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Biomedical subjects

A A Edwards

Publications and source records attributed to A A Edwards.

84 records · Page 5Linked to original sources
PubMed1979

Determination of the stopping cross-sections of N2, H2, CH4, C4H10 and C3H6 using alpha particles in the range 1 . 3--4 . 2 MeV.

The stopping cross-sections of N2, H2, CH4, C4H10 and C3H6 have been measured using natural alpha particles from a 238Pu source, with facilities to vary the energy in the range 1.3--4.2 MeV. The work is the extension of measurements made earlier, using C2H4 as the absorber, which showed discrepancies in comparison with results of other authors. The comparison is continued with the results presented here and brief comments made on the degree of agreement obtained.

Alkanes↗
PubMed1978

Chromosome aberrations induced in human lymphocytes by radiation from 252Cf.

In vitro dose--response curves of unstable chromosome aberrations in human lymphocytes have been obtained for 252Cf neutron radiation. The aberration yields fitted best to the linear function Y=aD, which is consistent with the single-track model of aberration formation for high LET radiation. The curves have been compared with others previously produced in this laboratory for several energies of neutrons and for 60Co gamma radiation. The r.b.e. for 252Cf with respect to 60Co is 27 at very low doses, decreasing to 6 at an aberration yield equivalent to 400 rad of 18 rad/hour gamma radiation. A profile of chromosome-aberration induction with depth in a perspex phantom was obtained by placing blood samples at several distances over the range 0.65-2.0 cm from the californium source. This profile was compared with depth-damage calculations for a radium needle. The r.b.e. of 252Cf radiation relative to 226Ra gamma radiation increased with the distance from the source, implying that californium is more effective at greater distances in destroying the ability of cells to divide, which may be an advantage in the treatment of large tumours.

Californium↗
PubMed1978

Comparison of the stopping cross-sections of ethylene and polyethylene using alpha particles in the energy range 1.5--4.2 MeV.

In order to design reliable gas-filled dosemeters it is necessary to have knowledge of the ratios of the stopping powers of various solids and their gaseous equivalents. This paper describes the measurement of the stopping cross-sections of ethylene and its polymer polyethylene using alpha particles, and compares the measurements with results published by other workers. The results indicate that there is no difference between the two sets of values, within the quoted errors. Reasons are suggested to account for part of the discrepancy between our results and those of others for thin solid sample measurements.

Alpha Particles↗
PubMed1977

The evidence for one-hit chromosome exchanges.

Luchnik [5] has recently questioned the need for a one-hit chromosome exchange mechanism to explain the dicentric yield in human lymphocytes following irradiation by low LET radiations. An analysis of more recent experimental data is given and this shows that models which approximate to the sum of a term proportional to dose and a term proportional to dose squared fit the available data better than a simple two-hit model. The fits however, are generally poor which is probably due to underestimating the errors involved.

Chromosome Aberrations↗
PubMed1976

Chromosome aberrations induced in human lymphocytes by neutron irradiation.

In vitro dose--response curves of unstable chromosome aberrations in human lymphocytes have been obtained for neutron spectra of mean energies 0-7, 0-9, 7-6 and 14-7 MeV. The aberration yields have been fitted to the quadratic function Y = alphaD + betaD2, which is consistent with the single-track and two-track model of aberration formation. However with high-LET radiation, the linear component of yield, corresponding to damage caused by single tracks, predominants, and this term becomes more dominant with increasing LET, so that for fission spectrum neutrons the relationship is linear, Y = alphaD. At low doses, such as those recieved by radiation workers, limiting r.b.e. values between 13 and 47 are obtained relative to 60Co gamma-radiation. At higher doses, as used in radiotherapy, the values are much lower; ranging from 2-7 to 8 at 200 rad of equivalent gamma-radiation. Both sets of r.b.e. values correlate well with track-averaged LET but not with dose-averaged LET. When the numbers of cells without aberrations are plotted against radiation dose, curves are obtained which are similar in shape to those for conventional cell-survival experiments with comparable neutron spectra. The Do values obtained in the present study are close to those from other cell system.

Chromosome Aberrations↗
PubMed1975

The relationship between chromosome aberrations and low LET radiation dose to human lymphocytes.

In vitro dose-response curves of unstable chromosome aberrations in human lymphocytes have been obtained for 250 kV X-rays and cobalt-60gamma-radiation. The aberration yields have been fitted to the quadratic function Y = alphaD +betaD2, which is consistent with the single-track and two-track model for aberration formation. The values of the coefficients alpha and beta support the hypothesis that the dose-rate effect is limited to the D2 term. The main difference between the coefficients for X- and gamma-radiation is in the alpha values, indicating that X-rays are slightly more efficient, at lower doses, in producing two lesions with a single ionizing track. The lower limits of dose estimate, with 500 cells analysed, are 4 rad for X-rays and 10 rad gamma-radiation. Further evidence is presented confirming that, for cytogenetic dosimetry, in vitro dose-response curves should be prepared by irradiating whole blood maintained at 37 degrees C and prior to PHA stimulation. Curves were plotted showing the variation of the number of cells without aberrations with radiation dose and the shape of these curves were compared with those from human cell survival experiments.

