bluuebunny/crossref_metadata_2025 huggingface dataset:
Controlling the conductance of molecular junctions using proton transfer reactions: A theoretical model study
Authors: Hofmeister Chriszandro , Coto Pedro B. , Thoss Michael
Published: February 2017

The influence of an intramolecular proton transfer reaction on the conductance of a molecular junction is investigated employing a generic model, which includes the effects of the electric field of the gate and leads electrodes and the coupling to a dissipative environment. Using a quantum master equation approach it is shown that, depending on the localization of the proton, the junction exhibits a high or low current state, which can be controlled by external electric fields. Considering different regimes, which range from weak to strong hydrogen bonds in the proton transfer complex and comprise situations with high and low barriers, necessary preconditions to achieve control are analyzed. The results show that systems with a weak hydrogen bond and a significant energy barrier for the proton transfer can be used as molecular transistors or diodes.
Expectation values of single-particle operators in the random phase approximation ground state
Authors: Kosov D. S.
Published: February 2017

We developed a method for computing matrix elements of single-particle operators in the correlated random phase approximation ground state. Working with the explicit random phase approximation ground state wavefunction, we derived a practically useful and simple expression for a molecular property in terms of random phase approximation amplitudes. The theory is illustrated by the calculation of molecular dipole moments for a set of representative molecules.
First principles investigation of copper and silver intercalated molybdenum disulfide
Authors: Guzman D. M. , Onofrio N. , Strachan A.
Published: February 2017

We characterize the energetics and atomic structures involved in the intercalation of copper and silver into the van der Waals gap of molybdenum disulfide as well as the resulting ionic and electronic transport properties using first-principles density functional theory. The intercalation energy of systems with formula (Cu,Ag)xMoS2 decreases with ion concentration and ranges from 1.2 to 0.8 eV for Cu; Ag exhibits a stronger concentration dependence from 2.2 eV for x = 0.014 to 0.75 eV for x = 1 (using the fcc metal as a reference). Partial atomic charge analysis indicates that approximately half an electron is transferred per metallic ion in the case of Cu at low concentrations and the ionicity decreases only slightly with concentration. In contrast, while Ag is only slightly less ionic than Cu for low concentrations, charge transfer reduces significantly to approximately 0.1 e for x = 1. This difference in ionicity between Cu and Ag correlates with their intercalation energies. Importantly, the predicted values indicate the possibility of electrochemical intercalation of both Cu and Ag into MoS2 and the calculated activation energies associated with ionic transport within the gaps, 0.32 eV for Cu and 0.38 eV for Ag, indicate these materials to be good ionic conductors. Analysis of the electronic structure shows that charge transfer leads to a shift of the Fermi energy into the conduction band resulting in a semiconductor-to-metal transition. Electron transport calculations based on non-equilibrium Green's function show that the low-bias conductance increases with metal concentration and is comparable in the horizontal and vertical transport directions. These properties make metal intercalated transition metal di-chalcogenides potential candidates for several applications including electrochemical metallization cells and contacts in electronics based on 2D materials.
Strain-induced valley conductance recovery in four-terminal graphene device
Authors: Yang Mou , Zhang Wenlian , Wang Ruiqiang
Published: February 2017

We investigated the valley dependent transport properties of a zigzag graphene ribbon attached with two strained side arms. The conductance of the zigzag ribbon for each valley is increased by the strain of the side arms. On the curves of conductance versus energy, step-like structures appear in some energy intervals, and in such intervals, the conductance does not decay when increasing the length of the intersection region. By applying a strain exceeding a critical amount, the conductance of valley K (K′) for the negative (positive) energies can be recovered to that of a graphene ribbon without side arms attached. The critical strain is compressive and is evaluated as about −10%. We explained all the features by means of the energy dispersion of the injection ribbon and that of the strained region.
Fluorosilicene/chlorosilicene bilayer semiconductor with tunable electronic and optical properties
Authors: Yang Q. , Zhang S. L. , Chen X. P. , Cai M. , Tan C. J.
Published: February 2017

Using comprehensive density functional theory calculations, the structural, electronic, and optical properties of novel fluorosilicene/chlorosilicene (F-silicene/Cl-silicene) heterobilayer are investigated. Our results unveil that the presence of hetero-halogen bonding (Si-F···Cl-Si) has a remarkable influence on the F-silicene/Cl-silicene bilayer. The F-silicene/Cl-silicene heterostructure in the most stable pattern has a moderate band gap of 0.309 eV, lower than that of isolated halogenated silicene. Encouragingly, F-silicene/Cl-silicene heterobilayers all have a direct band gap nature, irrespective of the stacking pattern, thickness and external electric fields (E-fields), which is an advantage over MoS2 layers. In addition, applying appropriate E-field leads to a significant enhancement of binding strength of the F-silicene/Cl-silicene heterobilayer. Especially, the band gap of the F-silicene/Cl-silicene heterobilayer can be effectively modulated by E-fields, even a semiconductor–metal transition occurs. Moreover, the interfacial hetero-halogen interaction changes the optical properties of isolated halogenated silicene; the adsorption edge of imaginary part of the dielectric function displays a corresponding redshift in comparison with that of isolated halogenated silicene, which makes the F-silicene/Cl-silicene heterostructure active over the visible range. The complete electron-hole separation also enhances the photocatalytic efficiency of the F-silicene/Cl-silicene heterobilayer. Overall, the moderate band gap, effective band gap modification by external E-field, robust direct band gap nature, suitable band edge positions, and type-II band alignment enable the F-silicene/Cl-silicene heterobilayer to have great potential applications in the field of optical and nanoelectronic devices.
Ultrafast photocurrent measurements of a black phosphorus photodetector
Authors: Youngblood Nathan , Li Mo
Published: February 2017

