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Investigates the nonlinear microwave response of superconducting yttrium barium copper oxide (YBCO) thin films. Comparison of the nonlinear response of thin films to crystals; Reduction of the third-order nonlinear response of YBCO thin-film materials; Impact of flux lines interaction on nonlinear response.

We have investigated power handling of high-temperature superconducting microstrip filters employing highly sensitive thermal imaging. At low power, the images show small heating effects localized to areas with high current densities (ΔT<0.5 K), consistent with the known surface resistance and simulations of the current distribution. The breakdown at high-power levels, however, is always nucleated by a frequency independent local hot spot (T>=Tc). Scanning electron microscopy analysis of this area reveals a flaw in the superconducting material, presumably reducing the local critical current. The maximum power handling of these filters is, therefore, still open to improvement. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: The TRIGA Mark II reactor at the University of Mainz provides ideal conditions for duplicating BNCT treatment as performed in Pavia, Italy, in 2001 and 2003 [Pinelli, T., Zonta, A., Altieri, S., Barni, S., Braghieri, A., Pedroni, P., Bruschi, P., Chiari, P., Ferrari, C., Fossati, F., Nano, R., Ngnitejeu Tata, S., Prati, U., Ricevuti, G., Roveda, L., Zonta, C., 2002. TAOrMINA: from the first idea to the application to the human liver. In: Sauerwein et al. (Eds.), Research and Development in Neutron Capture Therapy. Proceedings of the 10th International Congress on Neutron Capture Therapy, Monduzzi editore, Bologna, pp. 1065–1072]. In order to determine the optimal parameters for the planned therapy and therefore for the design of the thermal column, calculations were conducted using the MCNP-code and the transport code ATTILA. The results of the parameter study as well as a possible configuration for the irradiation of the liver are presented. [Copyright &y& Elsevier]

Abstract: For the application of the BNCT for the excorporal treatment of organs at the TRIGA Mainz, the basic characteristics of the radiation field in the thermal column as beam geometry, neutron and gamma ray energies, angular distributions, neutron flux, as well as absorbed gamma and neutron doses must be determined in a reproducible way. To determine the mixed irradiation field thermoluminescence detectors (TLD) made of CaF2:Tm with a newly developed energy-compensation filter system and LiF:Mg,Ti materials with different 6Li concentrations and different thicknesses as well as thin gold foils were used. [Copyright &y& Elsevier]

Boron determination in blood and tissue samples is a crucial task especially for treatment planning, preclinical research, and clinical application of boron neutron capture therapy (BNCT). Comparison of clinical findings remains difficult due to a variety of analytical methods, protocols, and standard reference materials in use. This paper addresses the comparability of inductively coupled plasma mass spectrometry, quantitative neutron capture radiography, and prompt gamma activation analysis for the determination of boron in biological samples. It was possible to demonstrate that three different methods relying on three different principles of sample preparation and boron detection can be validated against each other and yield consistent results for both blood and tissue samples. The samples were obtained during a clinical study for the application of BNCT for liver malignancies and therefore represent a realistic situation for boron analysis. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

In an effort to develop HTS superconducting filters with sufficient power handling capability for PCS (Personal Communication Services) base station transmit applications, we have undertaken a study of the power dependence of large area YBCO thin films on LaAlO/sub 3/ substrates. We employed a coplanar-wave-guide (CPW) resonator technique to obtain the changes of loss and inductance versus circulating microwave currents in the films. Data have been collected on uniform large area (2" diameter) films grown by coevaporation and off-axis sputtering techniques under varying deposition conditions. We found correlations between the RF power dependence and other film properties such as penetration depth and crystal structure. The most intrinsic sample, from the coevaporation technique, characterized by the smallest penetration depth, good orthorhombicity and absence of tetragonal phase, shows the least amount of nonlinearity. Such correlations can be used to prescreen films for fabrication and monitor the film production line. However, films from coevaporation and off-axis sputtering show very distinct power dependent behaviors. [ABSTRACT FROM PUBLISHER]