Adult↗
PubMed1975

The calculation of charged particle fluence and LET spectra for the irradiation of biologically significant materials by neutrons.

As a preliminary step to evaluating recent theories concerning the biological effect of ionizing radiation, the charged particle fluence distributions and the dose distribution in linear energy transfer have been computed analytically for targets of biological and dosimetric interest irradiated by neutrons. Specifically, 14.7 MeV neutrons, the 252Cf neutron spectrum and a cyclotron generated neutron spectrum are considered to irradiate water, tissue-equivalent plastic and standard man tissue and results are given for all these cases. From a knowledge of the target composition, and the cross-sections and kinetics of all the possible neutron induced reactions in the elements hydrogen, carbon, nitrogen and oxygen, the secondary particle spectrum is calculated. By combining with stopping power data for the ions in the target, the charged particle fluence spectra and dose distribution in linear energy transfer are derived. Secondary quantities computed are kerma, energy expended as nuclear elastic scattering, specific ionization and mean quality factor. Stopping powers have been derived from published atomic stopping powers by summing according to the Bragg rule. A comparison between tissue-equivalent plastic and standard man tissue had been made for each of the neutron spectra.

Californium↗
PubMedDate not supplied

[Prevention of gram-negative and gram-positive infections using 3 intravenous immunoglobulin preparations and therapy of experimental polymicrobial burn infection using intravenous Pseudomonas immunoglobulin G and ciprofloxacin in an animal model].

Three immunoglobulin preparations for intravenous infusion were compared in vivo to determine their relative protective capacity against several gram-negative and gram-positive pathogens. Polyglobin N is a conventional IgG concentrate. Psomaglobin N is identical in formulation to Polyglobin N but is prepared from the plasma of donors who have naturally high levels of antibody to lipopolysaccharide antigens of Pseudomonas aeruginosa. IgGMA is a conventional IgG concentrate containing 12% IgG and 16% IgA. In a murine model of burn wound sepsis the three IgG preparations were similarly protective against three or ten strains of P. aeruginosa. Psomaglobin N and Polyglobin N were significantly (p less than or equal to 0.015) more protective than IgG-MA against six of ten and three of ten strains of P. aeruginosa, respectively. In a murine model of Streptococcus pneumoniae type 3 pneumonia, the three Ig preparations were similarly protective. IgG-MA was significantly more protective (p less than or equal to 0.025) than Psomaglobin N and Polyglobin N against Salmonella typhimurium in murine peritonitis. However, the mean protective dose (PD50) of the two later preparations was less than or equal to 20 mg/kg body weight. In models of peritonitis both Psomaglobin N and Polyglobin N were more protective than IgGMA (p less than or equal to 0.004) against Haemophilus influenzae b, Klebsiella pneumoniae, Serratia marcescens 06:H3 and group B Streptococcus types 1b and 1c. Psomaglobin N and ciprofloxacin were employed to treat established polymicrobial murine burn wound sepsis resulting from contamination of the burn site with mixtures of P. aeruginosa and Staphylococcus aureus. Psomaglobin N or albumin was given once 16 h after challenge.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

ESR dosimetry of a deceased radiation worker.

A case of overexposure of an industrial radiographer using 192Ir sources and having a filmbadge dosimeter record of 104 mSv has been examined with ESR dosimetry of postmortem tooth and bone specimens. ESR measurements of the tooth enamel showed an intense signal of CO2- and gave the equivalent dose (ED) of 14 Gy by the additive dose method using gamma-rays from a source of 60Co. The doses for a finger bone and humerus were 14.7 and 7.0 Gy, respectively. It was concluded that he had been exposed to radiation repeatedly over 10 yr and that ESR dosimetry can give a life-long cumulative dose for personnel using radiation.

Bone and Bones↗
PubMedDate not supplied

A critical survey of fish measurements in populations of the southern Urals.

A critical survey of all published measurements made so far aimed at retrospective biological dosimetry using fluorescence in situ hybridisation (FISH) techniques on some workers at the Mayak reprocessing plant and on members of the Techa River cohort is given. Each individual has a recorded dose derived from personal monitoring measurements, usually external gamma-rays for Mayak workers or from reconstruction techniques, usually internally derived for the Techa River cohort. From the person's age, which affects the control level, and the stated dose, an expected number of translocations is calculated for each individual and comparisons made to the observed numbers of translocations. From this, an assessment of how well FISH studies can help to validate existing estimates of dose is made. This varies from study to study. Good agreement is generally obtained for the Techa River cohort and lower doses of the Mayak cohort. Rather poorer agreement applies to the more highly exposed Mayak workers. Some of the discrepancy could be because the FISH painting technique was new and was applied to populations before a proper investigation on how to use it for retrospective biological dosimetry had taken place. In addition, too few cells were generally scored per individual so that statistical uncertainties were large.

Aged↗