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Proton induced nuclear reactions were measured with stacked-foil technique on natural uranium targets in the energy range from 211 to 2,530 MeV at the Saturne II synchrocyclotron at the Laboratoire National Saturne/Saclay (France). Twenty-three reactions were determined by means of off-line γ-spectrometry. The obtained excitation functions have been compared with the earlier published data and the theoretical model INCL4 + ABLA.

We proposed a new nuclear reaction model in combination of Intra-Nuclear Cascade of Liege (INCL) and the Distorted Wave Born Approximation (DWBA) calculation, and incorporated it into the Particle and Heavy Ion Transport code System (PHITS). This model was applied to deuteron induced reactions on nat Li and 9 Be targets for deuteron incident energies of 40 and 18 MeV, respectively. Double-differential cross sections and neutron yields on thick targets obtained by PHITS using the model reproduce experimental data quite well.

We use particle-transport simulations to show that secondary pions play a crucial role for the development of the hadronic cascade and therefore for the production of neutrons and photons from thick spallation targets. In particular, for the n_TOF lead spallation target, irradiated with 20 GeV/c protons, neutral pions are involved in the production of ~90% of the high-energy photons; charged pions participate in ~40% of the integral neutron yield. Nevertheless, photon and neutron yields are shown to be relatively insensitive to large changes of the average pion multiplicity in the individual spallation reactions. We characterize this robustness as a peculiar property of hadronic cascades in thick targets., Comment: 17 pages, 14 figures. Submitted to Eur. Phys. J. A

Spallation reactions play an important role in many branches of physics. If the nuclear reaction induced by low energy neutrons as in nuclear power plants or research reactors can be based on cross section database, it is not the case for spallation reactions due to the energy range, from 100 MeV up to ~3 GeV, and to the candidate targets (all nuclei). Then these reactions have to be modeled. Developments of codes are linked to new experiment and this ex-plains why fifteen years ago a first benchmark has been launched, restricted to particle production, followed by a second one on residues. Since then new data have been measured and computer tools are improved day after day, so a new benchmark has been organized, under the auspices of the IAEA, taken into account all types of results, particle and residue production, with a possibility to update the data (experimental and code calculation) via a web site. Re-sults of the benchmark concerning both the analysis of the prediction capabilities of the seventeen model-participants and the first conclusions on the physics of spallation models are presented.

Spallation reactions play an important role in a wide domain of applications. In the simulation codes used in this field, the nuclear interaction cross-sections and characteristics are computed by spoliation models. The International Atomic Energy Agency (IAEA) has recently organised a benchmark of the spoliation models used or that could be used in the future into high-energy transport codes. The objectives were, first, to assess the prediction capabilities of the different spoliation models for the different mass and energy regions and the different exit channels and, second, to understand the reason for the success or deficiency of the models. Results of the benchmark concerning both the analysis of the prediction capabilities of the models and the first conclusions on the physics of spoliation models are presented.

International audience; This article focuses on spallation reactions, i.e. interactions of energetic nucleons, basically with a kinetic energy in the 100 MeV to a few GeV range, with a target nucleus. These processes are described rather successfully by the so-called Intranuclear Cascade (INC) plus evaporation models. They can be viewed as a first stage of nucleon-nucleon collisions, ejecting fast particles, followed by evaporation of slow particles from the target remnant. These cascade + evaporation models have, now, globally reached a high level of predictive power, owing in particular to successive research programs. The present work, which is an outcome of one of these programs, the recent European Union ANDES research program, deals with a set of reactions (or observable quantities), which can be due to a single collision, such as the one-nucleon removal reactions or the quasi-elastic elastic process. A survey of the experimental data is presented, which allows to clearly point out that, often, the INC models are unsatisfactory for the description of these peculiar events, whereas they are rather successful for the rest of the experimental data. This paradoxical situation is tentatively related to quasi-particle effects which are neglected in INC models.

In this paper we present for the first time the measured delayed neutron (DN) yields and time spectra from high-energy protons interacting with thick natPb targets. The 1GeV protons from the accelerator impinged on targets of different thicknesses producing a huge number of spallation-fission products, some of which can be DN precursors. After the beam is switched off, the DNs were detected with optimized 3He counter. The production yields of light DN precursors as 17N and “usual” fission products as 87Br and 88Br, which dominate the total DN activity, are obtained both for thin and thick targets. These new data are of great interest for the new generation high-power spallation targets based on liquid-metal technologies. Our findings also should help to constrain the physics models within the simulations codes.

