The HZETRN code has been developed over the past decade to evaluate the local radiation fields wi... more 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.
We present a summary of results from recent work in which we have compared nuclear fragmentation ... more We present a summary of results from recent work in which we have compared nuclear fragmentation cross section data to predictions of the PHITS Monte Carlo simulation. The studies used beams of 12 C, 35 Cl, 40 Ar, 48 Ti, and 56 Fe at energies ranging from 290 MeV/nucleon to 1000 MeV/nucleon. Some of the data were obtained at the Brookhaven National Laboratory, others at the National Institute of Radiological Sciences in Japan. These energies and ion species are representative of the heavy ion component of the Galactic Cosmic Rays (GCR), which contribute significantly to the dose and dose equivalent that will be received by astronauts on deep-space missions. A critical need for NASA is the ability to accurately model the transport of GCR heavy ions through matter, including spacecraft walls, equipment racks, and other shielding materials, as well as through tissue. Nuclear interaction cross sections are of primary importance in the GCR transport problem. These interactions generally cause the incoming ion to break up (fragment) into one or more lighter ions, which continue approximately along the initial trajectory and with approximately the same velocity the incoming ion had prior to the interaction. Since the radiation dose delivered by a particle is proportional to the square of the quantity (charge/velocity), i.e., to (Z/β)2 , fragmentation reduces the dose (and, typically, dose equivalent) delivered by incident ions. The other mechanism by which dose can be reduced is ionization energy loss, which can lead to some particles stopping in the shielding. This is the conventional notion of shielding, but it is not applicable to human spaceflight, since the particles in the GCR tend to be highly energetic and because shielding must be relatively thin in order to keep overall mass as low as possible, keeping launch costs within reason. To support these goals, our group has systematically measured a large number of nuclear cross sections, intended to be used as either input to, or validation of, NASA transport models. A database containing over 200 charge-changing cross sections, and over 2000 fragment production cross sections, is nearing completion, with most results available online. In the past year, we have been investigating the PHITS (Particle and Heavy Ion Transport System) model of Niita et al. For purposes of modeling nuclear interactions, PHITS combines the Jet AA Microscopic Transport Model (JAM) hadron cascade model, the Jaeri Quantum Molecular Dynamics (JQMD) model, and the Generalized Evaporation Model (GEM). We will present detailed comparisons of our data to the cross sections and fragment angular distributions that arise from this model. The model contains some significant deficiencies, but, as we will show, also represents a significant advance over older, simpler models of fragmentation. 504b030414000600080000002100828abc13fa0000001c020000130000005b436f6e74656e745f54797065735d2e78
Accelerated helium ions with mean energies at the target location of 3-7 MeV were used to simulat... more Accelerated helium ions with mean energies at the target location of 3-7 MeV were used to simulate alpha-particle radiation from radon daughters. The experimental setup and calibration procedure allowed determination of the helium-ion energy distribution and dose in the nuclei of irradiated cells. Using this system, the induction of DNA double-strand breaks and their spatial distributions along DNA were studied in irradiated human fibroblasts. It was found that the apparent number of double-strand breaks as measured by a standard pulsed-field gel assay (FAR assay) decreased with increasing LET in the range 67-120 keV/microm (corresponding to the energy of 7-3 MeV). On the other hand, the generation of small and intermediate-size DNA fragments (0.1-100 kbp) increased with LET, indicating an increased intratrack long-range clustering of breaks. The fragment size distribution was measured in several size classes down to the smallest class of 0.1-2 kbp. When the clustering was taken into account, the actual number of DNA double-strand breaks (separated by at least 0.1 kbp) could be calculated and was found to be in the range 0.010-0.012 breaks/Mbp Gy(-1). This is two- to threefold higher than the apparent yield obtained by the FAR assay. The measured yield of double-strand breaks as a function of LET is compared with theoretical Monte Carlo calculations that simulate the track structure of energy depositions from helium ions as they interact with the 30-nm chromatin fiber. When the calculation is performed to include fragments larger than 0.1 kbp (to correspond to the experimental measurements), there is good agreement between experiment and theory.
Accelerator-based measurements and model calculations have been used to study the heavy-ion radia... more 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.
