Biomedical subjects

C Zeitlin

Publications and source records attributed to C Zeitlin.

At least 19 recordsLinked to original sources

PubMed2005

Fragmentation of 1 GeV/nucleon iron ions in thick targets relevant for space exploration.

We have measured charged nuclear fragments produced by 1 GeV/nucleon 56Fe ions interacting with aluminium, polyethylene and lead. These materials are relevant for assessment of radiation risk for manned space flight. The data will be presented in a form suitable for comparison with models of nuclear fragmentation and transport, including linear energy transfer (LET) spectrum, fluence for iron and fragments, event-tack- and event-dose-averaged LET, total dose and iron contribution to dose.

Aluminum↗

PubMed2005

Validation of the HZETRN code for laboratory exposures with 1A GeV iron ions in several targets.

A new version of the HZETRN code capable of validation with HZE ions in either the laboratory or the space environment is under development. The computational model consists of the lowest order asymptotic approximation followed by a Neumann series expansion with non-perturbative corrections. The physical description includes energy loss with straggling, nuclear attenuation, nuclear fragmentation with energy dispersion and downshift. Measurements to test the model were performed at the Alternating Gradient Synchrotron and the NASA Space Radiation Laboratory at Brookhaven National Laboratory with iron ions. Surviving beam particles and produced fragments were measured with solid-state detectors. Beam analysis software has been written to relate the computational results to the measured energy loss spectra of the incident ions for rapid validation of modeled target transmission functions.

Aluminum↗

PubMed2005

Shielding and fragmentation studies.

Radiation dosimetry for manned spaced missions depends on the ability to adequately describe the process of high-energy ion transport through many materials. Since the types of possible nuclear interactions are many and complex, transport models are used which depend upon a reliable source of experimental data. To expand the heavy ion database used in the models we have been measuring charge-changing cross sections and fragment production cross sections from heavy-ion interactions in various elementa targets. These include materials flown on space missions such as carbon and aluminium, as well as those important in radiation dosimetry such as hydrogen, nitrogen and water. Measuring heavy-ion fragmentation through these targets also gives us the ability to determine the effectiveness of new materials proposed for shielding such as graphite composites and polyethylene hybrids. Measurement without a target present gives an indication of the level of contamination of the primary beam, which is also important in radiobiology experiments.

Construction Materials↗

PubMed2004

Overview of the Martian radiation environment experiment.

Space radiation presents a hazard to astronauts, particularly those journeying outside the protective influence of the geomagnetosphere. Crews on future missions to Mars will be exposed to the harsh radiation environment of deep space during the transit between Earth and Mars. Once on Mars, they will encounter radiation that is only slightly reduced, compared to free space, by the thin Martian atmosphere. NASA is obliged to minimize, where possible, the radiation exposures received by astronauts. Thus, as a precursor to eventual human exploration, it is necessary to measure the Martian radiation environment in detail. The MARIE experiment, aboard the 2001 Mars Odyssey spacecraft, is returning the first data that bear directly on this problem. Here we provide an overview of the experiment, including introductory material on space radiation and radiation dosimetry, a description of the detector, model predictions of the radiation environment at Mars, and preliminary dose-rate data obtained at Mars.

Astronauts↗

PubMed2004

Heavy ion observations by MARIE in cruise phase and Mars orbit.

The charged particle spectrum for nuclei from protons to neon, (charge Z=10) was observed during the cruise phase and orbit around Mars by the MARIE charged particle spectrometer on the Odyssey spacecraft. The cruise data were taken between April 23, 2001 and mid-August 2001. The Mars orbit data were taken March 5, 2002 through May 2002 and are scheduled to continue until August 2004. Charge peaks are clearly separated for charges up to Z=10. Especially prominent are the carbon and oxygen peaks, with boron and nitrogen also clearly visible. Although heavy ions are much less abundant than protons in the cosmic ray environment, it is important to determine their abundances because their ionization energy losses (proportional to Z2) are far more dangerous to humans and to instruments. Thus the higher charged nuclei make a significant contribution to dose and dose equivalent received in space. Results of the charged particle spectrum measurements will be reported.

Calibration↗

PubMed2003

Benchmark studies of the effectiveness of structural and internal materials as radiation shielding for the international space station.

