Analytical shielding calculations for a proton therapy facility

The University of Pennsylvania is building a proton therapy facility in collaboration with Walter Reed Army Medical Center. The proposed facility has four gantry rooms, a fixed beam room and a research room, and will use a cyclotron as the source of protons. In this study, neutron shielding considerations for the proposed proton therapy facility were investigated using analytical techniques and Monte Carlo simulated neutron spectra. Neutron spectra calculations were done using the GEANT4 (v6.2) simulation code for various materials: water, carbon, iron, nickel and tantalum to estimate the neutron production at proton beam energies of 100, 175 and 250 MeV. Dose equivalent calculations were performed using analytical methods at various critical points within the facility, by folding the GEANT4 produced neutron spectra with dose equivalent rate data from the National Council on Radiation Protection and Measurements (NCRP) Report #144.     

Radiological considerations for bulk shielding calculations of national synchrotron light source-II

Brookhaven National Laboratory is designing a new electron synchrotron for scientific research using synchrotron radiation. This facility, called the “National Synchrotron Light Source II” (NSLS-II), will provide x-ray radiation of ultra-high brightness and exceptional spatial and energy resolution. It will also provide advanced insertion devices, optics, detectors and robotics, and a suite of scientific instruments designed to maximize the scientific output of the facility. The project scope includes the design, construction, installation, and commissioning of the following accelerators: a 200 MeV linac, a booster synchrotron operating from 200 MeV to 3.0 GeV, and the storage ring which stores a maximum of 500 mA current of electrons at an energy of 3.0 GeV. It is planned to operate the facility primarily in a top-off mode, thereby maintaining the maximum variation in stored beam current to <1%. Because of the very demanding requirements for beam emittance and synchrotron radiation brilliance, the beam life-time is expected to be quite low, on the order of 2 h. Analysis of the bulk shielding for operating this facility and the input parameters used for this analysis have been discussed in this paper. The characteristics of each of the accelerators and their operating modes have been summarized with the input assumptions for the bulk shielding analysis.     

The ToF system for the PAMELA experiment: In flight performances

A Time of Flight (ToF) scintillator system has been developed for the PAMELA satellite-borne cosmic ray experiment. The main scientific goal of the experiment is the measurement of the antiproton and positron fluxes in the cosmic radiation over large energy ranges. The ToF system provides the fast trigger to the experiment, the rejection of albedo particles and the possibility to distinguish electrons from antiprotons up to about 1.5 GeV.In this paper we describe the performances of the ToF system measured on flight data.     

Measurements and calculations on the shielding effect of small slabs for 14 MeV neutrons

The shielding effect of small slab assemblies containing graphite, lead, lithium fluoride and uranium has been tested for 14 MeV source neutrons. Emergent neutron spectra were measured with an NE213 scintillation counter and gamma ray events were rejected by pulse shape discrimination. Calculations have also been made using the one-dimensional transport code ANISN and the ZZFEWG1/31-1F cross section data set, which is in P3 form, over the energy range 14 to 1.8 MeV. The small slabs with a point neutron source were simulated by using a spherical calculation with a nonreflecting inner boundary. Agreement between measurement and calculation indicates that at least for the materials studied the cross section set and calculation model are suitable for studying the behaviour of thin shields, such as sections of a fusion reactor blanket.     

建立质量考核制度的原则和方法(二)

本刊上期介绍了质量考核制度的特点与建立,本期将从建立质量考核制度的原则和方法方面提供一些思路。一、确定本组织质量管理和考核方面的基本思路首先,要明确组织的宗旨、机构性质、方针目标、发展方向等,也就是机构对自己要有一个明确的     

The resistance curve for subcritical cracks near the threshold

Thermodynamic analysis of brittle fracture specimens near the threshold developed by Rice (Thermodynamics of quasi-static growth of Griffith cracks, J Mech Phys Solid 26:61–78, 1978) is extended to specimens undergoing microstructural changes. The proposed extension gives rise to a generalization of the threshold concept that mirrors the way the resistance curve generalizes the fracture toughness. In the absence of experimental data, the resistance curve near the threshold is constructed using a basic lattice model.     

