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Development and operation of a computerized source controller for a gamma calibration well

Description: In the 1950s, the need for an accurately reproducible, real-time gamma calibration facility at the Oak Ridge National Laboratory (ORNL) was met with a manually operated radium source housed in a calibration well. This arrangement was quite satisfactory in the early days but was not able to keep pace with the increasing number of instruments necessary to support an expanding health physics program. Consequently, the hand crank was replaced by an electric motor in the early 1960s. This improvement made it possible to move the source at speeds up to 7 cm/s, resulting in a major increase in efficiency. This configuration served reliably for two decades but, by the 1980s, component aging and the growing scarcity of replacement parts led to the development of a third-generation source controller. The electric motor and vacuum-tube-driven power supply were replaced with a solid state power supply and a stepper motor interfaced to a microcomputer. The software written to operate the system is menu-driven, user-friendly, and provides the greatest flexibility and ease of use while minimizing learning time. The development and use of this control system will be discussed.
Date: January 1, 1986
Creator: Halliburton, R.E.
Partner: UNT Libraries Government Documents Department

Evaluation of the need for radiotherapy calibrations in the United States

Description: The custody, maintenance, and development of the United States national standards of measurement, together with the provision of calibration services related to these standards, has been assigned to the National Bureau of Standards (NBS) of the U. S. Department of Commerce. It may be that the present system of promulgation of radiation standards is no longer adequate for the United States. Ionizing radiation is being used increasingly for the treatment of cancer patients. At present, approximately 325,000 new cancer patients per year are given radiation treatment at over 1500 centers. With this growing use of ionizing radiations, an increased awareness of the importance of accurate and precise dosimetry has developed. To determine the adequacy of these dosimetric needs, the AAPM has initiated a national study which is being conducted by means of a mailed questionnaire, and by a limited number of site visits to individuals who are in charge of radiation therapy centers as well as to those who do the actual calibrations.
Date: January 1, 1977
Creator: Lanzl, L.H. & Rozenfeld, M.
Partner: UNT Libraries Government Documents Department

Traceability of radiation measurements: musings of a user

Description: Although users of radiation desire measurement traceability for a number of reasons, including legal, regulatory, contractual, and quality assurance requirements, there exists no real definition of the term in the technical literature. Definitions are proposed for both traceability and traceability to the National Bureau of Standards. The hierarchy of radiation standards is discussed and allowable uncertainties are given for each level. Areas of need with respect to radiation standards are identified, and a system of secondary radiation calibration laboratories is proposed as a means of providing quality calibrations and traceability on a routine basis.
Date: April 1, 1980
Creator: Kathren, R.L.
Partner: UNT Libraries Government Documents Department

A proton medical accelerator by the SBIR route: An example of technology transfer

Description: Medical facilities for radiation treatment of cancer with protons have been established in many laboratories throughout the world. Essentially all of these have been designed as physics facilities, however, because of the requirement for protons up to 250 MeV. Most of the experience in this branch of accelerator technology lies in the national laboratories and a few large universities. A major issue is the transfer of this technology to the commercial sector to provide hospitals with simple, reliable, and relatively inexpensive accelerators for this application. The author has chosen the SBIR route to accomplish this goal. ACCTEK Associates have received grants from the National Cancer Institute for development of the medical accelerator and beam delivery systems. Considerable encouragement and help has been received from Argonne National Laboratory and the Department of Energy. The experiences to date and the pros and cons on this approach to commercializing medical accelerators are described. 4 refs., 1 fig.
Date: January 1, 1988
Creator: Martin, R.L.
Partner: UNT Libraries Government Documents Department

Calculated thickness of tungsten alloy required for specified attenuation of gamma radiation from sup 137 CS

Description: The traditional method of evaluating and calibrating health physics instruments is to use a calibrator that consists of a single high-activity gamma radiation source with different attenuators to select the radiation level desired for tesing. To have accurate radiation intensities inside the calibrator cavity, the attenuators must be designed from precise absorption calculations. This paper reports calculations made to determine the thickness of tungsten alloy metal required for specific attenuation. These calculations include the buildup contribution by secondary scattering radiation, and they are compared to values calculated with the buildup factor omitted. 3 refs., 2 figs., 3 tabs.
Date: January 1, 1991
Creator: Chiles, M.M.; Allin, G.W. & Pace, J.V. III.
Partner: UNT Libraries Government Documents Department

Specific gamma-ray dose constants for nuclides important to dosimetry and radiological assessment

Description: Tables of specific gamma-ray dose constants (the unshielded gamma-ray dose equivalent rate at 1 m from a point source) have been computed for approximately 500 nuclides important to dosimetry and radiological assessment. The half life, the mean attenuation coefficient, and thickness for a lead shield providing 95% dose equivalent attenuation are also listed.
Date: May 1, 1982
Creator: Unger, L.M. & Trubey, D.K.
Partner: UNT Libraries Government Documents Department

