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We have studied the ESR response of alanine pellets with and without gadolinium exposed to the thermal column of the TRIGA Mark II research reactor at the University of Mainz (Germany). The choice of Gd as additive nucleus is due to its very high capture cross section to thermal neutrons and to the possibility for secondary particles produced after interaction with thermal neutrons of releasing their energy in the neighborhood of the reaction site. In particular, it was found that low concentration (5% by weight) of Gd brings about a neutron sensitivity enhancement of more than 10 times without heavily reducing tissue equivalence. Monte Carlo (MC) simulations of both response of alanine and Gd-alanine pellets with FLUKA code were performed and the results were compared with the experimental values.

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

For the optimization of the manufacturing process of multicrystalline silicon (mc-Si) for solar cells in order to reduce energy consumption and costs, it is important to know the distribution of the impurities. In our project, we analyzed the raw materials, the crucibles, and the solidified blocks (ingots) with different methods based on neutron activation. In this paper, we present the technique and the results of the boron and hydrogen determination with prompt gamma activation analysis (PGAA). We show that the distribution of boron in the ingots can be successfully described with a Scheil curve. Concerning the raw material, the most relevant information is the average elemental mass fraction. For this purpose, PGAA is well suited since it provides a bulk analysis with detection limits down to the low ng/g range for boron and µg/g range for hydrogen. In this context, the hydrogen content of fluidized bed reactor (FBR) feedstock is discussed in detail. These were the first extensive PGAA studies of the boron and hydrogen content in mc-Si.

Negli ultimi anni il crescente interesse verso la radioterapia a cattura neutronica (internazionalmente nota come Neutron Capture Therapy - NCT) per il trattamento di neoplasie ha stimolato diverse attività di ricerca finalizzate alla caratterizzazione del fascio utilizzato e all'ottimizzazione delle procedure radioterapiche. La corretta riuscita del trattamento NCT e il monitoraggio della dose impartita non possono prescindere dalla valutazione delle varie componenti del fascio impiegato (neutronica e fotonica). Infatti, durante le procedure di moderazione dei neutroni, si verifica la produzione di fotoni e la stima dei rischi a cui sono soggetti i tessuti sani sottoposti al campo misto necessita precise ed accurate misure della componente fotonica. Tra i vari sistemi dosimetrici trovano largo impiego i rivelatori a stato solido EPR (Risonanza Paramagnetica Elettronico) a base di alanina che presentano diversi vantaggi come la tessuto equivalenza per fasci di fotoni, la linearità della risposta in un ampio intervallo di dose, l'elevata stabilità dei radicali liberi radioindotti, la non distruttività della lettura del dosimetro e il basso costo dei dosimetri. Queste caratteristiche, se associate alla possibilità di riconoscere le varie componenti di un campo misto di radiazione, renderebbero l'alanina un ottimo candidato per le dosimetria in campi di neutroni-gamma. In questo lavoro abbiamo studiato la risposta di dosimetri di alanina con e senza gadolinio (Gd) irradiati nella colonna termica del reattore di ricerca di Mainz. I dosimetri di alanina semplice utilizzati sono stati prodotti da SynergyHealth (Germania), mentre i dosimetri con aggiunta di Gd sono stati prodotti presso l'Università di Palermo. Le irradiazioni sono state effettuate all'interno di contenitori di polietilene per garantire le condizioni di equilibrio di particelle cariche. Le misure EPR sono state effettuate mediante spettrometro Bruker ECS106 dotato di una cavità TE102 rettangolare. I risultati degli esperimenti EPR sono stati confrontati con le simulazioni Monte Carlo finalizzate ad ottenere informazioni sul contributo delle varie componenti (neutronica e fotonica) alla dose totale misurata mediante dosimetri EPR.

The development of Neutron Capture Therapy (NCT) for cancer treatments has stimulated the research for beam characterization in order to optimize the therapy procedures. The NCT has found to be promising for treatments of tumours which hardly can be treated with other techniques, such as gliomas. Alongside with the improvements of this technique, the development of procedures for the beam characterization arouses great interest in order to optimize the therapy protocol by reliably determining the various (neutronic and photonic) components of the mixed beam usually employed for therapy. Electron Paramagnetic Resonance (EPR) dosimetry for electron and photon beams with alanine has attracted the attention of many research groups for dosimetric purposes. Furthermore, the applications of EPR dosimetry for high LET radiation beams, such as carbon ions and neutrons, are continuously increasing. This is because of the very good dosimetric features of alanine EPR detectors such as: tissue equivalence for photon beams, linearity of its dose-response over a wide range, high stability of radiation induced free radicals, no destructive read-out procedure, no need of sample treatment before EPR signal measurement and low cost of the dosimeters. Moreover, in order to improve the sensitivity to thermal neutrons of alanine dosimeters the addition of nuclei such as gadolinium oxidewas previously studied. The choice of Gd as additive nucleus is due to its very high capture cross section to thermal neutrons and to the possibility for secondary particles produced after interaction with thermal neutrons of releasing their energy in the neighbourhood of the reaction site. In particular, it was found that low concentration (i.e. 5% by weight) of gadolinium oxide brings about an neutron sensitivity enhancement of more than 10 times without heavily reducing tissue equivalence. We have studied the response of alanine pellets with and without gadolinium exposed to the thermal column of the TRIGA Mark II research reactor at the University of Mainz. Pure alanine dosimeters used were produced by Synergy Health (Germany) whereas the Gd-added dosimeters were produced at the University of Palermo. The irradiations were performed inside polyethylene holders to guarantee charged particles equilibrium conditions. The results of EPR experiments are compared to Monte Carlo (MC) simulations aimed at obtaining information about the contribution of the various components to the total dose measured by means of EPR dosimeters. For alanine dosimeters a good agreement between experimental data and MC simulation have been achieved.