With its high mobility, narrow bandgap, and unique anisotropy, black phosphorus (BP) is a promising material for optoelectronic applications. Waveguide-integrated photodetectors with RC-limited speeds up to 3 GHz have been recently demonstrated at telecom wavelengths. To truly be competitive, however, BP photodetectors must reach speeds of tens of GHz. Here, we use BP's nonlinear photoresponse to measure the intrinsic speed of a BP photodetector using ultrafast pump-probe measurements. With this technique, we are able to observe how the detection speed depends on both the incident power and applied source-drain bias. A minimum response time of 60 ps was observed which corresponds to an intrinsic bandwidth of 9 GHz.
Assessing the water-purification service in an integrated agricultural wetland within the Venetian Lagoon drainage system
Authors: Pappalardo S. E. , Ibrahim H. Mohammad Saad , Cerinato S. , Borin M.
Published: February 2017

Wetlands are a cornerstone of beneficial ecosystem services, especially in intensive agricultural landscapes characterised by nutrient loss, and shallow and surface water bodies. Water-purification services can trap 80–90% of the sediments and eliminate 70–90% of the entering nitrogen. An experimental wetland of 3.2ha was created within the Venetian drainage system to control nutrient loss from croplands and protect surface water bodies. The aims of the present study were to assess the water-purification service by monitoring nutrient runoff and testing the adaptability of seven macrophyte species in a floating treatment wetland system. Results showed that median concentrations of total nitrogen were 2.43ppm at the inlet and 1.79ppm at the outlet, whereas after an extreme rainfall event, total nitrogen concentrations were 6.34ppm at the inlet and 1.29ppm at the outlet. Carex spp. adapted best to the floating wetlands (433.13gm–2 of biomass production), followed by Lythrum salicaria (210.32gm–2). Carex spp. had the highest total nitrogen uptake (4.84gm–2), mostly in roots (3.19gm–2), followed by L. salicaria with 2.35gm–2. Constructed wetlands could, therefore, play a crucial role in integrated agro-environmental management to control nutrient runoff from intensive cropping systems.
Larval otolith growth histories show evidence of stock structure in Northeast Atlantic blue whiting (Micromesistius poutassou)
Authors: Brophy Deirdre , King Pauline A.
Published: February 2017

Brophy, D., and King, P. A. 2007. Larval otolith growth histories show evidence of stock structure in Northeast Atlantic blue whiting (Micromesistius poutassou). – ICES Journal of Marine Science, 64: 1136–1144. Oceanographic modelling studies suggest that blue whiting (Micromesistius poutassou) larvae released on the Northeast Atlantic spawning grounds split into two branches, one following a northerly drift trajectory and the second drifting towards the south. This mechanism is proposed to restrict gene flow between northern and southern stock components. This study examined larval growth histories recorded in otoliths of adult blue whiting from three regions of the main spawning area and three feeding areas for evidence of divergent dispersal pathways. Increment measurements show that fish from the south of the spawning area on average grew significantly faster as larvae than those from the north of the spawning area, confirming that blue whiting spawning west of Ireland and Scotland do not form a randomly mixing unit, and that larval dispersal influences the subsequent distribution of spawning adults. Larval otolith growth rates in feeding blue whiting from the Bay of Biscay were significantly faster than those of fish from the Norwegian Sea feeding grounds, showing that mixing of fish from these areas is limited. Fish from the Bay of Biscay grew faster as larvae than fish from all regions of the main spawning area. The results support the proposed split in the blue whiting stock and signal caution for managing the fishery.
Diet of harbour seals and great cormorants in Limfjord, Denmark: interspecific competition and interaction with fishery
Authors: Andersen Signe M. , Teilmann Jonas , Harders Pernille B. , Hansen Else H. , Hjøllund Dorthe
Published: February 2017

Andersen, S. M., Teilmann, J., Harders, P. B., Hansen, E. H., and Hjøllund, D. 2007. Diet of harbour seals and great cormorants in Limfjord, Denmark: interspecific competition and interaction with fishery. – ICES Journal of Marine Science, 64: 1235–1245. Comparative studies on seasonal and regional variation in the diet of harbour seals and great cormorants were conducted in Limfjord, a semi-closed water system in northwest Denmark. To compare harbour seal diet from an open water system containing similar prey species, a small diet analysis from the western Baltic is included. Seal diet during spring reflected the abundance of Atlantic herring entering Limfjord to spawn (90% of the weight consumed), whereas during summer and autumn, seal diet was rather more mixed. The diet of seals in the Rødsand area and cormorants in Limfjord showed no marked seasonal trends. During spring, there was little overlap between seal and cormorant diets in Limfjord because seals fed almost exclusively on Atlantic herring, and they consumed significantly larger herring than did the cormorants. During summer and autumn, seal and cormorant diets overlapped markedly, although the fish items consumed by seals were generally larger. Few commercially targeted species were found in the stomachs and scats of seals and casts of great cormorants, but Atlantic herring were taken by the seals at a size greater than that allowed by the fishery.
The Application of the New ICRU Quantities for TLD Personnel Monitoring
Authors: Duftschmid K.E. , Strachotinsky C.
Published: February 2017

