Manfred Hofert

The Large Hadron Collider (LHC) in the LEP tunnel

After the remarkable start-up of LEP, the installation of a Large Hadron Collider, LHC, in the LEP tunnel will open a new era for the High Energy Physics. This report summarizes the main LHC parameters and subsytems and describes the more recent studies and developments.

Radiation levels in LEP, 1989–1995

Abstract This paper discusses the radiation levels monitored in and around the LEP tunnel and the underground experimental areas and in the environment on the surface, following the first six years of operation where the collider has mostly been working at 45 GeV (LEP phase I). At the end of 1995 the LEP II program was started, with an energy increase to 68 GeV. The radiation levels in the underground areas accessible during LEP operation are very low and on the surface the values of dose equivalent are not discernable from the background.

A PERSONAL NEUTRON MONITORING SYSTEM BASED ON SOLID STATE NUCLEAR TRACK DETECTORS

ABSTRACT The use of solid state nuclear track detectors for personal neutron monitoring around high energy particle accelerators has been extensively investigated at CERN. A system based on cellulose nitrate (LR115) as a track detector in contact with different radiators (boron and polycarbonate) has been proposed to replace the NTA neutron film used so far. The holes created in the cellulose nitrate layer by charged particles such as alpha particles and carbon recoils are counted after etching with a microscope connected to an image-analysing computer (Quantimet). The present paper describes the monitoring system chosen and presents the results of a large series of tests (calibration and field experiments) at CERN. The problems encountered in going from laboratory-scale tests to a large-scale routine use of the neutron monitoring system are discussed. The use of 6LiF/7LiF thermoluminescence detectors in conjunction with the track detector system to select the track detectors that require evaluation is proposed.

The decommissioning of accelerators: an exercise in the recycling of radioactive material

Compared with the number of nuclear power plants that will be decommissioned over the next few years accelerators are only a “small” source of radioactivity although at CERN the total amount of mostly metallic material activated in the operation of the accelerators is estimated to be of the order of 15 Mtons. Various existing approaches to classify and administer radioactive material will be presented with all of them clearly earmarked by the requirements of the nuclear cycle. There are however important differences between activation in reactors and accelerators that will be worked out. It will be shown that an attitude based on reuse or recycling of activated accelerator material should be preferred to the elimination as radioactive waste.

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.

An investigation of build-up effects in high energy radiation fields using a handi TEPC

ICRP considers that a dose limit of 2 mSv close to the body surface of a pregnant woman will ensure a dose limit of 1 mSv to the foetus. This assumption depends on the energy spectrum and composition of the radiation fields, especially those containing high energy particles such as are found around particle accelerators or in aircraft. In this work the response of a tissue-equivalent proportional counter in radiation fields of different composition and energy was measured as a function of depth in cylindrical phantoms. The decrease in dose and dose equivalent at a phantom depth equivalent to that of a foetus was 10% in a typical high energy stray radiation field and 30% for neutrons from a Pu-Be source. It is concluded that it would be prudent in these cases to limit the exposure of a pregnant woman to I mSv in order to ensure that the dose to the foetus stays below the same limit.