Accelerator-based measurements and model calculations have been used to study the heavy-ion radiation transport properties of materials in use on the International Space Station (ISS). Samples of the ISS aluminum outer hull were augmented with various configurations of internal wall material and polyethylene. The materials were bombarded with high-energy iron ions characteristic of a significant part of the galactic cosmic-ray (GCR) heavy-ion spectrum. Transmitted primary ions and charged fragments produced in nuclear collisions in the materials were measured near the beam axis, and a model was used to extrapolate from the data to lower beam energies and to a lighter ion. For the materials and ions studied, at incident particle energies from 1037 MeV/nucleon down to at least 600 MeV/nucleon, nuclear fragmentation reduces the average dose and dose equivalent per incident ion. At energies below 400 MeV/nucleon, the calculation predicts that as material is added, increased ionization energy loss produces increases in some dosimetric quantities. These limited results suggest that the addition of modest amounts of polyethylene or similar material to the interior of the ISS will reduce the dose to ISS crews from space radiation; however, the radiation transport properties of ISS materials should be evaluated with a realistic space radiation field.

Aluminum↗

PubMed2002

Monte Carlo transport model comparison with 1A GeV accelerated iron experiment: heavy-ion shielding evaluation of NASA space flight-crew foodstuff.

Deep-space manned flight as a reality depends on a viable solution to the radiation problem. Both acute and chronic radiation health threats are known to exist, with solar particle events as an example of the former and galactic cosmic rays (GCR) of the latter. In this experiment Iron ions of 1A GeV are used to simulate GCR and to determine the secondary radiation field created as the GCR-like particles interact with a thick target. A NASA prepared food pantry locker was subjected to the iron beam and the secondary fluence recorded. A modified version of the Monte Carlo heavy ion transport code developed by Zeitlin at LBNL is compared with experimental fluence. The foodstuff is modeled as mixed nuts as defined by the 71st edition of the Chemical Rubber Company (CRC) Handbook of Physics and Chemistry. The results indicate a good agreement between the experimental data and the model. The agreement between model and experiment is determined using a linear fit to ordered pairs of data. The intercept is forced to zero. The slope fit is 0.825 and the R2 value is 0.429 over the resolved fluence region. The removal of an outlier, Z=14, gives values of 0.888 and 0.705 for slope and R2 respectively.

Cosmic Radiation↗

PubMed2002

The response of a spherical tissue-equivalent proportional counter to iron particles from 200-1000 MeV/nucleon.

The radiation environment on board the space shuttle and the International Space Station includes high-Z and high-energy (HZE) particles that are part of the galactic cosmic radiation (GCR) spectrum. Iron-56 particles are considered to be one of the most biologically important parts of the GCR spectrum. Tissue-equivalent proportional counters (TEPCs) are used as active dosimeters on manned space flights. These TEPCs are further used to determine the average quality factor for each space mission. A TEPC simulating a 1-microm-diameter sphere of tissue was exposed as part of a particle spectrometer to (56)Fe particles at energies from 200-1000 MeV/nucleon. The response of TEPCs in terms of mean lineal energy, y(F), and dose mean lineal energy, y(D), as well as the energy deposited at different impact parameters through the detector was determined for six different incident energies of (56)Fe particles in this energy range. Calculations determined that charged-particle equilibrium was achieved for each of the six experiments. Energy depositions at different impact parameters were calculated using a radial dose distribution model, and the results were compared to experimental data.

Cosmic Radiation↗

PubMed2001

Shielded Heavy-Ion Environment Linear Detector (SHIELD): an experiment for the Radiation and Technology Demonstration (RTD) Mission.

Radiological assessment of the many cosmic ion species of widely distributed energies requires the use of theoretical transport models to accurately describe diverse physical processes related to nuclear reactions in spacecraft structures, planetary atmospheres and surfaces, and tissues. Heavy-ion transport models that were designed to characterize shielded radiation fields have been validated through comparison with data from thick-target irradiation experiments at particle accelerators. With the RTD Mission comes a unique opportunity to validate existing radiation transport models and guide the development of tools for shield design. For the first time, transport properties will be measured in free-space to characterize the shielding effectiveness of materials that are likely to be aboard interplanetary space missions. Target materials composed of aluminum, advanced composite spacecraft structure and other shielding materials, helium (a propellant) and tissue equivalent matrices will be evaluated. Large solid state detectors will provide kinetic energy and charge identification for incident heavy-ions and for secondary ions created in the target material. Transport calculations using the HZETRN model suggest that 8 g cm -2 thick targets would be adequate to evaluate the shielding effectiveness during solar minimum activity conditions for a period of 30 days or more.

Computer Simulation↗

PubMed2001

Creation and utilization of a World Wide Web based space radiation effects code: SIREST.

