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The optimized superconducting stellarator device Wendelstein 7-X (with major radius , minor radius , and plasma volume) restarted operation after the assembly of a graphite heat shield and 10 inertially cooled island divertor modules. This paper reports on the results from the first high-performance plasma operation. Glow discharge conditioning and ECRH conditioning discharges in helium turned out to be important for density and edge radiation control. Plasma densities of with central electron temperatures were routinely achieved with hydrogen gas fueling, frequently terminated by a radiative collapse. In a first stage, plasma densities up to were reached with hydrogen pellet injection and helium gas fueling. Here, the ions are indirectly heated, and at a central density of a temperature of with was transiently accomplished, which corresponds to with a peak diamagnetic energy of and volume-averaged normalized plasma pressure . The routine access to high plasma densities was opened with boronization of the first wall. After boronization, the oxygen impurity content was reduced by a factor of 10, the carbon impurity content by a factor of 5. The reduced (edge) plasma radiation level gives routinely access to higher densities without radiation collapse, e.g. well above line integrated density and central temperatures at moderate ECRH power. Both X2 and O2 mode ECRH schemes were successfully applied. Core turbulence was measured with a phase contrast imaging diagnostic and suppression of turbulence during pellet injection was observed.

Wendelstein 7-X, a superconducting optimized stellarator built in Greifswald/Germany, started its first plasmas with the last closed flux surface (LCFS) defined by 5 uncooled graphite limiters in December 2015. At the end of the 10 weeks long experimental campaign (OP1.1) more than 20 independent diagnostic systems were in operation, allowing detailed studies of many interesting plasma phenomena. For example, fast neutral gas manometers supported by video cameras (including one fast-frame camera with frame rates of tens of kHz) as well as visible cameras with different interference filters, with field of views covering all ten half-modules of the stellarator, discovered a MARFE-like radiation zone on the inboard side of machine module 4. This structure is presumably triggered by an inadvertent plasma-wall interaction in module 4 resulting in a high impurity influx that terminates some discharges by radiation cooling. The main plasma parameters achieved in OP1.1 exceeded predicted values in discharges of a length reaching 6 s. Although OP1.1 is characterized by short pulses, many of the diagnostics are already designed for quasi-steady state operation of 30 min discharges heated at 10 MW of ECRH. An overview of diagnostic performance for OP1.1 is given, including some highlights from the physics campaigns.

A custom-made 228Th source of several MBq activity was produced for the Borexino experiment for studying the external background of the detector. The aim was to reduce the unwanted neutron emission produced via (alpha,n) reactions in ceramics used typically for commercial 228Th sources. For this purpose a ThCl4 solution was converted chemically into ThO2 and embedded into a gold foil. The paper describes the production and the characterization of the custom-made source by means of gamma-activity, dose rate and neutron source strength measurements. From gamma-spectroscopic measurements it was deduced that the activity transfer from the initial solution to the final source was >91% (at 68% C.L.) and the final activity was (5.41+-0.30) MBq. The dose rate was measured by two dosimeters yielding 12.1 mSv/h and 14.3 mSv/h in 1 cm distance. The neutron source strength of the 5.41 MBq 228Th source was determined as (6.59+-0.85)/sec., 8 pages, 5 figures

In a recent work, we constructed modular multisphere system which expands upon the design of an existing, commercially available Bonner sphere system by adding concentric shells of copper, tungsten, or lead. Our modular multisphere system is referred to as the Bonner Sphere Extension (BSE). The BSE was tested in a high energy neutron beam (thermal to 800 MeV) at Los Alamos Neutron Science Center and provided improvement in the measurement of the neutron spectrum in the energy regions above 20 MeV when compared to the standard BSS ( Burgett, 2008 and Howell et al., 2009 ). However, when the initial test of the system was carried out at LANSCE, the BSE had not yet been calibrated. Therefore the objective of the present study was to perform calibration measurements. These calibration measurements were carried-out using monoenergetic neutron ISO 8529-1 reference beams at the Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany. The following monoenergetic reference beams were used for these experiments: 14.8 MeV, 1.2 MeV, 565 keV, and 144 keV. Response functions for the BSE were calculated using the Monte Carlo N-Particle Code, eXtended (MCNPX). The percent difference between the measured and calculated responses was calculated for each sphere and energy. The difference between measured and calculated responses for individual spheres ranged between 7.9% and 16.7% and the arithmetic mean for all spheres was (10.9 ± 1.8)%. These sphere specific correction factors will be applied for all future measurements carried out with the BSE.