The application of the new ICRU 39 quantities for a large TL personnel monitoring service has been studied. The comparison of the 'photon dose equivalent', used currently, with the new ICRU quantities for the energy range of 10 keVeff to 1250 keV (60Co) shows that the TLD system is readily suitable for the measurement of the new quantities. A simple calibration procedure based on the use of a cubic water phantom has been devised.
A Radiation Protection Service Using an Energy Discriminating Thermoluminescence Dosemeter
Authors: Curry R.G. , Dodson J. , Fernando F. , Sheppard R.M.
Published: February 2017

In collaboration with AEE Winfrith, Vinten Instruments has developed a 4-element TL dosemeter capable of measuring both skin and body dose and of estimating the effective energy of the incident radiation. This badge forms the basis of a Radiation Protection Service, using commercially available Vinten dosemeter readers and a minicomputer based recording keeping system. The service is operated by AEE Winfrith and an alternative 'main frame' record keeping system is available for long term record keeping. This paper reports on the hardware and software required for a commercial TLD system and the experience gained in its use.
Responses of Thermoluminescent Materials to Beta Radiation and Low Energy Photons
Authors: Francis T.M. , O'Hagan J.B. , Richards D.J. , Driscoll C.M.H.
Published: February 2017

The responses in terms of the individual dose equivalent, superficial, Hs(d), of a number of commercially available thermoluminescent materials to beta radiation were investigated and compared with the responses of the same materials to low energy photons. The maximum beta energies used ranged from 0.067 to 2.27 MeV and the photon energies ranged from 0.033 to 0.662 MeV. All irradiations were carried out on appropriate tissue-equivalent phantoms. The results of these studies serve to identify materials and configurations suitable for personal dosimetry in mixed beta-photon fields.
Chemiluminescence Accident Dosimetry with Drugs and Other Solid Materials
Authors: Hammermaier A. , Reich E. , Bögl W.
Published: February 2017

It has been shown that it is possible to measure radiation doses using the chemiluminescence (CL or lyoluminescence) of different solids. The purpose of this study was to find out whether chemiluminescence from drugs, as well as from other solid materials collected in the neighbourhood of a radiation accident, could be used to estimate the radiation dose to the people involved in the radiation accident. CL glow curves of 18 gamma ray irradiated powdered drugs were investigated. For seven selected pharmaceuticals, optimisation of the CL yield according to sample mass, pH of solution and concentration of luminol was performed. We found that with many powdered drugs, doses as low as about 1 Gy can be measured. The CL of 10 irradiated solid materials (hair, finger-nail clippings, chalk, cellulose, etc.) was investigated using luminol solutions. The results showed that it would be very difficult to observe a radiation induced chemiluminescence with doses of about 1 Gy, when using solid materials of minimum solubility in the luminol sensitiser system.
Auto-Regenerative TL Dating of Zircon Inclusions
Authors: Templer R.H.
Published: February 2017

Microscopic zircon crystals exist in small amounts in most pottery. Zircons are of particular interest because they are one of the few TL sensitive minerals whose palaeodose is almost entirely internal. Since the external dose normally contributes only 3% to the natural TL, errors introduced by uncertainties in the environmental dose rate are virtually eliminated. Because of their high internal dose rate one can date the last firing of the zircons by storing the grains for six months after measurement of the natural TL. During the storage a small TL signal will be auto-regenerated. The age is then given by Age = (Natural TL x storage time)/(Auto-regenerated TL). This technique overcomes the difficulties, encountered in the standard TL dating procedure, from zoned TL emission. However, this auto-regenerated TL signal is small, requiring the development of high sensitivity TL apparatus. A variety of samples have been successfully dated by this method, with dating accuracies of 4 to 45%. The results are reported here.
Use of Mohr's Salt for High Level Gamma Dosimetry (Up to 108 Gy)
Authors: Hickman C. , Lorrain S. , Barthe J.R. , Portal G.
Published: February 2017

Fricke's dosemeter, which has been used for many years as a transfer dosemeter for doses up to 400 Gy employs Mohrs salt Fe(SO4)2(NH4)26H2O in an ultra-pure solution. The originality of the method proposed is that the salt is irradiated in the solid state. Spectrophotometrc measurements are then made on the absorption peak (345 nm) of a solution of this salt in 0.1 N hydrochloric acid. The solution is more and more diluted as the dose increases in order to remain always under conditions where the Beer-Lambert law is applicable. Two series of experiments are described. In the first series, a 60Co source was used to irradiate small plastic containers filled with powdered Mohr salt. In the second series, 3 mm diameter glass tubes filled with powder were irradiated using a fuel element source (fuel elements from the OSIRIS reactor) which enabled very high integrated doses to be reached. The decaying fission products of this latter irradiator required regular determinations of the corresponding dose rates during irradiation. Alanine ESR dosimetry was used for this purpose. The method proposed is simple, cheap and accurate. A comparison with single crystal LiF measurements is made.
The Design Philosophy for an Automatic TLD System to Meet Current International Specifications
Authors: Haaslahti J.
Published: February 2017

