RESUMO
We report on the measurement of the ^{7}Be(n,p)^{7}Li cross section from thermal to approximately 325 keV neutron energy, performed in the high-flux experimental area (EAR2) of the n_TOF facility at CERN. This reaction plays a key role in the lithium yield of the big bang nucleosynthesis (BBN) for standard cosmology. The only two previous time-of-flight measurements performed on this reaction did not cover the energy window of interest for BBN, and they showed a large discrepancy between each other. The measurement was performed with a Si telescope and a high-purity sample produced by implantation of a ^{7}Be ion beam at the ISOLDE facility at CERN. While a significantly higher cross section is found at low energy, relative to current evaluations, in the region of BBN interest, the present results are consistent with the values inferred from the time-reversal ^{7}Li(p,n)^{7}Be reaction, thus yielding only a relatively minor improvement on the so-called cosmological lithium problem. The relevance of these results on the near-threshold neutron production in the p+^{7}Li reaction is also discussed.
RESUMO
The ISOLDE facility at CERN is one of the first facilities in the world dedicated to the production of the radioactive ion beams (RIB) and during all its working time underwent several upgrades. The goal of the latest proposed upgrade, 'The High Intensity and Energy ISOLDE' (HIE-ISOLDE), is to provide a higher performance facility in order to approximate it to the level of the next generation ISOL facilities, like EURISOL. The HIE-ISOLDE aims to improve significantly the quality of the produced RIB and for this reason the increasing of the primary beam power is one of the main objectives of the project. An increase in the nominal beam current (from 2 to 6 µA proton beam intensity) and energy (from 1.4 GeV to 2 GeV) of the primary proton beam will be possible due to the upgrade of CERN's accelerator infrastructure. The current upgrade means reassessment of the radiation protection and the radiation safety of the facility. However, an evaluation of the existing shielding configuration and access restrictions to the experimental and supply areas must be carried out. Monte Carlo calculations were performed in order to evaluate the radiation protection of the facility as well as radiation shielding assessment and design. The FLUKA-Monte Carlo code was used in this study to calculate the ambient dose rate distribution and particle fluxes in the most important areas, such as the experimental hall of the facility. The results indicate a significant increase in the ambient dose equivalent rate in some areas of the experimental hall when an upgrade configuration of the primary proton beam is considered. Special attention is required for the shielding of the target area once it is the main and very intensive radiation source, especially under the upgrade conditions. In this study, the access points to the beam extraction and beam maintenance areas, such as the mass separator rooms and the high voltage room, are identified as the most sensitive for the experimental hall from the radiation protection point of view.
Assuntos
Equipamentos de Proteção , Monitoramento de Radiação/instrumentação , Proteção Radiológica/instrumentação , Simulação por Computador , Desenho de Equipamento , Arquitetura de Instituições de Saúde , Humanos , Método de Monte Carlo , Nêutrons , Aceleradores de Partículas , Doses de Radiação , Monitoramento de Radiação/métodos , Proteção Radiológica/métodos , Medição de Risco/métodos , Fatores de Risco , SuíçaRESUMO
The high intensity and energy ISOLDE (HIE-ISOLDE) project is an upgrade to the existing ISOLDE facility at CERN. The foreseen increase in the nominal intensity and the energy of the primary proton beam of the existing ISOLDE facility aims at increasing the intensity of the produced radioactive ion beams (RIBs). The currently existing ISOLDE facility uses the proton beam from the proton-synchrotron booster with an energy of 1.4 GeV and an intensity up to 2 µA. After upgrade (final stage), the HIE-ISOLDE facility is supposed to run at an energy up to 2 GeV and an intensity up to 4 µA. The foreseen upgrade imposes constrains, from the radiation protection and the radiation safety point of view, to the existing experimental and supply areas. Taking into account the upgraded energy and intensity of the primary proton beam, a new assessment of the radiation protection and radiation safety of the HIE-ISOLDE facility is necessary. Special attention must be devoted to the shielding assessment of the beam dumps and of the experimental areas. In this work the state-of-the-art Monte Carlo particle transport simulation program FLUKA was used to perform the computation of the ambient dose equivalent rate distribution and of the particle fluxes in the projected HIE-ISOLDE facility (taking into account the upgrade nominal primary proton beam energy and intensity) and the shielding assessment of the facility, with the aim of identifying in the existing facility (ISOLDE) the critical areas and locations where new or reinforced shielding may be necessary. The consequences of the upgraded proton beam parameters on the operational radiation protection of the facility were studied.