548 Matching Results

Search Results

Advanced search parameters have been applied.

Use of wrist albedo neutron dosimeters

Description: We are developing a wrist dosimeter that can be used to measure the exposure at the wrist to x-rays, gamma rays, beta-particles, thermal neutrons and fast neutrons. It consists of a modified Hankins Type albedo neutron dosimeter and also contains three pieces of CR-39 plastic. ABS plastic in the form of an elongated hemisphere provides the beta and low energy x-ray shielding necessary to meet the requirement of depth dose measurements at 1 cm. The dosimeter has a beta window located in the side of the hemisphere oriented towards an object being held in the hands. A TLD 600 is positioned under the 1 cm thick ABS plastic and is used to measure the thermal neutron dose. At present we are using Velcro straps to hold the dosimeter on the inside of the wrist. 9 figures.
Date: January 1, 1983
Creator: Hankins, D.E.
Partner: UNT Libraries Government Documents Department

Development of an operational multicomponent personnel neutron dosimeter/spectrometer DOSPEC

Description: A multicomponent dosimeter has been developed that uses an albedo detector to provide the measurement of low energy neutrons and as a screening element. It also contains track detector components, CR-39 and polycarbonate, which are only processed if the TLD indicates there has been an exposure to neutrons. Since the three components have significantly different energy responses, the dosimeter can act as a crude spectrometer. This report describes the dosimeter and briefly summarizes its use experience. 10 refs., 2 figs., 2 tabs.
Date: October 26, 1983
Creator: Griffith, R.V. & McMahon, T.A.
Partner: UNT Libraries Government Documents Department

Photographic film as a pocket radiation dosimeter

Description: The energy dependence of film blackening is discussed and shown graphically. The exposure range of films is discussed, and blackening is plotted vs exposure for DuPont No. 502, and for the less sensitive DuPont No. 351. A plan is then described for monitoring radiation exposure to workers by requiring the worker to carry an x-ray film of dental packet size in a badge designed for the purpose. (LEW)
Date: April 25, 1944
Creator: Pardue, L.A.; Goldstein, N. & Wollan, E.O.
Partner: UNT Libraries Government Documents Department

Neutron response of a new albedo-neutron dosimeter

Description: The Los Alamos Scientific Laboratory is converting from a film badge to a badge containing thermoluminescent dosimeters (TLD's). The new dosimeter consists of a plastic badge holding an aluminum card which contains three TLD-700 and one TLD-600 Harshaw LiF chips. In the albedo-neutron portion of the badge, based on Hankins' design, the TLD-600 and one TLD-700 chips are shielded from thermal neutrons by 0.026-inch-thick cadmium. From the difference in readings of these two TLD's, the neutron dose is estimated. There is also a detachable holder for NTA film if needed to cover the neutron energy range not covered by the albedo-neutron badge. The neutron energy response of the new badge was measured, using monoenergetic sources over the range from 0.1 to 14 MeV and is compared with a calculated response over this range. Since NTA film cannot detect proton recoils from neutrons with energies less than 0.7 MeV, a primary advantage of the TLD albedo-neutron badge is its ability to record neutrons down to the cadmium cutoff. However, a major disadvantage is its sharp decrease in sensitivity with increasing energy. Data are given showing this. Using a BF/sub 3/ detector inside 9-inch and 3-inch polyethylene spheres containing cadmium, Hankins developed a method for applying energy calibration factors to the albedo-neutron TLD badge readings. This method is based on two premises: first, that the response in rem of the 9-inch sphere is independent of energy and second, that the response of the 3-inch sphere is similar to that of the TLD albedo-neutron badge. Measurements to test the validity of these premises are reported. The method requires initial 9-inch to 3-inch sphere ratios to be measured in each area where neutrons are encountered and periodic checks to detect changes which may occur.
Date: January 1, 1978
Creator: Blackstock, A.W.; Cortez, J.R.; Littlejohn, G.J. & Storm, E.
Partner: UNT Libraries Government Documents Department