Facilities and techniques for x-ray diagnostic calibration in the 100-eV to 100-keV energy range

Description: The Lawrence Livermore National Laboratory (LLNL) has been a pioneer in the field of x-ray diagnostic calibration for more than 20 years. We have built steady state x-ray sources capable of supplying fluorescent lines of high spectral purity in the 100-eV to 100-keV energy range, and these sources have been used in the calibration of x-ray detectors, mirrors, crystals, filters, and film. This paper discusses our calibration philosophy and techniques, and describes some of our x-ray sources. Examples of actual calibration data are presented as well.
Date: June 1, 1986
Creator: Gaines, J.L. & Wittmayer, F.J.
Partner: UNT Libraries Government Documents Department

Multigamma-ray calibration sources

Description: We have calibrated a self-consistent set of multigamma-ray standards using the automated multi-spectrometry ..gamma..-ray counting facility at LLNL's Nuclear Chemistry Division. Pure sources of long-lived activity were produced by mass separation and/or chemical purification. The sources were counted individually and in combination on several different calibrated spectrometer systems. These systems utilize various detectors ranging from small (x-ray) detectors to large volume high-purity Ge detectors. This has allowed the use of the most ideal individual detector-efficiency characteristics for the determination of the relative ..gamma..-ray intensities. Precise energy measurements, reported earlier (Meyer, 1976) have been performed by an independent method. Both the energy and ..gamma..-ray-emission probabilities determined compare well with independently established values such as the recent ICRM intercomparison of /sup 152/Eu. We discuss our investigations aimed at resolving the shape of the efficiency response function up to 10 MeV for large volume Ge(Li) and high-purity Ge detectors. Recent results on the ..gamma..-ray-emission probabilities per decay for /sup 149/Gd and /sup 168/Tm multigamma-ray sources are discussed. For /sup 168/Tm, we deduce a 0.01% ..beta../sup -/ branch to the 87.73-keV level in /sup 168/Yb rather than the previous value which was a factor of 200 greater. In addition, we describe current cooperative efforts aimed at establishing a consistent set of data for short-lived fission products. Included are recent measurements on the bromine fission products with ..gamma.. rays up to 7 MeV.
Date: May 1, 1983
Creator: Meyer, R.A. & Massey, T.N.
Partner: UNT Libraries Government Documents Department

/sup 235/U fission mass and counting comparison and standardization

Description: /sup 235/U sample mass intercomparisons carried out at different laboratories were compiled. The compilationn reveals a trend with the NBS mass scale being systematically higher by 0.7% than other mass scales. Present measurements by fast-neutron fission counting confirm this difference. The present measurements result in a unified mass scale with about 0.6% uncertainty. Mass scales from LASL, ANL (No.1) and the University of Michigan are in excellent agreement (approximately +-0.1%) and within approximately 0.3% of the unified mass scale. The uncertainty of the unified mass scale established with the present measurements reduced the uncertainty for /sup 235/U mass and fission counting by about a factor of 2 compared with the NBS /sup 235/U mass scale against which all previous comparisons were made.
Date: May 1, 1979
Creator: Poenitz, W.P.; Meadows, J.W. & Armani, R.J.
Partner: UNT Libraries Government Documents Department

Techniques of absolute low energy x-ray calibration

Description: Recent advances in pulsed plasma research, materials science, and astrophysics have required many new diagnostic instruments for use in the low energy x-ray regime. The characterization of these instruments has provided a challenge to instrument designers and provided the momentum to improve x-ray sources and dosimetry techniques. In this paper, the present state-of-the-art in low energy x-ray characterization techniques is reviewed. A summary is given of low energy x-ray generator technology and dosimetry techniques including a discussion of thin window proportional counters and ionization chambers. A review is included of the widely used x-ray data bases and a sample of ultrasoft x-ray measuring procedures, chopped x-ray source generators, phase sensitive detection of ultralow currents, and angular divergence measurements.
Date: January 1, 1986
Creator: Day, R.H.
Partner: UNT Libraries Government Documents Department

Design and performance of the 1. 5 MV injector for FXR

Description: The new flash x-ray machine (FXR) at LLNL is scheduled for completion in late 1981. This is a 54 module, linear induction accelerator, designed to deliver 500 Roentgen at 1 m as bremsstrahlung from a 20 MeV, 4 kA, 60 ns pulsed electron beam. The 1.5 MV, cold cathode injector makes use of six accelerator modules as voltage sources. High voltage testing of the accelerator modules and their associated pulse forming lines and Marx banks has been completed, and beam tests of the complete injector assembly are in progress. Design information and preliminary test results are presented.
Date: March 4, 1981
Creator: Kulke, B.; Ravenscroft, D.S. & Vogtlin, G.E.
Partner: UNT Libraries Government Documents Department

