William Atwell - Academia.edu (original) (raw)

Papers by William Atwell

Research paper thumbnail of Radiation Exposures from Several Ground Level Enhancements During the 23rd Solar Cycle

AIAA SPACE 2009 Conference & Exposition, 2009

Research paper thumbnail of Natural and Induced Environment in Low Earth Orbit

Nasa Sti Recon Technical Report N, May 1, 2002

The long-term exposure of astronauts on the developing International Space Station (ISS) requires... more The long-term exposure of astronauts on the developing International Space Station (ISS) requires an accurate knowledge of the internal exposure environment for human risk assessment and other onboard processes. The natural environment is moderated by the solar wind which varies over the solar cycle. The neutron environment within the Shuttle in low Earth orbit has two sources. A time dependent model for the ambient environment is used to evaluate the natural and induced environment. The induced neutron environment is evaluated using measurements on STS-31 and STS-36 near the 1990 solar maximum.

Research paper thumbnail of Radiological assessment for Space Station Freedom

Research paper thumbnail of Band Function Fit to 23rd Solar Cycle Ground Level Proton Events and Radiation Exposure Assessments

40th International Conference on Environmental Systems, 2010

Research paper thumbnail of Catenated Organic Compounds of Silicon, Germanium, Tin, and Lead

Advances in Organometallic Chemistry

Research paper thumbnail of Preliminary Radiation Analysis of the Total Ionizing Dose for the Resource Prospector Mission

AIAA SPACE 2014 Conference and Exposition, 2015

Research paper thumbnail of Comparison and Validation of FLUKA and HZETRN as Tools for Investigating the Secondary Neutron Production in Large Space Vehicles

AIAA SPACE 2014 Conference and Exposition, 2015

Research paper thumbnail of Estimating the Effects of Astronaut Career Ionizing Radiation Dose Limits on Manned Interplanetary Flight Programs

43rd International Conference on Environmental Systems, 2013

Research paper thumbnail of Investigation of HZETRN 2010 as a Tool for Single Event Effect Qualification of Avionics Systems - Part II

AIAA SPACE 2014 Conference and Exposition, 2015

Research paper thumbnail of Sub-GLE Solar Particle Events and the Implications for Lightly-Shielded Systems Flown During an Era of Low Solar Activity

Research paper thumbnail of Spacecraft SPE Shielding: SPE environment models and materials performance in a Cygnus PCM based EAM

Research paper thumbnail of Hydrogen-and Methane-Loaded Shielding Materials for Mitigation of Galactic Cosmic Rays and Solar Particle Events

Research paper thumbnail of The Preparation and Reactions of Some 7-Silanorbornadienes. I. An Approach to Dimethylsilylene

Journal of the American Chemical Society, 1964

... Page 3. 1598 HENRY GILMAN. STEVE GUST COTTIS, AND WILLIAM H. ATWELL Vol. 86 XIV ... of the sa... more ... Page 3. 1598 HENRY GILMAN. STEVE GUST COTTIS, AND WILLIAM H. ATWELL Vol. 86 XIV ... of the same solvent. The additions took approximately 4 hr. After allowing the reaction mixture to cool to room tem-perature, the solvents were removed under vacuum. ...

Research paper thumbnail of Improved model for solar cosmic ray exposure in manned Earth orbital flights

A calculational model is derived for use in estimating Solar cosmic ray exposure to critical body... more A calculational model is derived for use in estimating Solar cosmic ray exposure to critical body organs in low-Earth orbit at the center of a large spherical shield of fixed thickness. The effects of the Earth's geomagnetic field and the astronauts' self-shielding are evaluated explicitly. The geomagnetic field model is an approximate tilted eccentric dipole with geomagnetic storms represented as a uniform-impressed field. The storm field is related to the planetary geomagnetic index K(sub p). The code is applied to the Shuttle geometry using the Shuttle mass distribution surrounding two locations on the flight deck. The Shuttle is treated as pure aluminum and the astronaut as soft tissue. Short-term, average fluence over a single orbit is calculated as a function of the location of the lines of nodes or long-term averages over all lines of nodes for a fixed inclination.

Research paper thumbnail of Predictions of Cell Damage Rates for Lifesat Missions

Radiological experiments with cell cultures are expected to be performed on Lifesat to study poss... more Radiological experiments with cell cultures are expected to be performed on Lifesat to study possible gravitational dependence on cellular response. Predictions of cell damage rates for well-studied systems are expected to help guide in the selection of orbits and the design of experiments. In this report we estimate the fractions of cell death and neoplastic transformation of C3H10T1/2 cells (cultured mouse cells) for the proposed Lifesat orbits. The parametric cellular track model of Katz et al. (refs. 1 and 2) is employed using cellular response parameters derived from the experiments of Yang et al. (refs. 3 and 4). The contributions to the biological endpoints from the trapped protons and electrons, and GCR particles are considered for typical levels of spacecraft shielding. For the proton and GCR contributions the effects of nuclear reactions are taken into account. Expected counting rates for other possible cell culture experiments on Lifesat are discussed.