We assess the suitability of nuclear-reaction codes for the generation of accurate cross-section libraries targeted at the simulation of the transport of high-energy protons (up to 250 MeV) in the human body, or in any material containing light nuclides. To this end we present an extensive study of elastic, reaction and fragmentation cross sections for proton-induced reactions on several nuclides. We compare TALYS evaluations against experimental data and, wherever applicable, against the predictions of the INCL/ABLA07 nuclear-reaction model. The TALYS evaluations have been cast in the form of a new cross-section library, which also includes evaluated proton-proton cross sections based on the NN-OnLine tool.

International audience; It is a well-established fact that intranuclear-cascade models generally overestimate the cross sections for one-proton removal from heavy, stable nuclei by a high-energy proton beam, but they yield reasonable predictions for one-neutron removal from the same nuclei and for one-nucleon removal from light targets. We use simple shell-model calculations to investigate the reasons for this deficiency. We find that a refined description of the neutron skin and of the energy density in the nuclear surface is crucial for the aforementioned observables, and that neither ingredient is sufficient if taken separately. As a by-product, the predictions for removal of several nucleons are also improved by the refined treatment.

Recently a renewed interest in photonuclear reactions has appeared. It is motivated by a number of different applications where progress in reliable and, in some cases, very high-intensity electron accelerators was awaited. In particular, today's interest is linked to the nuclear material interrogation and non-destructive nuclear waste characterization, both based either on prompt neutron, or delayed neutron, or delayed gamma detection following photofission. The knowledge of photonuclear reactions is also extremely important in the design of electron accelerators used for medical applications, nuclear physics, photoneutron sources, radioactive ion beam production, etc. In this paper we present the photonuclear activation file (PAF) under development to be included into any material depletion code. By now the PAF contains the photonuclear cross-sections for more than 600 isotopes, fission fragment distributions and delayed neutron evaluations for most of the actinides in the photon energy range from 0 up to 25 MeV. Theoretical predictions, evaluated data files and available experimental data were used to construct the PAF, and some benchmarks are in progress to ensure its quality. The release of the first version of PAF is planned in 2006.

The state-of-the-art regarding the predicting capabilities of some of the physics models available in MCNPX for Accelerator-Driven System design is discussed. The identified remaining deficiencies, which originate either from a lack of experimental data or from not well understood physics mechanisms, are stressed. To solve these problems, more constraining experiments are now needed to allow a deeper understanding of the reaction mechanisms.

We measured integral thin target cross-sections for the proton-induced production of He-, Ne-, Ar-, Kr-, and Xe-isotopes from lead and bismuth from the respective reaction threshold up to 2.6 GeV. The production of noble gas isotopes from lead and bismuth is of special importance for design studies of accelerator driven nuclear reactors and/or energy amplifiers. For all experiments with proton energies above 200 MeV a new mini-stack approach was used instead of the stacked-foil technique in order to minimise influences of secondary particles. The phenomenology of the determined excitation functions enables us to distinguish between the different reaction modes fragmentation, hot and cold symmetric fission, asymmetric fission, and deep spallation. For lead more than 420 cross-sections for 23 nuclear reactions have been measured. While the lead data have already been published, here we present first results for the production of noble gas isotopes from bismuth. The experimental data are compared to results from the theoretical nuclear model code INCL4/ABLA. This comparison clearly indicates that experimental data are still needed because the predictive power of nuclear model codes, though permanently improving, does still not allow to reliably predict the cross-sections needed for most applications and irradiation experiments remain indispensable.

New improvements of the INCL4 cascade model, bearing on cluster production, nucleon and pion potentials and Pauli blocking at low energy, are reviewed.

Experimental results for the photofission of 238U with an endpoint Bremsstrahlung emission of 15 MeV are presented. Absolute yield and time characteristics of the delayed neutrons are extracted. In parallel, calculations for fission fragment distributions and corresponding delayed neutron parameters are given and compared to data.

