Concepts and approaches to in situ luminescence dating of Martian sediments

In this paper we present the concept of a robotic instrument for in situ luminescence dating of near-surface sediments on Mars. The scientific objectives and advantages to be gained from the development of such an instrument are described, and the challenges presented by the Mars surface environment to the design and operation of the instrument are outlined.

Para-aminosalicylic acid (PAS) desensitization review in a case of multidrug-resistant pulmonary tuberculosis

SETTING

Tertiary care hospital in the Upper Midwest, United States.

OBJECTIVE

Rapid desensitization to para-aminosalicylic acid (PAS) in a patient with previous hypersensitivity reaction and a review of published PAS desensitization protocols.

DESIGN

Composition and implementation of a short-course PAS desensitization protocol for a 34-year-old woman with multidrug-resistant (MDR) pulmonary tuberculosis, incorporating published experiences of PAS desensitization over the past 50 years.

RESULTS

We composed a protocol and successfully desensitized our patient to PAS (Paser granules). By starting with a low dose (50 mg), then doubling the PAS dose on each successive day, our patient was able to tolerate full dose in 1 week. No steroids were required and no adverse reactions were encountered. Previous published PAS desensitization protocols used starting doses of 10-500 mg, desensitization time ranges from 7 to 54 days and commonly used steroids or corticotropin.

CONCLUSION

Rapid desensitization to PAS can be successfully conducted within 1 week without the use of steroids or corticotropin. Given the limited number of drugs available for many patients with MDR-TB, desensitization to PAS is a valid alternative to drug discontinuation for patients with hypersensitivity reactions.

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.

Recent results form measurements of the energy spectrum of cosmic-ray induced neutrons aboard an ER-2 airplane and on the ground

Crews of future high-altitude commercial aircraft may be significantly exposed to atmospheric cosmic radiation from galactic cosmic rays (GCR). To help determine such exposures, the Atmospheric Ionizing Radiation Project, an international collaboration of 15 laboratories, made simultaneous radiation measurements with 14 instruments on a NASA ER-2 high-altitude aircraft. The primary instrument was a sensitive extended-energy multisphere neutron spectrometer, which was also used to make measurements on the ground. Its detector responses were calculated for neutrons and charged hadrons at energies up to 100 GeV using the radiation transport code MCNPX. We have now recalculated the detector responses including the effects of the airplane structure. We are also using new FLUKA calculations of GCR-induced hadron spectra in the atmosphere to correct for spectrometer counts produced by charged hadrons. Neutron spectra are unfolded from the corrected measured count rates using the MAXED code. Results for the measured cosmic-ray neutron spectrum (thermal to >10 GeV), total neutron fluence rate, and neutron dose equivalent and effective dose rates, and their dependence on altitude and geomagnetic cutoff generally agree well with results from recent calculations of GCR-induced neutron spectra.

Materials trade study for lunar/gateway missions

The National Aeronautics and Space Administration (NASA) administrator has identified protection from radiation hazards as one of the two biggest problems of the agency with respect to human deep space missions. The intensity and strength of cosmic radiation in deep space makes this a 'must solve' problem for space missions. The Moon and two Earth-Moon Lagrange points near Moon are being proposed as hubs for deep space missions. The focus of this study is to identify approaches to protecting astronauts and habitats from adverse effects from space radiation both for single missions and multiple missions for career astronauts to these destinations. As the great cost of added radiation shielding is a potential limiting factor in deep space missions, reduction of mass, without compromising safety, is of paramount importance. The choice of material and selection of the crew profile play major roles in design and mission operations. Material trade studies in shield design over multi-segmented missions involving multiple work and living areas in the transport and duty phase of space mission's to two Earth-Moon co-linear Lagrange points (L1) between Earth and the Moon and (L2) on back side of the moon as seen from Earth, and to the Moon have been studied. It is found that, for single missions, current state-of-the-art knowledge of material provides adequate shielding. On the other hand, the choice of shield material is absolutely critical for career astronauts and revolutionary materials need to be developed for these missions. This study also provides a guide to the effectiveness of multifunctional materials in preparation for more detailed geometry studies in progress.

Radiation risk and human space exploration

Radiation protection is essential to enable humans to live and work safely in space. Predictions about the nature and magnitude of the risks posed by space radiation are subject to very large uncertainties. Prudent use of worst-case scenarios may impose unacceptable constraints on shielding mass for spacecraft or habitats, tours of duty of crews on Space Station, and on the radius and duration of sorties on planetary surfaces. The NASA Space Radiation Health Program has been devised to develop the knowledge required to accurately predict and to efficiently manage radiation risk. The knowledge will be acquired by means of a peer-reviewed, largely ground-based and investigator-initiated, basic science research program. The NASA Strategic Plan to accomplish these objectives in a manner consistent with the high priority assigned to the protection and health maintenance of crews will be presented.