The Radiation Assessment Detector (RAD) on NASA's Mars Science Laboratory mission is being built ... more The Radiation Assessment Detector (RAD) on NASA's Mars Science Laboratory mission is being built to characterize the broad-spectrum of the surface radiation environment, including galactic cosmic radiation, solar proton events, and secondary neutrons. This overarching mission goal is met by RADs science objectives 1-5: 1.)Characterize the energetic particle spectrum incident at the surface of Mars, including direct and indirect radiation created in the atmosphere and regolith. 2.)Validate Mars atmospheric transmission models and radiation transport codes. 3.)Determine the radiation Dose rate and Equivalent Dose rate for humans on the Martian surface. 4.)Determine the radiation hazard and mutagenic influences to life, past and present, at and beneath the Martian surface. 5.)Determine the chemical and isotopic effects of energetic particle radiation on the Martian surface and atmosphere. To achieve these objectives, RAD will operate autonomously to provide measurements of protons from 10 to 100 MeV and heavy ions from 30 to 200 MeV/nuc, and discriminate between the various nuclei. RAD will also provide LET measurements and time series of SEP events and discriminate between neutrons and gamma rays. A pathfinder model with flight-like properties, and, by the time of the conference, a flight and flight spare model, have been tested at BNL, PTB, iThemba, CERN/CERF, and using various radioactive sources to demonstrate the measurement capabilities required by its science objectives. We will present first calibration results and compare them with GEANT4 simulations. The neutron-gamma discrimination can be achieved in a statistical manner using a combination of different scintillators1 and will also presented. Finally, we will discuss implications for the Ionizing RAdiation Sensor (IRAS) for ESA's ExoMars mission.
The Radiation Assessment Detector (RAD) is a compact, lightweight energetic particle an-alyzer th... more The Radiation Assessment Detector (RAD) is a compact, lightweight energetic particle an-alyzer that will fly on the NASA 2011 Mars Science Laboratory (MSL) Mission. RAD will detect and analyze energetic particle species (p, n, He, 2¡Z¡26) relevant for dosimetry on the Martian surface. The Galactic Cosmic Rays and Solar Energetic Particles produce both pri-mary and secondary radiation, with secondaries being created in both the atmosphere and the Martian regolith. Fully characterizing and understanding the surface radiation environment is fundamental to quantitatively assessing the habitability of Mars, and is an essential precursor measurement for future manned Mars missions. An extensive database to be used for calibration has been obtained for a wide range of energetic charged particle beams at the NASA Space Radiation Laboratory (NSRL) and the Heavy Ion Medical Accelerator in Chiba (HIMAC). Neutron calibration data at 5, 15, and 19 MeV were obtained at the Physikalisch-Technische Bundesanstalt. This talk will discuss the highlights of the RAD calibration campaigns and talk about what we have learned from these campaigns with respect to operating RAD on the Martian surface. We will also discuss other mission applications for RAD where dosimetry in mixed fields of energetic charged and neutral particles is needed.
The HZETRN code has been developed over the past decade to evaluate the local radiation fields wi... more 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.
We present a summary of results from recent work in which we have compared nuclear fragmentation ... more We present a summary of results from recent work in which we have compared nuclear fragmentation cross section data to predictions of the PHITS Monte Carlo simulation. The studies used beams of 12 C, 35 Cl, 40 Ar, 48 Ti, and 56 Fe at energies ranging from 290 MeV/nucleon to 1000 MeV/nucleon. Some of the data were obtained at the Brookhaven National Laboratory, others at the National Institute of Radiological Sciences in Japan. These energies and ion species are representative of the heavy ion component of the Galactic Cosmic Rays (GCR), which contribute significantly to the dose and dose equivalent that will be received by astronauts on deep-space missions. A critical need for NASA is the ability to accurately model the transport of GCR heavy ions through matter, including spacecraft walls, equipment racks, and other shielding materials, as well as through tissue. Nuclear interaction cross sections are of primary importance in the GCR transport problem. These interactions generally cause the incoming ion to break up (fragment) into one or more lighter ions, which continue approximately along the initial trajectory and with approximately the same velocity the incoming ion had prior to the interaction. Since the radiation dose delivered by a particle is proportional to the square of the quantity (charge/velocity), i.e., to (Z/β)2 , fragmentation reduces the dose (and, typically, dose equivalent) delivered by incident ions. The other mechanism by which dose can be reduced is ionization energy loss, which can lead to some particles stopping in the shielding. This is the conventional notion of shielding, but it is not applicable to human spaceflight, since the particles in the GCR tend to be highly energetic and because shielding must be relatively thin in order to keep overall mass as low as possible, keeping launch costs within reason. To support these goals, our group has systematically measured a large number of nuclear cross sections, intended to be used as either input to, or validation of, NASA transport models. A database containing over 200 charge-changing cross sections, and over 2000 fragment production cross sections, is nearing completion, with most results available online. In the past year, we have been investigating the PHITS (Particle and Heavy Ion Transport System) model of Niita et al. For purposes of modeling nuclear interactions, PHITS combines the Jet AA Microscopic Transport Model (JAM) hadron cascade model, the Jaeri Quantum Molecular Dynamics (JQMD) model, and the Generalized Evaporation Model (GEM). We will present detailed comparisons of our data to the cross sections and fragment angular distributions that arise from this model. The model contains some significant deficiencies, but, as we will show, also represents a significant advance over older, simpler models of fragmentation. 504b030414000600080000002100828abc13fa0000001c020000130000005b436f6e74656e745f54797065735d2e78
