Biomedical subjects

K A Higley

Publications and source records attributed to K A Higley.

6 recordsLinked to original sources

PubMed2004

Dose limits for man do not adequately protect the ecosystem.

As has been noted by both of our participants, it is interesting to see that their views approached agreement during the course of the debate. This is not altogether unexpected since the topic is on that has many facets. It is fair to say that protecting man is an appropriate starting point for the protection of other more, or less, radiosensitive life forms sharing the planet with us. That there may be special situations requiring attention has been recognized by both of our participants. That the ICRP recognizes the need for further work on this topic is encouraging for ourselves as well as the 'bugs and bunnies'.

Conservation of Natural Resources↗

PubMed2003

A kinetic-allometric approach to predicting tissue radionuclide concentrations for biota.

Allometry, or the biology of scaling, is the study of size and its consequences. It has become a useful tool for comparative physiology. There are several allometric equations that relate body size to many parameters, including ingestion rate, lifespan, inhalation rate, home range and more. While these equations were originally derived from empirical observations, there is a growing body of evidence that these relationships have their origins in the dynamics of energy transport mechanisms. As part of an ongoing effort by the Department of Energy in developing generic methods for evaluating radiation dose to biota, we have examined the utility of applying allometric techniques to predicting radionuclide tissue concentration across a large range of terrestrial and riparian species of animals. This particular study examined 23 radionuclides. Initial investigations suggest that the allometric approach can provide a useful tool to derive limiting values of uptake and elimination factors for animals.

Animals↗

PubMed2003

An experimental determination of FIDLER scanning efficiency at specific speeds.

As part of mass remediation efforts across the country some radiation detection systems are now being used in conjunction with data logging and positioning system technology. These systems can be used in the scanning mode, simultaneously recording both count rate and position. Following data analysis, hot spots can be identified and remediation efforts for that particular area can commence. This technique has been used for nearly a decade and has had success in accelerating preliminary remediation work while also reducing potential clean up costs. However, little work has been completed on how the sensitivity of these detection systems are affected when used with this technology because while the intrinsic efficiency of the detector is constant, scanning efficiency can vary depending on data sampling time and scanning speed. To better understand scanning efficiency for a detector attached to such a system, a device was developed which moved soil at a constant speed underneath a Field Instrument for Detecting Low Energy Radiation (FIDLER). Count rate was measured every 2 s as a 241Am source passed under the detector at speeds ranging from approximately 10 cm s(-1) to 100 cm s(-1). A surface source and a buried source were both examined. Experimental detection efficiency was calculated and compared to Monte Carlo generated results. For the surface source, the efficiency dropped to a value of approximately 1% at 100 cm s(-1). At the same speed, the buried source had a detection efficiency of 0.1%, primarily due to attenuation of the low energy photon in the soil. It was also noted that the response time of the meter affected the scanning efficiency. With a response time set at 1 s, higher average efficiencies were recorded but with a large standard deviation from the mean. Higher response time setting had the effect of reducing the variability of the reading but also reducing efficiency.

Americium↗

PubMed2001

An innovative technique in scanning land areas with a multi-FIDLER system.

Remediation can be a long and tedious effort. One possible step in this process is the scanning of land to locate elevated areas of radiological contamination. By adapting existing global positioning technology with radiation detection systems, this process can be significantly accelerated. The Field Instrument for Detecting Low Energy Radiation (FIDLER) was used in conjunction with a Global Positioning System (GPS) and Trimble data logger. With this system two different land areas were scanned using two different scanning methods. In the first method, three FIDLERs were attached to a baby jogger and were used to scan a 20-acre site devoid of vegetation. The second technique involved individuals carrying the instruments over a 15-acre site that contained vegetation. Here the FIDLERs were waved in front of the workers in 50-cm arcs. In all cases, radiological and position data were collected by the data loggers. Using these results, accurate maps were generated for each site clearly illustrating areas and spots of elevated activity. By employing this technique over 250,000 data points pertaining to position and count rate were used to map nearly 40 acres of land in under 3 wk.

Americium↗

PubMed2001

A dose reconstruction of 60Co-contaminated window frames in a Taiwanese school.

Since 1992, hundreds of buildings in Taiwan were discovered to have 60Co contamination in the structural rebar. The contamination resulted from improper handling of 60Co-contaminated scrap metal in 1982 and 1983, which subsequently was recycled and used throughout Taiwan. Hsin-hsin Kindergarten school enrolled about 600 students over the 10-y period before the contamination was discovered. Hsin-hsin Kindergarten had three 60Co-contaminated steel window frames with measured dose rates on contact up to 150 microSv h(-1). In this study, a range of potential doses received by the Hsin-hsin Kindergarten students were estimated using ISOSHLD dose modeling software. ISOSHLD is a rapid, inexpensive screening tool to reconstruct dose ranges. To assess the potential risks to habitants of the school for the first year after construction, calculated dose rate ranges of 0.08 microSv h(-1) to 75.38 microSv h(-1) were then applied to the International Commission [corrected] on Radiation Protection 60 nominal detriment coefficients for stochastic effects. Risk estimates ranged from 1.46 x 10(-4) to 7.42 x 10(-4) excess fatal cancers per lifetime.

Adolescent↗

PubMed2000

A comparison between default EGS4 and EGS4 with bound Compton cross sections when scattering occurs in bone and fat.

Computer simulation packages are important tools in understanding how radiation interacts with matter. EGS4 is a photon/electron Monte Carlo transport program that is employed in the health/medical physics field. Due to its high energy roots, the default version of EGS4 treats all electrons as unbound and therefore uses the Klein-Nishina cross section formula to determine Compton scattering angle distributions and the probability of Compton scattering through the branching ratio. Researchers have created improvements to EGS4 that account for the bound Compton cross section as well as other scattering properties. Numerical experiments were performed on both the default code and modified EGS4 to examine output differences in low Z materials such as fat and bone. Four incident photon energies were considered. At higher energies (500 keV and 1 MeV) the default and modified EGS4 codes produced results within 2sigma of one another. At 50 and 100 keV differences in scattering angle distribution and branching ratio values were found. In addition, the number of photoelectric absorptions and Compton scatters were also different at these energies.

Adipose Tissue↗