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Since the first particle accelerator’s construction in 1931, an exponential spread of these machines occurred worldwide, in different kinds of applications. Nowadays, these are mainly used for industrial (60%) and medical (35%) purposes and for scientific research (5%). High energy secondary mixed fields produced by the particle beams interaction with matter imply a complex environmental dosimetry and special radiation protection regulations able to guarantee workers and population safety. In the medical field, this aspect is particularly emphasized in hadrontherapy centres, where high energy charged particles such as protons and carbon ions modify environmental doses, with a significant increase in the neutron contribution. This work proposes a technique to identify points of losses of the primary particle beam around an acceleration ring and has been developed within the radiation protection section at the National Centre for Oncological Hadrontherapy situated in Pavia. In the first part, the radiation field produced by protons and carbon ions interactions with structural materials at different energies was investigated. The main instrument of analysis is the Monte Carlo code for particle transport FLUKA, supported by experimental measurements in the treatment room carried out with the rem counter LUPIN, designed for pulsed neutron fields dosimetry. This first step allowed an analysis of both the angular and energetic instrumental response and a comparison of experimental results with simulations. The second part proposes a description of the technique for beam loss positions reconstruction around the acceleration ring at CNAO based on the application of unfolding codes.

Low-level neutron measurements are required for applications such as environmental monitoring, measurements of weak sources and the determination of neutron fluxes at underground laboratories. When analyzing low-level neutron measurements, it is important to be able to distinguish the signal due to neutrons from any background term that may originate within the detector. A solution to this problem has been developed for the case of measurements carried out with 3He spherical proportional counters of the type which are often used in Bonner sphere spectrometers. To determine this background, measurements were carried out in the former UDO underground laboratory of the Physikalisch-Technische Bundesanstalt located in the Asse salt mine. The analysis of the data was carried out using Bayesian parameter estimation. The result of the analysis is a very general parameterised function that can be used to describe the pulse height spectrum due to the background of the proportional counters.

The neutron field of the PTB Thermal Neutron Calibration Facility was characterised with the help of the Bonner sphere spectrometer of PTB, NEutron MUltisphere Spectrometer (NEMUS). For the analysis of the Bonner sphere data an analytical model of the neutron energy distribution was used. The unfolding of neutron spectra was performed via the method of Bayesian parameter estimation. Comparison of the results of thermal neutron fluence and thermal ambient dose equivalent with the results of the reference method of gold activation showed a very good agreement. For fast neutrons the results obtained with NEMUS will serve as reference values for this facility. The facility is ready for use as a thermal neutron reference field for calibrations of neutron measuring devices.

Measurement of the energy spectrum of secondary neutrons were carried out at the OncoRay Proton Therapy facility in Dresden, following an approach originating in neutron metrology which is well suited for both the characterization of secondary neutron fields at proton therapy facilities and the validation of Monte Carlo simulations. For the experiment, a brass target was placed in the proton beam and Bonner spheres measurements were made at a distance of 2 m from the target and at different angles, 15° to 120°, with respect to the incoming proton beam. The measured spectra were compared to Monte Carlo simulations.

Radiation therapy with proton beams allows the deposition of high doses to the tumour while minimising dose to the surrounding tissue. During such treatment, the patient is also exposed to secondary radiation which produces an out-of-field dose that affects healthy tissue. The largest contribution to this out-of-field dose comes from neutron radiation; therefore, it is of interest to fully characterise the neutron field in the therapy room with measurements. This is usually done with Bonner sphere spectrometers using active detectors, typically 3He-filled proportional counters, as central thermal neutron sensors. Under the experimental conditions encountered in proton therapy facilities, a proper analysis of the measurements is impossible unless dead time corrections are implemented. In this paper, we present a method using a paralysable dead time model for carrying out such corrections for Bonner sphere measurements with 3He-filled proportional counters and apply it to data taken at the University Proton Therapy Dresden (UPTD) facility in double scattering mode. The neutron events were recorded with time stamps and, based on this time-resolved data, the measured neutron rate distribution was sampled. Since the neutron flux is proportional to the proton flux, the integral neutron flux is directly related to the proton dose. Hence, we were able to estimate the detector dead time from the measured rate distributions recorded for a set of measurements with different proton dose rates. Experimental measurements with different intensities of the proton field show that the corrections are in agreement within 0.5% for measured signal rates smaller than 15 × 103 counts per second and do not exceed 1% at 25 × 103 counts per second.

