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PubMed1993

The effect of the static magnetic field on the response of radiation survey instruments.

The effects on the response of eight radiation survey instruments in static magnetic fields up to 0.03 T (300 G) have been investigated. The instruments studied are the Xetex 303B Pacer, the Bicron Micro Rem survey meter, the Victoreen 450p survey meter, the Victoreen 440 survey meter, the SLAC orange meter, the Keithley 36150 survey meter, the Anderson-Braun neutron remmeter, and the Victoreen 488 neutron survey meter. The results show that the effect may depend on several factors such as instrument design, alignment of the instrument axis with the magnetic flux lines, whether the instrument is stationary or moving relative to the magnetic field, the direction of the movement relative to the magnetic flux lines, and the magnetic field intensity. Also presented are results of work to enhance magnetic shielding of some of the instruments.

Electromagnetic Fields↗
PubMed1994

Monte Carlo calculations of monoenergetic electron depth dose distributions in LiF chips: skin dose correction factors for beta rays.

Monte Carlo calculations have been carried out for monoenergetic electrons from 0.1 to 4 MeV irradiating LiF chips in both perpendicular and isotropic geometry. This enabled the calculation of skin dose correction factors (beta factors) for typical beta energy spectra as measured with a beta-ray spectrometer at CANDU nuclear generating stations. The correction factors were estimated by averaging the depth dose distributions for the monoenergetic electrons over the experimentally measured beta-ray spectra. The calculations illustrate the large uncertainty in beta factors arising from the unknown angular distribution of the beta-ray radiation field and uncertainties in the shape of the beta-ray spectra below 500 keV.

Fluorides↗
PubMed1994

The estimation of occupational effective dose in diagnostic radiology with two dosimeters.

Annual effective dose limits have been proposed by national and international radiation protection committees. Radiation protection agencies must decide upon a method of converting the radiation dose measured from dosimeters to an estimate of effective dose. A proposed method for the estimation of effective dose from the radiation dose to two dosimeters is presented. Correction factors are applied to an over-apron collar dose and an under-apron dose to estimate the effective dose. Correction factors are suggested for two cases, both with and without a thyroid shield. Effective dose may be estimated by the under-apron dose plus 6% of the over-collar dose if a thyroid shield is not worn or plus 2% of the over-collar dose if a thyroid shield is worn. This method provides a reasonable estimate of effective dose that is independent of lead apron thickness and accounts for the use of a thyroid shield.

Fluoroscopy↗
PubMed1995

Gas bremsstrahlung and associated photon-neutron shielding calculations for electron storage rings.

The EGS4 electron-photon Monte Carlo code has been used to study the characteristics of the bremsstrahlung x rays generated from the interaction of circulating electrons with the residual gas in accelerator storage rings. Gas bremsstrahlung dose rates are given for various opening angles as a function of the electron beam energy ranging from 0.5-10 GeV. Photon and neutron dose rates, generated from various devices struck by gas bremsstrahlung in a synchrotron radiation beamline, are also presented along with the photon spectral and transmission results. The EGS4-predicted results are found to be in basic agreement with the measurements made at the Stanford Synchrotron Radiation Laboratory. Figures, equations, and a simple method useful for the photon-neutron shielding design for beamlines are provided.

Neutrons↗
PubMed1995

A study of the angular dependence problem in effective dose equivalent assessment.

The newly revised American National Standard N13.11 (1993) includes measurements of angular response as part of personnel dosimeter performance testing. However, data on effective dose equivalent (HE), the principle limiting quantity defined in International Commission on Radiological Protection (ICRP) Publication 26 and later adopted by U.S. Nuclear Regulatory Commission (NRC), for radiation incident on the body from off-normal angles are little seen in the literature. The absence of scientific data has led to unnecessarily conservative approaches in radiation protection practices. This paper presents a new set of fluence-to-HE conversion factors as a function of radiation angles and sex for monoenergetic photon beams of 0.08, 0.3, and 1.0 MeV. A Monte Carlo transport code (MCNP) and sex-specific anthropomorphic phantoms were used in this study. Results indicate that Anterior-posterior (AP) exposure produces the highest HE per unit photon fluence in all cases. Posterior-anterior (PA) exposure produces the highest HE among beams incident from the rear half-plane of the body. HE decreases dramatically as one departs from the AP and PA orientations. The results also indicate that overestimations caused by using isotropic dosimeters in assessing effective dose equivalent from near-overhead and near-underfoot exposures are 550%, 390%, and 254% for 0.08, 0.3, and 1.0 MeV, respectively. Comparisons of the angular dependence of HE with those based on the secondary quantities defined in International Commission on Radiation Units and Measurements (ICRU) Reports 39, 43, and 47 show significant differences. This paper discusses why more accurate assessments of HE are necessary and possible. An empirical equation is proposed which can be used as the optimum dosimeter angular response function for radiation angles ranging from 0 degrees to 90 degrees for dosimeter calibration, performance testing, and design.