Lawrence Livermore Laboratory x-ray calibration facility

Description: An X-Ray Calibration and Standards Laboratory has been established at the Lawrence Livermore Laboratory to provide x-ray calibrations of various types of x-ray diagnostic equipment presently being utilized. This Laboratory is the outgrowth of many years of involvement in the development of x-ray generation and calibration equipment. X-ray calibrations in a steady state mode are available from 100 eV to 100 keV. Pulsed response and linearity studies as well as radiation damage studies can also be performed. A crystal fabrication, characterization and calibration facility is an integral part of the Laboratory. A general discussion of various equipment and capabilities within the Laboratory is presented.
Date: November 3, 1978
Creator: Gaines, J.L.
Partner: UNT Libraries Government Documents Department

Calculation of dosimetry parameters for fast neutron radiotherapy

Description: A computer simulation of the interactions of 50 MeV d/sup +/ on Be and 42 MeV p/sup +/ on Be neutron spectra with ICRU muscle tissue and Shonka A-150 tissue equivalent plastic was performed to allow computation of the charged particle spectra that result. Nuclear data were obtained from the Evaluated Nuclear Data File (ENDF) whenever possible and from the Intranuclear Cascade and Evaporation models otherwise. The dosimetry parameters calculated are: the kerma ratio, K/sub A-150//K/sub tissue/; the energy required to form an ion pair, W; and the stopping power ratio, S/sub g//sup W/.
Date: May 1, 1978
Creator: Wells, A.H.
Partner: UNT Libraries Government Documents Department

Modular design of H/sup /minus// synchrotrons for radiation therapy

Description: A modular synchrotron for accelerating H/sup /minus// ions, and a proton beam delivery system are being developed for radiation therapy with protons under SBIR grants from the National Cancer Institute. The advantage proposed for accelerating H/sup /minus// ions and utilizing change exchange as a slow extraction mechanism lies in enhanced control for the extracted beam current, important for beam delivery with raster scanning for 3D dose contouring of a tumor site. Under these grants prototype magnets and vacuum systems are being constructed, appropriate H/sup /minus// sources are being developed and beam experiments will be carried out to demonstrate some of the key issues of this concept. The status of this program is described along with a discussion of a relatively inexpensive beam delivery system and a proposed program for its development. 3 refs.
Date: January 1, 1988
Creator: Martin, R.L.
Partner: UNT Libraries Government Documents Department

Synchrotron radiation and biomedical imaging

Description: In this lecture we describe the characteristics of Synchrotron radiation as a source of X rays. We discuss the properties of SR arc sources, wigglers, undulators and the use of backscattering of laser light. Applications to angiography, X ray microscopy and tomography are reviewed. 16 refs., 23 figs.
Date: August 1, 1986
Creator: Luccio, A.
Partner: UNT Libraries Government Documents Department

Comparison of the SANDYL Monte-Carlo code calculations of 20. 9-MeV bremsstrahlung with published experimental data

Description: The new flash x-ray facility constructed at Site 300 of the Lawrence Livermore National Laboratory has a nominal operating electron energy of 20 MeV. The bremsstrahlung photons from this accelerator will be used for a variety of radiographic investigations of both thick and thin objects under explosively driven conditions. In order to properly design and interpret experiments, it is very useful to have a Monte-Carlo code to simulate the coupled electron-photon processes that occur both in the creation of the bremsstrahlung as well as in the collimation, the materials being radiographed and the detection system. One such code suitable for this purpose in many experimental situations is the SANDYL code, which has been used at this laboratory since 1974. This brief report is written to point out that if one uses the code's default values for some of the parameters involving the electron substep size, the code-predicted bremsstrahlung is higher than experimental data by about 60. This report also shows that as this parameter is made finer, the code prediction approaches the experimental results to within about 10. This report compares the published data of O'Dell et al for bremsstrahlung at 20.9 MeV with our SANDYL calculations. O'Dell et al used linac-produced bremsstrahlung to irradiate a D/sub 2/O secondary target cell. Neutrons from photodisintegration of the deuterium were energy analyzed by time-of-flight at 90/sup 0/ to the photon direction, and the disintegration cross-section tables were used to infer the bremsstrahlung spectrum and strength. Our SANDYL calculations for the angular distribution of photon MeV are compared to the data of Sandifer and George for the same target.
Date: April 27, 1983
Creator: Goosman, D.R.
Partner: UNT Libraries Government Documents Department