Recent developments in accelerator physics have led to new challenges for radiation protection dosimetry. As is well known, the ambient dose equivalent indicated by area monitors in high-energy neutron fields behind shielding is often unreliable. Therefore, it is desirable to measure the spectrum and to do "in-field" calibrations using the spectral information as reference. For this purpose, the PTB NEMUS (an extended-range Bonner sphere spectrometer) was modified with a new active thermal neutron detector based on silver activation capable of measuring in intense pulsed fields with high energies and fluence rates.

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.

The European Commission has funded within its 6th Framework Programme a three-year project (2005–2007) called CONRAD, COordinated Network for RAdiation Dosimetry. The organizational framework for this project was provided by the European radiation Dosimetry Group EURADOS. Work Package 6 of CONRAD dealt with “complex mixed radiation fields at workplaces” and in this context it organised a benchmark exercise, which included both measurements and calculations, in a stray radiation field at a high-energy particle accelerator at GSI, Germany. The aim was to intercompare the response of several types of active detectors and passive dosemeters in a well-characterised workplace field. The Monte Carlo simulations of the radiation field and the experimental determination of the neutron spectra with various Bonner Sphere Spectrometers are discussed in Rollet et al. (2008) and in Wiegel et al. (2008). This paper focuses on the intercomparison of the response of the dosemeters in terms of ambient dose equivalent. The paper describes in detail the detectors employed in the experiment, followed by a discussion of the results. A comparison is also made with the H*(10) values predicted by the Monte Carlo simulations and those measured by the BSS systems.

In neutron reference radiation fields, the conventional true value of the personal dose equivalent, H(p)(10), is derived from the spectral neutron fluence and recommended conversion coefficients. This procedure requires the phantom on which the personal dosemeter is mounted to be irradiated with a broad and parallel beam. In many practical situations, the change of the neutron fluence and/or the energy distribution over the surface of the phantom may not be neglected. For a selection of typical irradiation conditions in neutron reference radiation fields, the influence of this effect has been analysed using numerical methods. A further problem, which is of relevance for the calibration of dosemeters measuring both the neutron and the photon component of mixed fields, is the 'double counting' of the dose equivalent due to neutron-induced photons. The relevance of this conceptual problem for calibrations in mixed-field dosimetry was analysed.

Wendelstein 7-X (W7-X) is a large optimized stellarator (B=2.5T, V=30m3) aiming at demonstrating the reactor relevance of the optimized stellarators. In 2015 W7-X will begin its first operation phase (OP1.1) with five inertially cooled inboard limiters made of graphite. Assuming the heat loads can be spread out evenly between the limiters, 1 second discharges at 2 MW of ECRH heating power could be run in OP1.1. The expected plasma parameters will be sufficient to demonstrate the readiness of the installed diagnostics and even to run a first physics program. The diagnostics available for this first operation phase, including some special limiter diagnostics, and their capabilities are being presented. A shorter version of this contribution is due to be published in PoS at: 1st EPS conference on Plasma Diagnostics

A detailed analysis of the neutron radiation field was performed at selected positions inside the Krummel boiling water reactor. The measurements were performed with the PTB Bonner sphere spectrometer and with a newly developed directional neutron spectrometer based on silicon detectors mounted onto the surface of a 30 cm diameter polyethylene sphere. Both, angle-integrated and angle-differential spectral neutron fluences were determined in this way.

