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Los Alamos personnel and area criticality dosimeter systems

Description: Fissionable materials are handled and processed at the Los Alamos National Laboratory. Although the probability of a nuclear criticality accident is very remote, it must be considered. Los Alamos maintains a broad spectrum of dose assessment capabilities. This report describes the methods employed for personnel neutron, area neutron, and photon dose evaluations with passive dosimetry systems.
Date: June 1, 1981
Creator: Vasilik, D.G. & Martin, R.W.
Partner: UNT Libraries Government Documents Department

Evaluation of the /sup 63/Cu activation foil for determining the neutron dose in the energy range of 1 eV to 1 MeV

Description: The appropriateness of the /sup 63/Cu activation foil for determining the neutron dose in the energy region from 1 eV to 1 MeV has been investigated for spectra of seven different criticality accident configurations. A program was written for folding the published spectra with the /sup 63/Cu activation cross sections and with the fluence-to-dose or kerma conversion factors. It is shown that for these spectra the neutron dose and kerma result primarily from the energy region above 15 keV whereas the measured /sup 64/Cu activity is mainly determined by the fluence in the region between 1 eV and 15 keV. Uncertainties in the fluence spectrum in the low-energy region between 1 eV and 15 keV, which in reality do not affect the dose contribution, might lead to large deviations in the measured /sup 64/Cu activity and hence to the derived dose in the 1 eV to 1 MeV range. Use of /sup 10/B shielding for attenuating the fluence in the 1-eV to 15-keV region was evaluated, leading to the conclusion that the necessary amount of boron material is unacceptably large and would appreciably increase the cost of the dosimeter currently used at Los Alamos. The lower limit of neutron detectability would also be increased.
Date: August 1, 1984
Creator: Eisen, Y.; Vasilik, D.G. & Brake, R.J.
Partner: UNT Libraries Government Documents Department

Nuclear-accident dosimetry: measurements at the Los Alamos SHEBA critical assembly

Description: Criticality dosimeters were exposed to different degraded neutron and gamma-ray energy spectra from the Los Alamos Solution High Energy Burst Assembly (SHEBA). The liquid critical test assembly was operated in the continuous mode to provide a mixed source of neutron and gamma-ray radiation for the evaluation of Los Alamos criticality detector systems. Different neutron and gamma-ray spectra were generated by operating the reactor (a) shielded by 12 cm of Lucite, (b) unshielded, (c) shielded by 20 cm of concrete, and (d) shielded by 15 cm of steel. This report summarizes the dosimetry measurements conducted for these different configurations. In-air measurements were conducted with shielded and unshielded area and personnel dosimeters. Phantom measurements were made using personnel dosimeters. Combined blood-sodium and hair sulfur activation measurements of absorbed dose were also made. In addition, indium foils placed on phantoms were evaluated for the purpose of screening personnel for radiation exposure.
Date: July 1, 1981
Creator: Vasilik, D.G.; Martin, R.W. & Fuller, D.
Partner: UNT Libraries Government Documents Department

Portable neutron spectrometer/dosimeter

Description: As part of the continuing DOE effort to upgrade personnel neutron dosimetry, the Health Division at Los Alamos has developed a portable, battery-operated, computerized neutron spectrometer/dosimeter. The instrument has a built-in tissue-equivalent LET neutron detector, 128-channel pulse height analyzer with integral liquid crystal display, and a microcomputer system which calculates dose and dose rate from neutrons incident on the detector. The neutron spectrometer/dosimeter is designed around a linear energy transfer (LET) proportional counter. The instrument will, at the user's option, display a raw data spectrum or a spectrum of rad or rem as a function of keV per micron of equivalent tissue. The dosimeter will also calculate and display accumulated dose in millirad and millirem, as well as giving the user neutron dose rates in millirad and millirem per hour.
Date: January 1, 1982
Creator: Waechter, D.A.; Erkkila, B.H. & Vasilik, D.G.
Partner: UNT Libraries Government Documents Department

Computerized plutonium wound-analysis system

Description: A new plutonium wound monitor has been developed at Los Alamos to upgrade a system which has been in use for about five years. The instrument, called a Computerized Wound Screening System, is designed around a readily available personal computer. It includes a full-function 256-channel pulse height analyzer and software necessary to calculate plutonium and americium activity from a spectrum. This new system provides medical and health physics personnel with considerable flexability in recognizing and recording situations where a wound incurred in a plutonium processing facility might be contaminated. This flexibility includes fast, accurate determination of contaminants in a wound, hard copy printout of results, and full patient logging capabilities via flexible disk storage. Use of a low cost computer greatly simplifies hardware and software design, and makes duplication of the instrument very simple and inexpensive.
Date: January 1, 1983
Creator: Waechter, D.A.; Brake, R.J.; Vasilik, D.G. & Erkkila, B.H.
Partner: UNT Libraries Government Documents Department