We measured integral thin target cross sections for the proton-induced production of He-, Ne-, Ar-, Kr- and Xe-isotopes from lead from the respective reaction threshold up to 2.6 GeV. The production of noble gas isotopes from lead is of special importance for design studies of accelerator driven nuclear reactors and/or energy amplifiers. For all experiments with proton energies above 200 MeV a new mini-stack approach was used instead of the stacked-foil technique in order to minimise the influences of secondary particles on the residual nuclide production. About 420 cross sections for 23 nuclear reactions were determined. The phenomenology of the determined excitation functions enables us to distinguish between the different reaction modes fragmentation, hot and cold symmetric fission, asymmetric fission and deep spallation. Cross sections for the production of 21Ne and 38Ar measured below 100 MeV and 200 MeV, respectively, enable us to study nuclide production below the nominal Coulomb-barrier. The experimental data are compared to results from the theoretical nuclear model code INCL4/ABLA. While the model describes the production of 4He reasonably well, it underestimates the cross sections for Ne- and Ar-isotopes produced via deep spallation and/or multifragmentation by up to two orders of magnitude. For the Kr- and Xe-isotopes the agreement between modelled and measured data strongly depends on the reaction mechanisms. While INCL4/ABLA describes the production of n-poor Kr-isotopes via hot-symmetric fission and the production of Xe-isotopes via asymmetric fission reasonably well, i.e. within a factor of 2, the discrepancies between modelled and measured cross sections for the n-rich Kr-isotopes produced via cold symmetric fission are significantly larger. For the Xe-isotopes produced via spallation, i.e. at energies higher than about 600 MeV, the model completely fails to describe the experimental data. Therefore, the comparison of measured and modelled thin target cross sections clearly indicates that experimental data are still needed because the predictive power of nuclear model codes, though permanently improving, does still not allow to reliably predict the cross sections needed for most applications and irradiation experiments remain indispensable.

It is well known that intranuclear-cascade models generally overestimate the cross sections for one-proton removal from heavy, stable nuclei by a high-energy proton beam, but they yield reasonable predictions for one-neutron removal from the same nuclei and for one-nucleon removal from light targets. We use simple shell-model calculations to investigate the reasons of this deficiency. We find that a correct description of the neutron skin and of the energy density in the nuclear surface is crucial for the aforementioned observables. Neither ingredient is sufficient if taken separately., Presented at the 11th International Spring Seminar on Nuclear Physics. To be published in Journal of Physics: Conference Series

The purpose of this paper is twofold. First, we present the extension of the Li\`ege Intranuclear Cascade model to reactions induced by light ions. Second, we describe the C++ version of the code, which it is physics-wise equivalent to the legacy version, is available in Geant4 and will serve as the basis for all future development of the model. We describe the ideas upon which we built our treatment of nucleus-nucleus reactions and we compare the model predictions against a vast set of heterogeneous experimental data. In spite of the discussed limitations of the intranuclear-cascade scheme, we find that our model yields valid predictions for a number of observables and positions itself as one of the most attractive alternatives available to Geant4 users for the simulation of light-ion-induced reactions., Comment: Submitted to Phys. Rev. C

International audience; The predictive power of the last version INCL4.6 of the Liège Intranuclear Cascade model for spallation is reviewed. The good results obtained both at low and high energy extend the domain of validity of the model and allow the description of spallation reactions, except the coherent processes, by a unique model from a few MeV to a few GeV incident energy.

International audience; A crucial requirement in the development of liquid-metal spallation neutron target is knowledge of the composition and amount of volatile radionuclides that are released from the target during operation. It is also important to know the total amount produced, which could be released if there was an accident. One type is the lead-bismuth eutectic (LBE) target where different radionuclides can be produced following interaction with a high-energy proton beam, notably noble gases (Ar, Kr, Xe isotopes) and other relative volatile isotopes such as Hg and At. The results of an irradiation experiment performed at ISOLDE on a LBE target are compared with predictions from the MCNPX code using the latest developments on the Li'ege Intranuclear Cascade model (INCL4.6) and the CEM03 model. The calculations are able to reproduce the mass distribution of the radioisotopes produced, including the At production, where there is a significant contribution from secondary reactions. Subsequently, a post-irradiation examination of the irradiated target was performed. Investigations of both the tantalum target structure, in particular the beam window, and the leadbismuth eutectic were performed using several experimental techniques. No sign of severe irradiation damage, previously observed in other ISOLDE targets, was found.