Research paper thumbnail of Preliminary calculation of solar cosmic ray dose to the female breast in space mission

No regulatory dose limits are specifically assigned for the radiation exposure of female breasts ... more No regulatory dose limits are specifically assigned for the radiation exposure of female breasts during manned space flight. However, the relatively high radiosensitivity of the glandular tissue of the breasts and its potential exposure to solar flare protons on short- and long-term missions mandate a priori estimation of the associated risks. A model for estimating exposure within the breast is developed for use in future NASA missions. The female breast and torso geometry is represented by a simple interim model. A recently developed proton dose-buildup procedure is used for estimating doses. The model considers geomagnetic shielding, magnetic-storm conditions, spacecraft shielding, and body self-shielding. Inputs to the model include proton energy spectra, spacecraft orbital parameters, STS orbiter-shielding distribution at a given position, and a single parameter allowing for variation in breast size.

Research paper thumbnail of Space Shuttle dosimetry measurements with RME-III

A description of the radiation monitoring equipment (RME-III) dosimetry instrument and the result... more A description of the radiation monitoring equipment (RME-III) dosimetry instrument and the results obtained from six Space Shuttle flights are presented. The RME-III is a self-contained, active (real-time), portable dosimeter system developed for the USAF and adapted for utilization in measuring the ionizing radiation environment on the Space Shuttle. This instrument was developed to incorporate the capabilities of two earlier radiation instruments into a single unit and to minimize crew interaction times with longer battery life and expanded memory capacity. Flight data has demonstrated that the RME-III can be used to accurately assess dose from various sources of exposure, such as that encountered in the complex radiation environment of space.

Research paper thumbnail of Preliminary estimates of galactic cosmic ray exposures for manned interplanetary missions

Preliminary estimates of radiation exposures resulting from galactic cosmic rays are presented fo... more Preliminary estimates of radiation exposures resulting from galactic cosmic rays are presented for interplanetary missions. The calculations use the Naval Research Laboratory cosmic ray transport code. The heavy ion portion of the transport code can be used with any number of layers of target material, consisting of up to five different constituents per layer. The nucleonic portion of the transport code can be used with any number of layers of target material of arbitrary composition except hydrogen. Calculated galactic cosmic ray particle fluxes, doses, and dose equivalents behind various thicknesses of aluminum shielding are presented for solar maximum and solar minimum periods.

Research paper thumbnail of Radiation dose to critical body organs for October 1989 proton event

The Geostationary Operational Environmental Satellite (GOES-7) provides high-quality environmenta... more The Geostationary Operational Environmental Satellite (GOES-7) provides high-quality environmental data about the temporal development and energy characteristics of the protons emitted during a solar particle event. The GOES-7 time history of the hourly averaged integral proton flux for various particle kinetic energies are analyzed for the solar proton event occurring October 19-29, 1989. This event is similar to the August 1972 event that has been widely studied to estimate free-space and planetary radiation-protection requirements. By analyzing the time-history data, the dose rates, which can vary over many orders of magnitude in the early phases of the flare, can be estimated as well as the cumulative dose as a function of time. When basic transport results are coupled with detailed body organ thickness distributions calculated with the Computerized Anatomical Man and Computerized Anatomical Female models, the dose rates and cumulative doses to specific organs can be predicted. ...

Research paper thumbnail of Improvement of Risk Assessment from Space Radiation Exposure for Future Space Exploration Missions

Protecting astronauts from space radiation exposure is an important challenge for mission design ... more Protecting astronauts from space radiation exposure is an important challenge for mission design and operations for future exploration-class and long-duration missions. Crew members are exposed to sporadic solar particle events (SPEs) as well as to the continuous galactic cosmic radiation (GCR). If sufficient protection is not provided the radiation risk to crew members from SPEs could be significant. To improve exposure risk estimates and radiation protection from SPEs, detailed evaluations of radiation shielding properties are required. A model using a modern CAD tool ProE™, which is the leading engineering design platform at NASA, has been developed for this purpose. For the calculation of radiation exposure at a specific site, the cosine distribution was implemented to replicate the omnidirectional characteristic of the 4π particle flux on a surface. Previously, estimates of doses from SPEs to the blood forming organs (BFO) were made using an average body-shielding distribution ...