Bonner sphere measurements are presented for flights at altitudes of up to 12 km and geomagnetic latitudes between 26°N and 86°N and compared with results obtained by several survey meters. As an example of the natural neutron background near sea level, results from a recent longterm measurement campaign performed at the PTB site using an extended spectrometer are presented. The dependence of neutron fluence and ambient dose equivalent on the atmospheric pressure is demonstrated.

The original Bonner sphere spectrometer as it is used and characterized by PTB consists of 12 polyethylene spheres with diameters from 7.62 cm (3″) to 45.72 cm (18″) and a 3 He-filled spherical proportional counter used as a central thermal-neutron-sensitive detector and as a bare or cadmium-shielded bare detector. In this paper, a set of four new spheres made of polyethylene with copper or lead inlets is introduced. All spheres are less than 18 kg in mass and their responses to high energy neutrons increase with energy as a result of the increasing ( n , xn ) cross-sections of copper and lead. The fluence response matrix was calculated up to 10 GeV using an extended neutron cross-section library (LA150) and the MCNP(X) Monte Carlo code. Calibration measurements with neutron energies up to 60 MeV were used to compare the calculated response functions to measured values. For measurements outside the laboratory, a miniaturized, battery-powered electronic set-up was developed. This system with the additional, modified spheres is now called NEMUS —Neutron Multisphere Spectrometer.

Quasi-monoenergetic reference neutron beams in the energy range between 20 and 100 MeV have been produced and characterized with a proton recoil telescope, a scintillation spectrometer, a U-238 fission chamber and a Bonner sphere spectrometer. The beams are well suited for the calibration of detectors used in neutron spectrometry. A new method is described which reduces the correction for the contribution from low-energy neutrons present in the beams. (C) 2002 Elsevier Science B.V. All rights reserved.

An overview of the diagnostics which are essential for the first operational phase of Wendelstein 7-X and the set of diagnostics expected to be ready for operation at this time are presented. The ongoing investigations of how to cope with high levels of stray Electron Cyclotron Resonance Heating (ECRH) radiation in the ultraviolet (UV)/visible/infrared (IR) optical diagnostics are described.

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).

A prototype of a highly sensitive active personal neutron dosemeter has been developed. It consists of a stack of four silicon detectors sandwiched between layers acting as neutron converters, moderators and absorbers. Its response to quasi-monoenergetic neutrons with energies up to 45 MeV and photons with energies up to 7 MeV has been measured and/or calculated for different angles of incident radiation. The personal dose equivalent determined from the readings obtained in some fields with broad energy distributions deviates by less than 30% from the reference values, both for normal incidence and incidence at 60° to the normal. The detectibn threshold is about 3 μSv for fast neutrons, 1 μSv for intermediate neutrons and 0.007 μSv for thermal neutrons, even in mixed fields with a photon dose higher by a factor of 20. In addition, the evaluation procedures described give spectral and directional information about the field.

The high energy Monte Carlo codes MARS and FLUKA are compared as applied to calculations of neutron spectra in the atmosphere resulting from interactions of primary galactic cosmic rays (GCR) with the nuclei in the atmosphere. The calculational strategies of either code are discussed. The primary galactic spectrum at the top of the atmosphere and the model used for the atmosphere are presented in detail. MARS is used to calculate neutron energy spectra which before had been calculated with FLUKA and measured with Bonner spheres. The comparison shows acceptable agreement. Therefore, MARS is used to provide new data for the analysis of dosimetric measurements at flight altitudes. The new data encompass calculated angular distributions and energy spectra of neutrons, protons, photons and pions for the geographical position of Braunschweig and the Zugspitze. In addition, the influence of aluminium layers on these spectra is studied. These new data are expected to provide valuable support in the analysis of dosimetric measurements at flight altitudes. Throughout the paper, emphasis is placed on the discussion of the main sources of variance for these calculations.