In this work we report some preliminary results regarding the analysis of electron paramagnetic resonance (EPR) response of alanine pellets and alanine pellets added with gadolinium used for dosimetry at the TRIGA research reactor in Mainz, Germany. Two set-ups were evaluated: irradiation inside PMMA phantom and irradiation inside boric acid phantom. We observed that the presence of Gd 2 O 3 inside alanine pellets increases the EPR signal by a factor of 3.45 and 1.24 in case of PMMA and boric acid phantoms, respectively. We can conclude that in the case of neutron beam with a predominant thermal neutron component the addition of gadolinium oxide can significantly improve neutron sensitivity of alanine pellets. Monte Carlo (MC) simulations of both response of alanine and Gd-added alanine pellets with FLUKA code were performed and a good agreement was achieved for pure alanine dosimeters. For Gd 2 O 3 -alanine deviations between MC simulations and experimental data were observed and discussed. [ABSTRACT FROM AUTHOR]

Background: Fifty percent of the heavy element abundances are produced via slow neutron capture reactions in different stellar scenarios. The underlying nucleosynthesis models need the input of neutron capture cross sections. Purpose: One of the fundamental signatures for active nucleosynthesis in our galaxy is the observation of long-lived radioactive isotopes, such as 60Fe with a half-life of 2.60×106 yr. To reproduce this γ activity in the universe, the nucleosynthesis of 60Fe has to be understood reliably. Methods: An 60Fe sample produced at the Paul Scherrer Institut (Villigen, Switzerland) was activated with thermal and epithermal neutrons at the research reactor at the Johannes Gutenberg-Universität Mainz (Mainz, Germany). Results: The thermal neutron capture cross section has been measured for the first time to σth = 0.226(-0.049+0.044)b. An upper limit of σRI < 0.50b could be determined for the resonance integral. Conclusions: An extrapolation towards the astrophysically interesting energy regime between kT = 10 and 100 keV illustrates that the s-wave part of the direct capture component can be neglected. [ABSTRACT FROM AUTHOR]

Purpose: The response of alanine solid state dosimeters to ionizing radiation strongly depends on particle type and energy. Due to nuclear interactions, neutron fields usually also consist of secondary particles such as photons and protons of diverse energies. Various experiments have been carried out in three different neutron beams to explore the alanine dose response behavior and to validate model predictions. Additionally, application in medical neutron fields for boron neutron capture therapy is discussed. Methods: Alanine detectors have been irradiated in the thermal neutron field of the research reactor TRIGA Mainz, Germany, in five experimental conditions, generating different secondary particle spectra. Further irradiations have been made in the epithermal neutron beams at the research reactors FiR 1 in Helsinki, Finland, and Tsing Hua open pool reactor in HsinChu, Taiwan ROC. Readout has been performed with electron spin resonance spectrometry with reference to an absorbed dose standard in a 60Co gamma ray beam. Absorbed doses and dose components have been calculated using the Monte Carlo codes FLUKA and MCNP. The relative effectiveness (RE), linking absorbed dose and detector response, has been calculated using the Hansen & Olsen alanine response model. Results: The measured dose response of the alanine detector in the different experiments has been evaluated and compared to model predictions. Therefore, a relative effectiveness has been calculated for each dose component, accounting for its dependence on particle type and energy. Agreement within 5% between model and measurement has been achieved for most irradiated detectors. Significant differences have been observed in response behavior between thermal and epithermal neutron fields, especially regarding dose composition and depth dose curves. The calculated dose components could be verified with the experimental results in the different primary and secondary particle fields. Conclusions: The alanine detector can be used without difficulty in neutron fields. The response has been understood with the model used which includes the relative effectiveness. Results and the corresponding discussion lead to the conclusion that application in neutron fields for medical purpose is limited by its sensitivity but that it is a useful tool as supplement to other detectors and verification of neutron source descriptions. [ABSTRACT FROM AUTHOR]

In this work, we investigated the ability of a high-purity germanium detector connected to a trapezoid-filter-based data acquisition system to reliably record signals in spite of high sample activities. By activating multiple Na 2 CO 3 samples with different Na content, we were able to deduce efficiency, resolution and dead time of the system used as a function of the sample activity. Based on the results, we were able to find a setting which allows measurements of event rates up to 35 kHz per readout channel with an energy resolution of 0.3% at the 2754 keV 24 Na line. [ABSTRACT FROM AUTHOR]