Research paper thumbnail of Radiation Exposures from Several Ground Level Enhancements During the 23rd Solar Cycle

AIAA SPACE 2009 Conference & Exposition, 2009

Research paper thumbnail of Natural and Induced Environment in Low Earth Orbit

Nasa Sti Recon Technical Report N, May 1, 2002

The long-term exposure of astronauts on the developing International Space Station (ISS) requires... more The long-term exposure of astronauts on the developing International Space Station (ISS) requires an accurate knowledge of the internal exposure environment for human risk assessment and other onboard processes. The natural environment is moderated by the solar wind which varies over the solar cycle. The neutron environment within the Shuttle in low Earth orbit has two sources. A time dependent model for the ambient environment is used to evaluate the natural and induced environment. The induced neutron environment is evaluated using measurements on STS-31 and STS-36 near the 1990 solar maximum.

Research paper thumbnail of Radiological assessment for Space Station Freedom

Research paper thumbnail of Band Function Fit to 23rd Solar Cycle Ground Level Proton Events and Radiation Exposure Assessments

40th International Conference on Environmental Systems, 2010

Research paper thumbnail of Catenated Organic Compounds of Silicon, Germanium, Tin, and Lead

Advances in Organometallic Chemistry

Research paper thumbnail of Preliminary Radiation Analysis of the Total Ionizing Dose for the Resource Prospector Mission

AIAA SPACE 2014 Conference and Exposition, 2015

Research paper thumbnail of Comparison and Validation of FLUKA and HZETRN as Tools for Investigating the Secondary Neutron Production in Large Space Vehicles

AIAA SPACE 2014 Conference and Exposition, 2015

Research paper thumbnail of Estimating the Effects of Astronaut Career Ionizing Radiation Dose Limits on Manned Interplanetary Flight Programs

43rd International Conference on Environmental Systems, 2013

Research paper thumbnail of Investigation of HZETRN 2010 as a Tool for Single Event Effect Qualification of Avionics Systems - Part II

AIAA SPACE 2014 Conference and Exposition, 2015

Research paper thumbnail of Sub-GLE Solar Particle Events and the Implications for Lightly-Shielded Systems Flown During an Era of Low Solar Activity

Research paper thumbnail of Spacecraft SPE Shielding: SPE environment models and materials performance in a Cygnus PCM based EAM

Research paper thumbnail of Hydrogen-and Methane-Loaded Shielding Materials for Mitigation of Galactic Cosmic Rays and Solar Particle Events

Research paper thumbnail of The Preparation and Reactions of Some 7-Silanorbornadienes. I. An Approach to Dimethylsilylene

Journal of the American Chemical Society, 1964

... Page 3. 1598 HENRY GILMAN. STEVE GUST COTTIS, AND WILLIAM H. ATWELL Vol. 86 XIV ... of the sa... more ... Page 3. 1598 HENRY GILMAN. STEVE GUST COTTIS, AND WILLIAM H. ATWELL Vol. 86 XIV ... of the same solvent. The additions took approximately 4 hr. After allowing the reaction mixture to cool to room tem-perature, the solvents were removed under vacuum. ...

Research paper thumbnail of Improved model for solar cosmic ray exposure in manned Earth orbital flights

A calculational model is derived for use in estimating Solar cosmic ray exposure to critical body... more A calculational model is derived for use in estimating Solar cosmic ray exposure to critical body organs in low-Earth orbit at the center of a large spherical shield of fixed thickness. The effects of the Earth's geomagnetic field and the astronauts' self-shielding are evaluated explicitly. The geomagnetic field model is an approximate tilted eccentric dipole with geomagnetic storms represented as a uniform-impressed field. The storm field is related to the planetary geomagnetic index K(sub p). The code is applied to the Shuttle geometry using the Shuttle mass distribution surrounding two locations on the flight deck. The Shuttle is treated as pure aluminum and the astronaut as soft tissue. Short-term, average fluence over a single orbit is calculated as a function of the location of the lines of nodes or long-term averages over all lines of nodes for a fixed inclination.

Research paper thumbnail of Predictions of Cell Damage Rates for Lifesat Missions

Radiological experiments with cell cultures are expected to be performed on Lifesat to study poss... more Radiological experiments with cell cultures are expected to be performed on Lifesat to study possible gravitational dependence on cellular response. Predictions of cell damage rates for well-studied systems are expected to help guide in the selection of orbits and the design of experiments. In this report we estimate the fractions of cell death and neoplastic transformation of C3H10T1/2 cells (cultured mouse cells) for the proposed Lifesat orbits. The parametric cellular track model of Katz et al. (refs. 1 and 2) is employed using cellular response parameters derived from the experiments of Yang et al. (refs. 3 and 4). The contributions to the biological endpoints from the trapped protons and electrons, and GCR particles are considered for typical levels of spacecraft shielding. For the proton and GCR contributions the effects of nuclear reactions are taken into account. Expected counting rates for other possible cell culture experiments on Lifesat are discussed.

