Induced radioactivity studies of the shielding and beamline equipment of the high intensity proton accelerator facility at PSI (original) (raw)
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The LINAC-ADONE accelerator complex of the INFN-LNF Frascati National Laboratories, operating for 27 y prior to the commissioning of DA⌽NE, was dismantled in 1993. The scraps resulting from the decommissioning of LINAC-ADONE have been temporarily stored in the same Frascati laboratory, waiting for definitive disposal. Relying on recommendations of the IAEA, European Commission and Italian committees, an experimental characterization study of the LNF repository was performed. The main objective was a classification of the scraps on the basis of internationally recognized "clearance levels," which are 0.1 Bq g ؊1 for the isotopes of interest for this work. Secondly, a measurement of the materials suspected to be above 0.1 Bq g ؊1 was planned. Activation isotopes were expected from the aluminum, copper, steel, and iron of the LINAC and the ADONE ring sections. For screening purposes, the repository area has been divided into zones, where in-situ measurements with a portable HP-Ge detector have been performed. In addition, small samples have been cut from a representative number of pieces, and accurate laboratory measurements have been made with a low background HP-Ge spectrometer. The experimental results are in good agreement with other studies and show that a large part of the material is below the mentioned specific activity level.
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The 600 MeV synchro-cyclotron (SC) was the first accelerator that came into operation at CERN in 1957. It provided beams for CERN's first particle and nuclear physics experiments and operated for 33 years until it was shut down in 1990. In view of a planned partial decommissioning of the facility, a range of measurements were carried out to evaluate the levels of residual radioactivity in the accelerator and its surrounding after about 20 years of cooling time. Gamma spectrometry measurements were performed on 113 samples collected inside the three floors of the accelerator vault, on the cyclotron itself and on concrete samples taken from various parts of the building walls, up to a depth of 50 cm in the shield. About 40% of all samples contain traces of neutron-induced radionuclides, mainly 60 Co (in metals), 133 Ba, 137 Cs, 152 Eu and 154 Eu (in concrete). Values of specific activities range from 5 mBq/g to 781 Bq/g. The maximum activity induced in concrete was observed at the depth of 40 cm in the wall near the cyclotron extraction channel. The laboratory measurements were supplemented by in-situ gamma spectrometry performed with the ISOCS system. A complete dose rate survey was also performed yielding isodose maps of the three levels of the building. The isotope production and the residual radioactivity in the barite walls of the SC bunker were simulated with the FLUKA and JEREMY codes in use at CERN for predicting residual radioactivity in activated accelerator components, and the results compared with the gamma spectrometry data. A detailed comparison of calculated and measured specific activities shows generally good agreement, to within a factor 2 in most cases. These results serve as indirect validation of the capabilities of these codes to correctly predict residual radioactivity with only a very approximate knowledge of the irradiation profile and after a very long (20 years) cooling time. Overall the results provided in this paper may be of use for estimating residual radioactivity in proton accelerators of comparable energy and for benchmarking computer codes.
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Radioactive nuclides are produced at high-energy electron accelerators by different kinds of particle interactions with accelerator components and shielding structures. Radioactivity can also be induced in air, cooling fluids, soil and groundwater. The physical reactions involved include spallations due to the hadronic component of electromagnetic showers, photonuclear reactions by intermediate energy photons and low-energy neutron capture. Although the amount of induced radioactivity is less important than that of proton accelerators by about two orders of magnitude, reliable methods to predict induced radioactivity distributions are essential in order to assess the environmental impact of a facility and to plan its decommissioning. Conventional techniques used so far are reviewed, and a new integrated approach is presented, based on an extension of methods used at proton accelerators and on the unique capability of the FLUKA Monte Carlo code to handle the whole joint electromagnetic and hadronic cascade, scoring residual nuclei produced by all relevant particles. The radiation aspects related to the operation of superconducting RF cavities are also addressed.
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