Production and shielding of x rays from electron beam vapor sources

Description: Electron-beam vapor sources are now widely used in material processing sciences and coating technologies, such as the semiconductor industry for producing aluminum films on Si wafers; the metallurgical industry for melting, evaporating, and refining metals; and at Lawrence Livermore National Laboratory (LLNL) for vaporizing metals for laser isotope separation applications. Power for these sources ranges from the kW regime in the semiconductor industry to the multi-MW regime in laser separation technology. Operations of these sources can generate copious amounts of x rays by the direct and indirect interactions of the energetic electrons with the target materials. In this paper, we present the results of our calculations regarding the x-ray emission intensity, angular intensity and energy spectrum distribution, and shielding characteristics for vapor sources with acceleration voltages from 10 kV to 60 kV. 4 refs., 12 figs., 2 tabs.
Date: November 14, 1986
Creator: Singh, M.S.
Partner: UNT Libraries Government Documents Department

Gamma-ray energies from the /sup 14/N(n,. gamma. ) reaction

Description: A mass difference based B/sub n/(/sup 15/N) value was combined with ..gamma..-ray energy difference measurements to provide a consistent set of ..gamma..-ray energies from the /sup 14/N(n,..gamma..) reaction which are suitable for use as energy calibration standards in (n,..gamma..) spectroscopy.
Date: January 1, 1978
Creator: Greenwood, R C & Chrien, R E
Partner: UNT Libraries Government Documents Department

Initial characterization of a position-sensitive photodiode/BGO detector for PET (positron emission tomography)

Description: We present initial results of a position-sensitive photodiode/BGO detector for high resolution, multi-layer positron emission tomography (PET). Position sensitivity is achieved by dividing the 3 mm /times/ 20 mm rectangular photosensitive area along the diagonal to form two triangular segments. Each segment was individually connected to a low-noise amplifier. The photodiodes and crystals were cooled to /minus/100/degree/C to reduce dark current and increase the BGO signal. With an amplifier peaking time of 17 ..mu..sec, the sum of the signals (511 keV photopeak) was 3200 electrons with a full width at half maximum (fwhm) of 750 electrons. The ratio of one signal to the sum determined the depth of interaction with a resolution of 11 mm fwhm. 27 refs., 7 figs.
Date: November 1, 1988
Creator: Derenzo, S.E.; Moses, W.W.; Jackson, H.G.; Turko, B.T.; Cahoon, J.L.; Geyer, A.B. et al.
Partner: UNT Libraries Government Documents Department

Calibration of proportional counters in microdosimetry

Description: Many microdosimetric spectra for low LET as well as high LET radiations are measured using commercially available (similar to EG and G) Rossi proportional counters. This paper discusses the corrections to be applied to data when calibration of the counter is made using one type of radiation, and then the counter is used in a different radiation field. The principal correction factor is due to differences in W-value of the radiation used for calibration and the radiation for which microdosimetric measurements are made. Both propane and methane base tissue-equivalent (TE) gases are used in these counters. When calibrating the detectors, it is important to use the correct stopping power value for that gas. Deviations in y-bar/sub F/ and y-bar/sub D/ are calculated for /sup 60/Co using different extrapolation procedures from 0.15 keV/..mu..m to zero event size. These deviations can be as large as 30%. Advantages of reporting microdosimetric parameters such as y-bar/sub F/ and y-bar/sub D/ above a certain minimum cut-off are discussed.
Date: January 1, 1982
Creator: Varma, M.N.
Partner: UNT Libraries Government Documents Department

Spin-spin correlations in the one-dimensional spin-1/2 antiferromagnetic Heisenberg chain

Description: We have calculated the spin-spin correlations in the ground state of spin-1/2, one-dimensional, antiferromagnetic Heisenberg chain numerically. Using improved algorithms, we have been able to perform exact diagonalizations for lattices up to 30 sites and quantum Monte Carlo simulations for lattices up to 512 sites. This extensive range allows us to investigate the logarithmic dependence of spin-spin correlations. We present our results and discuss their implication. 11 refs., 1 fig., 2 tabs.
Date: January 1, 1990
Creator: Lin, H.Q. & Campbell, D.K.
Partner: UNT Libraries Government Documents Department

Calibration of a large hyperpure germanium array for in-vivo detection of the actinides with a tissue-equivalent torso phantom

Description: For calibration of the array for internally deposited /sup 238/Pu, /sup 239/Pu, and /sup 241/Am, a tissue-equivalent anthropomorphic phantom, was used for efficiency determinations at the ORNL facility. This phantom consists of a tissue-equivalent torso into which is imbedded an adult male skeleton, interchangeable organs containing a homogeneous distribution of various radionuclides, and two sets of chest overlay plates for simulation of progressively thicker tissue over the chest, as well as differing thoracic fat contents. (PSB)
Date: January 1, 1983
Creator: Berger, C.D. & Lane, B.H.
Partner: UNT Libraries Government Documents Department