The French laboratories in charge of 'neutron' dosimetry using the spectrometer 'ROSPEC', formed a working group in 2001. The participants began to study the behaviour of the instrument with a comparison exercise in broad energy neutron fields recommended by the International Organisation for Standardisation (ISO) and available at the LMDN in Cadarache. The complete version of the ROSPEC is made up of six spherical proportional counters fixed to a rotating platform. These counters cover different energy ranges which overlap each other to provide a link between the detectors, within the energy range from thermal neutrons to 4.5 MeV. The irradiation configurations chosen were ISO standard sources (Cf-252, Cf-252+D2O)(1Cd), Am-241-Be) and the SIGMA facility. The results show that the 'thermal and epithermal' neutron fluence was widely overestimated by the spectrometer in all configurations.

In criticality accident dosimetry and more generally for high dose measurements, special techniques are used to measure separately the gamma ray and neutron components of the dose. To improve these techniques and to check their dosimetry systems (physical and/or biological), a total of 60 laboratories from 29 countries (America, Europe, Asia) participated in an international intercomparaison, which took place in France from 9 to 21 June 2002, at the SILENE reactor in Valduc and at a pure gamma source in Fontenay-aux-Roses. This intercomparison was jointly organised by the IRSN and the CEA with the help of the NEA/OCDE and was partly supported by the European Communities. This paper describes the aim of this intercomparison, the techniques used by the participants and the two radiation sources and their characteristics. The experimental arrangements of the dosemeters; for the irradiations in free air or on phantoms are given. Then the dosimetric quantities measured and reported by the participants are summarised, analysed and compared with the reference values. The present paper concerns only the physical dosimetry and essentially experiments performed on the SILENE facility. The results obtained with the biological dosimetry are published in two other papers of this issue.

The Laboratory of External Dosimetry Studies and Researches (LRDE), associated laboratory to the Bureau National de Métrologie, is strongly involved in the reference establishment and calibration of instruments in neutron radiation fields provided by 241Am-Be, 252Cf and (252Cf + D2O)/Cd sources. In 1997, on the request of COFRAC, the LRDE has managed an Inter-Laboratory Test Program in 'neutron dosimetry' to compare the different standard calibration methods. The transfer instrument used was a "Harwell Monitor N91". The results of the participant were in good agreement but the associated uncertainties need to be revised by some of laboratories. According to the Mutual Recognition Arrangement signed in 1999, laboratories for metrology will have to assure the traceability of their references. In 2003-2005, the LRDE organises, with National Physical Laboratory (UK) and Physikalisch-Techische Bundesanstalt (Germany), an international comparison in 'neutron dosimetry'. Two transfer instruments, a "2202D" rate metre and a "Harwell Monitor N91", will be sent in turn to the participant laboratories for measurements at their own neutron sources facilities.

The variation of the response of the instruments with the neutron energy has to be determined in well-characterized monoenergetic neutron fields. The AMANDE facility will deliver such neutron fields between 2 keV and 20 MeV in an experimental hall designed with metallic walls for neutron scattering minimisation. The neutrons will be produced by nuclear interaction of accelerated protons or deuterons on thin targets of selected materials. The measuring devices to be characterised will be accurately placed with a fully automated detector transport system. The energy of the neutron field will be validated by time-of-flight experiments and a large set of standard detectors and fluence monitors will be used to determine the neutron fluence references. The scattered neutron fluence and dose equivalent were calculated by the MCNP Monte Carlo code at several measuring points in order to determine their contribution to the neutron field.

EVIDOS ('evaluation of individual dosimetry in mixed neutron and photon radiation fields') is an European Commission (EC)-sponsored project that aims at a significant improvement of radiation protection dosimetry in mixed neutron/photon fields via spectrometric and dosimetric investigations in representative workplaces of the nuclear industry. In particular, new spectrometry methods are developed that provide the energy and direction distribution of the neutron fluence from which the reference dosimetric quantities are derived and compared to the readings of dosemeters. The final results of the project will be a comprehensive set of spectrometric and dosimetric data for the workplaces and an analysis of the performance of dosemeters, including novel electronic dosemeters. This paper gives an overview of the project and focuses on the results from measurements performed in calibration fields with broad energy distributions (simulated workplace fields) and on the first results from workplaces in the nuclear industry, inside a boiling water reactor and around a spent fuel transport cask.

An international intercomparison of criticality accident dosimetry systems took place in the SILENE reactor, in June 2002. Participants from 60 laboratories irradiated their dosemeters (physical and biological) using two different configurations of the reactor. In preparation for this intercomparison, the leakage radiation fields were characterised by spectrometry and dosimetry measurements using the ROSPEC spectrometer associated with a NE-213 scintillator, ionisation chambers, GM counters, diodes and thermoluminescence dosemeters (TLDs). For this intercomparison, a large area was required to irradiate the dosemeters both in free air and on phantoms. Therefore, measurements of the uniformity of the field were performed with activation detectors and TLDs for neutron and gammas, respectively. This paper describes the procedures used and the results obtained.

