Hartwig Schaal

Evolution of a spallation reaction: experiment and Monte Carlo simulation

Abstract Reaction cross sections and production cross sections for neutrons, hydrogen, and helium have been measured for 1.2, 1.8 GeV p+Fe, Ni, Ag, Ta, W, Au, Pb and U and are compared with different intra-nuclear-cascade- combined with evaporation-models. Agreement for neutrons and considerable differences for light charged particles are observed between experiment and calculation as well as between different models. The discrepancies are associated with specific deficiencies in the models. The exclusive data measured with two 4π-detectors for neutron and charged particle detection allowed furthermore a systematic comparison of observables characteristic of different stages of the temporal evolution of a spallation reaction: inelastic collision probability, excitation energy distribution, pre-equilibrium emission, and inclusive production cross sections.

Helium production for 0.8–2.5 GeV proton induced spallation reactions, damage induced in metallic window materials

Production cross-sections for neutrons and charged particles as well as excitation energy distributions in spallation reactions were measured recently by the NESSI-collaboration and have been employed to test different intra nuclear cascade models and the subsequent evaporation. The INCL/GEMINI code, which describes best the experimental data has been employed to calculate the damage cross-sections in Fe and Ta as well as the He/dpa ratio as a function of proton energy. For the same amount of neutron production in a typical target of a spallation neutron source the proton beam induced radiation damage in an Fe window is shown to decrease almost linearly with proton energy. For heavier materials such as Ta a similar decrease of the radiation damage is found only for energies above about 3 GeV.

Radiation Shielding and Protection of the European Spallation Neutron Source (ESS)

The shielding and the radiation protection of high intensity spallation neutron sources as ESS has special features and importance compared to usual accelerator shielding and protection considerations. For the shielding we are interested in very thick shields, so small uncertainties e.g. in cross sections lead to large errors; we are interested in detailed predictions, such as accurate particle spectra over large energy ranges, and the geometries of interest are complex, e.g. shields with multiple beam holes. Containment of radioactivity for the high power target station is also a very important issue and has highest hazard. The different methods, which are used for designing the ESS shielding, are discussed. Comparison with performed measurements is also given.

Nuclear Simulation and Radiation Physics Investigations of the Target Station of the European Spallation Neutron Source

The European Spallation Neutron Source (ESS) delivers high-intensity pulsed particle beams with 5-MW average beam power at 1.3-GeV incident proton energy. This causes sophisticated demands on material and geometry choices and a very careful optimization of the whole target system. Therefore, complex and detailed particle transport models and computer code systems have been developed and used to study the nuclear assessment of the ESS target system. The purpose here is to describe the methods of calculation mainly based on the Monte Carlo code to show the performance of the ESS target station. The interesting results of the simulations of the mercury target system are as follows: time-dependent neutron flux densities, energy deposition and heating, radioactivity and afterheat, materials damage by radiation, and high-energy source shielding. The results are discussed in great detail. The validity of codes and models, further requirements to improve the methods of calculation, and the status of running and planned experiments are given also.

Light Particle Production in Spallation Reactions Induced by Protons of 0.8-2.5 GeV Incident Kinetic Energy

Absolute production cross sections have been measured simultaneously for neutrons and light charged particles in 0.8-2.5 GeV proton induced spallation reactions for a series of target nuclei from aluminum up to uranium. The high detection efficiency both for neutral and charged evaporative particles provides an event-wise access to the amount of projectile energy dissipated into nuclear excitation. Various intra nuclear cascade plus evaporation models have been confronted with the experimental data showing large discrepancies for hydrogen and helium production.

Experimental Investigation of Neutron Generation in Thick Target Blocks of Pb, Hg and W with 0.4 to 2.5 GeV Proton Beams

Detailed experimental neutron data relevant to the design of the target station of neutron spallation sources have been gathered by the NESSI-collaboration at the COSY accelerator in FZ Jülich. Numerous neutron multiplicity distributions and reaction probabilities have been measured for 0.4 to 2.5 GeV protons bombarding highly segmented target blocks from Pb, Hg and W of up to 35 cm in length and 15 cm in diameter with the intention to provide a comprehensive data base for the improvement and validation of existing reaction simulation codes.

Nuclear data status and needs for spallation physics investigations

Abstract The application potential of spallation facilities is widespread especially as intense neutron sources for solid state and nuclear physics, material damage studies, in medicine and radiobiology, simulation of space radiations, and nuclear technology. Nuclear data needed include total, elastic, non-elastic, and production cross sections. Particle yields are needed for source calculations. Data for operation of spallation sources include cross sections for transport, dosimetry, damage energy, transmutation, and gas production. In particular high energy cross section evaluation is considered besides material damage and gas production data.

Experiments and theoretical investigations for a high-energy source shielding experiment at the los alamos WNR facility

Abstract Spectrum averaged attenuation lengths for high-energy neutrons in iron were measured utilizing multireaction spallation detector and threshold detector foils. The experiment was set up inside the bulk shield of the Los Alamos WNR facility. Products from reactions thresholding up to 125 MeV were measured. For the energy range between 0.5 MeV and 125 MeV a spectrum averaged attenuation length of (153±9)g/cm2 was derived. The information of this experiment will be used to benchmark the computational models and radiation transport computer codes which have been implemented at KFA. First comparisons are given.

Evaluation of hydrogen data for cold neutron sources and their application to source design studies

Abstract Evaluation of group cross sections of hydrogen at 20 K temperature and the design calculations for the new cold source in the DIDO reactor in Julich are discussed.