Field calibration studies for ionisation chambers in mixed high-energy radiation fields

The monitoring of ambient doses at work places around high-energy accelerators is a challenging task due the complexity of the mixed stray radiation fields encountered. At CERN, mainly Centronics IG5 high-pressure ionisation chambers are used to monitor radiation exposure in mixed fields. The monitors are calibrated in the operational quantity ambient dose equivalent H*(10) using standard, source-generated photon- and neutron fields. However, the relationship between ionisation chamber reading and ambient dose equivalent in a mixed high-energy radiation field can only be assessed if the spectral response to every component and the field composition is known. Therefore, comprehensive studies were performed at the CERN-EU high-energy reference field facility where the spectral fluence for each particle type has been assessed with Monte Carlo simulations. Moreover, studies have been performed in an accessible controlled radiation area in the vicinity of a beam loss point of CERN's proton synchrotron. The comparison of measurements and calculations has shown reasonable agreement for most exposure conditions. The results indicate that conventionally calibrated ionisation chambers can give satisfactory response in terms of ambient dose equivalent in stray radiation fields at high-energy accelerators in many cases. These studies are one step towards establishing a method of 'field calibration' of radiation protection instruments in which Monte Carlo simulations will be used to establish a correct correlation between the response of specific detectors to a given high-energy radiation field.     

A measuring system with a recombination chamber for neutron dosimetry around medical accelerators

A measuring system for dosimetry of neutrons generated around medical electron accelerators is proposed. The system consists of an in-phantom tissue-equivalent recombination chamber and associated electronics for automated control and data acquisition. A second ionization chamber serves as a monitor of photon radiation. Two quantities are determined by the recombination chamber--the total absorbed dose and the recombination index of radiation quality. The ambient dose equivalent, H*(10), or neutron absorbed dose in an appropriate phantom, can be then derived from the measured values. Tests of the system showed that a 0.5% dose contribution of neutrons to the absorbed dose of photons could be detected and estimated under laboratory conditions. Preliminary tests at the 15 MV Varian Clinac 2300C/D medical accelerator confirmed that the measuring system could be used under clinical conditions. The H*(10) of the mixed radiation was determined with an accuracy of approximately 10%.     

Reusable shielding material for neutron- and gamma-radiation

At neutron research facilities all around the world radiation shieldings are applied to reduce the background of neutron and gamma radiation as far as possible in order to perform high quality measurements and to fulfill the radiation protection requirements.The current approach with cement-based compounds has a number of shortcomings:“Heavy concrete” contains a high amount of elements, which are not desired to obtain a high attenuation of neutron and/or gamma radiation (e.g. calcium, carbon, oxygen, silicon and aluminum).A shielding material with a high density of desired nuclei such as iron, hydrogen and boron was developed for the redesign of the neutron radiography facility ANTARES at beam tube 4 (located at a cold neutron source) of FRM-II. The composition of the material was optimized by help of the Monte Carlo code MCNP5. With this shielding material a considerable higher attenuation of background radiation can be obtained compared to usual heavy concretes.     

Global students

Universities-internationally-are confronting a revolution. While these institutions of higher education have evolved over the past centuries, the pace of change has not been as rapid as it is at the moment. This a because, at one level, the culture is changing, universities are moving from institutions which have been based on print, and the written word, to institutions that are part of the new digital age. One of the most important shifts taking place in this new context is that students are systematically being redefined as clients. This is partly a result of the overall emerging pattern of 'user pays' which is characteristic of the new information-as-commodity era. But this classification of students as consumers, or clients, is going to result in a startlingly different educational practice and philosophy around the world. To start with, universities are going to have to put more value on teaching and this represents a considerable shift in position. Students increasingly have new power that they can exercise. They are no longer confined to local or national institutions. They can vote with their virtual feet; they can enrol in any online university around the world. Possibly at even less cost. As distinct from the past, students in the future are going to be faced with an embarrassment of courses, as universities across the world compete for their business and try to make the quality of their teaching a selling point     

Fail-safe ion chamber beam loss monitor system for personnel protection

A fail-safe beam loss monitor system has been designed for use in the Los Alamos Neutron Scattering Center (LANSCE) Radiation Security System (RSS). The latest version (Model III) has been in use since 1991. This system has been carefully designed to protect personnel from large radiation doses caused by errant beam conditions during beam transport. Due to limited shielding between the beam transport lines and occupied areas, personnel can safely occupy these areas only if the beam losses in the transport lines are sufficiently low. Although the usual solution is to increase the bulk shielding between the beam lines and the occupied areas, the physical dimensions of the site do not permit additional shielding to be added. In this paper we will discuss the design and implementation of the fail-safe beam loss monitor system.     

