Depicting corrosion-born defects in pipelines with combined neutron/γ ray backscatter: a biomimetic approach.

The identification of corrosion, cracks and defects in pipelines used for transporting oil and gas can reduce the possibility of leaks, and consequently, it can limit the extent of an environmental disaster, public hazard and the associated financial impact of such events. Typically, corrosion in oil pipelines is measured with non-destructive ultrasonic or electromagnetic techniques, on the basis that corrosion and defects are often manifest as a change of thickness in the steel from which pipelines are made. However, such approaches are not practical for underground pipelines and their deployment can be complicated for the case of pipelines covered by insulation. In this paper, we present an innovative, non-destructive testing technique, which exploits the backscatter of a combination of fast-neutron and γ radiation from steel samples of a variety of thicknesses consistent with changes that might arise due to corrosion of a pipe wall. Our research demonstrates the potential to measure and characterise different steel thicknesses by detecting both the elastic, fast-neutron backscatter and the Compton-scattered γ radiations, simultaneously. Further, we demonstrate that the presence of insulation yields a consistent and separable influence on the experimental, wall-thickness measurements. The data from experimental measurements are supported by a comprehensive Monte Carlo computer simulation study.

ADDITIONAL CHARACTERISATION OF THE THERMAL NEUTRON PILE AT THE NATIONAL PHYSICAL LABORATORY, UK.

As part of its wide-ranging neutron metrology capabilities, the National Physical Laboratory in the UK has a thermal neutron facility in which accelerator-produced neutrons are moderated within a large assembly or pile of graphite bricks. The neutron field has previously been well characterised in terms of the fluence rate and energy spectrum at various irradiation positions. However, recent changes to the structure (e.g. enlarging the central irradiation cavity) have prompted a renewal and extension of this work. We have also used Monte Carlo modelling to improve our understanding of the pile's performance.

Results of field trials using the NPL simulated reactor neutron field facility.

The NPL simulated reactor neutron field facility provides neutron spectra similar to those found in the environs of UK gas-cooled reactors. Neutrons are generated by irradiating a thick lithium-alloy target with monoenergetic protons between 2.5 and 3.5 MeV (depending on the desired spectrum), and then moderated by a 40-cm diameter sphere of heavy water. This represents an extremely soft workplace field, with a mean neutron energy of 25 keV and, more significantly, a mean fluence to ambient dose equivalent conversion coefficient of the order of 20 pSv cm(2), approximately 20 times lower than those of the ISO standard calibration sources (252)Cf and (241)Am-Be. Results of field trials are presented, including readings from neutron spectrometers, personal dosimeters (active and passive) and neutron area survey meters, and issues with beam monitoring are discussed.

Improved measurements of neutron dose equivalent rates using a dual instrument technique.

A dual instrument technique, employing a neutron area survey meter and a tissue-equivalent proportional counter, has been developed to improve the measurement of neutron dose equivalent rates in workplace fields. A simple algorithm estimates the ambient dose equivalent response of the area survey meter from the ratio of the dose equivalent rates measured by the two instruments. This estimate can then be used to adjust the reading from the area survey meter, providing a better measure of the neutron ambient dose equivalent rate in the workplace. The technique was tested on 225 spectra from the neutron spectrum catalogue SPKTBIB.

CORRECTIONS ASSOCIATED WITH ON-PHANTOM CALIBRATIONS OF NEUTRON PERSONAL DOSEMETERS.

The response of neutron personal dosemeters as a function of neutron energy and angle of incidence is typically measured by mounting the dosemeters on a slab phantom and exposing them to neutrons from an accelerator-based or radionuclide source. The phantom is placed close to the source (75 cm) so that the effect of scattered neutrons is negligible. It is usual to mount several dosemeters on the phantom together. Because the source is close, the source distance and the neutron incidence angle vary significantly over the phantom face, and each dosemeter may receive a different dose equivalent. This is particularly important when the phantom is angled away from normal incidence. With accelerator-produced neutrons, the neutron energy and fluence vary with emission angle relative to the charged particle beam that produces the neutrons, contributing further to differences in dose equivalent, particularly when the phantom is located at other than the straight-ahead position (0° to the beam). Corrections for these effects are quantified and discussed in this article.

Modelling of neutron survey instrument performance and experimental validation of those calculated response data.

Three moderator-type neutron survey instruments have been modelled for energy and angle dependence of the response, in greater detail than before. These response data have been verified by comparison with published experimental measurements and measurements made specifically for this project. Influences on the instrument response have also been investigated. These have included its mode-of-use and perturbations caused by variations in the instrument manufacture. The implications of these new response data have been assessed by an extensive programme of folding the responses with workplace energy distributions.

Influence of titanium oxide and titanium peroxy gel on the breakdown of hyaluronan by reactive oxygen species.