The energy dependence of the fluence response of a neutron radiation protection monitor generally deviates considerably from that of the fluence-to-dose equivalent conversion function. For the dose determination in a given neutron field such a monitor must therefore be calibrated by determining its yield and the dose equivalent in a neutron field similar to the given field. A wide class of neutron fields encountered at workplaces can be characterized by a superposition of thermal neutrons, a 1/E part in the region of intermediate neutron energies and, occasionally, some high-energy neutrons, e.g. remains of down-scattered fission neutrons. Our approach is to mock up appropriate neutron calibration fields by the production of neutrons in an Li(p,n) reaction (thick target) and the modification of these initial spectra with a moderator assembly consisting of two spherical shells of polyethylene and graphite, respectively. We optimized this set-up by numerical simulation of the neutron spectra with the MCNP Monte Carlo code. Spectra were calculated for the primary and for the moderated source under different angles ϑ, referring to the direction of the incoming protons. The achieved values of the mean fluence-to-ambient dose equivalent conversion coefficients, h Φ ∗ (10) , range from 276 down to 16 pSv cm 2 . We present results of first measurements with Bonner spheres in the proposed neutron fields. We compare calculated count rates – i.e. folding the simulated neutron spectra with the Bonner sphere response functions – and the measured count rates.

The response functions of four widely used Bonner sphere spectrometers (BSS) with an Lil scintillator and different 3 He detectors were calculated by means of the three-dimensional Monte Carlo neutron transport code, MCNP, taking into consideration a detailed description of the detector set-up; they were then compared with experimental calibration data. The calculated response functions reproduce the calibration data in shape. A common adjustment factor is only needed to take into account the neutron detection efficiency of the central detector. An interpolation method proposed to correct the BSS response functions to another polyethylene density was verified.

In order to calibrate more accurately the neutron dosemeters involved in radiation protection, the concept of 'Realistic Neutron Calibration Fields' is considered as an appropriate alternative solution, making necessary new irradiation facilities which generate well-characterised neutron fields with energy and angular distributions replicating more closely practical workplace conditions. Several experienced laboratories have collaborated on a European project and proposed various approaches which are reviewed in this paper. A short description of the facilities currently in operation is given as well as a few characteristics of the available radiation fields. This description of the state of art is followed by a discussion of the problems to be solved for using such facilities for calibration purposes according to well-specified calibration procedures.

The stellarator Wendelstein 7-X (W7-X), presently under construction at the Max-Planck-Institute for Plasma Physics in Greifswald, will be equipped with a set of neutron monitors to measure the total annual neutron emission for official documentation and to provide information for plasma diagnostics purposes. The authors performed MCNP calculations to design and optimise the moderator geometry of the monitors to exhibit a nearly energy-independent response as well as particular angular responses for one central and two peripheral monitors. The monitors were designed with up to five neutron detector tubes with different sensitivity to thermal neutrons to cover the expected neutron emission rates of W7-X from 10(11) s(-1) to 10(16) s(-1). A prerequisite for the determination of the neutron emission produced by a D-D plasma is an in-situ calibration of the neutron monitors. Such a procedure requires a MCNP simulation of the entire geometry of the W7-X stellarator. In a first benchmark experiment during the assembly phase of W7-X, the validity of the W7-X MCNP model was tested.

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...

The applicability of CR-39 nuclear track detectors to the field of microdosimetry was experimentally investigated through a series of tests with monoenergetic charged particle fields. A special etching technique (intermittent etching and cleaning etch steps) was devised and employed to determine LET values along individual tracks on irradiated detector plates. The range of measurable LET values was inferred from the analysis of the etched track diameters created by monoenergetic protons, alpha particles and fission fragments. Based on these calibrations, measurements of track densities and LET distributions were performed at different depths in a CR-39 stack irradiated with 62 MeV protons.