Measurement of surface temperature and emissivity by a multitemperature method for Fourier-transform infrared spectrometers

Surface temperatures are estimated with high precision based on a multitemperature method for Fourier-transform spectrometers. The method is based on Planck's radiation law and a nonlinear least-squares fitting algorithm applied to two or more spectra at different sample temperatures and a single measurement at a known sample temperature, for example, at ambient temperature. The temperature of the sample surface can be measured rather easily at ambient temperature. The spectrum at ambient temperature is used to eliminate background effects from spectra as measured at other surface temperatures. The temperatures of the sample are found in a single calculation from the measured spectra independently of the response function of the instrument and the emissivity of the sample. The spectral emissivity of a sample can be measured if the instrument is calibrated against a blackbody source. Temperatures of blackbody sources are estimated with an uncertainty of 0.2-2 K. The method is demonstrated for measuring the spectral emissivity of a brass specimen and an oxidized nickel specimen.     

Neutron measurements around storage casks containing spent fuel and vitrified high-level radioactive waste at ZWILAG

Spectrometric and dosimetric measurements were made around a cask containing spent fuel and a cask containing high-level radioactive waste at the Swiss intermediate waste and spent fuel storage facility. A Bonner sphere spectrometer, an LB 6411 neutron monitor and an Automess Szintomat 6134A were used to characterise the n-gamma fields at several locations around the two casks. The results of these measurements show that the neutron fluence spectra around the cask containing radioactive waste are harder and higher in intensity than those measured in the vicinity of the spent fuel cask. The ambient dose equivalents measured with the LB 6411 neutron monitor are in good agreement with those obtained using the Bonner spheres, except for locations with soft neutron spectra where the monitor overestimates the neutron ambient dose equivalent by almost 50%.     

远离航道海域低频海洋环境噪声垂直指向性

海洋环境噪声垂直指向性是声呐背景场的典型空间特性之一,既可体现噪声源的空间特性及其传播特性,还可用来反演海洋环境的特征参数。分析了南海某岛礁海域实测海洋环境噪声的垂直指向性,发现当接收阵远离航道时,低频海洋环境噪声垂直指向性的主瓣集中在-30°～30°范围内(0°对应水平方向),且水平方向不存在凹槽。基于舰船自动识别系统(Automatic Identification System, AIS)航船分布数据得到简化航道区域航船噪声源模型,利用3D射线声传播算法,结合实际岛礁海域地形数据,计算的低频海洋环境噪声垂直指向性与实测数据处理结果相符。研究结果表明,当接收阵距航道较远时,由航道航船引起的低频海洋环境噪声以接近水平方向入射垂直接收阵,研究结果可为声呐在远离航道海域的性能提高提供技术支持。     

External doses in the environment from the Tokai-mura criticality accident

On 30 September 1999, a criticality accident occurred at a uranium processing plant operated by JCO in Tokai-mura, Japan and the criticality remained for about 20 h. Almost all doses to the neighbouring residents were brought by neutrons and gamma rays emitted from the facility rather than fission products released to the environment. External doses in the environment were evaluated using radiation monitoring data and radiation transport calculation. A pattern of the dose rate evolution was modelled based on the records of gamma ray monitors in the JCO facilities. Relations between the ambient dose equivalent rates of neutrons/gamma rays and the distance from the facility were determined from the monitoring data obtained around the accident site. Conversion from the ambient dose equivalent to the effective dose equivalent was made assuming the energy spectra calculated by the radiation transport code, ANISN. It was estimated that the people who stayed outside the 350 m zone would receive doses of less than 1 mSv.     