Dose-Response Relationship, Radiation↗
PubMed1995

History of the medical uses of radiation: regulatory and voluntary standards of protection.

The main focus of this paper is on the historical development of safety standards in the use of radiation or radioactive materials in medicine. However, to provide better understanding and perspective on this history, it must be interwoven with major events and advancements in the development and use of radiation, particularly in the field of medicine. Since this history, as well as that of major events that stimulated the development of radiation protection standards, is extensive, only a very brief overview can be given here. Thus, a sufficient list of references is also provided to allow further examination of detailed historical documentation, and to provide an easier entry into further research. Also, some identification of individuals who have made important contributions to the development of standards, but who are not widely identified in either the relevant standards or the historical literature, is included. This will aid the serious historian in examining files of organizations to uncover facts or rationale that could better explain historical events or developments.

Education↗
PubMed1995

A method for computing the decision level for samples containing radioactivity in the presence of background.

It is often necessary to make a decision whether or not a sample contains radioactivity in excess of background. The most common procedure is a deterministic approach that compares the result from each sample against a critical level, Lc. Originally Lc was derived from the case where each sample is paired with a blank or control that is known not to contain excess radioactivity. However, most analytic laboratories do not process a blank with each and every sample. Another approach computes Lc using a collection of measurements to form a "well defined" background. This paper presents a method for determining a decision level, L delta, that includes the uncertainties in both the mean and variance of background and how these combine to form uncertainties in estimating the tails of the background distribution. The values of L delta are greater than Lc for a given Type I error. It can be applied whenever the true distribution of background is either normal or log normal. The process is not restricted to counting statistics and is valid for identifying excess contamination of any type providing that unknown samples are processed identically to background samples.

Biological Assay↗
PubMed1995

High-energy gamma rays in Hiroshima and Nagasaki: implications for risk and WR.

Based on the DS86 dosimetry system, nearly all of the dose to survivors of the atomic bombings of Hiroshima and Nagasaki was due to unusually high-energy gamma rays, predominantly in the 2- to 5-MeV range. These high energies resulted in part from neutron capture gamma rays as the bomb neutrons penetrated large distances of air. Because of the inverse relationship between energy and biological effectiveness, these high-energy gamma rays are expected to be substantially less effective in producing biological damage than the radiations commonly used in radiobiology and risk assessment. This observation has implications for radiation protection and risk assessment.

Gamma Rays↗
PubMed1995

The national dose registry for radiation workers in Switzerland.

The national dose registry began operation in Switzerland in 1990. It is a database maintained by the Federal Office of Public Health. It contains personal, employment, and dosimetric data for all the radiation workers in the country. The data for about 60,000 currently employed radiation workers are transferred from ten external dosimetry services to the registry every month or every three months. The registry was initiated to assist national authorities in controlling and safekeeping of the occupational doses and to allow statistical evaluations. In autumn 1994 the new Radiation Protection Regulations came into effect. Based on the ICRP recommendations, the Regulations introduced lower limits for the annual dose, for the average dose over five years, and for pregnant women and defined the internal dose as an additive component to the total dose. All these items require a high quality registration of occupational doses. This can hardly be achieved without a central registry. This paper describes the design of the Swiss national dose registry in the frame of the particular organization of the personal dosimetry in this country. The database structure and the information content are presented. Special solutions for the data transfer have been found, as the registry is running completely decoupled from the dosimetry services. Applications of the registry for regulatory control, particularly in connection with the new Regulations are described. Some results of statistical analyses are presented. The possibilities and the limitations of using the registry for radioepidemiological studies are discussed.

Databases, Factual↗
PubMed1996

Statistical analysis of real-time, environmental radon monitoring results at the Fernald Environmental Management Project.