The object of this paper is to describe the elements of a new automatic TLD system intended to meet draft IEC/ISO proposals and ANSI requirements in the USA. Dosemeter badge design is based on ICRU recommendations. The basic intent has been to produce a standard system that can measure and file raw data that can be adapted to specific user requirements with software. The system consists of a programmable automatic reader, an automatic irradiator, a computer, and dosemeters for environmental, whole body, extremity, and clinical applications. The reader uses hot nitrogen heating and photon counting, and measurement conditions may be chosen with complete freedom. The reader can produce a real-time glow curve to assist in checking performance. Both reader and irradiator have an extremely simple mechanical system to allow user self-service and maintenance. The irradiator has a 90Sr-90Y source to permit programmed irradiation for calibration and materials sensitivity checks. Cassettes are used to hold TLD cards during processing. Cassette coding both identifies samples and calls measurement parameters into use from memory. The system can be programmed to measure all common materials and all common dosemeter elements (both square and round).
Analysis of Thermoluminescence Glow Curves of Mineral Sphene and Epidote for Radiation Damage Studies
Authors: Khalifa M.S. , Al-Khalifa I.J.M. , Durrani S.A.
Published: February 2017

Thermoluminescence (TL) properties of sphene and epidote are of interest in studies related to their radiation damage. Natural and artifically induced TL of these minerals has, therefore, been investigated. Both minerals exhibit complex glow curves with several overlapping peaks. The Tm-TSTOP thermal cleaning procedure has revealed three peaks in the ? ray induced glow curve of each mineral. That these peaks obey second order kinetics was indicated by the continuously slanting structure of the Tm-TSTOP curve. The TL parameters E and s have been calculated using (i) the initial rise method, and (ii) the glow-peak shape method. In general, the values of E calculated by the first method are found to be higher than those from the second. The TL curve-fitting method is also applied in order to calculate these parameters and to serve as a cross-check on the results.
Initial Spectra of Neutron-Induced Secondary Charged Particles
Authors: Gerstenberg H.M. , Caswelll R.S. , Coyne J.J.
Published: February 2017

Calculations have been made of the initial spectra of secondary charged particles which result from neutron interactions with materials such as tissue. These secondary particles are ions of H, D, He and the heavier recoil ions of Be, B, C, N and O. The spectra of the ions have been determined in 200 keV neutron energy bin sizes between 0 and 20 MeV as well as for 76 almost-logarithmic bins extending from thermal energy to 2 MeV. The primary input for these calculations is the ENDF/B-V nuclear data file from the National Nuclear Data Center at Brookhaven. Additional supplementary information is also needed on the angular distribution of neutron reactions leading to charged particles and on the final excitation of residual nuclei. Recently measured kerma factors in carbon disagree with those calculated using the nuclear cross section data from ENDF/B-V by as much as 25% in the region between 14 MeV and 18 MeV. A recently made evaluation of the carbon cross sections in the energy region between 5 MeV and 32 MeV is used here to calculate kerma and initial spectra at neutron energies of 16.9, 14.9, and 13.9 MeV; the results are then compared with that obtained using the ENDF/B-V data.
An Analytic Model for Ionisation Distributions Produced in Nanometre Volumes by Recoil Protons
Authors: Wilson W.E. , Paretzke H.G.
Published: February 2017

A concise mathematical model is presented for the fast computation of microdosimetric distributions for the number of ionisations produced in sub-cellular volumes by energetic protons of 0.3 to 20 MeV. The model is based on the results of extensive Monte Carlo computer simulations of charged particle tracks and can be used to take into account, with only a small computing effort, straggling and delta ray transport effects in the nanometre dosimetry of neutrons.
Restricted LET Remains a Good Parameter of Radiation Quality
Authors: Harder D. , Blohm R. , Kessler M.
Published: February 2017

A suitable physical parameter of radiation quality must represent not only the mean but also the fluctuation of the energy deposition per particle passage through that microscopic site of tissue in which proximity between radiation-induced lesions is decisive for the action mechanism. For sites of nanometre dimensions restricted LET is considered to have this property because (a) the distribution moments j and j2/j of the number j of ionisations per delta ray within the site are almost independent of the type and energy of the primary particle, and (b) the Poisson fluctuation of the number of primary ionisations within the site is determined by its mean value, which is proportional to restricted LET. Corresponding to this theoretical qualification as a suitable parameter, restricted LET has been experimentally identified as determining the yield factor a of various cellular radiation effects.
Model Calculations for Electrochemically Etched Neutron Detectors
Authors: Pitt E. , Scharmann A. , Werner B.
Published: February 2017