Organic NE213 liquid scintillator neutron detectors are commonly used at accelerator facilities for neutron beam diagnostics. In recent years, they have also been installed at nuclear fusion facilities to measure the neutron energy spectra from Deuterium (D) and Deuterium-Tritium plasmas, e.g., at the ASDEX Upgrade (Garching, Germany) and at the Joint European Torus (JET, Culham, UK). The NE213 equivalent scintillating material (now BC501A) of the detector is sensitive to neutron and gamma radiation, so pulse discrimination techniques are applied in order to obtain the measured neutron pulse height spectrum (PHS). If the neutron detector is stable, controlled, and well-characterized (i.e., its response function to incoming neutrons of known energy is determined with high accuracy), it can be used as a neutron spectrometer. The measured PHS can then be analyzed using standard techniques such as unfolding to determine the incoming neutron energy spectrum. This article focuses on the unfolding of neutron data measured in D plasma experiments at JET by a compact broadband neutron spectrometer using the maximum entropy unfolding code MAXED. A general method for optimizing MAXED input parameters is described and applied to the measured PHS to diagnose the effects of the auxiliary heating of JET D plasma on the neutron energy spectra.

CONUS is a novel experiment aiming at detecting elastic neutrino nucleus scattering in the fully coherent regime using high-purity Germanium (Ge) detectors and a reactor as antineutrino ($\bar\nu$) source. The detector setup is installed at the commercial nuclear power plant in Brokdorf, Germany, at a very small distance to the reactor core in order to guarantee a high flux of more than 10$^{13}\bar\nu$/(s$\cdot$cm$^2$). For the experiment, a good understanding of neutron-induced background events is required, as the neutron recoil signals can mimic the predicted neutrino interactions. Especially neutron-induced events correlated with the thermal power generation are troublesome for CONUS. On-site measurements revealed the presence of a thermal power correlated, highly thermalized neutron field with a fluence rate of (745$\pm$30)cm$^{-2}$d$^{-1}$. These neutrons that are produced by nuclear fission inside the reactor core, are reduced by a factor of $\sim$10$^{20}$ on their way to the CONUS shield. With a high-purity Ge detector without shield the $\gamma$-ray background was examined including highly thermal power correlated $^{16}$N decay products as well as $\gamma$-lines from neutron capture. Using the measured neutron spectrum as input, it was shown, with the help of Monte Carlo simulations, that the thermal power correlated field is successfully mitigated by the installed CONUS shield. The reactor-induced background contribution in the region of interest is exceeded by the expected signal by at least one order of magnitude assuming a realistic ionization quenching factor of 0.2., Comment: 28 pages, 28 figures

Radiation therapy is one of the most frequently used treatment modalities for cancer. While most patients receive photon therapy, a growing number of patients are treated with particles, mainly protons. Protons offer a more localized dose deposition compared to photon therapy. This allows a reduction of the dose that is applied by the primary beam to the healthy tissue outside the target volume. At the same time, the use of protons leads to a change in the composition of the secondary radiation field, when compared to photons. In most locations, the out-of-field dose is dominated by secondary neutrons. The out-of-field dose varies significantly in shape and magnitude. Currently, there is no established procedure to monitor the secondary neutron dose to the patients.This paper describes the simulation and measurement of the secondary neutron radiation field at the University Proton Therapy Dresden. The simulation uses a detailed model of the beam delivery system, an IBA universal nozzle. The simulations have been validated by a comprehensive set of extended range Bonner sphere spectrometer measurements, with the NEMUS spectrometer operated by the Physikalisch-Technische Bundesanstalt. The set of measurements covers all possible machine configurations for the double scattering mode. An excellent agreement between unfolded measurements and simulation predictions is achieved.The data show that the neutron field is varying strongly on the scale of a human body. This indicates that the use of fluence to dose conversion tables is not justified for neutron dose calculation in patients. Therefore, the presented data is of high importance for future studies of the organ doses in different treatment scenarios.

Ratios of H(p)(10) and H*(10) were determined with reference instruments in a number of workplace fields within the nuclear industry and used to derive workplace-specific correction factors. When commercial survey meter results together with these factors were applied to the results of the locally used personal dosemeters their results improved and became within 0.7 and 1.7 of the reference values or better depending on the response of the survey meter. A similar result was obtained when a correction was determined with a prototype reference instrument for H(p)(10) after adjustment of its response. Commercially available survey instruments both for photon and neutron H*(10) measurements agreed with the reference instruments in most cases to within 0.5-1.5. Those conclusions are derived from results reported within the EC supported EVIDOS contract.

The availability of active neutron personal dosemeters has made real time monitoring of neutron doses possible. This has obvious benefits, but is only of any real assistance if the dose assessments made are of sufficient accuracy and reliability. Preliminary assessments of the performance of active neutron dosemeters can be made in calibration facilities, but these can never replicate the conditions under which the dosemeter is used in the workplace. Consequently, it is necessary to assess their performance in the workplace, which requires the field in the workplace to be fully characterised in terms of the energy and direction dependence of the fluence. This paper presents an overview of developments in workplace neutron dosimetry but concentrates on the outcomes of the EVIDOS project, which has made significant advances in the characterisation of workplace fields and the analysis of dosemeter responses in those fields. © The Author 2007. Published by Oxford University Press. All rights reserved.

