Physics-related epistemic uncertainties in proton depth dose simulation

A set of physics models and parameters pertaining to the simulation of proton energy deposition in matter are evaluated in the energy range up to approximately 65 MeV, based on their implementations in the Geant4 toolkit. The analysis assesses several features of the models and the impact of their associated epistemic uncertainties, i.e. uncertainties due to lack of knowledge, on the simulation results. Possible systematic effects deriving from uncertainties of this kind are highlighted; their relevance in relation to the application environment and different experimental requirements are discussed, with emphasis on the simulation of radiotherapy set-ups. By documenting quantitatively the features of a wide set of simulation models and the related intrinsic uncertainties affecting the simulation results, this analysis provides guidance regarding the use of the concerned simulation tools in experimental applications; it also provides indications for further experimental measurements addressing the sources of such uncertainties.Comment: To be published in IEEE Trans. Nucl. Sc

Measurement of the thermal expansion coefficient of an Al-Mg alloy at ultra-low temperatures

We describe a result coming from an experiment based on an Al-Mg alloy (~ 5% Mg) suspended bar hit by an electron beam and operated above and below the termperature of transition from superconducting to normal state of the material. The amplitude of the bar first longitudinal mode of oscillation, excited by the beam interacting with the bulk, and the energy deposited by the beam in the bar are the quantities measured by the experiment. These quantities, inserted in the equations describing the mechanism of the mode excitation and complemented by an independent measurement of the specific heat, allow us to determine the linear expansion coefficient of the material.Comment: 13 pages, 4 figure

PHOTONEUTRON SOURCE BY HIGH ENERGY ELECTRONS ON HIGH Z TARGET: COMPARISON BETWEEN MONTE CARLO CODES AND EXPERIMENTAL DATA

ne, in the National Laboratory of Frascati, near Rome (Italy). Neutrons are produced sending high energy electrons to impinge on an optimized Tungsten target. This source could be suitably used for calibration of neutron detectors as well as for material and nuclear science investigations. Moreover photoneutron processes are encountered in many physics domains: from accelerator to reactor physics, mainly related to neutron shielding issues in high Z materials, used for gamma shielding.This work presents the Monte Carlo simulations performed with different codes (FLUKA and MCNPX) to estimate the neutron rate and energy spectrum, obtained when 510 MeV electrons are sent against the designed target. Finally, the comparison of the Monte Carlo predictions of neutron and photon fluences around the target with the experimental values is discussed

Research on Mechanism of Formulation and Change of Stereotype: A Case Study of Hero Stereotype in Historical and Revolutionary Movies

刻板印象是人们头脑中关于世界的先在图景，是人们对社会某一类群体概括性的知识结构，它在社会互动中规范着人们的价值判断和行为反应。刻板印象一旦形成就具有了很强的稳定性。发源于西方的刻板印象研究已经有80多年的历史，其中，刻板印象的形成与变化研究是学者关注的热点之一。研究结果表明，社会关系、大众媒介以及个人心理结构是影响刻板印象形成与变化的主要因素。新中国成立以来，中国人认识社会的主要依据是革命历史影片塑造的英雄刻板印象。它为中国人民“提供了认识中国近代史的观念、方法和结论，同时也营造了利于浮现的、表象化的历史图景”。[1]本研究从刻板印象生成与变化的角度出发，探讨中国革命历史影片中英雄刻板印象的媒...It has been more than 80 years since the study of stereotyping emerged in western country. Defined as stored general knowledge on characteristics of a social group of people, stereotype is a kind of preconception about the world for people in their mind, which regulates their conduct and value judgment in their social interaction. Once it is formed, stereotype would have a strong stability, which ...学位：文学硕士院系专业：新闻传播学院广告学系_传播学学号：1052006115025

14 MeV neutrons for 99Mo/99mTc production: Experiments, simulations and perspectives

Background: the gamma-emitting radionuclide Technetium-99m (99mTc) is still the workhorse of Single Photon Emission Computed Tomography (SPECT) as it is used worldwide for the diagnosis of a variety of phatological conditions.99mTc is obtained from99Mo/99mTc generators as pertechnetate ion, which is the ubiquitous starting material for the preparation of99mTc radiopharmaceuticals.99Mo in such generators is currently produced in nuclear fission reactors as a by-product of235U fission. Here we investigated an alternative route for the production of99Mo by irradiating a natural metallic molybdenum powder using a 14-MeV accelerator-driven neutron source. Methods: after irradiation, an efficient isolation and purification of the final99mTc-pertechnetate was carried out by means of solvent extraction. Monte Carlo simulations allowed reliable predictions of99Mo production rates for a newly designed 14-MeV neutron source (New Sorgentina Fusion Source). Results: in traceable metrological conditions, a level of radionuclidic purity consistent with accepted pharmaceutical quality standards, was achieved. Conclusions: we showed that this source, featuring a nominal neutron emission rate of about 1015s−1, may potentially supply an appreciable fraction of the current99Mo global demand. This study highlights that a robust and viable solution, alternative to nuclear fission reactors, can be accomplished to secure the long-term supply of99Mo

Quantification of the validity of simulations based on Geant4 and FLUKA for photo-nuclear interactions in the high energy range

Photo-nuclear interactions are relevant in many research fields of both fundamental and applied physics and, for this reason, accurate Monte Carlo simulations of photo-nuclear interactions can provide a valuable and indispensable support in a wide range of applications (i.e from the optimisation of photo-neutron source target to the dosimetric estimation in high energy accelerator, etc). Unfortunately, few experimental photo-nuclear data are available above 100 MeV, so that, in the high energy range (from hundreds of MeV up to GeV scale), the code predictions are based on physical models. The aim of this work is to compare the predictions of relevant observables involving photon-nuclear interaction modelling, obtained with GEANT4 and FLUKA, to experimental data (if available), in order to assess the code estimation reliability, over a wide energy range. In particular, the comparison of the estimated photo-neutron yields and energy spectra with the experimental results of the n@BTF experiment (carried out at the Beam Test Facility of DaΦne collider, in Frascati, Italy) is here reported and discussed. Moreover, the preliminary results of the comparison of the cross sections used in the codes with the“evaluated’ data recommended by the IAEA are also presented for some selected cases (W, Pb, Zn)

Quantification of the validity of simulations based on Geant4 and FLUKA for photo-nuclear interactions in the high energy range

Photo-nuclear interactions are relevant in many research fields of both fundamental and applied physics and, for this reason, accurate Monte Carlo simulations of photo-nuclear interactions can provide a valuable and indispensable support in a wide range of applications (i.e from the optimisation of photo-neutron source target to the dosimetric estimation in high energy accelerator, etc). Unfortunately, few experimental photo-nuclear data are available above 100 MeV, so that, in the high energy range (from hundreds of MeV up to GeV scale), the code predictions are based on physical models. The aim of this work is to compare the predictions of relevant observables involving photon-nuclear interaction modelling, obtained with GEANT4 and FLUKA, to experimental data (if available), in order to assess the code estimation reliability, over a wide energy range. In particular, the comparison of the estimated photo-neutron yields and energy spectra with the experimental results of the n@BTF experiment (carried out at the Beam Test Facility of DaΦne collider, in Frascati, Italy) is here reported and discussed. Moreover, the preliminary results of the comparison of the cross sections used in the codes with the“evaluated’ data recommended by the IAEA are also presented for some selected cases (W, Pb, Zn)