Experiences in environmental monitoring with BeO ceramic dosimeters

Description: Ceramic BeO disks used as radiation detectors have been evaluated in environmental radiation fields by observing the TL and TSEE signals given off after heating the disks. Fluxes of low energy photons cause the values for the two apparent exposure rates to diverge; this provides a measure of the quality of the photon radiation field. The mean of the TL and TSEE derived exposure rates is close to the exposure rate as determined by other means. The TL-TSEE dosimeters perform satisfactorily provided moisture is not allowed to condense onto the BeO and wet its surface when the temperature falls below the dew point. Thin impervious plastic packets or aluminium cans, containing silica gel desiccant, provide adequate protection. (auth)
Date: January 1, 1975
Creator: Gammage, R.B. & Haywood, F.F.
Partner: UNT Libraries Government Documents Department

Effect of energy dependence on the evaluations of albedo neutron dosimeters

Description: Albedo neutron dosimeters have proven to be effective as a method of measuring the dose from low-energy neutrons that other types of personnel neutron dosimeters do not detect. Many albedo neutron dosimeters have been designed, and some are being used extensively. All albedo neutron dosimeters are energy- dependent, becoming less sensitive as the energy of the neutrons is increased. In this paper the energy dependence and the effect it has on the evaluation of the dose are discussed. Numerous measurements are shown which were made under field conditions at five reactors, two accelerators, a radiochemistry facility, two plutonium facilities, a low-scatter neutron irradiation facility, three storage vaults, and at the N.B.S. low-energy neutron beams. These measurements show the limits imposed by the energy dependence on the evaluation of the dose determined by albedo neutron dosimeters. In most cases evaluation of an individual's dose occurring in a single facility can be reasonably accurate, but it must be known in which facility the person was exposed. Procedures using the incident thermal neutron response of TLDs located on top of the dosimeter to correct for the energy dependence are discussed; and errors caused by wearing a dosimeter improperly are evaluated. (auth)
Date: November 21, 1975
Creator: Hankins, D.E.
Partner: UNT Libraries Government Documents Department

Energy Response and Physical Reoperties of NTA* Personnel NeutronDosimeter Nuclear Track Film

Description: This paper reports the chemical and physical properties of the NTA film packet. It correlates with these properties the response of this packet to neutrons of various energies. In this correlation the concept of the track unit is introduced as a basic unit for reporting film-packet response.
Date: March 13, 1961
Creator: Lehman, Richard L.
Partner: UNT Libraries Government Documents Department

LET response of solid-state detectors. A review

Description: From fourth international symposium on microdosimetry; Verbania, Italy (27 Sep 1973). It is shown in a review of the LET response of various solidstate dosimeters such as TLD, RPL, TSEE, and photographic film that most of them exhibit (as predicted by the model of trap saturation by low-energy delta rays in a cylindrical zone around particle tracks) a more or less pronounced decrease in sensitivity with increasirg LET. The relationship between trap density (low LET saturation dose) and relative high LET (alpha particle) efficiency as well as some changes in the TL or TSEE curves can also be explained by this model. There are, however, apparently also some qualitative differences between the effects of low LET and high LET radiation, which indicate semi-permanent structural changes along high-LET particle tracks. It is concluded that both trap saturation and structural damage contribute to varying degrees, depending on lattice characteristics and the nature of the observed effect, to the detector response. (auth)
Date: January 1, 1973
Creator: Becker, K.
Partner: UNT Libraries Government Documents Department