Three-dimensional shielding calculations for the IFMIF neutron source using a coupled Monte Carlo/Deterministic computational scheme

Shielding calculations for the International Fusion Materials Irradiation Facility (IFMIF) are complicated due to the geometrical complexity of the target system and the large-scale bulk shields around the source target. Three-dimensional shielding calculations were performed by using a newly developed Monte Carlo/Deterministic computational scheme. The neutron-photon fluxes and dose rate distributions in the back wall of the Test Cell and the access/maintenance room are presented and compared with previous shielding calculations. The results demonstrate that this coupled scheme is an useful computational tool for three-dimensional shielding analyses of complex and large nuclear facilities.     

Neutron and photon shielding benchmark calculations by MCNP on the LR-0 experimental facility

In the framework of the REDOS project, the space-energy distribution of the neutron and photon flux has been calculated over the pressure vessel simulator thickness of the LR-0 experimental reactor, Rez, Czech Republic. The results calculated by the Monte Carlo code MCNP4C are compared with the measurements performed in the Nuclear Research Institute, Rez. The spectra have been measured at the barrel, in front of, inside and behind the pressure vessel in different configurations. The neutron measurements were performed in the energy range 0.1-10 MeV. This work has been done in the frame of the 5th Frame Work Programme of the European Community 1998-2002.     

Magnetic shielding of a large volume for an experiment on quasi free neutron oscillation

Results of the shielding against the Earth's magnetic field on a large volume are given. The experimental procedure is based on a multilayer μ-metal shield and a series of correcting electric coils. A final average value of (8.1±4.4) mG is obtained in a volume of about 20 m³.     

方圆北楼太阳能空调系统设计

以方圆北楼空调供热综合系统设计为背景，在深入了解太阳能制冷和采暖原理的基础上，综述太阳能制冷技术的发展历史以及国内外研究现状，分析太阳能制冷循环和采暖的意义，并通过热力计算，选用平板型集热器、单级溴化锂制冷机组和平板型热水器为系统主要设备。另外还对该技术进行技术可行性和经济性分析，对于利用现有太阳能热水器技术开发制冷空调具有现实意义。     

The dose mapping system for the electromagnetic calorimeter of the BaBar experiment at SLAC

An array of 116 p-channel radiation-sensitive MOSFET transistors (RadFETs) has been commissioned for the BaBar experiment at the PEP-II accelerator at the Stanford Linear Accelerator Center (SLAC). The aim of this system is to map the integrated dose absorbed by different regions of the calorimeter during the course of the experiment. This paper reports the design, characterization and installation of the sensors and briefly describes the readout system designed by co-workers. The response at low doses and the temperature coefficient for 130 RadFETs has been determined. At a “read” current of 160 μA an average shift in voltage of 51±4 mV was measured at an integrated dose of 30 rad with a temperature coefficient of 2.3±0.3 mV/°C. Calibration for high doses is also described. The system provides a novel method for real-time measurements of the spatial distribution of ionizing radiation dose within a large particle physics experiment.     

A scintillation-solid state detector for a system for the complex monitoring and diagnostics of subcritical electronuclear equipment

A diagnostic instrument in which a combination of a plastic scintillator and a solid-state photomultiplier is used as a nuclear radiation detector, is described. The detector is designed to record x-ray, gamma-ray, and neutron radiation in experimental nuclear power plant.     

多层建筑中庭防排烟系统设计

介绍了某多层建筑(商场)中庭防排烟系统的设计，认为此类建筑的中庭应当设置防排烟设施，并有必要对其设置依据、方法、排烟量计算等相关问题开展深入的研究和讨论，制订出相应的规范条文。     

Multipoint Thomson scattering system for the extrap Z-pinch experiment

A Thomson scattering system for simultaneous measurements of the electron temperature and density at three different positions and at two different times during a single plasma shot has been developed for a Z-pinch experiment. The plasma in the pinch is characterized by densities in the range from 5 × 10²⁰ to 10²² m⁻³, temperatures up to 30 eV and a pinch radius of the order of 1 cm. The spatial resolution of three points with 3 mm between points is obtained by imaging the plasma onto a matrix of quartz optical fibres at the output slit of the spectrometer. Thus only one spectrometer is used together with 15 PM-tubes to detect the scattered radiation as well as the background radiation. Due to the relatively dense plasma prevailing in this Z-pinch discharge the number of scattered photons is large and the photon to electron conversion noise is small. Therefore the background radiation is the most important factor limiting the accuracy of the measurements.     