Indoor radon and thoron levels in Neendakara and Chavara regions of southern coastal Kerala, India

Some areas of the world, called high background radiation areas (HBRAs), have anomalously high levels of natural background radiation and the population residing in the areas is exposed to higher levels of radiation doses than other parts of the world where the natural radioactivity contents are normal. In the present investigation, levels of radon, thoron and their progeny are studied in 110 houses in the coastal region of the Kollam district in the state of Kerala, India using the multi-detector twin cup dosimeter. Among these, 10 houses were studied in detail with five dosimeters in each house. Radon activity concentrations were found to vary from 7 to 100 Bqm(-3) and that of thoron from 4 to 66 Bqm(-3) in Neendakara panchayat. In Chavara panchayat, the variations of radon concentrations were from 7 to 83 Bqm(-3) and thoron concentrations were varied from 4 to 86 Bqm(-3). The occurrence of radon and thoron concentrations in the dwellings for both study areas shows that in 50% of the dwellings, the concentration of radon is about 25 Bqm(-3) and in 60% of the dwellings thoron concentration is about 15 Bqm(-3). The ratio of thoron-to-radon concentrations in the dwellings showed a mean value 0.55 (GM=0.45) for the region.     

A wide-range direction neutron spectrometer

A new device is presented which has been developed for measuring the energy and direction of distribution of neutron fluence in fields of broad energy spectra (thermal to 100 MeV) and with a high background of photon, electron and muon radiation. The device was tested in reference fields with different energy and direction distributions of neutron fluence. The direction-integrated fluence spectra agree fairly well with reference spectra. In all cases, the ambient and personal dose equivalent values calculated from measured direction-differential spectra are within 35% of the reference values. Independent measurements of the directional dose equivalent were performed with a directional dose equivalent monitor based on superheated drop detectors.     

In situ long-term monitoring system for radioactive contaminants

A long-term in situ subsurface instrument for monitoring radioactive contaminant plumes, as an alternative to soil analysis, is described. A portable, laser-based reader optically stimulates luminescence from sensors, each containing an Al2O3:C dosemeter. The sensors, designed for placement at various subsurface locations around a waste site, are allowed to accumulate dose for a predetermined time that is based on the instrument's minimum detectable dose (MDD). The reader is then attached to the sensor by fibre optic cable to read the accumulated dose; an increase above natural background levels indicating the presence of leaked radioactivity. Based on an MDD of 5 microGy, it is shown that the sensor can measure soil concentrations of 1.85 Bq cm(-3) after an exposure time of 50 h for 137Cs and 67 h for 90Sr/90Y. Discrimination between beta and gamma radiation is possible using an end cap placed over one of the two paired sensors, allowing simultaneous measurement of 137Cs and 90Sr/90Y in a mixed field. The monitor system represents a substantial improvement over quarterly soil sampling because of a greatly increased measurement frequency and the ability to perform measurements reproducibly.     

Examination of issues related to the development and implementation of real-time operational safety monitoring tools in the nuclear power industry

In recent years, risk and reliability techniques have been increasingly used to optimize deterministic requirements and to improve the operational safety of nuclear power stations. This paper discusses the historical development and current status of implementation of real-time operational safety monitoring tools in the nuclear power industry worldwide. A safety monitor is defined as a PC-based risk management tool, based on a plant specific PSA, which can be used to manage plant safety during the day-to-day operation of a nuclear power plant by planning maintenance activities and providing advisory information to plant operational staff in order to avoid high risk plant configurations. As this technique has only been applied in a few plants worldwide, the technology is still evolving and there are several technical and implementation-related issues which still need to be resolved. This paper attempts to summarize all such issues and describe how they have been addressed in several different applications of this technology around the world.     

Activity Concentration of 137Cs in soil samples from Punjab province (Pakistan) and estimation of gamma-ray dose rate for external exposure

Punjab is one of the most populated provinces of Pakistan having 34 districts. There is always a need to have baseline background level information about 137Cs and the corresponding gamma-ray doses to the population. In this respect, soil samples were collected to a depth of 30-50 cm from all 34 district headquarters of the Punjab province of Pakistan and 137Cs activity concentrations were measured. 137Cs activity concentration was found to be in the range from 1.1 +/- 1.0 to 5.3 +/- 2.5 Bq kg(-1). The average value of estimated external gamma-ray dose rate from all 34 districts of Punjab province was computed to be 0.18 +/- 0.07 nSv h(-1) from 137Cs in soil samples. The measured 137Cs activity concentration range was compared with the reported ranges in the literature from some of the other locations in the world. Results obtained in this study show that 137Cs concentration is of a lower level in the investigated area. The average value of estimated external effective dose rate is found far below the dose rate limit of 1.0 mSv y(-1) for members of the general public recommended by the International Commission on Radiological Protection (ICRP) as well as the external gamma radiation dose of 0.48 mSv y(-1) received per head from the natural sources of radiation assessed by UNSCEAR (2000). It is concluded that 137Cs soil contamination does not pose radiation hazards to the population in the investigated areas.     