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.

Within the EC project EVIDOS (‘Evaluation of Individual Dosimetry in Mixed Neutron and Photon Radiation Fields’), different types of active neutron personal dosemeters (and some passive ones) were tested in workplace fields at nuclear installations in Europe. The results of the measurements which have been performed up to now are summarised and compared to our currently best estimates of the personal dose equivalent H p (10). Under- and over-readings by more than a factor of two for the same dosemeter in different workplace fields indicate that in most cases the use of field-specific correction factors is required.

The response of albedo dosemeters depends on the energy and angle of the incident neutron radiation. For their use as personal dosemeters, a field-calibration factor has to be applied. The presently used single sphere method for field calibration can be extended and optimised by putting five albedo dosemeters on the surface of a polyethylene sphere and two TL cards in the centre. To investigate the potential of this extension, reference measurements and Monte Carlo calculations were performed and the fluence response of the detectors at different positions on and within the sphere was determined. Calculated response functions demonstrate that information on the energy and directional distribution of neutron fluence can be extracted with this simple set-up for unknown neutron fields.

The analysis of Bonner sphere measurements is typically done using unfolding codes. However, it is very difficult to implement reliable uncertainty propagation in standard unfolding procedures. An alternative approach, which does provide reliable estimates of the uncertainties of neutron spectra leading to rigorous estimates of uncertainties of the dose, is to analyze the data using Bayesian parameter estimation. In this work, we extend previous approaches and apply this method to secondary neutrons from radiation therapy proton beams. This requires introducing a parameterized model which can describe the main features of the neutron spectra. We choose the parameterization based on information that is available from measurements and detailed Monte Carlo simulations. To demonstrate the validity of this approach, we consider the results of an experiment carried out at the experimental hall at the OncoRay proton therapy facility in Dresden.

The first part of this article provides a concise survey of some of the mathematical methods that have been proposed for neutron spectrum unfolding. The aim is to give a pedagogical introduction to the subject without going into a detailed discussion of technical issues. The second part of this article concerns the evaluation of uncertainties. Spectra derived using unfolding techniques (and any quantities computed from these spectra; e.g., fluences and doses) will be subject to uncertainties and it is important to provide estimates of these uncertainties. This is not straightforward, due in part to the special role played by the prior information. It is shown that an approach using Bayesian parameter estimation can overcome these difficulties.

Recent developments in accelerator physics have led to new challenges for radiation protection dosimetry. Doses have to be determined for workplace fields which are characterized by high-energy radiation, a dominant contribution from neutrons, high intensities and pulsed time structure This may present problems for active measuring devices. As is well known, the ambient dose equivalent is often underestimated by area monitors operating in high-energy neutron fields behind shielding. Therefore, it is desirable to calibrate survey monitors in a characterized neutron field with the type of spectral fluence distribution that is expected behind shielding, i.e. where the main dose from neutrons arises from two peaks with mean energies of about 1 MeV and 100 MeV, respectively. Such a neutron fluence distribution is produced by the irradiation of a Fe-target with 200 MeV/u 12C-ions. Measurements with the extended range Bonner sphere spectrometer NEMUS of PTB were performed at two positions inside the experimental area Cave A of the heavy-ion synchrotron SIS at GSI. The measured neutron spectra show different fluence contributions for the two peaks at the two positions. The results were compared to Monte Carlo Simulations with MCNPX and FLUKA.

Extended-range Bonner sphere spectrometers are well suited for spectrometry in neutron fields that extend from thermal energies to a few hundred mega-electron-volts. The data analysis, however, is not straightforward, and it is of interest to evaluate how well the main features of the spectrum can be determined by the measurements and to estimate the uncertainties of integral quantities of interest, e.g., fluence and dose. In this paper, we apply Bayesian parameter estimation to this problem. We use simulated data that model measurements made in neutron fields behind shielding at high-energy accelerators.

Extended-Range Bonner sphere spectrometers (ERBSSs) are well suited for measurements in high-energy stray neutron fields, where neutron energies extend from thermal to a few hundred MeV. These fields typically have a thermal peak, a fairly flat intermediate region, a medium energy peak at ∼1 MeV and a high-energy peak at ∼ a few 100 MeV. The data analysis is not straightforward: it requires unfolding with response functions that have a substantial amount of overlap, and the responses of the modified spheres (which provide information about the fluence at high energies) increase dramatically above ∼100 MeV. In this paper, I try to determine which of the main features of the spectrum are well determined by the data given optimal methods of analysis, and which features are subject to ambiguity. To do this, I analyse ERBSS measurements using two methods of analysis that are particularly useful for this purpose, Bayesian parameter estimation and maximum entropy unfolding.

