No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

There is increasing public concern over the possible harmful effects of extra-low-frequency (ELF) electromagnetic (em) fields. A variety of harmful effects have been linked with em field exposure, for example depression and suicide, carcinogenesis, birth defects, and spontaneous abortion. The epidemiological evidence, especially the more recent studies, suggests that there may be a small increased risk of childhood cancers in those living near overhead power lines. However laboratory evidence to date does not support this link. An epidemiological correlation does not necessarily imply a causal relationship: to confirm such a relationship, biological and laboratory evidence is required. This work studies the magnitude of human exposure to ELF magnetic fields from overhead power lines and visual display units (VDUs) and also investigates possible health effects at the microscopic level through cell culture experiments. From the epidemiological evidence, an effect threshold of approximately 300 nT was estimated. Detailed magnetic field distributions were measured round a variety of visual display units and only a very few emitted magnetic fields even close to the 300 nT threshold. Following an in-depth case study of a VDU operator who suffered from a combination of symptoms including eyestrain and headaches, a study of the health of nearly 200 office workers and VDU users was set up. The aims of the study were to investigate the range and severity of symptoms suffered by VDU users, to investigate possible causes and to study response to VDU work at an individual level. It was found that those working between 10 and 30 hours per week at a VDU were more likely to suffer symptoms of ill health. In contrast, those working more than 30 hours per week at a VDU were not more likely to suffer symptoms when compared with a control group of those working less than 10 hours per week at a VDU. In particular, increased reporting of eye problems and fatigue were most strongly associated with VDU work.

A 700 keV Van de Graaff accelerator was used to accelerate protons onto solid targets of different light elements to produce ultrasoft, characteristic X-rays (< 5 keV). The proton energies were calibrated using the (p, y) resonances at 633 keV in Aluminium and at 340 and 483 keV in Fluorine. The X-ray emission characteristics of Aluminium, Carbon, Gold, Silicon/Carbon, Silicon/Nitrogen and Titanium/Boron were studied as a function of incident proton energy, angle of inclination of the target (30° - 60° to the proton beam) and angle of detection of the X-rays (40° - 130° to the beam). Detection of the X-rays was achieved using a gas-flow proportional counter directly coupled to a low-noise pre-amplifier. The resulting spectra, recorded on a multichannel analyser, were well fitted by linear combinations of single Gaussian curves to give peak position (X-ray energy), width and area (X-ray intensity). Carbon contamination of the target surface was studied in detail for the Aluminium target. A number of low beam currents onto the target (10 - 70 nA) were used for total irradiation times of up to 17 hours in order to establish the degree of overall X-ray energy mixing. The information gained from the study of both the Carbon contamination and the X-ray emission characteristics was used to propose practical optimum conditions for the production of ultrasoft X-rays by proton bombardment in their application to biological and biochemical irradiations. A computer code, capable of following the electron track histories resulting from ultrasoft X-ray interactions has been used to compare the details of such energy deposition with the results of mammalian cell irradiations made at the M. R. C. Radiobiology Unit for a number, of different ultrasoft X-ray energies. Such a-comparison has been used to try to identify the mechanisms of radiation action. Included in this work is the application of the computer code to a variety of. characteristic X-ray photon energies, thus extending the available, calculated data.

A model based on Monte Carlo techniques is developed to transport ionising radiation through the radiation head of a 6MV linear accelerator fitted with multileaf collimators Major emphasis is given to the detailed geometrical descriptiqn of the multileaf collimator. The model produces dose distributions in water from photon beams defined by the jaws and the multileaf collimator. The model accounts for contaminant electrons in the photon beam, off-axis x-ray radiation originating at the collimator and the transmission and penumbra effects of the side planes and front face of the leaves in the multileaf collimator Dose distributions in water calculated by the model are compared with experiment using lonisation chambers, diodes and film and found to be within 1 5% The transmission and the penumbra of the multileaf collimator leaves calculated by the Monte Carlo model are compared with experiment and found to be in good agreement