A comprehensive real-time, environmental radon monitoring program is being conducted at the Fernald Environmental Management Project, where a large quantity of radium-bearing residues have been stored in two covered earth-bermed silos. Statistical analyses of radon measurement results were conducted to determine what impact, if any, radon emitted by the radium bearing materials contained in the silos has on the ambient radon concentration at the Fernald Environmental Management Project site. The distribution that best describes the outdoor radon monitoring data was determined before statistical analyses were conducted. Random effects associated with the selection of radon monitoring locations were accommodated by using nested and nested factorial classification models. The Fernald Environmental Management Project site was divided into four general areas according to their characteristics and functions: 1) the silo area, where the radium-bearing waste is stored; 2) the production/administration area; 3) the perimeter area, or fence-line, of the Fernald Environmental Management Project site; and 4) a background area, located approximately 13 km from the Fernald Environmental Management Project site, representing the naturally-occurring radon concentration. A total of 15 continuous, hourly readout radon monitors were installed in these 4 areas to measure the outdoor radon concentration. Measurement results from each individual monitor were found to be log-normally distributed. A series of contrast tests, which take random effects into account, were performed to compare the radon concentration between different areas of the site. These comparisons demonstrate that the radon concentrations in the production/administration area and the perimeter area are statistically equal to the natural background, whereas the silo area is significantly higher than background. The study also showed that the radon concentration in the silo area was significantly reduced after a sealant barrier was applied to the contents of the silos.

Environmental Monitoring↗
PubMed1996

Internal exposure from the ingestion of foods contaminated by 137Cs after the Chernobyl accident. Report 1. General model: ingestion doses and countermeasure effectiveness for the adults of Rovno Oblast of Ukraine.

The Chernobyl accident, which occurred in April 1986, resulted in the atmospheric release of about 70--100 PBq of 137Cs. This paper examines the doses to the adult population of the northern part of Rovno Oblast, Ukraine, from ingestion of 137Cs. Fallout of 137Cs in these regions was lower than in other regions of Ukraine. However, the transfer of 137Cs from soil to milk in the region considered is high (up to 20 Bq L-1 per kBq m-2) and results in the predominance of internal doses compared to those from external exposure. Numerous measurements of 137Cs soil deposition, 137Cs milk contamination, and 137Cs body burden have been made in the area and form the basis of a general model of internal exposure from the ingestion of foods contaminated by 137Cs. This paper has two main purposes. The first is to develop the general phenomenological description of the process leading to internal exposure from the ingestion of 137Cs contaminated foods in the situation where different countermeasures are realized. The second is to apply the model for the adult population of the northern part of the Rovno Oblast (first report) for the limited time period of up to six years after the accident. The doses actually received by the adults are estimated to be four to eight times smaller than the doses calculated for the situation without countermeasures.

Adult↗
PubMed1996

Assessment of personnel protective equipment use at two Department of Energy facilities.

Research facilities under the jurisdiction of the United States Department of Energy are required to formally report significant radioactive contamination incidents to the Department of Energy under Department of Energy Order 5000.3. Through the reporting process, the Department of Energy is given a detailed incident description through a notification report, periodically apprised of subsequent facility response through update reports, and informed of the corrective actions that the facility will implement to prevent incident recurrence through a final report. For tracking and trending purposes, the notification, update, and final reports are entered into the Department of Energy Occurrence Reporting and Processing System database. This paper details an analysis that was performed on the radioactive contamination incident reports that were entered into the Department of Energy Occurrence Reporting and Processing System database by two similar research facilities at Los Alamos National Laboratory. The analysis focused on personnel protective equipment requirements at the two facilities to determine whether personal skin and clothing contamination incidents could be better avoided.

Health Physics↗
PubMed1996

Bases for secondary standards for residual radionuclides in soil and some recommendations for cost-effective operational implementation.

The future use of land contaminated with radionuclides depends upon scientifically defensible bases for setting limits for radionuclides in soil. The purpose of this work is to develop such bases for establishing "posting criteria" to protect nonradiological workers at the Nevada Test Site and to provide a rationale for cost-effective measurements to readily determine the boundary conditions. The analysis begins with a mandated limit on total effective dose equivalent (1 mSv y(-1)) via all pathways. The possible pathways of exposure are external gamma exposure, inhalation of resuspended material, and incidental soil ingestion. These pathways are evaluated for each radionuclide of interest on the Nevada Test Site, and the results are used to define for each radionuclide the deposition-density limits for each pathway of exposure. The minimum deposition-density limits are noted to occur via the external gamma-exposure pathway for most radionuclides; exceptions are incidental soil ingestion for 90Sr/90Y and inhalation for 238Pu, 239,240Pu, and 241Am. The limiting values of deposition density or average concentration in soil are then determined appropriately by combining all pathways. Procedures are developed for dealing with mixtures of many radionuclides and to apply the principles developed so that even a simple measurement of external gamma-exposure rate may be used to define the boundary conditions in the field, provided that the relative abundance of the radionuclide mixture is known and that the defining level of exposure rate is sufficiently above background.