Performance of low pressure tissue equivalent chambers and a new method for parameterizing the dose equivalent

Description: The performance of spherical tissue equivalent chambers with equivalent diameters between 0.5 and 2..mu.. was tested experimentally using monoenergetic and polyenergetic neutron sources in the energy region of 10 keV to 14.5 MeV. Theoretical calculations were performed in order to obtain a simple algorithm for deriving the dose equivalent from the measured data. The algorithm relates the number of recoil particles to the dose equivalent, rather than having a one-to-one correspondence between the lineal energy and the linear energy transfer of the recoil particles. The calculations took into account neutron interactions with hydrogen atoms in the chamber wall as well as in the gas, and also the finite energy resolution determined by both the detector and the electronic system. Qualitatively, the calculations well dscribe the experimental results. The algorithm that was developed determines the neutron dose equivalent, from the data of the 0.5..mu.. chamber, to better than +-20% over the energy range of 30 keV to 14.5 MeV. The same algorithm also determines the dose equivalent from the data of the 2..mu.. chamber to better than +-20% over the energy of 70 keV to 14.5 MeV. The efficiency of the chambers is low and has an average value of 330 counts per mrem, or equivalently about 0.2 c/s per mrem/h. This efficiency enables the measurement of dose equivalent rates only above 100 mrem/h for an integration period of 3 seconds. However, integrated dose equivalents can be mesured as low as 0.1 mrem.
Date: September 1, 1986
Creator: Eisen, Y.; Vasilik, D.G.; Brake, R.J.; Erkkila, B.H. & Littlejohn, G.J.
Partner: UNT Libraries Government Documents Department

High-energy neutron dosimetry at the Clinton P. Anderson Meson Physics Facility

Description: Neutron energy spectrum measurements performed at the Clinton P. Anderson Meson Physics Facility indicated potential areas for high energy neutron exposure to personnel. The low sensitivity of the Los Alamos thermoluminescent dosimeter (TLD) to high energy neutrons warranted issuing a NTA dosimeter in addition to the TLD badge to employees entering these areas. The dosimeter consists of a plastic holder surrounding NTA film that has been desiccated and sealed in a dry nitrogen environment. A study of the fading of latent images in NTA film demonstrated the success of this packaging method to control the phenomenon. The Los Alamos NTA dosimeter is characterized and the fading study discussed. 10 refs., 4 figs., 2 tabs.
Date: January 1, 1990
Creator: Mallett, M. W.; Vasilik, D. G.; Littlejohn, G. J. & Cortez, J. R.
Partner: UNT Libraries Government Documents Department

An optimal target-filter system for electron beam generated x-ray spectra

Description: An electron beam generated x-ray spectrum consists of characteristic x rays of the target and continuous bremsstrahlung. The percentage of characteristic x rays over the entire energy spectrum depends on the beam energy and the filter thickness. To determine the optimal electron beam energy and filter thickness, one can either conduct many experimental measurements, or perform a series of Monte Carlo simulations. Monte Carlo simulations are shown to be an efficient tool for determining the optimal target-filter system for electron beam generated x-ray spectra. Three of the most commonly used low-energy x-ray metal targets (Cu, Zn and Mo) are chosen for this study to illustrate the power of Monte Carlo simulations.
Date: April 1, 1994
Creator: Hsu, Hsiao-Hua; Vasilik, D. G. & Chen, J.
Partner: UNT Libraries Government Documents Department

The use of microdosimetric techniques in radiation protection measurements

Description: A major objective of radiation protection is to determine the dose equivalent for routine radiation protection applications. As microdosimetry has developed over approximately three decades, its most important application has been in measuring radiation quality, especially in radiation fields of unknown or inadequately known energy spectra. In these radiation fields, determination of dose equivalent is not straightforward; however, the use of microdosimetric principles and techniques could solve this problem. In this paper, the authors discuss the measurement of lineal energy, a microscopic analog to linear energy transfer, and demonstrate the development and implementation of the variance-covariance method, a novel method in experimental microdosimetry. This method permits the determination of dose mean lineal energy, an essential parameter of radiation quality, in a radiation field of unknown spectrum, time-varying dose rate, and high dose rate. Real-time monitoring of changes in radiation quality can also be achieved by using microdosimetric techniques.
Date: January 1, 1997
Creator: Chen, J.; Hsu, H.H.; Casson, W.H. & Vasilik, D.G.
Partner: UNT Libraries Government Documents Department