In order for humans and electronics to fully and safely operate in the space environment, codes like HZETRN (High Charge and Energy Transport) must be included in any designer's toolbox for design evaluation with respect to radiation damage. Currently, spacecraft designers do not have easy access to accurate radiation codes like HZETRN to evaluate their design for radiation effects on humans and electronics. Today, the World Wide Web is sophisticated enough to support the entire HZETRN code and all of the associated pre and post processing tools. This package is called SIREST (Space Ionizing Radiation Effects and Shielding Tools). There are many advantages to SIREST. The most important advantage is the instant update capability of the web. Another major advantage is the modularity that the web imposes on the code. Right now, the major disadvantage of SIREST will be its modularity inside the designer's system. This mostly comes from the fact that a consistent interface between the designer and the computer system to evaluate the design is incomplete. This, however, is to be solved in the Intelligent Synthesis Environment (ISE) program currently being funded by NASA.

Algorithms↗

PubMed1999

Neutron yields from 155 MeV/nucleon carbon and helium stopping in aluminum.

Neutron fluences have been measured from 155 MeV/nucleon 4He and 12C ions stopping in an Al target at laboratory angles between 10 and 160 deg. The resultant spectra were integrated over angle and energy above 10 MeV to produce total neutron yields. Comparison of the two systems shows that approximately two times as many neutrons are produced from 155 MeV/nucleon 4He stopping in Al and 155 MeV/nucleon 12C stopping in Al. Using an energy-dependent geometric cross-section formula to calculate the expected number of primary nuclear interactions shows that the 12C + Al system has, within uncertainties, the same number of neutrons per interaction (0.99 +/- 0.03) as does the 4He + Al system (1.02 +/- 0.04), despite the fact that 12C has three times as many neutrons as does 4He. Energy and angular distributions for both systems are also reported. No major differences can be seen between the two systems in those distributions, except for the overall magnitude. Where possible, the 4He + Al spectra are compared with previously measured spectra from 160 and 177.5 MeV/nucleon 4He interactions in a variety of stopping targets. The reported spectra are consistent with previously measured spectra. The data were acquired to provide data applicable to problems dealing with the determination of the radiation risk to humans engaged in long-term missions in space; however, the data are also of interest for issues related to the determination of the radiation environment in high-altitude flight, with shielding at high-energy heavy-ion accelerators and with doses delivered outside tumor sites treated with high-energy hadronic beams.

Altitude↗

PubMed1998

Validation of a comprehensive space radiation transport code.

The HZETRN code has been developed over the past decade to evaluate the local radiation fields within sensitive materials on spacecraft in the space environment. Most of the more important nuclear and atomic processes are now modeled and evaluation within a complex spacecraft geometry with differing material components, including transition effects across boundaries of dissimilar materials, are included. The atomic/nuclear database and transport procedures have received limited validation in laboratory testing with high energy ion beams. The codes have been applied in design of the SAGE-III instrument resulting in material changes to control injurious neutron production, in the study of the Space Shuttle single event upsets, and in validation with space measurements (particle telescopes, tissue equivalent proportional counters, CR-39) on Shuttle and Mir. The present paper reviews the code development and presents recent results in laboratory and space flight validation.

Algorithms↗

PubMed1998

Wall effects observed in tissue-equivalent proportional counters from 1.05 GeV/nucleon iron-56 particles.

Tissue-equivalent proportional counters (TEPCs) have been used to measure energy deposition in simulated volumes of tissue ranging in diameter from 0.1 to 10 microm. There has been some concern that the wall used to define the volume of interest could influence energy deposition within the sensitive volume because it has a density significantly greater than that of the cavity gas. These effects become important for high-velocity heavy ions. Measurements of energy deposition were made for 1 GeV/nucleon iron particles in a TEPC simulating a 1-microm-diameter sphere of tissue. The TEPC was nested within a particle spectrometer that provided identification and flight path of individual particles. Energy deposition was studied as a function of pathlength through the TEPC. Approximately 30% of the energy transfer along trajectories through the center of the detector escapes the sensitive volume. The response of the TEPC, for trajectories through the detector, is always larger than calculations for energy loss in a homogeneous medium. This enhancement is greatest for trajectories near the cavity/wall interface. An integration of the response indicates that charged-particle equilibrium is essentially achieved for a wall thickness of 2.54 mm. However, estimates of the linear energy transfer for the incident particles are influenced by these wall effects.