Research paper thumbnail of Preliminary calculation of solar cosmic ray dose to the female breast in space mission

No regulatory dose limits are specifically assigned for the radiation exposure of female breasts ... more No regulatory dose limits are specifically assigned for the radiation exposure of female breasts during manned space flight. However, the relatively high radiosensitivity of the glandular tissue of the breasts and its potential exposure to solar flare protons on short- and long-term missions mandate a priori estimation of the associated risks. A model for estimating exposure within the breast is developed for use in future NASA missions. The female breast and torso geometry is represented by a simple interim model. A recently developed proton dose-buildup procedure is used for estimating doses. The model considers geomagnetic shielding, magnetic-storm conditions, spacecraft shielding, and body self-shielding. Inputs to the model include proton energy spectra, spacecraft orbital parameters, STS orbiter-shielding distribution at a given position, and a single parameter allowing for variation in breast size.

Research paper thumbnail of Space Shuttle dosimetry measurements with RME-III

A description of the radiation monitoring equipment (RME-III) dosimetry instrument and the result... more A description of the radiation monitoring equipment (RME-III) dosimetry instrument and the results obtained from six Space Shuttle flights are presented. The RME-III is a self-contained, active (real-time), portable dosimeter system developed for the USAF and adapted for utilization in measuring the ionizing radiation environment on the Space Shuttle. This instrument was developed to incorporate the capabilities of two earlier radiation instruments into a single unit and to minimize crew interaction times with longer battery life and expanded memory capacity. Flight data has demonstrated that the RME-III can be used to accurately assess dose from various sources of exposure, such as that encountered in the complex radiation environment of space.

Research paper thumbnail of Preliminary estimates of galactic cosmic ray exposures for manned interplanetary missions

Preliminary estimates of radiation exposures resulting from galactic cosmic rays are presented fo... more Preliminary estimates of radiation exposures resulting from galactic cosmic rays are presented for interplanetary missions. The calculations use the Naval Research Laboratory cosmic ray transport code. The heavy ion portion of the transport code can be used with any number of layers of target material, consisting of up to five different constituents per layer. The nucleonic portion of the transport code can be used with any number of layers of target material of arbitrary composition except hydrogen. Calculated galactic cosmic ray particle fluxes, doses, and dose equivalents behind various thicknesses of aluminum shielding are presented for solar maximum and solar minimum periods.

Research paper thumbnail of Radiation dose to critical body organs for October 1989 proton event

The Geostationary Operational Environmental Satellite (GOES-7) provides high-quality environmenta... more The Geostationary Operational Environmental Satellite (GOES-7) provides high-quality environmental data about the temporal development and energy characteristics of the protons emitted during a solar particle event. The GOES-7 time history of the hourly averaged integral proton flux for various particle kinetic energies are analyzed for the solar proton event occurring October 19-29, 1989. This event is similar to the August 1972 event that has been widely studied to estimate free-space and planetary radiation-protection requirements. By analyzing the time-history data, the dose rates, which can vary over many orders of magnitude in the early phases of the flare, can be estimated as well as the cumulative dose as a function of time. When basic transport results are coupled with detailed body organ thickness distributions calculated with the Computerized Anatomical Man and Computerized Anatomical Female models, the dose rates and cumulative doses to specific organs can be predicted. ...

Research paper thumbnail of Improvement of Risk Assessment from Space Radiation Exposure for Future Space Exploration Missions

Protecting astronauts from space radiation exposure is an important challenge for mission design ... more Protecting astronauts from space radiation exposure is an important challenge for mission design and operations for future exploration-class and long-duration missions. Crew members are exposed to sporadic solar particle events (SPEs) as well as to the continuous galactic cosmic radiation (GCR). If sufficient protection is not provided the radiation risk to crew members from SPEs could be significant. To improve exposure risk estimates and radiation protection from SPEs, detailed evaluations of radiation shielding properties are required. A model using a modern CAD tool ProE™, which is the leading engineering design platform at NASA, has been developed for this purpose. For the calculation of radiation exposure at a specific site, the cosine distribution was implemented to replicate the omnidirectional characteristic of the 4π particle flux on a surface. Previously, estimates of doses from SPEs to the blood forming organs (BFO) were made using an average body-shielding distribution ...