Electrochemical etching has been established as a common method for visualisation of nuclear tracks in solid state nuclear track detectors. Usually the Mason equation, which describes the amplification of the electrical field strength at the track tip, is used to explain the treeing effect of electrochemical etching. The yield of neutron-induced tracks from electrochemically etched CR-39 track detectors was investigated with respect to the electrical parameters. A linear dependence on the response from the macroscopic field strength was measured which could not be explained by the Mason equation. It was found that the reality of a recoil proton track in the detector does not fit the boundary conditions which are necessary when the Mason equation is used. An alternative model was introduced to describe the track and detector geometry in the case of a neutron track detector. The field strength at the track tip was estimated with this model and compared with the experimental data, yielding good agreement.
Progress Towards a European Filtered Neutron Beam Facility
Authors: Harvey J.R. , Mill A.J.
Published: February 2017

A feasibility study of a filtered neutron beam facility on the high flux reactor at the Petten establishment of the Joint Research Centre of the Commission of the European Communities has been undertaken. The facility would, in the first instance, have eight beams with energies ranging from 100 eV to 120 keV, and three possible irradiation geometries. It would have a range of applications in science, technology and medicine. The replies to a questionnaire on probable utilisation, recently distributed in Europe by the Commission of the European Communities, are analysed.
Photoneutron Production and Dosimetry in Tissue During High Energy Bremsstrahlung Radiotherapy
Authors: Allen P.D. , Chaudhri M.A.
Published: February 2017

The total yield of photoneutrons from soft-tissue-equivalent material irradiated with bremsstrahlung of end point energy from 6 MeV to 28 MeV has been measured using the 35 MeV University of Melbourne Betatron and a 4p Halpern type neutron detector. The results are compared with calculations based on the cross sections for neutron production of the constituent elements of tissue (H, C, N and O). It is shown that the less common isotopes of the constituent elements (2H, 13C, 15N, 17O, 18O) must be included to obtain agreement with the measured yields. The dose imparted to tissue by the photoneutrons is estimated for the energy range from 6 MeV to 30 MeV and compared with other available measurements/estimations. Further, the dose equivalent due to all photonuclear reactions in tissue is estimated for energies of 24 MeV and 30 MeV.
Applicability of TLD-700 Detectors for Dosimetry in d(14)+Be Neutron Fields
Authors: Meissner P. , Bienek U. , Rassow J.
Published: February 2017

The glow curve of TLD-700 at higher temperatures has its main maximum at about 200 oC. At about 270 oC there is a much smaller second peak. These two peaks exhibit different LET dependences. For photons both peaks are supralinear. In this work the photon and neutron sensitivities for neutrons which were produced by bombarding a thick beryllium target with 14 MeV deuterons (d(14)+Be neutrons) and for gamma rays are determined in the dose range up to 2.1 Gy which is relevant for clinical neutron dosimetry. In addition the two peak method used for TLD-300 is transferred to TLD-700 and the accuracy of the dose determination is tested.
Experience in Neutron Dose Measurements with Mailable Pin Diodes
Authors: Reft C.S. , Kuchnir F.T.
Published: February 2017

We have investigated the performance characteristics of PIN diodes as neutron dosemeters. Data were obtained on dose response as a function of accumulated dose and neutron beam quality. We have studied fading characteristics at room temperature and developed a technique for partially annealing the radiation damage. After two years of experience with PIN diodes we tested them for their usefulness as mail dosemeters among the six neutron therapy facilites in the United States. Our results show that intercomparison of calibrated neutron beams is achievable with a precision of ±3%.
Radon Exhalation from the Soil
Authors: Keller G. , Schütz M.
Published: February 2017

The exhalation of radon from the soil is the main source for high radon concentration in dwellings. A study of the mechanism of exhalation, its dependence on various parameters and the entry points for radon in houses are presented. Electrostatic deposition of the radon daughter products on a surface barrier detector and subsequent analysis of the measured alpha spectra allows one to determine the exhalation rates of 222Rn and 220Rn directly from the soil. For a sampling time of two hours, the lower limit of detection of our equipment was found to be 0.3 x 10-3 Bq.m-2.s-1 for 222Rn. In the south-west part of Germany, the 222Rn exhalation rates from the soil vary approximately between 2 x 10-3 and 100 x 10-3 Bq.m-2.s-1. The water content of the investigated soil, its actual porosity and its radium content determine the radon migration through the pores. For example in regions with volcanic rocks the exhalation rates are up to 10 times higher than in sandstone areas. Some special constructive measures to reduce the entry of radon in buildings are proposed.
A Simple Model for Estimating the Mixing Depth from the Diurnal Variation of Atmospheric 222Rn Concentration
Authors: Fujinami N. , Esaka S.
Published: February 2017

A simple model is proposed for estimating the mixing depth from the diurnal variation of 222Rn concentration in surface air. The comparison is described between the mixing depth calculated with the model and that determined from observations of temperature profiles with rawinsondes, which indicates good agreement.
Uranium in Humans
Authors: Fisenne I.M. , Perry P.M. , Harley N.H.
Published: February 2017

