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Composite damage track-albedo personnel neutron dosimeter for general use

Description: No known detector or series of detectors in personnel neutron dosimeters have correct dose equivalent energy-dependence. Useful dosimeter performance is assumed by calibrating dosimeters for the exposure spectrum. This method implies that the exposure spectrum will be constant within a given facility or the wearer will not be exposed to different spectra in other areas. Since exposure spectra are known to vary widely a composite damage track-albedo personnel neutron dosimeter was developed to separately respond to the softer and more energetic parts of various spectra. The relationships of the responses of the elements vary with different spectra and are used to convert dosimeter readings to dose equivalent. Measurements indicate that dose equivalent deviation was less than approximately 50 percent for unshielded lucite and steel shielded HPRR spectra, monoenergetic spectra from 4.7 to 15 MeV, a $sup 252$Cf spontaneous neutron spectrum and an AmBe spectrum. Dosimeter sensitivity was similar to present NTA film methods. The composite personnel neutron dosimeter was also tested with calculated spectra by simulating badge response through known energy-dependence of the badge elements. Dose equivalent deviation was less than approximately 20 percent for 19 significantly different assumed spectra. Thus, the experimental and calculational results support adherence to the dose equivalent for common exposure spectra. (auth)
Date: January 1, 1975
Creator: Distenfeld, C.H.
Partner: UNT Libraries Government Documents Department

Radiography with heavy particles

Description: The failure of x-ray diagnostic techniques to accurately detect tumors and other regions of abnormal density in soft tissue has been, for many years, a significant shortcoming of this important technique in medicine. Accelerated heavy particles with plastics for track detection can be used to record small differences in density in soft tissues which may correspond to biological structures and abnormalities. In heavy-particle radiography (HPR), plastic detectors are well suited for recording images since their threshold nature makes them insensitive to spurious low-LET radiations and light secondaries. Sources of error which limit the resolution of HPR are inversely dependent on the atomic mass number (A) of the incident particle. Range straggling, responsible for loss of depth resolution, is proportional to A$sup -$ $sub 0$ $sup 5$ while multiple scattering which degrades lateral resolution is approximately proportional to A$sup -0$.$sup 395$. Recent experiments showing calcification in human blood vessels and soft tissue features in rats underline the potential of HPR as a diagnostic tool. High-resolution, three-dimensional reconstructions are possible using multiple layer plastic detectors and the short exposure time produces blur- free radiographs of specimens whose internal structure may be in motion. (auth)
Date: August 1, 1975
Creator: Benton, E.V.; Henke, R.P.; Tobias, C.A. & Cruty, M.R.
Partner: UNT Libraries Government Documents Department

Neutron-charged-particle reactions in CR-39 calculated using MCNP and LAHET

Description: A problem in using Bonner spheres for the spectroscopy of neutron of energy greater than 20 MeV is that the response functions for differing polyethylene thicknesses become similar in shape, making the spectral unfolding quite difficult. The possibility that use of a neutron detector such as CR-39 that is sensitive to high-energy neutrons combined with a lead radiator that has a significant variation of cross section due to the Pb(n,xn) reaction above 20 MeV, led to the theoretical investigation of the response of a CR-39 detector with lead in front of it. The authors have calculated the response of CR-39 (polyallyl-diglycol carbonate) in terms of charged particles produced per-unit-incident neutron for a foil of 2-cm diameter and 0.15-cm thick. They also calculated another set, using cylindrical slugs of lead of 2-cm diameter and 1-cm and 2-cm thick, with the foil positioned on the end of the slug so that the neutron beam had to pass through the lead. MCNP was used to calculate the responses in all three cases for energies from 0.1 MeV to 20 MeV. LEHET was applied to calculations from 0.1 MeV to 1,000 MeV. The MCNP calculation yields H(n,p), C(n,{alpha}), and O(n,{alpha}) reactions; the LAHET computation produces the sum of proton recoil and deuteron, triton, and alpha-particle production. The LAHET calculation indicates that the enhanced response due to Pb(n,xn) production may prove useful in neutron spectroscopy.
Date: December 31, 1996
Creator: Hsu, H.H. & Devine, R.T.
Partner: UNT Libraries Government Documents Department

Preliminary studies for a high energy neutron area monitor

Description: Track etch detectors were exposed to neutrons produced by a spallation target struck by a beam of 800 MeV protons. The fields were filtered by 0, 10, and 40 centimeters of polyethylene. The track etch dosimeters were exposed on a polyethylene phantom. The dosimeters were exposed bare and behind lead filters of 0.25, 0.50, 0.75, 1.00, 1.25 and 1.50 cm of lead with the face of the dosimeter perpendicular to the beam and bare and behind lead filters of 0.50, 1.0, and 1.5 cm of lead with angle of incidence 45{degree} and 75{degree}. Monte Carlo calculations of these experimental configurations were done using MCNP and LAHET with input from the calculated spectra. These results are compared with the experimental results to understand the basic processes involved in the production of tracks with high energy neutrons and develop a high energy neutron area monitor.
Date: December 1, 1998
Creator: Devine, R.T. & Hsu, H.H.
Partner: UNT Libraries Government Documents Department