The molecular events occurring at the interface between titanium and connective tissue were investigated in order to help explain the unique biocompatible properties of titanium implants and their successful osseointegration into bone tissue. In this study the influence of commercially pure titanium and titanium peroxy gels on the breakdown of the connective tissue component and serum derived factor, hyaluronan, by reactive oxygen species (ROS), produced during the insertion of an implant in vivo, was examined. Hyaluronan breakdown was monitored in vitro in the presence of a hydroxyl radical flux, generated in the presence and absence of titanium powder and discs. Parallel studies examined the breakdown of hyaluronan by hydroxyl radicals in the presence of a titanium peroxy gel, prepared by incubation of the titanium powder or discs in concentrated hydrogen peroxide. The hyaluronan degradation products were separated according to their hydrodynamic size by gel exclusion chromatography. Similarly, experiments were also performed examining the degradation of 2-deoxy-D-ribose by a hydroxyl radical flux in order to demonstrate the detrimental potential of the hydroxyl radicals and to provide a measure of the effectiveness of titanium and titanium peroxy gels as scavengers of ROS. Titanium reduced the harmful effects of the hydroxyl radicals on the breakdown of hyaluronan, presumably acting as a scavenger for the reactive species, possibly by absorbing them into its surface oxide layer, which spontaneously forms on the surface. In contrast, the formation of a titanium peroxy gel from the titanium powder or on the surface of titanium discs enhanced breakdown of both the hyaluronan chains and 2-deoxy-D-ribose. The implications of these findings with regards to the biocompatible nature of the titanium and the ability of these implants to successfully osseointegrate are discussed.

The value of arm circumference measurements in assessing chronic energy deficiency in Third World adults.

OBJECTIVE: To assess the usefulness of mid-upper arm circumference (MUAC) as a substitute for body mass index (BMI: kg/m2) or an additional measure of adult nutritional state. DESIGN: Variously sampled adults aged 18-60 years from selected regions of five African countries, India, China and Papua New Guinea were measured. SUBJECTS: 2421 men and 3248 women were measured for their heights, weights and MUAC. Of these, 1569 men and 1905 women also had their triceps skinfold thickness measured, thus allowing additional estimates of muscle area circumferences and fat areas in the arm. RESULTS: MUAC and BMI were highly correlated in each national group; each group's MUAC differed from the overall mean MUAC at any BMI value by < 10%. Women's MUACs were smaller than men's at equivalent BMIs. Increases in MUAC with age were statistically significant but trivial. Muscle and fat measurements showed similar increases with BMI; a larger muscle mass in men explained their greater MUACs but muscle differences alone did not explain national variations in MUAC. The -1 SD MUAC value, taken as an independent measure of peripheral tissue wasting, readily distinguished those with a BMI < 16.0 from those with a BMI > 18.5; intermediate grades of BMI were poorly specified by MUAC values. CONCLUSION: MUAC values of 23.0 cm in men and 22.0 cm in women are useful cut-off points for simple screening of nutritional state. In combination with BMI it may provide a more refined classification of CED. This new combined classification scheme may be a better means of discriminating the at-risk underweight adults from those who are thin but not at risk.

In situ neutron spectrometry to 60 MeV in a water phantom exposed to a cancer therapy beam.

In-air and in-phantom neutron spectra have been measured between 10 and 60 MeV for two field sizes on the Clatterbridge cyclotron by unfolding the response of a specially built NE213 scintillator. The in-phantom measurements show distinct spectral hardening with depth, which is reflected in changes in the spectrum-averaged mean neutron energy. These findings are confirmed using Monte Carlo calculations.

Effectiveness of selected granular acaricide formulations in suppressing populations of Ixodes dammini (Acari: Ixodidae): short-term control of nymphs and larvae.

Applications of selected granular acaricide formulations to the shrub layer of forested habitats during the peak activity periods of Ixodes dammini Spielman, Clifford, Piesman & Corwin nymphs and larvae significantly reduced the abundance of these stages on Peromyscus leucopus. The granules effectively penetrated growing vegetation and suppressed populations of subadult ticks questing in the leaf litter. The use of granular acaricide formulations provides the only documented method of control of free-living I. dammini nymphs and larvae in dense vegetation. As such, this technique will serve as a major component of any integrated control program against this vector tick species.

Effectiveness of an aerial application of carbaryl in controlling Ixodes dammini (Acari: Ixodidae) adults in a high-use recreational area in New Jersey.

Lyme disease risk reduction through the control of the principal tick vector, Ixodes dammini Spielman, Clifford, Piesman & Corwin, has become a major issue facing public health agencies in many endemic states. Where large tracts of land are involved, established methods of I. dammini control are impractical. An aerial application of carbaryl directed against fall populations of I. dammini adults resulted in 93.8% control after 96 h. Control persisted through the following spring. The usefulness of aerial applications may be limited to areas where logistic constraints obviate the use of conventional ground applications.

