CERN, Geneva
Modern particle interaction and transport codes such as FLUKA allow one to predict radioactivity and associated residual dose rates caused by high energy beam losses in accelerator components in great detail. Phaenomenological models of high energy hadronic interactions linked to sophisticated generalized cascade, pre-equilibrium and fragmentation models are able to describe the production of individual radioactive nuclides with good accuracy (often within less than 20%), as comprehensive benchmark studies have demonstrated. The calculation of induced radioactivity has thus become an integral part of design studies for high energy beam absorbers. Results provide valuable information on material choices, handling constraints and waste disposal and allow an early optimization of components in order to increase the efficiency of the later operation of the facility while keeping doses to personnel as low as reasonably achievable. The present paper gives examples of both generic studies with FLUKA for different absorber materials as well as studies for collimators and absorbers of the Large Hadron Collider.
Fermilab, Batavia
Recent developments in the MARS15 code are described for the critical modules related to demands of hadron and lepton colliders and Megawatt proton and heavy-ion beam facilities. Details of advanced models for particle production and nuclide distributions in nuclear interactions at medium and high energies, energy loss, atomic displacements and gas production are presented along with benchmarking against data wherever is possible. Examples are given for the most demanding areas. The current experimental activities are described towards reduction of existing uncertainties in simulations.
BNL, Upton, Long Island, New York
Fermilab, Batavia
Proton irradiation effects on materials supporting high power experiments have been studied extensively using the BNL 200 MeV proton beam and the target station of the Linear Isotope Producer (BLIP). The goal has been to (a) observe changes in physio-mechanical properties in widely used materials and in new alloys and composites induced by energetic protons, (b) identify thresholds of flux/fluence, (c) study the role of temperature in damage reversal, and (d) correlate damage effects of different species such as energetic protons and neutrons. Experience data from experiments, i.e. NuMI, on target performance have been integrated with observations and aided by simulation studies to assess the role of energy and irradiation rate. Based on the correlation experimental results, experience data and simulation studies, new irradiation experiments linked to the long baseline neutrino experiment (LBNE) have been designed and performed. Results of irradiation studies in support of the neutrino factory initiative, the LBNE and the LHC will be presented and coupled with confirmatory simulations employed to reconcile experimental observations with anticipated NuMI target performance.
GSI, Darmstadt
STU, Bratislava
Assessment of the radiation hazards from activated accelerator components due to beam-losses is a serious issue for high-energy hadron facilities. Important radiation-safety principle ALARA (As Low As Reasonably Achievable) calls for minimizing exposure to people. That is why the uncontrolled beam-losses must be kept on the reasonable low level. The beam-losses below 1 W/m are considered as a tolerable for “hands-on” maintenance on proton accelerators. The activation of the heavy-ion accelerators is in general lower than the activation of the proton machines. In our previous work, we estimated the "hands-on" maintenance criteria for heavy ions up to uranium in stainless steel and copper by scaling the existing criterion for protons. It was found out that the inventory of the isotopes and their relative activities do not depend on the primary-ion mass but depend on the target material. For this reason in the present work the activation of other important accelerator construction materials carbon and aluminum was studied using the FLUKA code.
ANL, Argonne
Atomic displacements by high energy particles in a crystalline solid induce formation of point defects and defect clusters of vacancies and interstitial atoms. The damaged microstructure results in significant changes in materials physical and mechanical properties. Besides displacement damage, nuclear transmutation reactions occur, producing He and H gas atoms that can have pronounced effect on materials performance even at low concentrations. Radiation effects in materials have been studied using various irradiation sources, and, radiation damage correlation is essential so that radiation effects produced by different irradiation sources can be compared and data can be transferred or extrapolated. The parameter commonly used to correlate displacement damage is the total number of displacements per atom (dpa). Considering that several aspects of radiation exposure can give rise to property changes, the extent of radiation damage cannot be fully characterized by a single parameter. This paper will discuss damage correlation under various irradiation environments, key irradiation parameters and their effects on irradiation-induced property changes.