In this work we have studied the response of alanine pellets with and without gadolinium exposed to the thermal column of the TRIGA Mark II research reactor at the University of Mainz

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 FLUCK 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.

Purpose:Boron Neutron Capture Therapy (BNCT) is a special kind of particle therapy, based on the neutron induced fission of the boron isotope 10B [1]. We have performed dosimetry experiments on the mixed neutron and gamma fields at the TRIGA Mark II research reactor in Mainz. Commonly, dosimetry in such fields is realized by foil activation and ion chambers [2]. Here we investigate alanine as an easier and more robust alternative dosimeter.Methods:We have performed four phantom experiments at the TRIGA Mark II research reactor in Mainz [3], in a predominantly thermal neutron field with a strong gamma component. All alanine pellets irradiated are manufactured and read out at the National Physical Laboratory (NPL), United Kingdom [4]. To predict the dose and its components for each pellet, the Hansen & Olsen detector response model [5] is applied along together with FLUKA [6].Results:The measured dose response of all pellets could be reproduced by calculations within a uncertainty of 5 %. For all experiments three dose components have been separated. A proton dose is generated in the 14N(n,p)14C reaction. Secondary gammas are generated by various (n,γ) reactions, dominated by the 2.2 MeV photon from neutron capture of hydrogen. The primary gamma dose deposited originate from the reactor core itself.Conclusion:Alanine dosimeters are suitable of measurements in mixed neutron fields and the alanine response in thermal neutron fields can be fully understood by the used interpretation model. In further experiments the dosimeters will be exposed to higher neutron energies, which are more typical for BNCT treatments.References:[1] Barth, R.F; 2009: Boron neutron capture therapy at the crossroads: Challenges and opportunities. Applied Radiation and Isotopes 67, 3-6.[2] Rogus, R.D.; Harling, O.K.; Yanch, J.C.; 1994: Mixed field dosimetry of epithermal neutron beams for boron neutron capture therapy at the MITR‐II research reactor. Medical Physics 21, 1611-1626.[3] Hampel, G.; Blaickner, M.; Knorr,J.; Kratz, J.V.; Lizón Aguilar, A.; Minouchehr, S. et al.; 2009: Irradiation facility at the TRIGA Mainz for treatment of liver metastases. Applied Radiation and Isotopes 67, 238-241.[4] Sharpe, P.; Sephtan, J.; 2000: An automated system for the measurement of alanine/EPR dosimeters. Applied Radiation and Isotopes 52, 1185-1188.

The thermal column of the TRIGA reactor in Mainz is being used very effectively for medical and biological applications. The BNCT (boron neutron capture therapy) project at the University of Mainz is focussed on the treatment of liver tumours, similar to the work performed at Pavia (Italy) a few years ago, where patients with liver metastases were treated successfully by combining BNCT with auto-transplantation of the organ. Here, in Mainz, a preclinical trial has been started on patients suffering from liver metastases of colorectal carcinoma. In vitro experiments and the first animal tests have also been initiated to investigate radiobiological effects of radiation generated during BNCT. For both experiments and treatment, a reliable dosimetry system is necessary. From work elsewhere, the use of alanine detectors appear to be an appropriate dosimetry technique.

25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion, 6-10 September 2010, Valencia, Spain; 3591-3593, The concept of the epitaxial wafer equivalent (EpiWE) is pursued at the Fraunhofer ISE as an option to reduce the cost of silicon solar cells. Within this concept, only a small amount of the expensive high purity silicon is needed for the epitaxial deposition on a low-cost substrate made from low-quality silicon. A challenging task is the control of the impurity contents in the low-grade silicon substrate. Especially transition metals like Fe, Mn, and Cr act as recombination centres and degrade the minority carrier lifetime once they diffuse into the active layer. Gettering with HCl gas is an effective and fast method to reduce the metals mentioned above to an appropriate level and can be performed prior to the epitaxial deposition. This paper presents a reduction of metal impurity concentrations up to two orders of magnitude obtained by HCl gettering of metallurgical grade (MG) and upgraded metallurgical grade (UMG) silicon. Additionally, solar cell results are shown, demonstrating the improvement of EpiWE solar cells by HCl gas gettering.