Evaluation of the US Army DT-236 battlefield personnel dosimetry system

Description: Performance characteristics of the US Army DT-236 battlefield personnel dosimetry system were evaluated using the Health Physics Research Reactor at Oak Ridge National Laboratory. The DT-236 dosimeter is designed to measure total (neutron plus gamma) radiation dose using a radiophotoluminescent (RPL) detector for gamma rays and a silicon diode for fast neutrons. Areas considered in this evaluation included preirradiation dose indication; accuracy and precision of total, gamma, and neutron dose measurements; fading; angular response; temperature dependence; and relative dosimeter response in air and on various body locations. Experimental results for a variety of radiation fields and dose levels indicate that the existing system overestimates total, neutron, and gamma radiation doses in air by about 20 to 60% relative to reference values. Associated measurement precisions were about +-5% of the means for doses above approximately 0.5 Gy. Fading characteristics, angular dependence, and temperature dependence of the RPL and diode systems were consistent with results expected based on detector characteristics and previous performance studies. Recommendations to improve existing reader performance and measurement accuracy are also presented.
Date: June 1, 1986
Creator: Swaja, R.E.; Oyan, R.; Sims, C.S. & Dooley, M.A.
Partner: UNT Libraries Government Documents Department

Personnel-dosimetry intercomparison studies at the Oak Ridge National Laboratory

Description: Since 1974, seven annual personnel dosimetry intercomparison studies have been conducted at the Oak Ridge National Laboratory using the Health Physics Reactor. These studies have produced more than 2000 measurements by 72 participating organizations of neutron and gamma dose equivalents between 0.1 to 15.0 mSv in six mixed radiation fields. The relative performance of three basic types of personnel neutron dosimeters (nuclear emulsion film, thermoluminescent, and track-etch) and two basic types of gamma dosimeters (film and thermoluminescent) was assessed based on experimental results obtained during the seven intercomparisons.
Date: January 1, 1982
Creator: Swaja, R.E. & Sims, C.S.
Partner: UNT Libraries Government Documents Department

New technique to improve the accuracy of albedo neutron dosimeter evaluations

Description: The calibration factor for albedo neutron dosimeters varies greatly depending upon the energy of the neutrons in the exposure. Calibration results obtained over an eight-year period at each Lawrence Livermore National Laboratory facility where neutron exposure may occur were reviewed. A stronger relationship than expected was found between the ratio of the readings of the 9-in. to 3-in. spheres and the percent thermal. Readings from personnel and albedo badges were reviewed. The readings were consistent with the use of a calibration factor for the albedo dosimeter which varies with changes in the ratio of the personnel and albedo dosimeter TLD readings. 2 references, 6 figures. (ACR)
Date: January 1, 1984
Creator: Hankins, D.E.
Partner: UNT Libraries Government Documents Department

Neutron dosimetry of the Little Boy device

Description: Neutron dose rates at several angular locations and at distances out to 0.5 mile have been measured during critical operation of the Little Boy replica. We used modified remmetes and thermoluminescent dosimetry techniques for the measurements. The present status of our analysis is presented including estimates of the neutron-dose-relaxation length in air and the variation of the neutron-to-gamma-ray dose ratio with distance from the replica. These results are preliminary and are subject to detector calibration measurements.
Date: January 1, 1984
Creator: Pederson, R.A. & Plassmann, E.A.
Partner: UNT Libraries Government Documents Department

Hanford beta-gamma personnel dosimeter prototypes and evaluation

Description: Upgraded and modified Hanford dosimeter prototypes were evaluated for possible use at Hanford as a primary beta-gamma dosimeter. All prototypes were compatible with the current dosimeter card and holder design, as well as processing with the automated Hanford readers. Shallow- and deep-dose response was determined for selected prototypes using several beta sources, K-fluorescent x rays and filtered x-ray techniques. All prototypes included a neutron sensitive chip. A progressive evaluation of the performance of each of the upgrades to the current dosimeter is described. In general, the performance of the current dosimeter can be upgraded using individual chip sensitivity factors to improve precision and an improved algorithm to minimize bias. The performance of this dosimeter would be adequate to pass all categories of the ANSI N13.11 performance criteria for dosimeter procesors, provided calibration techniques compatible with irradiations adopted in the standard were conducted. The existing neutron capability of the dosimeter could be retained. Better dosimeter performance to beta-gamma radiation can be achieved by modifying the Hanford dosimeter so that four of the five chip positions are devoted to calculating these doses instead of the currently used two chip positions. A neutron sensitive chip was used in the 5th chip position, but all modified dosimeter prototypes would be incapable of discriminating between thermal and epithermal neutrons. An improved low energy beta response can be achieved for the current dosimeter and all prototypes considered by eliminating the security credential. Further improvement can be obtained by incorporating the 15-mil thick TLD-700 chips.
Date: April 1, 1983
Creator: Fix, J.J.; Holbrook, K.L. & Soldat, K.L.
Partner: UNT Libraries Government Documents Department