Overview of atmospheric ionizing radiation (AIR) research: SST-present

The Supersonic Transport (SST) program, proposed in 1961, first raised concern for the exposure of pregnant occupants by solar energetic particles (SEP), and neutrons were suspected to have a main role in particle propagation deep into the atmosphere. An eight-year flight program confirmed the role of SEP as a significant hazard and of the neutrons as contributing over half of the galactic cosmic ray exposures, with the largest contribution from neutrons above 10 MeV. The FAA Advisory Committee on the Radiobiological Aspects of the SST provided operational requirements. The more recent lowering of ICRP-recommended exposure limits (1990) with the classification of aircrew as "radiation workers" renewed interest in GCR background exposures at commercial flight altitudes and stimulated epidemiological studies in Europe, Japan, Canada and the USA. The proposed development of a High Speed Civil Transport (HSCT) required validation of the role of high-energy neutrons, and this resulted in ER-2 flights at solar minimum (June 1997) and studies on effects of aircraft materials on interior exposures. Recent evaluation of health outcomes of DOE nuclear workers resulted in legislation for health compensation in year 2000 and recent European aircrew epidemiological studies of health outcomes bring renewed interest in aircraft radiation exposures. As improved radiation models become available, it is imperative that a corresponding epidemiological program of US aircrew be implemented.

A new dynamical atmospheric ionizing radiation (AIR) model for epidemiological studies

A new Atmospheric Ionizing Radiation (AIR) model is currently being developed for use in radiation dose evaluation in epidemiological studies targeted to atmospheric flight personnel such as civilian airlines crewmembers. The model will allow computing values for biologically relevant parameters, e.g. dose equivalent and effective dose, for individual flights from 1945. Each flight is described by its actual three dimensional flight profile, i.e. geographic coordinates and altitudes varying with time. Solar modulated primary particles are filtered with a new analytical fully angular dependent geomagnetic cut off rigidity model, as a function of latitude, longitude, arrival direction, altitude and time. The particle transport results have been obtained with a technique based on the three-dimensional Monte Carlo transport code FLUKA, with a special procedure to deal with HZE particles. Particle fluxes are transformed into dose-related quantities and then integrated all along the flight path to obtain the overall flight dose. Preliminary validations of the particle transport technique using data from the AIR Project ER-2 flight campaign of measurements are encouraging. Future efforts will deal with modeling of the effects of the aircraft structure as well as inclusion of solar particle events.

Lunar lava tube radiation safety analysis

For many years it has been suggested that lava tubes on the Moon could provide an ideal location for a manned lunar base, by providing shelter from various natural hazards, such as cosmic radiation, meteorites, micrometeoroids, and impact crater ejecta, and also providing a natural environmental control, with a nearly constant temperature, unlike that of the lunar surface showing extreme variation in its diurnal cycle. An analysis of radiation safety issues on lunar lava tubes has been performed by considering radiation from galactic cosmic rays (GCR) and Solar Particle Events (SPE) interacting with the lunar surface, modeled as a regolith layer and rock. The chemical composition has been chosen as typical of the lunar regions where the largest number of lava tube candidates are found. Particles have been transported all through the regolith and the rock, and received particles flux and doses have been calculated. The radiation safety of lunar lava tubes environments has been demonstrated.

A simple model for straggling evaluation

Some straggling models had largely been abandoned in favor of Monte Carlo simulations of straggling which are accurate but time consuming, limiting their application in practice. The difficulty of simple analytic models is the failure to give accurate values past 85% of the particle range. A simple model is derived herein based on a second order approximation upon which rapid analysis tools are developed for improved understanding of material charged particle transmission properties.

A method for calculating proton-nucleus elastic cross-sections

Recently [Nucl. Instr. and Meth. B 145 (1998) 277; Extraction of in-medium nucleon-nucleon amplitude from experiment, NASA-TP, 1998], we developed a method of extracting nucleon-nucleon (N-N) cross-sections in the medium directly from experiment. The in-medium N-N cross-sections form the basic ingredients of several heavy-ion scattering approaches including the coupled-channel approach developed at the NASA Langley Research Center. We investigated [Proton-nucleus total cross-sections in coupled-channel approach, NASA/TP, 2000; Nucl. Instr. and Meth. B 173-174 (2001) 391] the ratio of real to imaginary part of the two body scattering amplitude in the medium. These ratios are used in combination with the in-medium N-N cross-sections to calculate proton-nucleus elastic cross-sections. The agreement is excellent with the available experimental data. These cross-sections are needed for the radiation risk assessment of space missions.