Abstract: This study investigates the dosimetric feasibility of Boron Neutron Capture Therapy (BNCT) of explanted livers in the thermal column of the research reactor in Mainz. The Monte Carlo code MCNP5 is used to calculate the biologically weighted dose for different ratios of the 10B-concentration in tumour to normal liver tissue. The simulation results show that dosimetric goals are only partially met. To guarantee effective BNCT treatment the organ has to be better shielded from all gamma radiation. [Copyright &y& Elsevier]

Abstract: Standard wafer solar cells are made of near-semiconductor quality silicon. This high quality material makes up a significant part of the total costs of a solar module. Therefore, new concepts with less expensive so called solar grade silicon directly based on physiochemically upgraded metallurgical grade silicon are investigated. Metallurgical grade silicon contains large amounts of impurities, mainly transition metals like Fe, Cr, Mn, and Co, which degrade the minority carrier lifetime and thus the solar cell efficiency. A major reduction of the transition metal content occurs during the unidirectional crystallization due to the low segregation coefficient between the solid and liquid phase. A further reduction of the impurity level has to be done by gettering procedures applied to the silicon wafers. The efficiency of such cleaning procedures of metallurgical grade silicon is studied by instrumental neutron activation analysis (INAA). Small sized silicon wafers of approximately 200mg with and without gettering step were analyzed. To accelerate the detection of transition metals in a crystallized silicon ingot, experiments of scanning whole vertical silicon columns with a diameter of approximately 1cm by gamma spectroscopy were carried out. It was demonstrated that impurity profiles can be obtained in a comparably short time. Relatively constant transition metal ratios were found throughout an entire silicon ingot. This led to the conclusion that the determination of several metal profiles might be possible by the detection of only one “leading element”. As the determination of Mn in silicon can be done quite fast compared to elements like Fe, Cr, and Co, it could be used as a rough marker for the overall metal concentration level. Thus, a fast way to determine impurities in photovoltaic silicon material is demonstrated. [Copyright &y& Elsevier]

Abstract: As part of the studies on Boron Neutron Capture Therapy at the University of Mainz, Germany, a clinical trial has been started in which, four patients suffering from liver metastases of colorectal carcinoma have been enrolled. Specimens of blood and healthy tissue samples taken from the patients were measured at the PGAA facilities at the HFR in Petten, The Netherlands, and at the FRM II in Munich, Germany. From the measured boron concentrations, pharmacokinetic curves and blood-to-tissue concentration ratios were produced. [Copyright &y& Elsevier]

Abstract: At the ultracold neutron (UCN) source of the TRIGA research reactor in Mainz, we have measured for the first time the material optical wall-potential of cubic boron nitride. The measurements were performed with a time-of-flight (TOF) spectrometer. The samples investigated had a wall-potential of . This value is in good agreement with the result extracted from neutron reflectometry data and theoretical expectations. Because of its high critical velocity for UCN and its good dielectric characteristics, cubic boron nitride coatings (isotopically enriched) will be useful for a number of applications in UCN experiments. [Copyright &y& Elsevier]

Abstract: The effort towards a new measurement of the neutron electric dipole moment (nEDM) at the Paul Scherrer Institut''s (PSI) new high intensity source of ultracold neutrons (UCN) is described. The experimental technique relies on Ramsey''s method of separated oscillatory fields, using UCN in vacuum with the apparatus at ambient temperature. In the first phase, R&D towards the upgrade of the RAL/Sussex/ILL apparatus is being performed at the Institut Laue-Langevin (ILL). In the second phase the apparatus, moved from ILL to PSI, will allow an improvement in experimental sensitivity by a factor of 5. In the third phase, a new spectrometer should gain another order of magnitude in sensitivity. The improvements will be mainly due to (1) much higher UCN intensity, (2) improved magnetometry and magnetic field control, and (3) a double chamber configuration with opposite electric field directions. [Copyright &y& Elsevier]