红外辐射温度计的辐射源尺寸效应修正

红外辐射温度计在低温测量的辐射源尺寸效应（SSE） 的规律不同于高温测量。基于以虚拟探测器温度消除背景辐射影响的SSE计算模型,推导了在不同源尺寸和不同背景条件下辐射温度计输出的SSE影响修正公式;得出不同源尺寸条件下辐射温度计温度示值的SSE影响修正的理论解析表达式。在源温度低于或接近背景温度时修正模型与高温测量SSE修正模型有显著差异。所得结果适用于任意温度下对单波段辐射温度计的SSE影响修正。     

面向畲族地区的创新发展模式设计

目的在社会发展的进程中,关注少数民族地区的生存问题,充分整合其特色的当地资源,以创新的发展模式来适应社会的进步,有利于少数民族文化的传承和发展。方法以人口较少的畲族为研究对象,对其历史背景、社会环境及文化内容等多方面进行研究。采用以设计介入的方式探究社会创新理论应用于少数民族地区文化传承中的可能性,并针对文成县畲族地区的具体情况进行调研,提炼出地区品牌以服务设计为导向的可持续创新方法,构建出符合当地情况并以文化发展为主的服务生态系统。结论社会创新可以成为少数民族地区发展的战略工具,以此来打造体验模式、民族品牌、生产模式及服务设计等各个层面,成为少数民族地区获得可持续发展的方法之一,进而拉动少数民族地区的经济发展,以期为其他少数民族地区的发展提供借鉴,促进各民族文化繁荣。     

Simulation of secondary particle production and absorbed dose to tissue in light ion beams

During radiation therapy with an ion beam, the production of secondary particles like neutrons, protons and heavier ions contribute to the dose delivered to tumour and healthy tissues outside the treated volume. Also, the secondary particles leaving the patient are of interest for radiation background around the ion-therapy facility. Calculations of secondary particle production and the dose absorbed by water, soft tissue and a multi-material phantom simulating the heterogeneous media of the patient body were performed for protons, helium, lithium and carbon ions in the energy range up to 400 MeV u(-1). The Monte Carlo code SHIELD-HIT for transport of protons and light ions in tissue-like media was used in these studies. The neutron ambient dose-equivalent, H*(10), was determined for neutrons leaving the water phantom irradiated with different light ion beams. The comparison of calculated secondary particle production in the water and PMMA phantoms irradiated with helium and carbon ions shows satisfactory agreement with experimental data.     

Easy ambient sonic-spray ionization mass spectrometry combined with thin-layer chromatography

On-spot detection and analyte characterization on thin-layer chromatography (TLC) plates is performed via ambient desorption/ionization and (tandem) mass spectrometry detection, that is, via easy ambient sonic spray ionization mass spectrometry (EASI-MS). As proof-of-principle cases, mixtures of semipolar nitrogenated compounds as well as pharmaceutical drugs and vegetable oils have been tested. The technique has also been applied to monitor a chemical reaction of synthetic importance. EASI is the simplest and gentlest ambient ionization technique currently available, assisted solely by N2 (or air). It uses no voltages, no electrical discharges; no UV or laser beams, and no high temperature and is most easily implemented in all API mass spectrometers. TLC is also the simplest, fastest, and most easily performed chromatographic technique. TLC plus EASI-MS therefore provide a simple and advantageous combination of chromatographic separation and sensitive detection of the TLC spots as well as on-spot MS or MS/MS characterization. The favorable characteristics of TLC-EASI-MS indicate advantageous applications in several areas such as drug and oil analysis, phytochemistry and synthetic chemistry, forensics via reliable counterfeit detection, and quality control.     

Measurement of natural background radiation intensity on a train

This work aims to measure different components of natural background radiation on a train. A radiation measurement system consisting of four types of radiation detectors, namely, a Berkeley Lab cosmic-ray detector, moderated (3)He detector, high-pressure ionisation chamber and NaI(Tl) spectrometer, associated with a global positioning system unit was established for this purpose. For the commissioning of the system, a test measurement on a train along the railway around the northern Taiwan coast from Hsinchu to Hualien with a distance of ～ 275 km was carried out. No significant variation of the intensities of the different components of natural background radiation was observed, except when the train went underground or in the tunnels. The average external dose rate received by the crew of the train was estimated to be 62 nSv h(-1).