Accelerated helium ions with mean energies at the target location of 3-7 MeV were used to simulat... more Accelerated helium ions with mean energies at the target location of 3-7 MeV were used to simulate alpha-particle radiation from radon daughters. The experimental setup and calibration procedure allowed determination of the helium-ion energy distribution and dose in the nuclei of irradiated cells. Using this system, the induction of DNA double-strand breaks and their spatial distributions along DNA were studied in irradiated human fibroblasts. It was found that the apparent number of double-strand breaks as measured by a standard pulsed-field gel assay (FAR assay) decreased with increasing LET in the range 67-120 keV/microm (corresponding to the energy of 7-3 MeV). On the other hand, the generation of small and intermediate-size DNA fragments (0.1-100 kbp) increased with LET, indicating an increased intratrack long-range clustering of breaks. The fragment size distribution was measured in several size classes down to the smallest class of 0.1-2 kbp. When the clustering was taken into account, the actual number of DNA double-strand breaks (separated by at least 0.1 kbp) could be calculated and was found to be in the range 0.010-0.012 breaks/Mbp Gy(-1). This is two- to threefold higher than the apparent yield obtained by the FAR assay. The measured yield of double-strand breaks as a function of LET is compared with theoretical Monte Carlo calculations that simulate the track structure of energy depositions from helium ions as they interact with the 30-nm chromatin fiber. When the calculation is performed to include fragments larger than 0.1 kbp (to correspond to the experimental measurements), there is good agreement between experiment and theory.
Accelerator-based measurements and model calculations have been used to study the heavy-ion radia... more 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.
The Radiation Assessment Detector (RAD) on NASA's Mars Science Laboratory mission is being built ... more The Radiation Assessment Detector (RAD) on NASA's Mars Science Laboratory mission is being built to characterize the broad-spectrum of the surface radiation environment, including galactic cosmic radiation, solar proton events, and secondary neutrons. This overarching mission goal is met by RADs science objectives 1-5: 1.)Characterize the energetic particle spectrum incident at the surface of Mars, including direct and indirect radiation created in the atmosphere and regolith. 2.)Validate Mars atmospheric transmission models and radiation transport codes. 3.)Determine the radiation Dose rate and Equivalent Dose rate for humans on the Martian surface. 4.)Determine the radiation hazard and mutagenic influences to life, past and present, at and beneath the Martian surface. 5.)Determine the chemical and isotopic effects of energetic particle radiation on the Martian surface and atmosphere. To achieve these objectives, RAD will operate autonomously to provide measurements of protons from 10 to 100 MeV and heavy ions from 30 to 200 MeV/nuc, and discriminate between the various nuclei. RAD will also provide LET measurements and time series of SEP events and discriminate between neutrons and gamma rays. A pathfinder model with flight-like properties, and, by the time of the conference, a flight and flight spare model, have been tested at BNL, PTB, iThemba, CERN/CERF, and using various radioactive sources to demonstrate the measurement capabilities required by its science objectives. We will present first calibration results and compare them with GEANT4 simulations. The neutron-gamma discrimination can be achieved in a statistical manner using a combination of different scintillators1 and will also presented. Finally, we will discuss implications for the Ionizing RAdiation Sensor (IRAS) for ESA's ExoMars mission.
The Radiation Assessment Detector (RAD) is a compact, lightweight energetic particle an-alyzer th... more The Radiation Assessment Detector (RAD) is a compact, lightweight energetic particle an-alyzer that will fly on the NASA 2011 Mars Science Laboratory (MSL) Mission. RAD will detect and analyze energetic particle species (p, n, He, 2¡Z¡26) relevant for dosimetry on the Martian surface. The Galactic Cosmic Rays and Solar Energetic Particles produce both pri-mary and secondary radiation, with secondaries being created in both the atmosphere and the Martian regolith. Fully characterizing and understanding the surface radiation environment is fundamental to quantitatively assessing the habitability of Mars, and is an essential precursor measurement for future manned Mars missions. An extensive database to be used for calibration has been obtained for a wide range of energetic charged particle beams at the NASA Space Radiation Laboratory (NSRL) and the Heavy Ion Medical Accelerator in Chiba (HIMAC). Neutron calibration data at 5, 15, and 19 MeV were obtained at the Physikalisch-Technische Bundesanstalt. This talk will discuss the highlights of the RAD calibration campaigns and talk about what we have learned from these campaigns with respect to operating RAD on the Martian surface. We will also discuss other mission applications for RAD where dosimetry in mixed fields of energetic charged and neutral particles is needed.
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