Gases↗

PubMed1998

Detailed characterization of the 1087 MeV/nucleon iron-56 beam used for radiobiology at the alternating gradient synchrotron.

We report beam characterization and dosimetric measurements made using a 56Fe beam extracted from the Brookhaven National Laboratory Alternating Gradient Synchrotron (AGS) with a kinetic energy of 1087 MeV/nucleon. The measurements reveal that the depth-dose distribution of this beam differs significantly from that obtained with a 600 MeV/nucleon iron beam used in several earlier radiobiology experiments at the Lawrence Berkeley National Laboratory's BEVALAC. We present detailed measurements of beam parameters relevant for radiobiology, including track- and dose-averaged linear energy transfer (LET), fragment composition and LET spectra measured behind sample holders used in irradiations of biological samples. We also report measurements of fluence behind three depths (1.94, 4.68 and 9.35 g cm(-2)) of polyethylene targets with the 1087 MeV/nucleon beam, and behind 1.94 g cm(-2) of polyethylene with a 610 MeV/nucleon beam delivered by the AGS. These results are compared to earlier measurements with the 600 MeV/nucleon beam at the BEVALAC.

Iron↗

PubMed1997

Heavy fragment production cross sections from 1.05 GeV/nucleon 56Fe in C, Al, Cu, Pb, and CH2 targets.

We have obtained charge-changing cross sections and partial cross sections for fragmentation of 1.05 GeV/nucleon Fe projectiles incident on H, C, Al, Cu, and Pb nuclei. The energy region covered by this experiment is critical for an understanding of galactic cosmic ray propagation and space radiation biophysics. Surviving primary beam particles and fragments with charges from 12 to 25 produced within a forward cone of half-angle 61 mrad were detected using a silicon detector telescope to identify their charge and the cross sections were calculated after correction of the measured yields for finite target thickness effects. The cross sections are compared to model calculations and to previous measurements. Cross sections for the production of fragments with even-numbered nuclear charges are seen to be enhanced in almost all cases.

Aluminum↗

PubMed1996

The fragmentation of 510 MeV/nucleon iron-56 in polyethylene. I. Fragment fluence spectra.

The fragmentation of 510 MeV/nucleon iron ions in several thicknesses of polyethylene has been measured. Non-interacting primary beam particles and fragments have been identified and their LETs calculated by measuring ionization energy loss in a stack of silicon detectors. Fluences, normalized to the incident beam intensity and corrected for detector effects, are presented for each fragment charge and target. Histograms of fluence as a function of LET are also presented. Some implications of these data for measurements of the biological effects of heavy ions are discussed.

Algorithms↗

PubMed1996

The fragmentation of 510 MeV/nucleon iron-56 in polyethylene. II. Comparisons between data and a model.

The results of a Monte Carlo model for calculating fragment fluences and LET spectra are compared to data taken with 600 MeV/nucleon iron ions incident on an accelerator beamline configured for irradiation of biological samples, with no target and with 2, 5 and 8 cm of polyethylene. The model uses a multi-generation nuclear fragmentation code, coupled with a formulation of ionization energy loss based on the Bethe-Bloch equation. In the region where the data are reliable and the experimental acceptance is well understood, many of the features of the experimental spectra are well replicated by the model. To obtain good agreement with the experimental data, the model must allow for at least two generations of fragment production in the target.

Algorithms↗

PubMed1994

The influence of dose, dose-rate and particle fragmentation on cataract induction by energetic iron ions.

Because activities in space necessarily involve chronic exposure to a heterogeneous charged particle radiation field it is important to assess the influence of dose-rate and the possible modulating role of heavy particle fragmentation on biological systems. Using the well-studied cataract model, mice were exposed to plateau 600 MeV/amu 56Fe ions either as acute or fractionated exposures at total doses of 5 - 504 cGy. Additional groups of mice received 20, 360 and 504 cGy behind 50 mm of polyethylene, which simulates body shielding. The reference radiation consisted of 60Co gamma radiation. The animals were examined by slit lamp biomicroscopy over their three year life spans. In accordance with our previous observations with heavy particles, the cataractogenic potential of the 600 MeV/amu 56Fe ions was greater than for low-LET radiation and increased with decreasing dose relative to gamma-rays. Fractionation of a given dose of 56Fe ions did not reduce the cataractogenicity of the radiation compared to the acute regimen. Fragmentation of the beam in the polyethylene did not alter the cataractotoxicity of the ions, either when administered singly or in fractions.

Animals↗