System architecture and hardware design of the CDF XFT online track processor

Description: A trigger track processor is being designed for CDF Run 2. This processor identifies high momentum (P{sub T} > 1.5 GeV/c) charged tracks in the new central outer tracking chamber for the CDF II detector. The design of the track processor, called the eXtremely Fast Tracker (XFT), is highly parallel and handle an input rate of 183 Gbits/sec and output rate of 44 Gbits/sec. The XFT is pipelined and reports the results for a new event every 132ns. The XFT uses three stages, hit classification, segment finding, and segment linking. The pattern recognition algorithms for the three stages are implemented in Programmable Logic Devices (PLDs) which allow for in-situ modification of the algorithm at any time. The PLDs reside on three different types of modules. Prototypes of each of these modules have been designed and built, and are working. An overview of the hardware design and the system architecture are presented.
Date: November 5, 1999
Creator: al., Scott Holm et
Partner: UNT Libraries Government Documents Department

Personnel neutron dosimetry using electrochemically etched CR-39 foils

Description: A personnel neutron dosimetry system has been developed based on the electrochemical etching of CR-39 plastic at elevated temperatures. The doses obtained using this dosimeter system are more accurate than those obtained using other dosimetry systems, especially when varied neutron spectra are encountered. This Cr-39 dosimetry system does not have the severe energy dependence that exists with albedo neutron dosimeters or the fading and reading problems encountered with NTA film. The dosimetry system employs an electrochemical etch procedure that be used to process large numbers of Cr-39 dosimeters. The etch procedure is suitable for operations where the number of personnel requires that many CR-39 dosimeters be processed. Experience shows that one full-time technician can etch and evaluate 2000 foils per month. The energy response to neutrons is fairly flat from about 80 keV to 3.5 MeV, but drops by about a factor of three in the 13 to 16 MeV range. The sensitivity of the dosimetry system is about 7 tracks/cm/sup 2//mrem, with a background equivalent to about 8 mrem for new CR-39 foils. The limit of sensitivity is approximately 10 mrem. The dosimeter has a significant variation in directional dependence, dropping to about 20% at 90/sup 0/. This dosimeter has been used for personnel neutron dosimetry at the Lawrence Livermore National Laboratory for more tha 18 months. 6 refs., 23 figs., 2 tabs.
Date: September 17, 1986
Creator: Hankins, D.E.; Homann, S. & Westermark, J.
Partner: UNT Libraries Government Documents Department

Neutron response characteristics of CR-39 polymer for reactor and dosimetry applications

Description: A desensitized etching technique has been developed which has resulted in an excellent differential energy response for alpha particles in the energy range 3 to 14 MeV. This response complements the previously reported differential proton and integral alpha energy responses obtained with different etching techniques. Proton recoil track yields and diameter distributions have been measured for CR-39 polymer solid state track recorders which were exposed to monoenergetic neutron sources in the energy range 0.57 to 15.1 MeV using various thicknesses and types of proton radiator materials.
Date: September 4, 1981
Creator: Ruddy, F.H.; Gold, R.; Preston, C.C.; Roberts, J.H.; Benton, E.V. & Schraube, H.
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

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

Personnel dosimetry of radon and radon daughters

Description: From symposium on noble gases; Las Vegas, Nevada, USA (24 Sep 1973). During the past five years of increased interest in monitoring the individual exposure of persons to radon and, more importantly, radon progeny attached to aerosol particles, several devices have been proposed. These include the following: (a) passive detectors based on nuclear track emulsions and track etching foils; (b) semi-active systems in which the aerosols are collected electrostatically and detected by scintillator/film combinations or track etching; and (c) active systems based on the collection of aerosols on a fiiter, and integrating measurement of the alpha flux from the filter by TLD or track films. All these systems have drawbacks, which have been minimized in a small active system based on alpha particle track etching which was originally developed at ORNL in 1969. Since then it has undergone substantial laboratory and field testing, and has been subjected to various improvements. The system is briefly discussed. (auth)
Date: January 1, 1973
Creator: Becker, K.
Partner: UNT Libraries Government Documents Department

Procedures for the use of Lexan and Makrofol SSNTDs in the detection of environmental concentrations of {sup 235}U and {sup 239}Pu