Measurements of the environmental and metabolic behaviour of the naturally occurring radionuclides have provided necessary information on the behaviour of stable elements and have been useful analogues in the study of man-made radionuclides. Uranium has been studied primarily because of its role in the nuclear industry and its possible effects as a heavy metal in occupational exposure cases. There is abundant literature dealing with uranium studies in animals, and some literature on human studies with chronically ill patients. Relatively few data are available which document the uranium concentrations in humans under chronic, low level environmental conditions. Some recent bone measurements performed at the US Department of Energy, Environmental Measurements Laboratory are presented. For comparison, a summary of published information on uranium concentrations in blood, soft tissues and bones of humans is also presented. These data are selected to eliminate results from areas of known elevated natural radionuclide levels and occupational or controlled experimental exposure cases. From the measurements of the uranium concentration in bone from 12 countries, it is possible to derive a cumulative frequency distribution for the sampled populations.
The Flow and Diffusion of Radon Isotopes in Fractured Porous Media: Part 1, Finite Slabs
Authors: Schery S.D. , Holford D.J. , Wilson J.L. , Phillips F.M.
Published: February 2017

In the conventional equations used to describe gaseous transport of radon isotopes through fractured porous media the two processes responsible for radon movement are diffusion and pressure-driven flow (advection). Fractures in a porous medium can be especially effective for pressure-driven transport but lateral diffusion can be a strong mitigating influence. The interplay of diffusion and flow is examined for a fractured concrete slab and a fractured, high-diffusivity layer between a house and an underlying radium-rich medium. For underpressures common in houses, fractures only a fraction of a millimetre wide in concrete are important and often big enough to ensure flow transport of radon with small diffusive loss. In contrast, fractures several millimetres wide through high-diffusivity layers several metres thick such as sand may be unimportant for radon transport due to large lateral diffusive losses.
Comparison of Predicted and Measured Variations of Indoor Radon Concentration
Authors: Arvela H. , Voutilainen A. , Mäkeläinen I. , Castrén O. , Winqvist K.
Published: February 2017

Prediction of the variations of indoor radon concentration were calculated using a model relating indoor radon concentration to radon entry rate, air infiltration and meteorological factors. These calculated variations have been compared with seasonal variations of 33 houses during 1-4 years, with winter-summer concentration ratios of 300 houses and the measured dirunal variation. In houses with a slab in ground contact the measured seasonal variations are quite often in agreement with variations predicted for nearly pure pressure difference driven flow. The contribution of a diffusion source is significant in houses with large porous concrete walls against the ground. Air flow due to seasonally variable thermal convection within eskers strongly affects the seasonal variations within houses located thereon. Measured and predicted winter-summer concentration ratios demonstrate that, on average, the ratio is a function of radon concentration. The ratio increases with increasing winter concentration. According to the model the diurnal maximum caused by a pressure difference driven flow occurs in the morning, a finding which is in agreement with the measurements. The model presented can be used for differentiating between factors affecting radon entry into houses.
Preliminary Survey of Indoor Radon Concentrations in Portuguese Houses from High Natural Radioactivity Regions
Authors: Faisca M.C. , de Bettencourt A.O.
Published: February 2017

The exploration of uranium ore started in Portugal at the beginning of the century, firstly for the extraction of radium and later for uranium. Radium processing wastes, uranium tailings, and their possible use in buildings contribute significantly to the enhancement of radon levels. A screening survey of indoor radon concentrations is initiated in houses from the granitic region of Beira Alta, in particular in the surroundings of an abandoned radium salts factory, near the mine and chemical treatment installations of Urgeirica, and the town of Guarda. Passive detectors are exposed for periods of one to two months. The preliminary results of this survey programme are presented and discussed. Indoor levels up to the order of 3 x 103 Bq.m-3 have been detected at Urgeirica as well as near the old radium salts factory at Barracao. These concentrations are compared with results for houses from the town of Guarda and also for some houses from the region of Lisbon.
Radon in an Alum Shale Rich Norwegian Area
Authors: Stranden E. , Strand T.
Published: February 2017

Alum shale is known to contain enhanced levels of radium, and may thus be a source of enhanced radon concentrations. The Hedemarken area in the south-eastern part of Norway has, due to its high geological occurrence of alum shale, been the subject of an extensive study on indoor radon. Measurements of the activity concentration of soil and shale, radon exhalation from the ground and from geological samples, are reported, together with measurements of indoor radon concentrations in about 200 houses. In about 70 houses, the radon concentration exceeded 400 Bq.m-3, and the highest concentration (mean value for a house) was 5300 Bq.m-3. Radon exhalation measurements from the ground suggest that the alum shale areas generally should be classified as high radon risk areas.
The Search for Radon Sources, A Multidisciplinary Task
Authors: Surbeck H.
Published: February 2017

In a city in the Swiss Jura, well known for its watch industry, there are high 222Rn concentrations in many houses (up to 4 kBq.m-3 in living rooms). Clear 226Ra contamination is present in and near former workshops that had processed radium activated paint, but enhanced radon levels are also measured in houses free from any contamination; thus the origin of the radon problem in this city is by no means clear. The methods used to localise the radium sources, to reveal the origin (natural or artificial) and to study the radon transport to the houses are presented.
Strategies to Reduce Exposure to Indoor Radon
Authors: Castrén O.
Published: February 2017

Various possible national strategies are analysed as to their cost-effectiveness. The estimated cost per averted collective dose, irrespective of who is juridically responsible for the cost, is used as a measure of the rationality of the strategy. The results show that the most cost-effective strategy is to find the dwellings with the highest indoor radon concentrations and to reduce the radon entry into them from the ground. Preventing radon entry into new houses does not seem to be as cost-effective as repairing existing houses. This is mainly due to the cost and difficulty of identifying in advance the building sites where an unacceptable level of concentration will occur unless preventive measures are taken. The analysis also shows that random sampling cannot be recommended for performing large scale surveys in a country with large geographical differences in radon occurrence. The sampling density should be higher in areas with higher concentrations.
Radon Reduction Techniques for Finnish Small Houses
Authors: Lehtoviita T.
Published: February 2017

