The influence of the type of filling gas on the response of ionisation chambers to a mixed high-energy radiation field

Radiation protection dosimetry in radiation fields behind the shielding of high-energy accelerators such as CERN is a challenging task and the quantitative understanding of the detector response used for dosimetry is essential. Measurements with ionisation chambers are a standard method to determine absorbed dose (in the detector material). For applications in mixed radiation fields, ionisation chambers are often also calibrated in terms of ambient dose equivalent at conventional reference radiation fields. The response of a given ionisation chamber to the various particle types of a complex high-energy radiation field in terms of ambient dose equivalent depends of course on the materials used for the construction and the chamber gas used. This paper will present results of computational studies simulating the exposure of high-pressure ionisation chambers filled with different types of gases to the radiation field at CERN's CERN-EU high-energy reference field facility. At this facility complex high-energy radiation fields, similar to those produced by cosmic rays at flight altitudes, are produced. The particle fluence and spectra calculated with FLUKA Monte Carlo simulations have been benchmarked in several measurements. The results can be used to optimise the response of ionisation chambers for the measurement of ambient dose equivalent in high-energy mixed radiation field

Field calibration studies for ionisation chambers in mixed high-energy radiation fields

The monitoring of ambient doses at work places around high-energy accelerators is a challenging task due the complexity of the mixed stray radiation fields encountered. At CERN, mainly Centronics IG5 high-pressure ionisation chambers are used to monitor radiation exposure in mixed fields. The monitors are calibrated in the operational quantity ambient dose equivalent H*(10) using standard, source-generated photon- and neutron fields. However, the relationship between ionisation chamber reading and ambient dose equivalent in a mixed high-energy radiation field can only be assessed if the spectral response to every component and the field composition is known. Therefore, comprehensive studies were performed at the CERN-EU high-energy reference field facility where the spectral fluence for each particle type has been assessed with Monte Carlo simulations. Moreover, studies have been performed in an accessible controlled radiation area in the vicinity of a beam loss point of CERN's proton synchrotron. The comparison of measurements and calculations has shown reasonable agreement for most exposure conditions. The results indicate that conventionally calibrated ionisation chambers can give satisfactory response in terms of ambient dose equivalent in stray radiation fields at high-energy accelerators in many cases. These studies are one step towards establishing a method of ‘field calibration' of radiation protection instruments in which Monte Carlo simulations will be used to establish a correct correlation between the response of specific detectors to a given high-energy radiation fiel

Response of neutron detectors to high-energy mixed radiation fields

Radiation protection around CERN's high-energy accelerators represents a major challenge due to the presence of complex, mixed radiation fields. Behind thick shielding neutrons dominate and their energy ranges from fractions of eV to about 1 GeV. In this work the response of various portable detectors sensitive to neutrons was studied at CERN's High-Energy Reference Field Facility (CERF). The measurements were carried out with conventional rem counters, which usually cover neutron energies up to 20 MeV, the Thermo WENDI-2, which is specified to measure neutrons up to several GeV, and a tissue-equivalent proportional counter. The experimentally determined neutron dose equivalent results were compared with Monte Carlo (MC) simulations. Based on these studies field calibration factors can be determined, which result in a more reliable estimate of H*(10) in an unknown, but presumably similar high-energy field around an accelerator than a calibration factor determined in a radiation field of a reference neutron sourc

The response of TL lithium fluoride detectors to 24 GeV/c protons for doses ranging up to 1 MGy

A new method of thermoluminescent (TL) measurement of radiation doses ranging from micrograys up to a megagray has been recently developed at IFJ. This method is based on a newly discovered behavior of LiF:Mg,Cu,P detectors at doses exceeding 1 kGy. Significant changes in their glow-curves are observed at higher doses; of special importance is occurrence of a new, well separated peak for doses above 50 kGy, thus these detectors can be used for measurements of doses at ultra-high dose range. In order to check the glow-curve features in the high dose region for different types of LiF:Mg,Cu,P and LiF:Mg,Ti detectors after irradiation with heavy charged particles, tests at the 24 GeV/c proton beam of IRRAD1 irradiation zone at the CERN Proton Synchrotron accelerator up to 1 MGy were performed. The occurrence of the high dose peak in the glow-curve of LiF:Mg,Cu,P detectors resulting from heavy particles irradiation was confirmed. Results of this investigation are presented in this paper. (C) 2010 Elsevier Ltd. All rights reserved

The response of different types of TL lithium fluoride detectors to high-energy mixed radiation fields

Thermoluminescent (TL) dosimeters are routinely used to monitor absorbed doses in many kinds of radiation fields which contain photons, electrons and neutrons. However, TLDs are mainly calibrated to photon sources. We studied the response of TLDs to complex secondary fields arising during the operation of high-energy accelerators (e.g. the Large Hadron Collider (LHC) at CERN). The experiments were conducted at the CERN–EU high-energy reference field facility (CERF). Six different LiF-based TLDs (MTS-N, MTS-7, MTS-6, MCP-N, MCP-7, MCP-6) were exposed to various secondary CERF's fields (both for high and low doses), by placing them at various positions: at the target and concrete top and side positions. For the experiment at the target the corresponding Monte Carlo calculations were also carried out using the FLUKA transport code and compared with experimental results. In addition, alanine dosimeters were used as an independent reference. The results show that TLDs are well suited for monitoring radiation fields around the LHC. Nevertheless, further investigations are required, some of which are in progress

Regional Radiation Pneumonitis After SIRT of a Subcapsular Liver Metastasis: What is the Effect of Direct Beta Irradiation?

We herein present a patient undergoing selective internal radiation therapy with an almost normal lung shunt fraction of 11.5 %, developing histologically proven radiation pneumonitis. Due to a predominance of pulmonary consolidations in the right lower lung and its proximity to a large liver metastases located in the dome of the right liver lobe a Monte Carlo simulation was performed to estimate the effect of direct irradiation of the lung parenchyma. According to our calculations direct irradiation seems negligible and RP is almost exclusively due to ectopic draining of radioactive spheres