As a contribution to the FREE FLYER BIOSTACK EXPERIMENT (A0015) we have flown CR-39 plastic nuclear track detectors on board LDEF. Although low energy fully-ionized galactic cosmic rays should not reach this orbit due to geomagnetic shielding we found stopping nuclei with energies of some hundred MeV/nucleon. Directions of incidence, nuclear charge and energy spectra of these particles are presented and discussed.

The stellarator W7-X, presently under construction at the Institute for Plasma Physics in Greifswald, will be equipped with a set of neutron monitors in order to study the time behaviour of neutron emission generated during D-D plasma operation and neutral beam heating with Deuterium. Each of these neutron monitors consists of several neutron detector tubes inserted in a dedicated moderator. The neutron monitors at W7-X are designed to monitor neutron yields with a time resolution of 5 ms and with a statistical uncertainty of better than 15%. One of the monitors is located in the centre above the stellarator. The other five monitors are distributed around the torus. A prerequisite for the determination of the absolute neutron source strength produced by D(d,n)3He fusion reactions in the plasma is an in-situ calibration with a neutron source of known source strength. During such a calibration procedure, the neutron source will be moved along the torus axis and the count rates of the different neutron monitors will be measured. In a first benchmark experiment, an 241AmBe neutron source was moved along the torus axis within one module of the stellarator and the neutron signals were measured by a De Pangher Long Counter outside of the cryostat chamber as a function of the neutron source position. These measurements have been compared with predictions of Monte Carlo calculations (MCNP) of the neutron propagation from the location of the neutron source to the long counter. The concept of neutron monitors will be reported together with results from the benchmark experiment and results from MCNP calculations. The neutron monitor system is the first part of several neutron diagnostic systems such as neutron activation system, neutron profile camera planned for future neutron analysis. A short survey of these neutron diagnostic tools of W7-X will be given.

We have investigated the fragmentation of $^{197}\mathrm{Au}$ projectiles at 0.85 to 1 GeV/nucleon in collisions with targets (${\mathrm{CH}}_{2}$${)}_{\mathit{n}}$, C, and Pb. Using plastic nuclear track detectors all projectile fragments with charge 6\ensuremath{\le}${\mathit{Z}}_{\mathit{F}}$\ensuremath{\le}77 produced in a collision were observed in coincidence. The combination of C and (${\mathrm{CH}}_{2}$${)}_{\mathit{n}}$ data allows us to extract the hydrogen component in measured distributions by the use of the statistical subtraction method. Our data show a target dependence of the multifragmentation process which indicates a nonequilibrated source of the fragments and/or the influence of the target nucleus on the relation between size and excitation energy of the spectator. In comparison to the prediction of the statistical model, the transverse momentum dispersions are enhanced with a dominant contribution by Coulomb repulsion between the fragments. Based on the sum of transverse momentum vectors of all fragments we conclude that multifragmentation is observed in collisions with a large momentum and energy transfer to the prefragment. Correlations in the azimuthal emission angles of the fragments are caused by mutual repulsion and momentum conservation. The idea that a liquid-gas phase transition of nuclear matter is the origin of multifragmentation is supported by our observations.

We exposed stacks containing plastic nuclear track detectors and different target materials to heavy ions at the Berkeley BEVALAC. Interactions of the beam particles with Ag and C target nuclei and with the constituents of our detector material CR-39 (C 12 H 18 O 7 ) were studied in detail. For each interaction vertex all projectile fragments with charge Z-6 were measured and their emission angles were determined. Charge yields, transverse momenta, correlations in charge and angle are studied separately for different multiplicities M of observed fragments. We present results of experiments with 980 MeV/nucleon Au projectiles on a Ag/CR-39 target, 1050 MeV/nucleon Au projectiles on a C target and with 920 MeV/nucleon U projectiles on a Ag/CR-39 target.

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.