The general principles and design methods of developed radon gas reduction techniques for Finnish small houses are discussed. Most of these methods have been worked out since 1984 in the Laboratory of Structural Engineering and Building Physics at the Helsinki University of Technology in cooperation with the Ministry of the Environment, the Finnish Centre of Radiation and Nuclear Safety and private building material companies. This work has concerned basic research and some practical development projects concerning radon gas reduction methods for existing dwellings and new detached houses. The results have been very encouraging. As a result of these research projects reports and guidebooks have been published in which the developed reduction techniques are presented. Also a design method of groundbased structures based on radon classification of soil has been developed. This article is a review of the results achieved.
Radon Reduction in Homes: Research Phase to Operational Phase
Authors: Mardis H.M. , Guimond R.J. , Fisher E.
Published: February 2017

The United States Environmental Protection Agency's (USEPA) House Evaluation Program (HEP) is an on-going programme designed to transfer research findings on radon diagnostic and mitigation technologies to the general public. The HEP accomplishes this technology transfer by providing guidance and hands-on training to States, homeowners, and local contractors while conducting radon diagnostics and mitigation design planning in houses. An overview of the HEP is given and the programme's accomplishments and findings to date are discussed.
Towards an Ab Initio Evaluation of the Wave-Vector- and Frequency-Dependent Dielectric Response Function for Crystalline Water
Authors: Zaider M. , Fry J.L. , Orr D.E.
Published: February 2017

We describe an ab initio calculation of the properties of energy loss by electrons in crystalline water using its dielectric response function, e(q), ?), where q and ? are, respectively, the wave vector and frequency. The calculation was performed on a model system (cubic ice) in order to take advantage of its ordered structure (i.e. Bloch's theorem), but also because of evidence that liquid water in biological systems ('structured' water) contains residues with tetrahedral structure (i.e. ice) over time scales of at least 10-11 s. The main features of the calculation are: (a) e(q,w) is evaluated in the random phase approximation (we used the expression given by Ehrenreich and Cohen), (b) the crystal potential is expressed as a sum of water-molecule self-consistent potentials, and (c) wave functions are expanded using tight binding functions (ultimately employing a Gaussian base set). A total of seven states (bands), five occupied and two conduction, are considered. We report the band structure and the density of states of the crystal, as well as values of e(q,w) at selected values of q and w. Results are compared with energy loss measurements and with absorption spectra (XPS, UPS, and VUV data). The possibility of using an empirical combination of molecular potentials as a phenomenological Hamiltonian is also examined.
Determination of Photon and Neutron Dose Fractions with Tissue-Equivalent Proportional Counters
Authors: Schrewe U.J. , Schuhmacher H. , Brede H.J. , Dietze G.
Published: February 2017

The separation of dose fractions due to neutrons and photons by means of tissue-equivalent proportional counters was investigated for ten different neutron fields. Nearly monoenergetic neutrons of energies between 12 keV and 1.2 MeV were produced by 7Li(p,n)7Be and 3H(p,n)3He reactions using pulsed proton beams. Time-of-flight (TOF) techniques were applied to distinguish between prompt neutrons and prompt photons originating from the neutron source. Dose fractions caused by the room background radiation were separated and subtracted. The dose distributions, d(y), obtained for prompt neutrons could therefore be analysed in the whole range of lineal energies, y, which overlap with events from photons. The logarithm of y.d(y) was found to be proportional to the logarithm of y. The slopes depend only slightly on the neutron energy. The experimentally determined shape of the dose distribution was compared with theoretical ion yield spectra. A procedure for separating neutron-photon dose fractions is discussed which does not require TOF techniques.
Analysis of Biological Effectiveness of Heavy Ions Using Two Microdosimetric Approaches
Authors: Waligorski M.P.R. , Morstin K. , Bond V.P. , Baum J.W.
Published: February 2017

Experimental data on chromosome aberrations induced in CH2B2 mammalian cells by heavy ion beams were analysed using a hit-size effectiveness approach and a cellular track structure theory. The two approaches, based on rather incompatible premises, differ widely in their predictions of low level radiation risk from X ray or gamma ray fields, and in their predictions of RBE-LET dependences. Though for different reasons, both approaches suggest limitations in applying the present formulations of dose and of dose related RBE or Quality Factors in the low level region of interest in radiation protection.
RBE-LET Relationships for V79 Cells Irradiated with Low Energy Protons
Authors: Belli M. , Cera F. , Cherubini R. , Ianzini F. , Moschini G. , Sapora O. , Simone G. , Tabocchini M.A. , Tiveron P.
Published: February 2017