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.

Optimized shielding for space radiation protection

Future deep space mission and International Space Station exposures will be dominated by the high-charge and -energy (HZE) ions of the Galactic Cosmic Rays (GCR). A few mammalian systems have been extensively tested over a broad range of ion types and energies. For example, C3H10T1/2 cells, V79 cells, and Harderian gland tumors have been described by various track-structure dependent response models. The attenuation of GCR induced biological effects depends strongly on the biological endpoint, response model used, and material composition. Optimization of space shielding is then driven by the nature of the response model and the transmission characteristics of the given material.

Visual assessment of the radiation distribution in the ISS Lab module: visualization in the human body

The US Lab module of the International Space Station (ISS) is a primary working area where the crewmembers are expected to spend majority of their time. Because of the directionality of radiation fields caused by the Earth shadow, trapped radiation pitch angle distribution, and inherent variations in the ISS shielding, a model is needed to account for these local variations in the radiation distribution. We present the calculated radiation dose (rem/yr) values for over 3,000 different points in the working area of the Lab module and estimated radiation dose values for over 25,000 different points in the human body for a given ambient radiation environment. These estimated radiation dose values are presented in a three dimensional animated interactive visualization format. Such interactive animated visualization of the radiation distribution can be generated in near real-time to track changes in the radiation environment during the orbit precession of the ISS.

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.

Radiation protection using Martian surface materials in human exploration of Mars

To develop materials for shielding astronauts from the hazards of GCR, natural Martian surface materials are considered for their potential as radiation shielding for manned Mars missions. The modified radiation fluences behind various kinds of Martian rocks and regolith are determined by solving the Boltzmann equation using NASA Langley's HZETRN code along with the 1977 Solar Minimum galactic cosmic ray environmental model. To develop structural shielding composite materials for Martian surface habitats, theoretical predictions of the shielding properties of Martian regolith/polyimide composites has been computed to assess their shielding effectiveness. Adding high-performance polymer binders to Martian regolith to enhance structural properties also enhances the shielding properties of these composites because of the added hydrogenous constituents. Heavy ion beam testing of regolith simulant/polyimide composites is planned to validate this prediction. Characterization and proton beam tests are performed to measure structural properties and to compare the shielding effects on microelectronic devices, respectively.

Neutron environments on the Martian surface

Radiation is a primary concern in the planning of a manned mission to Mars. Recent studies using NASA Langley Research Center's HZETRN space radiation transport code show that the low energy neutron fluence on the Martian surface is larger than previously expected. The upper atmosphere of Mars is exposed to a background radiation field made up of a large number of protons during a solar particle event and mixture of light and heavy ions caused by galactic cosmic rays at other times. In either case, these charged ions interact with the carbon and oxygen atoms of the Martian atmosphere through ionization and nuclear collisions producing secondary ions and neutrons which then interact with the atmospheric atoms in a similar manner. In the past, only these downward moving particles have been counted in evaluating the neutron energy spectrum on the surface. Recent enhancements in the HZETRN code allow for the additional evaluation of those neutrons created within the Martian regolith through the same types of nuclear reactions, which rise to the surface. New calculations using this improved HZETRN code show that these upward moving neutrons contribute significantly to the overall neutron spectrum for energies less than 10 MeV.

Synthesis and protein kinase inhibitory activity of balanol analogues with modified benzophenone subunits

A series of analogues of the protein kinase C (PKC) inhibitory natural product balanol which bear modified benzophenone subunits are described. The analogues were designed with the goal of uncovering structure-activity features that could be used in the development of PKC inhibitors with a reduced polar character compared to balanol itself. The results of these studies suggest that most of the benzophenone features found in the natural product are important for obtaining potent PKC inhibitory compounds. However, several modifications were found to lead to selective inhibitors of the related enzyme protein kinase A (PKA), and several specific modifications to the polar structural elements of the benzophenone were found to provide potent PKC inhibitors. In particular, it was found that replacement of the benzophenone carboxylate with bioisosteric equivalents could lead to potent analogues. Further, a tolerance for lipophilic substituents on the terminal benzophenone ring was uncovered. These results are discussed in light of recently available structural information for PKA.