The new version (INCL4.6) of the Li`ege intranuclear cascade (INC) model for the description of spallation reactions is presented in detail. Compared to the standard version (INCL4.2), it incorporates several new features, the most important of which are: (i) the inclusion of cluster production through a dynamical phase space coalescence model, (ii) the Coulomb deflection for entering and outgoing charged particles, (iii) the improvement of the treatment of Pauli blocking and of soft collisions, (iv) the introduction of experimental threshold values for the emission of particles, (v) the improvement of pion dynamics, (vi) a detailed procedure for the treatment of light-cluster induced reactions taking care of the effects of binding energy of the nucleons inside the incident cluster and of the possible fusion reaction at low energy. Performances of the new model concerning nucleon-induced reactions are illustrated. Whenever necessary, the INCL4.6 model is coupled to the ABLA07 deexcitation model and the respective merits of the two models are then tentatively disentangled. Good agreement is generally obtained in the 200 MeV-2 GeV range. Below 200 MeV and down to a few tens of MeV, the total reaction cross section is well reproduced and differential cross sections are reasonably well described. The model is also tested for light-ion induced reactions at low energy, below 100 MeV incident energy per nucleon. Beyond presenting the update of the INCL4.2 model, attention has been paid to applications of the new model to three topics for which some particular aspects are discussed for the first time: production of clusters heavier than alpha particles, longitudinal residue recoil velocity and its fluctuations, total reaction cross section and the residue production cross sections for low energy incident light ions., Comment: 29 pages, 26 figures

International audience; Liquid lead-bismuth eutectic (LBE) is often considered as a possible target in spallation neutron sources. Anexperiment has been performed in 2005 at ISOLDE (CERN), in which LBE has been irradiated by 1.0 and 1.4GeV protons and isotopes of astatine, a volatile precursor of Po, have been found. Until recently no modelwas able to reproduce this astatine production, which is due either to double charge exchange reactions,Bi(p,π-xn)At, or to secondary reactions induced by helium nuclei. Recently, both parts of the spallation modelcombination INCL4-Abla have been improved leading to the new versions, INCL4.6-ABLA07. In particular,an additional mechanism to produce light and intermediate mass fragments has been added and special carehas been paid to the low energy reactions. This paper first shows that all the basic features of the differentreactions leading to astatine production are well predicted by the new model. The model, implemented into abeta version of MCNPX2.7 is then used to simulate the ISOLDE experiment. A very good agreement with theexperimental data is observed.

We use the tools of hybrid intranuclear-cascade/nuclear-de-excitation models to evaluate the sensitivity of several physical observables to the inclusion of a multifragmentation stage in the deexcitation chain and assess the need for a multifragmentation model in the quantitative description of p + 56 Fe and p + 136 Xe reactions at 1-GeV incident energy. We seek clear signatures of multifragmentation by comparing different state-of-the-art de-excitation models coupled with intranuclear-cascade models and by focusing on discriminating observables such as correlations and fragment longitudinal-velocity distributions. None of the considered observables can be unambiguously interpreted as a multifragmentation footprint. The experimental data are best described as originating from sequential binary decays. However, no de-excitation model can reproduce the experimental longitudinal-volocity distributions from 1-GeV p + 136 Xe.

We use the tools of hybrid intranuclear-cascade/nuclear-deexcitation models to evaluate the sensitivity of several physical observables to the inclusion of a multifragmentation stage in the deexcitation chain and assess the need for a multifragmentation model in the quantitative description of $p$ + ${}^{\text{5}6}$Fe and $p$ + ${}^{\text{1}36}$Xe reactions at 1-GeV incident energy. We seek clear signatures of multifragmentation by comparing different state-of-the-art deexcitation models coupled with intranuclear-cascade models and by focusing on discriminating observables such as correlations and fragment longitudinal-velocity distributions. None of the considered observables can be unambiguously interpreted as a multifragmentation footprint. The experimental data are best described as originating from sequential binary decays. However, no deexcitation model can reproduce the experimental longitudinal-velocity distributions from 1-GeV $p$ + ${}^{\text{1}36}$Xe.