Mutation curves of V79 Chinese hamster cells irradiated with low energy proton beams of LET ranging from 10 to 34 keV.µm-1 have been studied in the dose range of 0.5 - 2.0 Gy and compared with that obtained using 200 kV X rays. A substantial difference in the number of induced mutants, at the same dose, has been found when comparing protons and X rays, protons being more effective. The relative biological effectiveness (RBE) for mutation, evaluated as the a/ax ratios, were found to be significantly higher than those expected using heavier particles, in agreement with the results recently obtained for survival. This finding is discussed in terms of general validity of the 'classical' RBE-LET relationship when different types of radiations are compared.
Radiobiological Effects of Intracellular 210Po Alpha Emissions: A Comparison with Auger Emitters
Authors: Howell R.W. , Narra V.R. , Rao D.V. , Sastry K.S.R.
Published: February 2017

A daughter product of 226Ra, 210Po, emits 5.3 MeV a particles. The kinetics of uptake, retention, and cytotoxicity of 210Po-citrate have been studied in Chinese hamster V79 cells. The survival of V79 cells is exponentially dependent on the absorbed dose to the cell nucleus, the mean lethal dose (D37) being 700 mGy. These results, when compared with those obtained for Auger electron emitters incorporated into the DNA of V79 cells, confirm that Auger cascades are as effective as high LET a particles in causing biological damage.
Role of Dy in the Thermoluminescence of CaSO4:Dy
Authors: Morgan M.D. , Stoebe T.G.
Published: February 2017

Building on recent models of the thermoluminescence (TL) process in CaSO4:Dy, work is undertaken to delineate more specifically the role of the Dy impurity in the TL process. Thermally stimulated currents observations show that the recombination mechanism for peak 3 is bimolecular while that for peak 1 is monomolecular. TL results clearly show that the absence of Dy removes the dosimetric peak 3 near 220 oC in this material. Apparently, only Dy impurity develops the appropriate SO4  --VCa centres needed for observation of these peaks. The peak-3-related centres are shown to be quite different in behaviour from that of the structurally similar peak-1 - related SO4  --VCa centres. These results emphasise the importance of Dy impurities in stabilising the TL process needed to observe the dosimetric peak in this system.
Dosimetric Properties of Carbon Loaded LiF Detectors for Beta Photon Extremity Dosimetry
Authors: Burgkhardt B. , Klipfel A.
Published: February 2017

The dosimetric properties of carbon loaded LiF detectors manufactured by Alnor and Vinten are presented in comparison with various LiF detectors. In particular, the beta and photon response, the residual reading after repeated annealing in the oven or reader as well as light sensitivity and fading are discussed. In comparison with LiF detectors of 240 mg.cm-2, LiF + C detectors indicate a photon response of only 2% and in finger rings irradiated on a finger phantom an unexpected high photon energy response. Regarding repeated use, oven annealing in air or N2 affects mainly Vinten LiF + 1%C by discoloration and reduces the 147Pm response of LiF + C detectors by between 1% and 6% per N2 annealing, whereas reader annealing in the Toledo and Alnor reader does not affect the relative beta response. The residual dose H0 of LiF + C remains sufficiently low after oven annealing, but increases for Alnor LiF + 4% C after reader annealing, which is therefore more suitable for Vinten LiF + 1% C. Spurious detector reading exceeds H0 and its standard deviation by a factor of 2 to 3.
Natural CaF2 and Na2B4O7 Thermoluminescence Detector Sensitive to Thermal Neutrons
Authors: Fratin L. , Cruz M.T.
Published: February 2017

A thermoluminescence detector (TLD) sensitive to thermal neutrons based on CaF2 (nat) bound with Na2B4O7 has been produced. A second TLD using NaCl as a binder was used to measure the gamma component in the neutron irradiation field. The production techniques were established. Three different grain sizes were used to study the sensitivity and reproducibility of the detectors produced. Tests for neutron fluence determination within the range of interest for radiation protection (1 - 10 x 108nth.cm-2) showed that the sensitivity of the detectors has to be increased to allow their use in personnel monitoring.
The Relative, Prompt, Fast Neutron Kerma to RPL Conversion Efficiency ?n/?gamma of SEI and Toshiba FD-P10-7 RPL Glass Dosemeters
Authors: Croft S. , Weaver D.R.
Published: February 2017

Recently we have reported the measurement of the fast neutron sensitivities of SEI and Toshiba FD-P10-7 RPL glass dosemeters over the energy range En = 0.2 MeV to 15 MeV. Here we analyse these measurements within the framework of kerma calculations in order to extract ?n(En)/??(60Co), the prompt, fast neutron kerma to RPL conversion efficiency relative to the gamma kerma to RPL conversion efficiency measured using 60Co gamma radiation. In order to do this, both the prompt and activation neutron kerma factors of the two dosemeter materials were generated. The measured RPL sensitivities were corrected for the effects of glass activation on the basis of the calculated activation kerma before the ?n(En/??(60Co) values were calculated. Thus the parameter obtained relates specifically to the prompt action of fast neutrons, and as such, sheds light on the sensitivity of SEI and FD-P10-7 glasses to heavily ionising particulate radiation. It was found the ?n(En)/??(60Co) varied with energy in a similar way for both dosemeter types. Over the neutron energy range studied, the ?n(En)/??(60Co) ratio averaged 0.19 for SEI glass and 0.17 for Toshiba FD-7 glass. These values are consistent with the RPL conversion efficiencies, reported by other workers, for heavy charged particles acting on RPL dosemeters of similar composition.