Calibration of personal dosemeters in terms of the ICRU operational quantities

Description: The International Commission on Radiological Units and Measurements (ICRU) has defined several new operational quantities for radiation protection purposes. The quantities to be used for personal monitoring are defined at depths in the human body. Because these quantities are impossible to measure directly, the ICRU has recommended that personal dosemeters should be calibrated under simplified conditions on an appropriate phantom, such as the ICRU sphere. The US personal dosimetry accreditation programs make use of a 30 {times} 30 {times} 15 cm polymethymethacrylate (PMMA) phantom, therefore it is necessary to relate the response of dosemeters calibrated on this phantom to the ICRU operational quantities. Calculations of the conversion factors to compute dosemeter response in terms of the operational quantities have been performed using the code MCNP. These calculations have also been compared to experimental measurements using thermoluminescent (TLD) detectors.
Date: May 1, 1992
Creator: McDonald, J.C. (Pacific Northwest Lab., Richland, WA (United States)) & Hertel, N.E. (Texas Univ., Austin, TX (United States). Dept. of Mechanical Engineering)
Partner: UNT Libraries Government Documents Department

Personnel neutron dosimetry

Description: This edited transcript of a presentation on personnel neutron discusses the accuracy of present dosimetry practices, requirements, calibration, dosemeter types, quality factors, operational problems, and dosimetry for a criticality accident. 32 figs. (ACR)
Date: April 1, 1982
Creator: Hankins, D.
Partner: UNT Libraries Government Documents Department

Calibration of personnel dosimeters

Description: Methods of calibrating both film and thermoluminescent dosimeters (TLD) to photon and electron radiations are described. K fluorescent x-rays, heavily filtered x-ray beams, and isotope gamma rays are used at the Los Alamos calibration facility to measure the energy and angular response of radiation detectors over a photon energy range of 10 to 1000 keV. Beam spectra, alignment, size and uniformity are discussed. The energy and angular response of dosimeters to electrons is measured with beta-emitting isotopes varying in maximum energy from 770 to 2300 keV.
Date: January 1, 1977
Creator: Storm, E.; Cortez, J.R. & Littlejohn, G.J.
Partner: UNT Libraries Government Documents Department

Personnel neutron dosimetry at Department of Energy facilities

Description: This study assesses the state of personnel neutron dosimetry at DOE facilities. A survey of the personnel dosimetry systems in use at major DOE facilities was conducted, a literature search was made to determine recent advances in neutron dosimetry, and several dosimetry experts were interviewed. It was concluded that personnel neutron dosimeters do not meet current needs and that serious problems exist now and will increase in the future if neutron quality factors are increased and/or dose limits are lowered.
Date: August 1, 1980
Creator: Brackenbush, L.W.; Endres, G.W.R.; Selby, J.M. & Vallario, E.J.
Partner: UNT Libraries Government Documents Department

Introduction to albedo neutron dosimeters

Description: The design, operation, calibration, and performance of albedo neutron dosimeters are discussed. An albedo neutron dosimeter is designed to measure the flux of thermal neutrons which leave the body when a person is exposed to fast energy neutrons. The fast neutrons are scattered and moderated in the body, and many have lost most of their initial energy and emerge as thermal neutrons. The albedo neutron dosimeter is designed to detect this flux of thermal neutrons by using a thermal neutron detector. This could be any type of thermal neutron detector but in practical applications lithium fluoride (LiF) thermoluminescence dosimeters (TLDs) are most frequently used. Various types of albedo neutron dosimeters are described. (WHK)
Date: January 16, 1978
Creator: Hankins, D.E.
Partner: UNT Libraries Government Documents Department