A realistic field facility to simulate reactor spectra.

The design construction and characterisation of a simulated realistic neutron workplace field is described. Utilising a low-energy primary source of neutrons based on the 7Li(p,n) reaction, and a heavy water moderator, a broad spectrum is produced with energies extending from thermal to about 1 MeV. The field simulates the type of spectra encountered around UK gas-cooled reactors.

The evaluation and use of a portable TEPC system for measuring in-flight exposure to cosmic radiation.

A recent EC directive has called for all member states to introduce legislation covering the assessment and restriction of air crew exposure to cosmic radiation. In the UK the Civil Aviation Authority, in conjunction with the Department of the Environment. Transport and the Regions issued guidelines suggesting the use of a predictive code such as CARI for this purpose. In order to validate the use of calculated route doses, an extensive programme of measurements is being carried out on long haul routes in conjunction with Virgin Atlantic Airways, using a prototype HAWK TEPC developed by Far West Technology. This programme began in January 2000 and by the end of February 2001 had resulted in the accumulation of data from 74 flights. In this paper the instrument design is discussed, together with the calibration programme. An overview of the in-flight results is also presented, including comparisons between measurements and calculations, which indicates that CARI under-predicts the route doses by approximately 20%.

TEPC measurements in commercial aircraft.

The collaborative project involving the Mullard Space Science Laboratory (MSSL), Virgin Atlantic Airways (VAA), the UK Civil Aviation Authority (CAA) and the UK National Physical Laboratory (NPL) has been performing tissue-equivalent proportional counter measurements of cosmic ray doses in commercial aircraft since January 2000. In that time data have been recorded on over 700 flights, including over 150 flights with Air New Zealand (ANZ). This substantial set of data from the southern hemisphere is an ideal complement to the London-based measurements performed primarily on VAA flights. Although some ANZ data remains to be analysed, dose information from 111 flights has been compared with the CARI and EPCARD computer codes. Overall, the agreement between the measurements and EPCARD was excellent (within 1% for the total ambient dose equivalent), and the difference in the total effective doses predicted by EPCARD and CARI was <5%.

Practical implications of neutron survey instrument performance.

Improvements have been made to the Monte Carlo modelling used to calculate the response of the neutron survey instruments most commonly used in the UK, for neutron energies up to 20 MeV. The improved modelling of the devices includes the electronics and battery pack, allowing better calculations of both the energy and angle dependence of response. These data are used to calculate the response of the instruments in rotationally and fully isotropic, as well as unidirectional fields. Experimental measurements with radionuclide sources and monoenergetic neutron fields have been, and continue to be made, to test the calculated response characteristics. The enhancements to the calculations have involved simulation of the sensitivity of the response to variations in instrument manufacture, and will include the influence of the user and floor during measurements. The practical implications of the energy and angle dependence of response, variations in manufacture, and the influence of the user are assessed by folding the response characteristics with workplace energy and direction distributions.

Angle dependence of response characteristics of neutron survey instruments.

Neutron area survey instruments are designed to have an approximately isotropic response. In practice, the response cannot be perfectly isotropic for instruments that do not have spherical symmetry, and for all instruments it is modified by the inclusion of batteries, electronics, handles, etc. This affects the ability of the survey instrument to measure accurately an isotropic dose equivalent quantity. Measurements of the angle dependence of response for four of the most commonly used designs of survey instrument (Harwell 0949, Mark 7 NRM, NM2 and Studsvik 2202D) have been performed in a low-scatter room using radionuclide and monoenergetic neutron sources. The Monte Carlo code MCNP has been used to model the responses and to investigate their sensitivity to the polyethylene density, counting gas pressure and other manufacturing tolerances. Preliminary modelling results are presented here.

Penicillins, cephalosporins, quinolones.

This article details the mechanisms of action, antimicrobial spectrum, pharmacokinetics, and adverse reactions of these three antibiotics.

A digital approach to neutron-γ imaging with a narrow tungsten collimator aperture and a fast organic liquid scintillator detector.

A digital neutron-γ imaging technique for mixed radiation field is described. The imaging system is based upon an organic liquid scintillator detector, a narrow tungsten collimator, fast digitiser and adjustable equatorial mount. Radioactive sources have been attached to a vertical plane and the digitiser has been used to digitise neutron and γ events. The digitised events have been discriminated using pulse gradient analysis and images have been generated of the count distribution in the source plane.

Geometry corrections for cylindrical neutron area survey meters.

MCNP calculations have been performed to investigate the effects of beam divergence on the response of selected cylindrical neutron area survey meters irradiated by selected neutron sources. By comparing the results to calculations performed using plane-parallel beam irradiations, geometry correction factors have been calculated that can be applied to instrument calibrations. The results indicate that the effective centres of cylindrical detectors may not lie on the axis of symmetry, as previously assumed.