The new CANEL/T400 facility has been set-up at the Institute for Radiological Protection and Nuclear Safety (IRSN) to produce a realistic neutron field. The accurate characterisation of this neutron field is mandatory since this facility will be used as a reference neutron source. For this reason an international measuring campaign, involving four laboratories with extensive expertise in neutron metrology and spectrometry, was organised through a concerted EUROMET project. Measurements were performed with Bonner sphere (BS) systems to determine the energy distribution of the emitted neutrons over the whole energy range (from thermal energy up to a few MeV). Additional measurements were performed with proton recoil detectors to provide detailed information in the energy region above 90 keV. The results obtained by the four laboratories are in agreement with each other and are compared with a calculation performed with the MCNP4C Monte-Carlo code. As a conclusion of this exercise, a reliable characterisation of the CANEL/T400 neutron field is obtained.

The Laboratory of Studies and Research in External Dosimetry (LRDE) associated to the National Office for Metrology (BNM) has to maintain the traceability of the French references for the calibration of neutron dosimeters. The LRDE owns a facility which provides some conventional neutron spectra from sources of Am-241-Be, Cf-252, and (Cf-252 + D2O)(/Cd) recommended by ISO standards. These ISO spectra appear not appropriated to simulate some kind of workplace spectra. In order to have similar radiation conditions between the calibration and the use of the device, LRDE has built facilities ("SIGMA" and "CANEL") providing some neutron spectra from thermal to fast energies reproducing those encountered in workplaces.

For many years, the laboratory of external dosimetry studies and researches of the Institute for Radiological Protection and Nuclear Safety (IRSN) has developed several facilities providing neutron fields: isotopic reference sources, realistic spectra and thermal neutron fields. In order to extend its set of neutron reference fields, the IRSN has decided to acquire a 2MV tandem electrostatic accelerator to produce reference monoenergetic neutron beams between 2keV and 20MeV with metrological quality. A new building, housing the accelerator, has been optimized in order to reduce as much as possible the background due to scattered neutrons. All these facilities will represent one of the most complete set of neutron reference fields for neutron metrology and dosimetry.

The study of the physicochemical characteristics of titanium thin films and the corresponding deuterium absorption/desorption kinetics was performed. In order to optimize the production of high-energy neutrons the behaviour of deuteride titanium targets has been studied experimentally by bombardment with 120 and 350kV deuterons by means of electrostatic accelerators. The importance of the deposit evaporation conditions on the efficiency of neutron emission is clearly demonstrated as well as the thermomechanical stability of the Ti thin film by deuteron bombardment. The main parameters involved in the targets behaviour have been discussed from a thermodynamical approach.

As part of a programme on simulation of realistic neutron spectra at workplaces, a new facility based on the H-2(d,n)He-3 reaction (abbrev.: DD) which yields a 3.3 MeV neutron field, is being developed at the IPSN/SDOS Laboratory in Cadarache. Additional shields at the exit of an accelerator target can provide, in the laboratory, a replication of some spectral conditions encountered in practice. Spectra resulting from this reaction will complete those obtained from the DT process in the same laboratory. Reasons for using the DD reaction and the associated particle counting technique as a monitor of neutron flux are presented. Instead of detecting the alpha particle from the DT reaction, protons are counted from the competitive reaction H-2(d,p)H-3 with respect to the DD reaction. The fact that the two last reactions are involved in the monitoring and are markedly anisotropic in the CM system, means that a more complex situation has to be dealt with to calculate the neutron yield per proton measured in a solid angle. A conversion factor between neutrons and protons must be calculated and compared with reference measurements performed with several instruments. Based on the new assembly, a 'realistic' spectrum calculated with the MCNP code is proposed. Results from the MCNP code are multiplied by a (n,p) factor calculated by another program, MONITOR, which takes into account the kinematics, the cross sections and the energies involved in the reactions. The theoretical fluence predicted at a reference point in this spectrum is validated directly with the area monitor previously calibrated through a specific methodology. This work provides a new tool of investigation to obtain realistic neutron spectra to be used in the calibration of radiation protection instruments that should fulfil the ICRP recommendations, as given in ICRP Publication 60.

In order to fulfil the ICRP Recommendations, as given in ICRP publication 60, regarding the primary dose limits and the revised quality factors, substantial improvements to the characteristics of current dosimetric instruments are necessary. This statement is particularly true for neutron monitoring; neutron individual dosemeters suffer from an evident lack of accuracy and sensitivity. As to area dosemeters, the energy dependence of their response is far from being satisfactory over the whole energy range. Until more elaborate systems appear on the market, a step towards obtaining more reliable values of dose derived from current devices can be obtained by considering carefully the calibration conditions for dosemeters. This paper deals with the calibration procedures as defined or in preparation in the relevant ISO committees, in the frame of the so-called realistic neutron spectra, which replicate some of the neutron spectra encountered at workplaces. Taking into account the energy response of a particular dosimetric device, the influence of several energy distributions of the calibration field on the indication of the dosemeter to be tested are quantified and compared with;the calibration factor calculated from monoenergetic references. The experimental part of the work at the IPSN/SDOS facility in the Cadarache research centre is expected to illustrate the contribution of the realistic neutron spectra to the problem of calibration of radiation protection instruments.