Applicability of 1994-1995 USRADS{reg_sign} surveys of Bear Creek Valley flood plain and Operable Unit 1 to the radiological characterization of Y-12 grassy/wooded areas

This document, provided in support of the Y-12 Site Radiological Characterization Study, analyzes the utility of data from two reports by Chemrad Tennessee Corporation in identifying radiological contamination in excess of contamination control guidelines at the surface of soils in the Bear Creek Valley Flood Plain (BCVFP) and in Y-12 Operable Unit 1 (OU1). The Chemrad reports were developed under subcontract to Science Applications International Corporation for their remedial investigation of these sites for Martin Marietta Energy Systems Environmental Restoration Division. Surveys were performed by Chemrad using the UltraSonic Ranging and Data System (USRADS{reg_sign}), which utilizes ultrasonic triangulation to determine the location of a survey technician at the same time that radiological monitoring data are telemetered from his instruments to a remote receiving station. Floor monitor and Geiger-Mueller pancake meter results from the USRADS{reg_sign} surveys are shown to be sufficiently precise to reliably detect contamination in excess of the limiting radioactivity value of 1,000 dpm/100 cm{sup 2} for removable uranium contamination specified in 10 CFR 835 Appendix D. MicroRem meter survey results, also included as part of the USRADS{reg_sign} surveys, indicate that the derived limiting value of 56.8 {mu}rem/h for penetrating dose at 1 m (corresponding to 100 mrem/{gamma}) was not exceeded. However, both the pancake meter and floor monitor results suggest that surface contamination exceeding 1,000 dpm/100 cm{sup 2} is not uncommon. Sites in OU1 and BCVFP were visited, and independent surveys made with hand-held instruments, to confirm conclusions about the USRADS{close_quote} survey results and to verify that these results are from contamination uniformly distributed on the soil surface, and not from discrete sources which are not likely transferred to shoes, vehicles, or clothing

Calculations for high-energy radiations

The theoretical high-energy dosimetry program, developed over the past decade in the Health Physics Division of the Oak Ridge National Laboratory, is described briefly. Some selected results are presented to illustrate the calculational capabilities that exist. These examples include depth-dose curves for broad, parallel beams of 2 GeV protons and 1 GeV neutrons incident laterally on a tissue slab and activation calculated as a function of depth in a water phantom exposed to a beam of 400 MeV neutrons. Because of their planned use in cancer radiotherapy research, pions are under extensive study. The Monte Carlo computer code, PION-I, was developed to calculate the penetration of pions in materials (containing H, C, N, and O) exposed to pion beams. Good agreement is found between calculated and measured curves in water. Calculated L.E.T. distributions at various depths are shown. The pattern of energy deposition around pion capture sites is analyzed. T-i kidney cell survival levels are predicted for pion beams based on data of Todd and on the survival model of Katz

Interface effects on dose distributions in irradiated media

It has long been recognized that nonuniformities in dose distributions may occur in the immediate vicinity of a boundary between two different media. Considerable work has been done to determine interface effects in media irradiated by photons or in media containing ..beta..- or ..cap alpha..-particle emitters. More recently interface effects have become of interest in additional problems, including pion radiotherapy and radiation effects in electronic microcircuits in space vehicles. These problems arise when pion capture stars or proton-nucleus interactions produce a spectrum of charged nuclear fragments near an interface. The purpose of this paper is to examine interface effects in detail as to their specific origin. We have made Monte Carlo calculations of dose distributions near an interface in a systematic way for a number of idealized cases in order to indicate the separate influences of several factors including different stopping powers of the two media, nonconstancy (e.g., Bragg peak) in the energy loss curve for the particles, different particle spectra in the two media, and curvature of the boundary between the two media

Microscopic description of energy deposition in tissue by pion beams

Direct experimental information about the results of the capture of stopped negative pions by oxygen and carbon nuclei is scant. The Monte Carlo computer program, PION-1, has been developed to provide the needed data. The spatial distribution of the dose in a water target calculated from PION-1 is in good agreement with that measured in a typical experiment. This program transports each primary particle in a pion beam (i.e., pion, n'uon, or electron) individually until it interacts, leaves the target, or stops. Multiple scattering and range straggling are included. For each interaction the program produces a set of secondary particles (protons, neutrons, alpha particles, recoil nuclei, etc.), which it also transports. From the complete microscopic picture thus generated, the dose from each type of particle, the LET distributions, etc. can be tabulated in any desired manner. PION-1 was used to obtain such information for tissue targets irradiated by pion beams. The breakdown of the components of dose in various volume elements within the beam (in the plateau and in the peak) and outside the beam was calculated. A discussion is given of the details of the nature of the dose in these various positions as well as some observations about details of pion capture stars. The energy deposited within various microscopic volume elements, as well as the LET distribution, is described. A discussion is also given of the results of weighing the dose with RBE-LET values given by Todd as well as the application of the cell survival model of Katz. (auth

Statistical fluctuations in heavy-charged-particle tracks

We present the results of the following Monte Carlo track-segment calculations for protons with energies of 1, 2, 5, and 10 MeV in liquid water: (1) radial dose around a long segment of a proton track; (2) energy-loss straggling distributions for protons of different energies in 1 ..mu..m of water; (3) the distribution in the average absorbed dose around track segments of various lengths; (4) the relative standard deviations in these distributions as functions of the length of the track segments. Calculations such as those presented here are useful for studying track phenomena on a microdosimetric scale, where statistical fluctuations are substantial

Inelastic cross sections for electron interactions in liquid water

The task was to develop a set of cross sections for electron inelastic processes in liquid water suitable for use in a Monte Carlo transport calculation. Results are plotted as inverse mean free paths vs electron energy. (DLC

Calculated distance distributions of energy transfer events in irradiated liquid water

Histories from a Monte Carlo electron transport calculation in liquid water are analyzed to obtain the distance distribution functions, t(x) and T(x), of energy transfer events. These functions, which give the average energy transferred within a distance x from an arbitrary transfer event, are presented for irradiation by monoenergetic electrons of several energies between 500 eV and 1 MeV, for monoenergetic photons of 10, 50, and 200 keV energy and for 65 kVp and 200 kVp x rays and /sup 60/Co..gamma.. rays. The dose average lineal energy in spherical sites as a function of site radius is also presented for these same photon spectra

Calculation of heavy-ion tracks in liquid water

Detailed Monte Carlo calculations are presented of proton and alpha-particle tracks in liquid water. The computations treat the interactions of the primary particle and all secondary electrons on a statistical, event-by-event basis to simulate the initial physical changes that accompany the passage of an ion through water. Our methods for obtaining the cross sections needed for such calculations are described. Inelastic scattering probabilities (inverse mean free paths) are derived from a complex dielectric response function constructed for liquid water, based on experimental and theoretical data. Examples of partial cross sections for ionization and excitation by protons are shown. The computation of electron transport and energy loss includes exchange, elastic scattering, and a scheme for the delocalization of energy shared collectively by a large number of electrons in the condensed medium. Several examples of calculated proton and alpha-particle tracks are presented and discussed. The meaning and significance of the concept of a ''track core'' is briefly addressed in the light of this work. The present paper treats only the initial, physical changes produced by radiation in water (in approx. 10/sup -15/ sec in local regions of a track). The work described here is used in calculations that we have reported in other publications on the later chemical development of charged-particle tracks. 10 refs., 6 figs