International audience; The MEGAwatt PIlot Experiment (MEGAPIE) project was started in 2000 to design, build, and operate a liquid lead-bismuth eutectic (LBE) spallation neutron target at the power level of 1 MW. The target was irradiated for 4 months in 2006 at the Paul Scherrer Institute in Switzerland. Gas samples wereextracted in various phases of operation and analyzed by g spectroscopy, leading to the determination of the main radioactive isotopes released from the LBE. Comparison with calculations performed using several validated codes (MCNPX2.5.0/CINDER’90, FLUKA/ORIHET, and SNT) yields the ratio between simulated in-target isotope production rates and experimental amounts released at any given time. This work underlines the weak points of spallation models for some released isotopes. Also, results provide relevant information for safety and radioprotection in an accelerator-driven system and more particularly for the gas management in a spallation target dedicated to neutron production facilities.

In this article we present the development of a new photonuclear activation library for the CINDER’90 evolution code (LANL). The IAEA evaluations for 164 isotopes are explicitly included and more than 600 isotopes are added using the HMS‐ALICE predictions. GNASH evaluations are used in the case of actinides.

A survey is given about efforts undertaken during the HINDAS project to investigate the energy dependence of residual nuclide production by proton‐induced reactions from thresholds up to 2.6 GeV. For proton‐induced reactions, our experiments aimed to further develop and complete the cross‐section database that was established by our collaboration in recent years. It was extended to the heavy‐target elements Ta, W, Pb, and Bi for energies up to 2.6 GeV. In addition, new measurements for the target element iron were performed up to 2.6 GeV and for natural uranium for energies from 21 MeV to 69 MeV. For the target element lead, a comprehensive set of excitation functions published recently was completed by AMS‐measurements of cross sections for the production of the long‐lived radionuclides Be‐10, Al‐26, Cl‐36, and I‐129 and by mass spectrometric measurements for stable and radioactive rare gas isotopes of He, Ne, Ar, Kr, and Xe. Comprehensive tests of the nuclear‐reaction codes TALYS and INCL4+ABLA, which were developed within the HINDAS project, were performed with the new experimental results over the entire energy range.

The next generation spallation neutron sources, neutrino factories or RIB production facilities currently being designed and constructed world wide will increase the average proton beam power on target by a few orders of magnitude. Increased proton beam power results in target thermal hydraulic issues leading to new target designs, very often based on liquid metal technologies such as Hg, Pb, or PbBi. Radioactive nuclides produced in liquid metal targets are transported into hot cells, into pumps or close to electronics with radiation sensitive components. Besides the considerable amount of photon activity in the irradiated liquid metal, a significant amount of the Delayed Neutron (DN) precursor activity can be accumulated in the target fluid. The transit time from the front of a liquid metal target into areas, where DNs may be important, can be as short as a few seconds, i.e. well within one half‐life of many DN precursors. Therefore, it seems very important to evaluate the DN flux as a function of position and determine if DNs may contribute significantly to the activation and dose rates. The multi‐particle transport code MCNPX combined with the material evolution program CINDER’90 is used to predict the DN precursors and construct the DN tables. These DN tables are employed within the generalized geometrical model of the MegaPie spallation target at PSI (Switzerland). We show that the contribution of DNs and prompt spallation neutrons to the total neutron flux is comparable at the very top of the liquid PbBi loop. We also demonstrate that these estimates of DNs within MCNPX are very much model‐dependent. No experimental data are available for DN yields and time spectra from high energy fission‐spallation reactions. An experiment to perform these measurements is proposed.

This article presents calculations of photonuclear reaction cross sections for actinides by using different reaction codes, namely an improved version of HMS‐ALICE and GNASH. The GDR parameters from the RIPL2 data library are used to describe the total photo‐absorption cross section. In general, our results show satisfactory agreement with experimental data and IAEA evaluations. We plan to include our GNASH evaluations for 235U, 238U, 237Np, 239Pu, 240Pu and 241Am into a new release of the ENDF‐B/VII data files.

Experimental and theoretical studies were performed to complete the data sets on the production of residue nuclides in natural Bi irradiated with protons. For the long-lived and difficult to measure isotopes 108mAg, 10Be, 26Al as well as 129I and 36Cl, chemical systems had been developed aimed to isolate them from the bismuth matrix. The separation methods are based on distillation, precipitation and ion exchange. From the content of the radionuclides determined by accelerator mass spectrometry and γ-spectrometry, the production cross sections in the proton energy range from 100 to 2600 MeV were calculated. The experimental results were compared with theoretical predictions. Significant deviations between experiment and theory over the whole energy range were observed with increasing discrepancies for the production of the lighter residue nuclides.