Measurements and Monte Carlo calculations with the extended-range Bonner sphere spectrometer at high-energy mixed fields

Abstract

The use of spectrometry to provide information for neutron radiation protection has become an increasingly important activity over recent years. The need for spectral data arises because neither area survey instruments nor personal dosimeters give the correct dose equivalent results at all neutron energies. It is important therefore to know the spectra of the fields in which these devices are used. One of the systems most commonly employed in neutron spectrometry and dosimetry is the Bonner Sphere Spectrometers (BSS). The extended-range BSS that was used for this work, consists of 7 spheres with an overall response to neutrons up to 2 GeV. A 3He detector is used as a thermal counter in the centre of each sphere. In the context of this thesis the BSS was calibrated in monoenergetic neutron fields at low and intermediate energies. It was also used for measurements in several high energy mixed fields. These measurements have led to the calculation of neutron yields and spectral fluences from unshielded targets. Such data are very useful for shielding calculations and other radiation protection measurements. Furthermore, an upgrade of the response of the BSS to charged hadrons was achieved. Among the fields were the BSS has been tested, the CERF facility is of particular interest. It is installed in one of the secondary beam lines from the Super Proton Synchrotron (SPS) in the French site of CERN. The particle composition and spectral fluences outside the shielding of CERF simulate those in the cosmic radiation field at commercial flight altitudes. In the last decade interest has arisen in CERF from research institutions working in the space programme. There is therefore a need for setting-up a new exposure area reproducing the radiation environment found outside the atmosphere or inside a space vessel. The results from Monte Carlo studies that have been carried out for this purpose show a good agreement with experimental data taken inside the MIR space station. Therefore, CERF may prove to be a very useful tool for further tests with the BSS system, towards its upgrade for measurements in cosmic ray fields.