Within the EC project EVIDOS, 17 different mixed neutron-photon workplace fields at nuclear facilities (boiling water reactor, pressurised water reactor, research reactor, fuel processing, storage of spent fuel) were characterised using conventional Bonner sphere spectrometry and newly developed direction spectrometers. The results of the analysis, using Bayesian parameter estimation methods and different unfolding codes, some of them especially adapted to simultaneously unfold energy and direction distributions of the neutron fluence, showed that neutron spectra differed strongly at the different places, both in energy and direction distribution. The implication of the results for the determination of reference values for radiation protection quantities (ambient dose equivalent, personal dose equivalent and effective dose) and the related uncertainties are discussed.

Workplace neutron spectra from nuclear facilities obtained within the European project EVIDOS are compared with those of the simulated workplace fields CANEL and SIGMA and fields set-up with radionuclide sources at the PTB. Contributions of neutrons to ambient dose equivalent and personal dose equivalent are given in three energy intervals (for thermal, intermediate and fast neutrons) together with the corresponding direction distribution, characterised by three different types of distributions (isotropic, weakly directed and directed). The comparison shows that none of the simulated workplace fields investigated here can model all the characteristics of the fields observed at power reactors. © The Author 2007. Published by Oxford University Press. All rights reserved.

Some recent JET campaigns, with the introduction of a trace amount (nT/nD < 5%) of tritium into D plasmas and third harmonic ICRH acceleration of 4He, provided unique opportunities to test 'burning plasma' diagnostics. In particular, new approaches and techniques were investigated for the detection of neutrons, ? particles and the fuel mixture. With regard to neutron detection, the recent activity covered aspects such as calibration and cross validation of the diagnostics, measurement of the spatial distribution of the neutrons, particle transport and neutron spectrometry. The first tests of some newneutron detection technologies were also undertaken during the Trace Tritium Experiment campaign. To improve JET's diagnostic capability in the field of ? particles, a significant development programme was devoted to the measurement of their confinement and imaging with ? -ray spectroscopy. A new approach for the fusion community to measuring the fast ion losses, based on the activation technique, was also attempted for the first time on JET. An assessment of the neutral particle analyser's potential to determine the fuel mixture and the particle transport coefficients is under way.

Detectors made from artificial chemical vapor deposition (CVD) single crystal diamond are very promising candidates for applications where high resolution neutron spectrometry in very high neutron fluxes is required, for example in fusion research. We propose a Bayesian method to estimate the neutron response function of the detector for a continuous range of neutron energies (in our case, 10 MeV ≤ En ≤ 16 MeV) based on a few measurements with quasi-monoenergetic neutrons. This method is needed because a complete set of measurements is not available and the alternative approach of using responses based on Monte Carlo calculations is not feasible. Our approach uses Bayesian signal-background separation techniques and radial basis function interpolation methods. We present the analysis of data measured at the PTB accelerator facility PIAF. The method is quite general and it can be applied to other particle detectors with similar characteristics.

The resolving power of a multisphere neutron spectrometer is determined using the approach of Backus and Gilbert.

MAXED was developed to apply the maximum entropy principle to the unfolding of neutron spectrometric measurements. The approach followed in MAXED has several features that make it attractive: it permits inclusion of a priori information in a well-defined and mathematically consistent way, the algorithm used to derive the solution spectrum is not ad hoc (it can be justified on the basis of arguments that originate in information theory), and the solution spectrum is a non-negative function that can be written in closed form. This last feature permits the use of standard methods for the sensitivity analysis and propagation of uncertainties of MAXED solution spectra. We illustrate its use with unfoldings of NE 213 scintillation detector measurements of photon calibration spectra, and of multisphere neutron spectrometer measurements of cosmic-ray induced neutrons at high altitude (∼20 km) in the atmosphere.

This work compares the results of four different unfolding codes, MSANDB, MAXED, FRUIT and BONMA, which are based on different unfolding techniques. Additionally, Bayesian parameter estimation is also considered. All unfolding codes were supplied with the same set of input data acquired at the Environmental Research Station 'Schneefernerhaus' on the Zugspitze mountain, corresponding to continuous measurements of secondary neutrons from cosmic radiation. The HMGU high-energy extended Bonner sphere spectrometer (BSS), consisting of 16 measuring channels with (3)He proportional counters, was used as a reference BSS. The differences in the neutron spectra obtained with the different unfolding codes are discussed, and the uncertainties of integral quantities, like neutron fluence and ambient dose equivalent, are quantified.