We analyze the largest set of fragment coincidence data at present available, that of the preceding paper. This set contains all projectile fragments 6\ensuremath{\le}Z\ensuremath{\le}65 produced in 6610 events of Au+Ag and Au+CR-39. We introduce a classification scheme based on the number of heavy fragments in order to define multifragmentation, spallation, and fission events. The multiplicity distribution P(${\mathit{m}}_{\mathit{Z}}$) is Poissonian, and the mean multiplicity as a function of Z can be described either by a power law or by an exponential. The slopes are independent of the projectile energy but depend on the target. While all investigated observables indicate that the multifragmentation in the case of a Ag target is a statistical process, we observe angular correlations in the case of the CR-39 target which indicate that probably the geometry and not the excitation energy is essential. Charge correlations are strong and only partially understood as yet. We find no positive sign for a liquid gas phase transition.

We started a research program using heavy ion beams at the GSI Darmstadt accelerator to investigate radiation effects of heavy ions in microelectronic devices. The understanding of these radiation effects is of particular importance to estimate the radiation rise for microelectronic parts exposed to the cosmic radiation during space missions. In order to expose static RAM devices to heavy ion beams a test system was installed. Additionally we use CCD image sensors to measure the amount of charge deposited inside the sensitive volume of single picture elements. Measurements will be performed with ions of different charge and energy up to 1 GeV/N to investigate the LET dependence of the effects and possible influence of the track structure. The experimental setup is described in this paper and first results are presented.

A new detector system has been developed for time resolved flux measurements of collimated D-D neutrons in large magnetic confinement fusion experiments. The novel detection concept, called the special absorber neutron detector moderator assembly, is to place a scatterer behind a collimator and to detect the scattered neutrons in a small Bonner sphere. The system has been optimized by means of the Monte Carlo neutron photon transport code (MCNP) simulations and is capable to be extended for a neutron profile camera. First tests and calibration measurements of a system using a 3 in. Bonner sphere have been carried out in the 2.5 MeV neutron field at the accelerator facility of the Physikalisch-Technische Bundesanstalt in Braunschweig. The numerical and experimental results are presented. The measurements differ from the calculated values by a factor of about 1.09. It is questionable if these discrepancies can be explained by differences in the shielding, moderator and detector characteristics employed in t...

In this paper we present a signaling mechanism of spacial divided network conditions in order to guarantee quality of service (QoS) in a vehicular ad hoc network (VANET) The target application shares information of sensed objects in the surrounding of the vehicles with its VANET neighbor nodes Therefore each vehicle broadcasts information of its surrounding periodically which leads to an unscalable bandwidth consumption as the density of communication nodes rises A higher network load will also lead to a higher latency of the transmitted data as the probability is that nodes have to wait for a free channel. The latency of data acquired from onboard sensors is critical if it is shared with other nodes as the validity of the data is1 ow. We present a signaling method based on a spatial partitioning in order to detect redundant source nodes for the same information. Avoiding redundant broadcasts will limit the application's bandwidth consumption and therefore the latency of the messages can be improved.

In recent years research on active safety systems with the main focus on environment sensing has been done. Therefore vehicles are equipped with sensors which record information about the nearby traffic situation and possible hazards. For anticipatory driving additional information outside of the range of the sensors' area needs to be collected. This can be done by introducing data transfer between vehicles, which allows to gather data of a larger area and therefore improves the anticipatory capabilities of the system. One main aspect in the data exchange between vehicles is the organization of the access to the medium. It has to be able to cope with all the problems of mobile ad-hoc networks. Especially the hidden station problem is an important factor in vehicular ad-hoc networks (VANETs). But also the high density of nodes, high dynamics and a limited data rate require a fair and efficient access to the medium. In this paper we present a medium access scheme for vehicular ad-hoc networks which is based on clustering of the vehicles. Thus the effect of hidden stations can be minimized, which leads to a more reliable data transfer than IEEE 802.11 based systems can provide.