Abstract: At the Paul Scherrer Institute (PSI), a very intense source of ultracold neutrons (UCN) is being built. The UCN converter of solid deuterium must be contained in a vessel. Produced UCN leave that vessel through its top lid. To decide on the design of the vessel and the top lid, we have measured the transmission of neutrons with velocities between 3 and 20m/s through different material foils. Contrary to expectations, we found that transmission through aluminium and aluminium alloys is equal or even higher compared to zirconium and reactor-grade zirconium alloys, respectively. [Copyright &y& Elsevier]

We have determined for the first time the velocity distribution of neutrons from a solid 2H2 ultracold neutron (UCN) source. The spectrum rises sharply above 4.5m/s and has a maximum around 7m/s after transport in an 8m long guide. The number of neutrons in the UCN velocity range (< 7m/s) may be increased by a factor of two by placing the experiment 1m above the UCN source level. [ABSTRACT FROM AUTHOR]

Abstract: Photon dose measurements in radiation fields having the proper characteristics for boron neutron capture therapy (BNCT) present several troubles. The thermal neutron flux is very high and produces a significant contribution to the response of most dosimeters. The consistency of photon dose measurements with :Tm and LiF:Mg, Ti thermoluminescent dosimeters has been studied. A method is described for obtaining the gamma dose with TLD-700 and some results are presented to test its reliability. [Copyright &y& Elsevier]

Abstract: Strong fields of thermal and epithermal neutrons as used for Boron Neutron Capture Therapy (BNCT) show a relatively small gamma dose. However, for accurate dose estimation, both the neutron as well as the gamma component has to be considered. Different approaches have been studied with various thermoluminescence detectors (TLDs). As a result, CaF2:Tm detectors (TLD-300) are attributed to be most insensitive to thermal neutrons but not tissue-equivalent. In this paper we focus on the measurement of the gamma dose with TLD-300 in mixed irradiation fields. To overcome the disadvantage of being not tissue-equivalent, a study on energy compensation filters was performed. The paper comprises also calibrations of TLD-300 using energy compensation filters at the PTB-reference field for thermal neutrons, and first test experiments at the TRIGA Mainz including simulations. [Copyright &y& Elsevier]

The production rates of ultracold neutrons (UCN) with a solid deuterium converter have been measured at the pulsed reactor TRIGA Mainz. Exposed to a thermal neutron fluence of $\ensuremath \sim 1\cdot 10^{13}$ n·cm^-2·pulse^-1, the number of detected very cold and ultracold neutrons ranges up to 200 000 at 7mol of solid deuterium (sD2) in combination with a pre-moderator (mesitylene). About 50% of the measured neutrons can be assigned to UCN with energies E of $\ensuremath V_{\rm F}({\rm sD}_2)\leq E \leq V_{\rm F}{\rm (guide)}$ where V F( sD 2) = 105 neV and V F( guide) = 190 neV are the Fermi potentials of the sD2 converter and our stainless steel neutron guides, respectively. Thermal cycling of solid deuterium, which was frozen out from the gas phase, considerably improved the UCN yield, in particular at higher amounts of sD2. [ABSTRACT FROM AUTHOR]

Abstract: We describe the status of the new measurement of the neutron electric dipole moment (nEDM) to be performed at the strong source of ultra-cold neutrons at the Paul Scherrer Institut. The experimental technique is based on Ramsey''s method of separated oscillatory fields, applied to UCN stored in vacuum in a chamber at room temperature. Our approach is performed in three phases: in phase one, new components have been developed and tested at the Institut Laue-Langevin. Phase two is being performed at PSI, where the apparatus was moved in 2009. Here, together with the optimization of the magnetic environment, the prospective UCN density of ∼ 100 cm-3 should enable an improvement of the currently best limit by a factor of five within two years of data taking. In the third phase, a new spectrometer will then gain another order of magnitude in sensitivity. The improvements will be mainly due to (1) much higher UCN intensity, (2) improved magnetometry and magnetic field control, and (3) a double chamber configuration with opposite electric field directions. [Copyright &y& Elsevier]