A new thermal neutron calibration facility based on a moderator assembly has been set up at PTB. It consists of 16 (241)Am-Be radionuclide sources mounted in a graphite block, 1.5 m wide, 1.5 m high and 1.8 m deep. The sources are distributed to eight different positions, at a mean distance of ∼1.25 m from the front face of the moderator. The neutron field at the reference position, 30 cm in front of the moderator device and 75 cm above the floor, has been characterised using calculations, Bonner sphere measurements and gold foil activation. First results are shown. The field is highly thermalised: 99 % in terms of fluence. It is quite homogenous within a 20 cm×20 cm area, but the absolute value of the thermal neutron fluence rate is small and yields an ambient dose equivalent rate of 3 µSv h(-1).

We report on measuring techniques for neutrons that have been developed at the Physikalisch-Technische Bundesanstalt (PTB), the German National Metrology Institute. PTB has characterized radioactive sources used in the BOREXINO and XENON100 experiments. For the BOREXINO experiment, a {sup 228}Th gamma radiation source was required which would not emit more than 10 neutrons per second. The determination of the neutron emission rate of this specially designed {sup 228}Th source was challenging due to the low neutron emission rate and because the ratio of neutron to gamma radiation was expected to be extremely low, of the order of 10{sup −6}. For the XENON100 detector, PTB carried out a high accuracy measurement of the neutron emission rate of an AmBe source. PTB has also done measurements in underground laboratories. A two month measurement campaign with a set of {sup 3}He-filled proportional counters was carried out in PTB's former UDO underground laboratory at the Asse salt mine. The aim of the campaign was to determine the intrinsic background of detectors, which is needed for the analysis of data taken in lowintensity neutron fields. At a later time, PTB did a preliminary measurement of the neutron fluence rate at the underground laboratory Felsenkeller operatedmore » by VKTA. By taking into account data from UDO, Felsenkeller, and detector calibrations made at the PTB facility, it was possible to estimate the neutron fluence rate at the Felsenkeller underground laboratory.« less

We describe the analysis of neutron fluence rate measurements that were carried out at the underground laboratory Felsenkeller, near Dresden, Germany, which is at a depth of 47 m. At this depth, neutrons are mainly produced by natural radioactivity via spontaneous fission and (α, n) reactions, and by reactions induced by cosmic-ray muons. The measurements were made with the NEMUS Bonner sphere spectrometer. This system consists of a set of moderating spheres of different diameters and a 3He-filled proportional counter placed at the center of each sphere. Due to time constraints, it was only possible to use three of the spheres and the “bare detector” (i.e., a 3He-filled proportional counter without a moderating sphere). In addition to the measurements carried out at Felsenkeller, we also made low-level measurements with a set of 3He-filled proportional counters in the UDO underground laboratory at the Asse salt mine, near Braunschweig, Germany, which is at a depth of 490 m. The neutron background at UDO i...

Detectors made from artificial chemical vapor deposition single crystal diamond have shown great potential for fast neutron spectrometry. In this paper, we present the results of measurements made at the Physikalisch-Technische Bundesanstalt accelerator using neutron fields in the energy range from 7 MeV to 16 MeV. This study presents the first results of the characterization of the detector in this energy range.

The Compact Neutron Spectrometer (CNS) is a Joint European Torus (JET) Enhancement Project, designed for fusion diagnostics in different plasma scenarios. The CNS is based on a liquid scintillator (BC501A) which allows good discrimination between neutron and gamma radiation. Neutron spectrometry with a BC501A spectrometer requires the use of a reliable, fully characterized detector. The determination of the response matrix was carried out at the Ion Accelerator Facility (PIAF) of the Physikalisch-Technische Bundesanstalt (PTB). This facility provides several monoenergetic beams (2.5, 8, 10, 12 and 14 MeV) and a 'white field'(Emax ~17 MeV), which allows for a full characterization of the spectrometer in the region of interest (from ~1.5 MeV to ~17 MeV. The energy of the incoming neutrons was determined by the time of flight method (TOF), with time resolution in the order of 1 ns. To check the response matrix, the measured pulse height spectra were unfolded with the code MAXED and the resulting energy distributions were compared with those obtained from TOF. The CNS project required modification of the PTB BC501A spectrometer design, to replace an analog data acquisition system (NIM modules) with a digital system developed by the 'Ente per le Nuove tecnologie, l'Energia e l'Ambiente' (ENEA). Results for the new digital system were evaluated using new software developed specifically for this project., Proceedings of FNDA 2011

Extended-range Bonner sphere spectrometers are widely used for radiation dosimetry at high-energy accelerators, where the main contributor to the radiation dose is the neutron component. However, they typically provide a very limited amount of information and have poor resolving power. The data analysis presents difficulties because it requires solving an inverse problem that is highly under-determined. One approach to solving the inverse problem is to use a parameterized model of the spectrum and Bayesian parameter estimation. This approach has the advantage of providing rigorous estimates of uncertainties. The space of solutions, however, is limited by the model, which may not be general enough to account for all the relevant structure that may be present in the neutron energy spectrum. The aim of this work is to examine a generalization using entropic priors which allows for a larger space of solutions. The method has been tested using simulated data that model measurements made in neutron fields behind shielding at high-energy accelerators.