Vehicle-to-vehicle communication is a promising technology for enhanced road safety as it provides the possibility to get a detailed knowledge about the traffic situation a long way ahead. Vehicles transmit information about nearby dangers like obstacles on the road as well as warning messages over long distances to all vehicles in a certain area. Therefore the dissemination of the data has to be done in broadcast transmission. This transmission concept causes severe problems regarding the organization of the medium access. The often used RTS/CTS mechanism is no longer feasible, which is especially problematic in road scenarios, where the hidden station problem is a major cause of data loss due to collisions. In addition the regarded data makes high demands on the provided quality of service. Especially reliability and delay are crucial for the efficiency of the warning system. In this paper we introduce a concept for a medium access control which minimizes the effects of the hidden station problem by introducing a clustering scheme. Therefore clusterheads among the vehicles are selected, which are then responsible for assigning bandwidth to the other vehicles in their clusters. This paper presents an algorithm for selecting the clusterheads along with a concept for assigning bandwidth to the nodes.

The European Commission is funding within its Sixth Framework Programme a three-year project (2005-2007) called CONRAD, COordinated Network for RAdiation Dosimetry. The organisational framework for this project is provided by the European Radiation Dosimetry Group EURADOS. One task within the CONRAD project, Work Package 6 (WP6), was to provide a report outlining research needs and research activities within Europe to develop new and improved methods and techniques for the characterisation of complex radiation fields at workplaces around high-energy accelerators, but also at the next generation of thermonuclear fusion facilities. The paper provides an overview of the report, which will be available as CERN Yellow Report. © The Author 2007. Published by Oxford University Press. All rights reserved.

In this poster we present a cross-layer design between packet routing and medium access control (MAC) for a vehicular ad hoc network (VANET) in order to guarantee special quality of service (QoS) requirements. As precondition we consider vehicles equipped with driving- assistant-systems that exchange environmental object information through the network. By the use of wireless communication the vehicles can share their environment data and extend their environment model. This collected object information gets obsolete after some time because of the fast changing surroundings of a vehicle. Therefore it should be distributed to other vehicles with a lower delay than the data gets outdated. This introduces a special low delay QoS requirement the VANET has to provide to the application.

Measured neutron energy fluences from high-energy heavy ion reactions through targets several centimeters to several hundred centimeters thick were compared with calculations made using the recently developed general-purpose particle and heavy ion transport code system (PHITS). It was confirmed that the PHITS represented neutron production by heavy ion reactions and neutron transport in thick shielding with good overall accuracy.

The neutron energy spectrum of the JRC 2 4 1 Am-Li(α,n) radionuclide source has been measured at the PTB in Germany using various spectrometry systems, such as Bonner spheres, proton recoil counters and NE213 liquid scintillators. The source photon spectrum has been measured and the neutron contamination due to traces of beryllium through the 9 Be(α,n) 1 2 C reaction has been determined. The effects associated with source encapsulation and the materials it contains have been investigated previously, using Monte Carlo simulations, the various structures seen in the spectra have been explained and the anisotropy of fluence distributions in 4π have been calculated and compared to measurements. These extensive high resolution spectrometry measurements have been coupled to Monte Carlo calculations to provide a realistic spectrum and new spectrum-averaged fluence-to-dose equivalent conversion coefficients for the actual 2 4 1 Am-Li source.

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.

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.

Radiation effects of cosmic ray nuclei are generally described as a function of the particle LET. For a large number of space missions LET spectra have been measured and models have been developed to calculate these spectra that include the effects of geomagnetic shielding and shielding provided by material. In this paper we compare measured and calculated LET spectra. For low earth orbits events with high local energy deposition, i.e., short range secondaries, contribute significantly to the measured spectra. These events are produced by nuclear interactions, mainly induced by protons from the south atlantic anomaly. The technique to include these contributions in the models depends on the size of radiation sensitive volumes. For sizes comparable to or larger than the range of target secondaries it is essential to separate contributions by target interactions from those of cosmic rays. This separation is possible in experiments which use stacks of plastic nuclear track detectors. The yield of short range events generated by protons and measured in the detector can be calibrated from accelerator experimental data. We present first results for CR-39 detectors.