Cost-Benefit Analysis↗
PubMed1996

Assessing the service provided by an institutional radiation safety survey program.

Routine radiation safety surveys are a required part of every institutional radiation protection program. Although mandated by regulation, surveys are really performed to help clinicians and researchers establish and maintain radiologically-safe working and learning environments. In some cases, however, the priorities established by a radiation protection program may not coincide with the needs perceived by the institution's workers, leading to possible alienation, dissatisfaction, and non-compliance with policies, procedures, and regulations. To determine if a typical survey program was perceived as providing a good or valued service to workers, a simple questionnaire was created and utilized for a 6-mo period The results obtained from this targeted assessment tool indicate that the radiation safety survey services were perceived as useful by most of the workers. In addition, the actual process of comment solicitation provided a positive feedback mechanism from the service recipients to the radiation safety staff, managers, committee members, and institution administrators.

Humans↗
PubMed1996

Various approaches to damage assessment.

There are two main approaches used to assess the damage to human health from exposure to low-level ionizing radiation. The first is a realistic best-estimate approach. The second is performed in support of the development of radiation standards to protect workers and the public, and tends to overestimate risk. This paper reviews these approaches to damage assessments as they have been applied to the development of radiation protection standards and current estimates of risk. Technical issues affected by these two different approaches include use of the linear hypothesis, use of relative and absolute risk projection models, dose-rate effectiveness factor, appropriateness of data sets, and the transfer of risks between populations. The prudent approach may be justified for radiation protection purposes, but scientific estimates of risk should reflect the state-of-the-science and include estimates of uncertainty.

Accidents↗
PubMed1996

The use of cell-oriented factors and the hit size effectiveness function in radiation protection.

It has long been argued that ionizing radiation can be considered to interact with matter in discrete, randomly occurring energy transferring events ("hits") and that the resulting microscopically nonuniform pattern of energy deposition strongly influences the biological effect of a given exposure. Microdosimetric measurements combined with cellular biological response data in the form of a "hit size effectiveness function" (HSEF) suggest a possible cell-oriented alternative method of correlating exposure with effect at low levels of any radiation or mixture of radiations. The instrumentation required, the validity of the approach, and its practical usefulness in radiation protection are examined, and its application to space radiation exposure is proposed as a test case.

Aerospace Medicine↗
PubMed1996

Present concept on current water protection and remediation activities for the areas contaminated by the 1986 Chernobyl accident.

The results of radiation monitoring data and migration pathway analysis of water bodies within areas affected by the 1986 Chernobyl accident provide a unique opportunity for decision-makers working in other extensively contaminated regions to optimize their approaches to surface and groundwater protection. Most engineering measures within the Chernobyl 30-km exclusion zone were focused on preventing secondary contamination of surface and groundwater from entering the Pripyat River and the Kiev Reservoir. However, implementation of these measures required huge financial and human resources. Therefore, lessons about post-accidental water protection activities can be learned from the Chernobyl example.

Humans↗
PubMed1996

Environmental monitoring for a low-level radioactive waste management facility: incinerator operations.

An environmental monitoring program has been developed for Harvard University, Southborough campus, to assess the local environmental concentrations of radionuclides released in incinerator effluents. The campus is host to the University's low-level radioactive waste management facility, which consists of 6,000 drum capacity decay-storage buildings; a 250 drum capacity decay-storage freezer; and a controlled-air incinerator. Developmental considerations were based on the characteristics and use of the incinerator, which has a capacity of 8 tons per day and is operated 5% of the time for the volume reduction of Type 0 and Type 4 wastes contaminated with a variety of radionuclides used in biomedical research-some in microsphere form. Monitoring was established for air, leafy vegetation, leaf-litter, and surface soil media. Field sampling was optimized regarding location and time based on the action of atmospheric, terrestrial, and biotic transport mechanisms. Preliminary results indicate transient concentrations of 3H and 125I in vegetation directly exposed to the dispersing plume. Measurable particulate depositions have not been observed.

Environmental Monitoring↗