Description: Solid State Nuclear Track Detectors are used to study a variety of atomic particles. Polycarbonate SSNTD is used to study environmental concentrations of {sup 235}U and {sup 239}Pu in human urine and feces through fission track analysis. The samples of interest are deposited upon a Lexan slide, covered with a piece of Makrofol and exposed to a neutron fluence of 1.1 X 10{sup 17}. The fissile isotopes in the sample fission and the resulting fission fragments pass through either the surface of the Lexan or the surface of the Makrofol. The positive Coulombic attraction of the ionized fission fragments causes the electrons of the polycarbonate lattice to move towards the path of these particles, resulting in the breakage of chemical bonds in the lattice. The detector is then chemically etched in 6.5 N KOH that preferentially dissolves the damaged polycarbonate left in the path of the fission fragment. The chemically etched fission tracks are permanent records of the path of the fission fragment. The etched fission tracks in Lexan are optically counted using a microscope and the fission tracks in Makrofol are counted using a Spark Chamber. The amount of fissile material in the original sample can be calculated from the number of fission tracks. This paper presents further details of procedures for etching fission tracks in Lexan and Makrofol and for operating a Spark Chamber to count etched fission tracks in Makrofol. The physics of fission track formation in dielectric detectors is also discussed, as well as the physics of the Spark Chamber.
Date: March 1, 1993
Creator: Henderson, C.L.
Partner: UNT Libraries Government Documents Department

Energy gain of highly charged ions in front of LiF

Description: We present estimates of the energy gain of highly charged ions approaching a LiF surface, based on a modified classical-over-barrier model for insulators. The analysis includes the energy gain by image acceleration as well as the deceleration due to charge-up of the surface in a staircase sequence. The role of the frequency-dependent dielectric response of LiF is emphasized. The resulting velocity dependent total energy gain is studied in detail and the results are compared with experimental data.
Date: September 24, 1996
Creator: Haegg, L.; Reinhold, C. O. & Burgdoerfer, J.
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

Buffon needle method of track counting

Description: A new technique of quantitative track counting, the Buffon needle method, is advanced. It is based on random sampling of the solid state track recorder (SSTR) surface. This new method extends quantitative track scanning to track densities well up into the track pile-up regime. It is shown that the Buffon needle method possesses a reduced dependence upon both track density nonuniformity and track size distribution. Sources of experimental error arising in the Buffon needle method are assessed. The validity of the Buffon needle method is demonstrated down to at least the 10% uncertainty level (1sigma) by manual sampling of high fission track density mica SSTR observed with scanning electron microscopy.
Date: September 4, 1981
Creator: Gold, R.; Roberts, J.H. & Ruddy, F.H.
Partner: UNT Libraries Government Documents Department

Review of the state of the art in personnel neutron monitoring with solid state detectors

Description: Albedo systems are the mainstay at many facilities and continue to be refined. Advanced electrochemical etching techniques for CR-39 now yield a dose equivalent response that is nearly constant from 0.1 to 4.0 MeV. Recent studies include use of converters to enhance CR-39 response at both low and high energies. Methods have been suggested for use of CR-39, either alone or in conjunction with albedo and other detectors to provide spectral information as a step to more accurate dosimetry. Limitations in the use of CR-39 primarily center on the lack of consistent, high-quality, dosimetry-grade material, significant angular dependence, and poor dose equivalent response at both low and high energies. Work continues on silicon diodes, with some new designs. The most attractive new dosimetry technique is the bubble-damage or superheated drop detector. Metal-on-silicon (MOS) microelectronics present exciting possibilities for the future. 25 refs., 6 figs.
Date: October 2, 1987
Creator: Griffith, R.V.
Partner: UNT Libraries Government Documents Department

Developments in solid state detectors for personnel neutron dosimetry

Description: The personnel neutron exposure potential at the Lawrence Livermore National Laboratory is more diverse than at many other facilities, due to the wide range of neutron producing activities. Albedo energy response problems in the face of the diversity of sources, and a concern about possible photon interferences with the neutron albedo response, have prompted development of some additional dosimetry techniques to augment the personnel monitoring program. This work now consists of two programs - the dosimeter/spectrometer (DOSPEC) in which track etch detectors are added to the albedo badge to provide some energy evaluation and gamma insensitivity, and development of solid state thin film MOS detectors to provide a real time, gamma insensitive dosimeter.
Date: July 23, 1981
Creator: Griffith, R.V.; Davidson, K.J.; Miller, D.E. & Vindelov, K.E.
Partner: UNT Libraries Government Documents Department

Systematic approach to personnel neutron monitoring

Description: NTA film and albedo detectors represent the major portion of personnel dosimeters now used for occupational neutron monitoring. However, recent attention to the spectral response of these systems has demonstrated the need for detectors that have a better match to the fields being monitored. Recent developments in direct recoil track etch dosimeters present some intriguing alternatives, and careful use of /sup 237/Np fission fragment detectors offers the advantage of a good dose equivalent spectral match. Work continues on a number of other new detector mechanisms, but problems with sensitivity, energy response, gamma interference, etc., continue to prevent development of most mechanisms into viable personnel dosimeters. Current dosimeter limitations make a systematic approach to personnel neutron monitoring particularly important. Techniques have been developed and tested, using available portable survey instruments, that significantly improve the quality of dosimeter interpretation. Even simple spectrometry can be done with modest effort, significantly improving the health physicists ability to provide accurate neutron monitoring.
Date: January 1, 1980
Creator: Griffith, R.V. & Hankins, D.E.
Partner: UNT Libraries Government Documents Department