Luisa Ulrici

Neutron production from 158 GeV/c per nucleon lead ions on thin copper and lead targets in the angular range 30-135°

Abstract The neutron emission from 5, 10 and 20 mm thick lead and 10 and 20 mm thick copper targets bombarded by a lead ion beam with momentum of 158 GeV/c per nucleon were measured at the CERN Super Proton Synchrotron. The neutron yield and spectral fluence per incident ion on target were measured with an extended range Bonner sphere spectrometer in the angular range 30–135° with respect to beam direction. Monte Carlo simulations with the FLUKA code were performed to establish a guess spectrum for the unfolding of the experimental data. The results have shown that, lacking Monte Carlo radiation transport codes dealing with ions with masses larger than 1 amu, a reasonable prediction can be carried out by scaling the result of a Monte Carlo calculation for protons by the projectile mass number to the power of 0.85–0.95 for a lead target and 0.88–1.03 for a copper target.

Predicting Induced Radioactivity at High-Energy Electron Accelerators

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.

Neutron measurements in the stray field produced by 158 GeV c(-1) per nucleon lead ion beams.

This paper discusses measurements carried out at CERN in the stray radiation field produced by 158 GeV c(-1) per nucleon 208Pb82+ ions. The purpose was to test and intercompare the response of several detectors, mainly neutron measuring devices, and to determine the neutron spectral fluence as well as the microdosimetric (absorbed dose and dose equivalent) distributions in different locations around the shielding. Both active instruments and passive dosimeters were employed, including different types of Andersson-Braun rem counters, a tissue equivalent proportional counter, a set of superheated drop detectors, a Bonner sphere system, and different types of ion chambers. Activation measurements with 12C plastic scintillators and with 32S pellets were also performed to assess the neutron yield of high energy lead ions interacting with a thin gold target. The results are compared with previous measurements and with measurements made during proton runs.

Instrument response in complex radiation fields

This paper aims at giving an overview of the main issues for estimating the radiation protection quantities in complex radiation fields. The measurability (or non-measurability) of the radiation protection quantities is discussed together with the main approaches for their estimate. The main mechanisms through which the various components of complex radiation fields are generated are also outlined. The main instruments employed for estimating the radiation protection quantities are described and discussed together with their response. Finally, a practical example is given, by discussing the results of an inter-comparison exercise held at the Gesellschaft für Schwerionenforschung mbH in Darmstadt (Germany) in the framework of the COordinated Network for RAdiation Dosimetry project, funded by the European Commission.

Radioactive waste management and decommissioning of accelerator facilities

During the operation of high-energy accelerators, the interaction of radiation with matter can lead to the activation of the machine components and of the surrounding infrastructures. As a result of maintenance operation and during decommissioning of the installation, considerable amounts of radioactive waste are evacuated and shall be managed according to the radiation-protection legislation. This paper gives an overview of the current practices in radioactive waste management and decommissioning of accelerators.

Induced Activity Calculations in View of the Large Electron Positron Collider Decommissioning

The future installation of the Large Hadron Collider (LHC) in the tunnel presently housing the Large Electron Positron collider (LEP) requires the dismantling of the latter after more than 10 years of operation. The decommissioning of an accelerator facility leads to the production of large amounts of waste, which in the case of an electron accelerator mostly is of very low level of radioactivity. LEP is classified as Nuclear Basic Installation (Installation Nucléaire de Base, INB) in France, where no unconditional clearance levels are fixed for the specific activity in materials to be released into the public domain. In the case of LEP, the possible sources of induced activity taken here into account are: localised beam losses, distributed beam losses and synchrotron radiation. Reference values of induced specific activity at saturation, normalised to lost beam power, were determined by comparing Monte-Carlo calculations carried out with the FLUKA code and experimental results. These figures are directly employed to estimate the expected amount of low level radioactivity around localised beam loss points in LEP. Regarding the synchrotron radiation, calculations of the total production of radionuclides from photon, thermal neutron and fast neutron activation in the aluminium vacuum chamber, the lead shielding and the magnet pole-faces of a dipole, showed that at beam energies less than 105 GeV, none of the components will be considered as radioactive for decay periods of longer than ten days.