The compact neutron spectrometer project was initiated to develop a device able to study fast neutrons produced by fusion reactions in a tokamak. The goal is to provide a fully characterized BC501A detector using a digital acquisition system developed by ENEA. The pulse height resolution and the response matrix of the detector are determined using experimental data acquired at the PTB facility. To achieve this goal, methods of data analysis involving entropy maximization and new software were developed. The methods are described and the current results for the pulse height resolution are presented.

A compact NE213 liquid scintillation neutron spectrometer with a new digital data acquisition (DAQ) system is now in operation at the Physikalisch-Technische Bundesanstalt (PTB). With the DAQ system, developed by ENEA Frascati, neutron spectrometry with high count rates in the order of 5×10(5) s(-1) is possible, roughly an order of magnitude higher than with an analog acquisition system. To validate the DAQ system, a new data analysis code was developed and tests were done using measurements with 14-MeV neutrons made at the PTB accelerator. Additional analysis was carried out to optimize the two-gate method used for neutron and gamma (n-γ) discrimination. The best results were obtained with gates of 35 ns and 80 ns. This indicates that the fast and medium decay time components of the NE213 light emission are the ones that are relevant for n-γ discrimination with the digital acquisition system. This differs from what is normally implemented in the analog pulse shape discrimination modules, namely, the fast and long decay emissions of the scintillating light.

An accelerator-driven thermal neutron facility for boron neutron capture therapy of skin melanoma is currently under construction at the Legnaro National Laboratories, Italy. The installation relies on the production of neutrons from a thick beryllium target bombarded with 5 MeV protons. A complete set of double differential data, i.e. angle- and energy-differential neutron spectra produced by the beryllium target, is necessary for the Monte Carlo-based design of the installation. For this purpose, double differential fluence measurements are currently performed with the "BINS" neutron spectrometer using 5 MeV protons at the "CN" Van de Graaf accelerator. This spectrometer uses a superheated emulsion of dichlorotetrafluoroethane which is sequentially operated at 25, 30, 35, 40, 45, 50 and 55 degrees C and thus provides a series of seven sharp thresholds covering the 0.1-10 MeV neutron energy interval. Deconvolution of the data is performed with the code "MAXED", which is based on the maximum entropy principle. The analysis of our first neutron spectrometry measurements at angles of 0 degrees, 40 degrees, 80 degrees and 120 degrees supports the viability of the BINS spectrometry method for the generation of the required double differential data.

The European Commission has funded within its 6th Framework Programme a three-year project (2005–2007) called CONRAD, COordinated Network for RAdiation Dosimetry . A major task of the CONRAD Work Package “ complex mixed radiation fields at workplaces ” was to organise a benchmark exercise in a workplace field at a high-energy particle accelerator where neutrons are the dominant radiation component. The CONRAD benchmark exercise took place at the Gesellschaft fur Schwerionenforschung mbH (GSI) in Darmstadt, Germany in July 2006. In this paper, the results of the spectrometry using four extended -range Bonner sphere spectrometers of four different institutes are reported. Outside Cave A the neutron spectra were measured with three spectrometers at six selected positions and ambient dose equivalent values were derived for use in the intercomparison with other area monitors and dosemeters. At a common position all three spectrometers were used to allow a direct comparison of their results which acts as an internal quality assurance. The comparison of the neutron spectra measured by the different groups shows very good agreement. A detailed analysis presents some differences between the shapes of the spectra and possible sources of these differences are discussed. However, the ability of Bonner sphere spectrometers to provide reliable integral quantities like fluence and ambient dose equivalent is well demonstrated in this exercise. The fluence and dose results derived by the three groups agree very well within the given uncertainties, not only with respect to the total energy region present in this environment but also for selected energy regions which contribute in certain strength to the total values. In addition to the positions outside Cave A one spectrometer was used to measure the neutron spectrum at one position in the entry maze of Cave A. In this case a comparison was possible to earlier measurements.

Neutron survey instruments have been exposed at all the measurement locations used in the EVIDOS project. These results have an important impact in the interpretation of the results from the project, since operationally the survey instrument will be used for an initial assessment of and routine monitoring of the ambient dose equivalent dose rate. Additionally, since the response of these instruments is in some cases very well characterised, their systematic deviations from the reference quantities provide an important verification of the determination of those quantities.

