepant resonance parameters. No experimental data below 10keV are available. All of this has motivated a proposal of experiment at the n_TOF facility at CERN. A setup was designed and tested in 2011. Some results of the successful test will be shown. The experiment is scheduled for the period November to December 2012.

Temperature-tuned Maxwell–Boltzmann neutron spectra for kT ranging from 30 up to 50 keV for nuclear astrophysics studies

The need of neutron capture cross section measurements for astrophysics motivates present work, where calculations to generate stellar neutron spectra at different temperatures are performed. The accelerator-based (7)Li(p,n)(7)Be reaction is used. Shaping the proton beam energy and the sample covering a specific solid angle, neutron activation for measuring stellar-averaged capture cross section can be done. High-quality Maxwell-Boltzmann neutron spectra are predicted. Assuming a general behavior of the neutron capture cross section a weighted fit of the spectrum to Maxwell-Boltzmann distributions is successfully introduced.

Using a Tandem Pelletron accelerator to produce a thermal neutron beam for detector testing purposes

Active thermal neutron detectors are used in a wide range of measuring devices in medicine, industry and research. For many applications, the long-term stability of these devices is crucial, so that very well controlled neutron fields are needed to perform calibrations and repeatability tests. A way to achieve such reference neutron fields, relying on a 3 MV Tandem Pelletron accelerator available at the CNA (Seville, Spain), is reported here. This paper shows thermal neutron field production and reproducibility characteristics over few days.

New Gamma-Radiation Facility for Device Testing in Spain

Only few laboratories around the world are available for complete testing of devices to be used in space missions. RADLAB can achieve the standards and meet special requests, in the lead to complete component qualification.

Margenau–Brink alpha model with central Jastrow and linear state-dependent correlations for p-shell nuclei

Wave functions based on the alpha cluster model of Margenau–Brink without effective interactions have been obtained for p-shell nuclei. In this approach the constituent clusters are located at fixed centers which are taken as variational parameters. The trial wave functions have been built up with correct total angular momentum and include central Jastrow and linear state dependent correlations. The ground state and the 2 + and 4 + excited states of 8 Be, 12 C, and the ground state of 16 Oa re studied. The role of the different correlation mechanisms incorporated by the trial wave function is analyzed and the results are compared with previous calculations. The energies of the different bound states have been calculated by using the Variational Monte Carlo method.  2002 Elsevier Science B.V. All rights reserved.

Projected-deformed wavefunctions with central Jastrow and linear state-dependent correlations for 8Be and 12C

Trial wavefunctions including angular momentum projection and deformations, with linearized state-dependent and central Jastrow-type correlations are used to study the ground state rotational band of both 8 Be and 12 C nuclei. The competition between deformations, central Jastrow-type correlations and operatorial linear correlations is systematically analysed on different properties such as the energy, the square root mean radii, and transition amplitudes of the rotational band. A study of the one- and two-body spatial ground state densities is also carried out. All the matrix elements have been calculated by performing Monte Carlo simulations. 1. Introduction Short-range correlations play an important role in quantum mechanics calculations of nuclear bound states by using realistic or semi-realistic potentials. They are tailored to take care properly of the effects of the nucleon–nucleon potential at low distances and can be considered to be similar for the ground and excited states. Medium- and long-range effects are usually thought to be responsible for the differences between bound states and are reasonably well described by using the mean-field approximation. Within this scheme, and by means of a suitable choice of the model, the effects arising from collective movements, pairing effects or α-cluster couplings may be included. The fact that short-range effects can be treated independently of medium- and long-range ones is the cornerstone of the Jastrow theory and is used to generate variational correlation factors. The use of Jastrow-type trial wavefunctions gives rise to great difficulties in computing the expectation values which constitutes its major drawback in practical implementations. These trial wavefunctions are written as � = F� , where F is the correlation factor which takes