Linear Energy Transfer (LET) spectra have been measured for lunar missions and for several near Earth orbits ranging from 28 deg to 83 deg inclination. In some of the experiments the flux of Galactic Cosmic Rays (GCR) was determined separately from contributions caused by interactions in the detector material. Results of these experiments are compared to model calculations. The general agreement justifies the use of the model to calculate GCR fluxes. The magnitude of variations caused by solar modulation, geomagnetic shielding, and shielding by matter determined from calculated LET spectra is generally in agreement with experimental data. However, more detailed investigations show that there are some weak points in modeling solar modulation and shielding by material. These points are discussed in more detail.

In reply to the Comment of Morrissey we present the standard deviations [sigma] of distributions of transverse momentum components under the assumption that the ratios [ital A]/[ital Z] of fragments are determined by the parametrization of Suemmerer [ital et] [ital al]. These results do not change in comparison to those derived with a ratio [ital A]/[ital Z] equal to that of the projectile as presented by Dreute [ital et] [ital al].

We present measurements of LET spectra for near earth orbits with various inclinations and altitudes. A comparison with calculated LET spectra shows that the contribution from direct ionizing galactic cosmic rays is well described by the models. An additional contribution to the spectra originates from stopping protons and from nuclear interactions of particles with material. In the case of an interaction a large amount of energy is deposited in a small volume by target recoils or target fragments. These events will be called short range (SR) events. For a low inclination orbit radiation belt protons are the main source of these events while galactic protons become more important when increasing the inclination to near polar orbits. We show that the contribution of SR events for orbits with low altitude (324 km) and 57 degrees inclination is comparable to that for an orbit with 28 degrees inclination at a high altitude (510 km).

The long duration exposure facility (LDEF), launched into a 258 nautical mile orbit with an inclination of 28.5 degrees, remained in space for nearly 6 yr. The 21,500 lb NASA satellite was one of the largest payloads ever deployed by the Space Shuttle. LDEF completed 32,422 orbits and carried 57 major experiments representing more than 200 investigators from 33 private companies, 21 universities and nine countries. The experiments covered a wide range of disciplines including basic science, electronics, optics, materials, structures and power and propulsion. A number of the experiments were specifically designed to measure the radiation environment. These experiments are of specific interest, since the LDEF orbit is essentially the same as that of the Space Station Freedom. Consequently, the radiation measurements on LDEF will play a significant role in the design of radiation shielding of the space station. The contributions of the various authors presented here attempt to predict the major aspects of the radiation exposure received by the various LDEF experiments and therefore should be helpful to investigators who are in the process of analyzing experiments which may have been affected by exposure to ionizing radiation. The paper discusses the various types and sources of ionizing radiation including cosmic rays, trapped particles (both protons and electrons) and secondary particles (including neutrons, spallation products and high-LET recoils), as well as doses and LET spectra as a function of shielding. Projections of the induced radioactivity of LDEF are also discussed.

A stack containing plastic nuclear track detectors and Ag target foils was exposed to a {sup 197}Au beam with an energy of 980 MeV/nucleon. The analysis was restricted to energies between beam energy and 200 MeV/nucleon. 2496 collisions with Ag target nuclei and 4114 with the lighter constituents H, C, and O of the detector material were analyzed in detail. For all interactions, projectile fragments with charge {ital Z}{sub {ital F}}{ge}6 were measured and their emission angles were determined. This paper describes the experiment and presents charge yields and results about transverse momenta for events with different multiplicities. Details of multiplicity distributions, correlations between fragments and signatures related to multifragmentation as a critical process are discussed in a separate paper.