Within the EC project EVIDOS, double-differential (energy and direction) fluence spectra were determined by means of novel direction spectrometers. By folding the spectra with fluence-to-dose equivalent conversion coefficients, contributions to H*(10) for 14 directions, and values of the personal dose equivalent Hp(10) and the effective dose E for 6 directions of a person's orientation in the field were determined. The results of the measurements and calculations obtained within the EVIDOS project in workplace fields in nuclear installations in Europe, i.e., at Krummel (boiling water reactor and transport cask), at Mol (Venus research reactor and fuel facility Belgonucleaire) and at Ringhals (pressurised reactor and transport cask) are presented.

The Institute for Radiological protection and Nuclear Safety was engaged in the EC funded EVIDOS project to provide reference spectrometry data using its Bonner sphere system. The data were processed by means of two unfolding codes, NUBAY and GRAVEL, both provided by the Physikalisch-Technische Bundesanstalt. The NUBAY program, based on Bayesian parameter estimation methods, assumes a parameterised spectrum and provides posterior probability distributions for the parameters. The code GRAVEL, an iterative algorithm based on SAND-II, was used with various default spectra, among them the NUBAY solution. The BS measurements were used to establish the neutron fluence energy distributions and reference values for the neutron ambient dose equivalent. As this quantity depends strongly on the high energy neutrons, a sensitivity analysis was done by unfolding the BS data with GRAVEL using the NUBAY solution spectrum as default with various changes in the parameters of the high energy peak. This new method of analysing Bonner sphere data allowed the determination of reliable neutron spectra, as well as a very good estimate of the corresponding integral quantities with small associated uncertainties.

The paper presents the main conclusions and recommendations derived from the EVIDOS project, which is supported by the European Commission within the 5th Framework Programme. EVIDOS aims at evaluating state of the art neutron dosimetry techniques in representative workplaces of the nuclear industry with complex mixed neutron-photon radiation fields. This analysis complements a series of individual papers which present detailed results and it summarises the main findings from a practical point of view. Conclusions and recommendations are given concerning characterisation of radiation fields, methods to derive radiation protection quantities and dosemeter results.

This paper mainly aims at presenting the measurements and the results obtained with the electronic personal neutron dosemeter Saphydose-N at different facilities. Three campaigns were led in the frame of the European contract EVIDOS ('Evaluation of Individual Dosimetry in Mixed Neutron and Photon Radiation Fields'). The first one consisted in the measurements at the IRSN French research laboratory in reference neutron fields generated by a thermal facility (SIGMA), radionuclide ISO sources (241AmBe; 252Cf; 252Cf(D2 O)\Cd) and a realistic spectrum (CANEL/T400). The second one was performed at the Krümmel Nuclear Power Plant (Germany) close to the boiling water reactor and to a spent fuel transport cask. The third one was realised at Mol (Belgium), at the VENUS Research Reactor and at Belgonucléaire, a fuel processing factory. © 2006 Oxford University Press.

EVIDOS is an EC sponsored project that aims at an evaluation and improvement of radiation protection dosimetry in mixed neutron/photon fields. This is performed through spectrometric and dosimetric investigations during different measurement campaigns in representative workplaces of the nuclear industry. The performance of routine and, in particular, novel personal dosemeters and survey instruments is tested in selected workplace fields. Reference values for the dose equivalent quantities, H*(10) and Hp(10) and the effective dose E, are determined using different spectrometers that provide the energy distribution of the neutron fluence and using newly developed devices that determine the energy and directional distribution of the neutron fluence. The EVIDOS project has passed the mid-term, and three measurement campaigns have been performed. This paper will give an overview and some new results from the third campaign that was held in Mol (Belgium), around the research reactor VENUS and in the MOX producing plant of Belgonucléaire. © 2006 Oxford University Press.

This work describes spectral distributions of neutrons obtained as function of energy and direction at four workplace fields at the Krümmel reactor in Germany. Values of personal dose equivalent Hp(10) and effective dose E are determined for different directions of a person's orientation in these fields and readings of personal neutron dosemeters - Especially electronic dosemeters - Are discussed with respect to Hp(10) and E. © 2006 Oxford University Press.