序列型地震作用下AP 1000核反应堆屏蔽厂房损伤灾变精细化分析

以AP1000核反应堆屏蔽厂房结构为研究对象,在单一和序列型地震动作用下对屏蔽厂房的整体动力灾变行为进行损伤评估,在此基础上基于分区理念,将其沿高度方向分为9个环带区(BS-1,BS-2,MS-1 ～ MS-7)、沿环带方向间隔15°划分24个子区(C1 ～C24),在序列型设计和超设计地震作用下探讨了各精细化子区域的...     

Neutron shielding calculations in a proton therapy facility based on Monte Carlo simulations and analytical models: criterion for selecting the method of choice

Proton therapy facilities are shielded to limit the amount of secondary radiation to which patients, occupational workers and members of the general public are exposed. The most commonly applied shielding design methods for proton therapy facilities comprise semi-empirical and analytical methods to estimate the neutron dose equivalent. This study compares the results of these methods with a detailed simulation of a proton therapy facility by using the Monte Carlo technique. A comparison of neutron dose equivalent values predicted by the various methods reveals the superior accuracy of the Monte Carlo predictions in locations where the calculations converge. However, the reliability of the overall shielding design increases if simulation results, for which solutions have not converged, e.g. owing to too few particle histories, can be excluded, and deterministic models are being used at these locations. Criteria to accept or reject Monte Carlo calculations in such complex structures are not well understood. An optimum rejection criterion would allow all converging solutions of Monte Carlo simulation to be taken into account, and reject all solutions with uncertainties larger than the design safety margins. In this study, the optimum rejection criterion of 10% was found. The mean ratio was 26, 62% of all receptor locations showed a ratio between 0.9 and 10, and 92% were between 1 and 100.     

铁镍合金对复合电磁屏蔽材料性能的影响

在导电组分中添加磁性合金粉末,利用复合效应增加电磁屏蔽材料的吸收损耗,以获得较好的屏蔽效能。通过在12%体积分数的金属镍粉中添加不同体积分数的FeNi合金,研究了复合材料中FeNi合金对电磁屏蔽效能的影响。实验结果表明,当加入4%体积分数的FeNi合金时,屏蔽效能最好。分析得出FeNi合金粉末的加入能够增加材料的磁导率,增加材料对电磁波的吸收,在提升屏蔽效能的同时达到低二次污染的目的。     

Measurement system for evaluation of the muon chambers for the LHCb experiment

In a detector with the complexity of the LHCb, where only for the muon system more than 1300 chambers, divided into 20 different types, will be used, resulting on more than 120 k channels to be readout, it is of crucial importance to study the many types of chambers to create a complete knowledge of the detector operation and to guarantee a high-quality performance during the experiment. To make it possible, a complete setup was built and a C++ based software was developed to carry out a set of measurements on the full-equipped chambers of the LHCb muon detector. The setup is made of front-end control electronics, high-voltage supply and acquisition circuitry while the software, running on a PC, remotely controls each element of the system and implements a number of automatized procedures to assess the main characteristics of the chambers.The main advantages of this system are its versatility and speed of measurement which are crucial to the experiment since there is the need to characterize every single chamber before final installation. Moreover, in this work it was proposed to measure the starting knee of the high-voltage operational plateau without the use of an external trigger by making use of the internal structure of the chambers. Two laboratories were prepared at CERN (European Laboratory for Particle Physics) to receive this system; one used to test chambers arrived from the CERN itself and the PNPI (Petersburg Nuclear Physics Institute) production sites, and one to test the chambers arrived from the INFN (National Institute of Nuclear Physics) production sites. In this document, the hardware and software setup will be presented together with the measurement-oriented implementations.     

A luminosity monitor system for the JETSET experiment at LEAR

A luminosity-monitor system for the JETSET experiment at LEAR is described. Four silicon-strip detectors are used as position sensitive devices to monitor the elastic p-scattering. The design concept, data-acquisition and results of the detector system are presented. On-line monitoring is used to assure the proper operation of the JETSET experiment.     

平面材料屏蔽效能的屏蔽房测试方法

针对目前一些新型平面屏蔽材料的特性和标准测试方法中存在的不足,提出了两种平面材料屏蔽效能的屏蔽房测试方法,为平面材料的屏蔽性能实验提供了完善的实验手段,为准确评估平面材料的屏蔽效能提供了实验途径.同时,为大型孔缝结构的耦合实验和防护设备的性能检测提供了实验平台.通过实际测试应用,证明了实验方法的有效性和合理性.