During the JET Trace Tritium campaign a few new neutron diagnostic systems were deployed under different plasma scenarios to provide information on the total neutron emission and its spatial and energy distribution. The 14MeV neutron yield was measured with a chemical vapour deposited (CVD) diamond detector. Comparison with the JET 14MeV monitors (Si diodes) illustrates the good performance of the CVD device. Key information on the tritium transport and the behaviour of fast particles in the plasma was obtained from the spatially and temporally measurements of neutron emission from the upgraded neutron profile cameras which also provide an independent measure of the total neutron yield. Spatial asymmetries in the neutron emission were observed which is evidence for the influence of fast particles on the plasma. With regard to the energy distribution of the neutron emission, a spectrometer based on a liquid organic scintillator with n-γ pulse shape discrimination (PSD) features was installed. The results demonstrate that such system can operate in real fusion experiments as compact broadband neutron (1.5 MeV < E n

The development of new spectrometers that are sensitive to the directional distribution of neutrons requires new unfolding methods that can determine the distribution of the neutron fluence as a function of energy and angle. Such information is needed to compute non-isotropic dosimetric quantities (e.g. personal dose equivalent and effective dose). We describe an unfolding method that applies the maximum entropy principle to this problem. It maximises the relative entropy, defined as the information-theory entropy of the distribution of the neutron fluence relative to a distribution that encodes prior knowledge, subject to constraints imposed by the measurements. We provide examples of the applicability of the method using data from two directional spectrometers of different design that have been developed in the context of EVIDOS, a project concerning mixed neutron-photon field analysis in the nuclear industry.

Within the EU Project EVIDOS, a spectrometer with 24 silicon detectors mounted on the surface of a polyethylene sphere is used for the determination of the energy and direction distribution of neutrons and photons. It has been characterized with respect to neutron radiation with energies from thermal up to 15 MeV and to photon radiation with energies from 65 keV to 6 MeV. The first measurements described here were performed in the simulated workplace field, CANEL, at Cadarache, with the purpose of checking the instrument and the unfolding procedures.

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.

One of our two methods for fast-neutron imaging with spectrometric capability is presented here. It is a neutron-counting technique based on a hydrogenous neutron converter coupled to Gaseous Electron Multipliers (GEM). The principles of the detection techniques and the optimization of the converter, electron amplification and the readout are described. Evaluation of the properties is derived from a experiment in a pulsed neutron beam of spectral distribution between 2 and 10 MeV.

A directional spectrometer that uses a superheated emulsion of dichlorotetrafluoroethane at the centre of a 30 cm diameter moderating-sphere of nylon-6. The system has a telescope-design wherein the detector views a narrow solid angle of about 1/6 steradians. The hydrogenous sphere effectively attenuates laterally incident neutrons, thus providing a strong angular dependence of the response. The central detector is sequentially operated at seven temperatures between 25 and 55 degrees C in order to generate a matrix of nested response functions suitable for few-channel spectrometry. The response matrix of the system has been determined by calibrations with monoenergetic neutrons and by Monte Carlo neutron transport calculations. The double-differential unfolding method developed for this system applies the principle of maximum entropy and allows for the rigorous use of all a priori information. The spectrometer is intended for use in the mixed neutron/photon fields encountered in the nuclear power industry, being suitable for spatially distributed radiation sources with maximum neutron energies up to 10 MeV.

Crews working on present-day jet aircraft are a large occupationally exposed group with a relatively high average effective dose from galactic cosmic radiation. Crews of future high-speed commercial aircraft flying at higher altitudes would be even more exposed. To help reduce the significant uncertainties in calculations of such exposures, the atmospheric ionizing radiation (AIR) project, an international collaboration of 15 laboratories, made simultaneous radiation measurements with 14 instruments on five flights of a NASA ER-2 high-altitude aircraft. The primary AIR instrument was a highly sensitive extended-energy multisphere neutron spectrometer with lead and steel shells placed within the moderators of two of its 14 detectors to enhance response at high energies. Detector responses were calculated for neutrons and charged hadrons at energies up to 100 GeV using MCNPX. Neutron spectra were unfolded from the measured count rates using the new MAXED code. We have measured the cosmic-ray neutron spectrum (thermal to >10 GeV), total neutron fluence rate, and neutron effective dose and dose equivalent rates and their dependence on altitude and geomagnetic cutoff. The measured cosmic-ray neutron spectra have almost no thermal neutrons, a large “evaporation” peak near 1 MeV and a second broad peak near 100 MeV which contributes about 69% of the neutron effective dose. At high altitude, geomagnetic latitude has very little effect on the shape of the spectrum, but it is the dominant variable affecting neutron fluence rate, which was eight times higher at the northernmost measurement location than it was at the southernmost. The shape of the spectrum varied only slightly with altitude from 21 km down to 12 km (56–201 g cm −2 atmospheric depth), but was significantly different on the ground. In all cases, ambient dose equivalent was greater than effective dose for cosmic-ray neutrons.

Reliable neutron dosimetry requires knowledge of the neutron spectrum. We discuss the problem of analyzing data from a multisphere neutron spectrometer to infer the energy spectrum of the incident neutrons and describe the code MAXED, a computer program developed to apply the maximum entropy principle to this problem. The code and documentation are available from the authors upon request.