Implications of new measurements of O-16 + p + C-12,13, N-14,15 for the abundances of C, N isotopes at the cosmic ray source

The fragmentation of a 225 MeV/n O-16 beam was investigated at the Bevalac. Preliminary cross sections for mass = 13, 14, 15 fragments are used to constrain the nuclear excitation functions employed in galactic propagation calculations. Comparison to cosmic ray isotonic data at low energies shows that in the cosmic ray source C-13/C approximately 2% and N-14/0=3-6%. No source abundance of N-15 is required with the current experimental results

Uncertainties in Estimates of the Risks of Late Effects from Space Radiation

The health risks faced by astronauts from space radiation include cancer, cataracts, hereditary effects, and non-cancer morbidity and mortality risks related to the diseases of the old age. Methods used to project risks in low-Earth orbit are of questionable merit for exploration missions because of the limited radiobiology data and knowledge of galactic cosmic ray (GCR) heavy ions, which causes estimates of the risk of late effects to be highly uncertain. Risk projections involve a product of many biological and physical factors, each of which has a differential range of uncertainty due to lack of data and knowledge. Within the linear-additivity model, we use Monte-Carlo sampling from subjective uncertainty distributions in each factor to obtain a Maximum Likelihood estimate of the overall uncertainty in risk projections. The resulting methodology is applied to several human space exploration mission scenarios including ISS, lunar station, deep space outpost, and Mar's missions of duration of 360, 660, and 1000 days. The major results are the quantification of the uncertainties in current risk estimates, the identification of factors that dominate risk projection uncertainties, and the development of a method to quantify candidate approaches to reduce uncertainties or mitigate risks. The large uncertainties in GCR risk projections lead to probability distributions of risk that mask any potential risk reduction using the "optimization" of shielding materials or configurations. In contrast, the design of shielding optimization approaches for solar particle events and trapped protons can be made at this time, and promising technologies can be shown to have merit using our approach. The methods used also make it possible to express risk management objectives in terms of quantitative objective's, i.e., the number of days in space without exceeding a given risk level within well defined confidence limits

Reliability assessment based on degradation measurements: How to compare some models?

An important issue in the validation of mechanical parts for vehicles is reliability assessment for high mileages, by means of tests. Since the tests should be as short as possible, and for parts subjected to degradation mechanism, such as wear or crack propagation, it would be appropriate using degradation measurements (such as mass loss or crack length) in order to estimate reliability. In this study, we present some statistical approaches responding to this concern and propose a method to compare theses models. Different types of data can be available; in this paper, we only consider the case in which one measure is available for each part. Only linear degradation is studied

Degradation test plan for Wiener degradation processes

This study describes an approach to design degradation validation test plan using the Wiener process. This approach allows to link accelerated test results and field reliability without acceleration laws but using a global severity factor when the component to test is not an innovation and an old version is in field. In this condition, field data is available. The field degradation level can be measured and compared to degradation obtained in test. The test severity is evaluated with field and test degradation measurements. We use the same test severity to design a test plan for the new version of component. This test plan is designed to demonstrate a field reliability target with confidence level. The final test plan is obtained using experimental feedback, tests results and numerical simulations. This study shows the necessity to strengthen the test acceptance criterion when the test duration is reduced. This method allows to quantify this

Deuteron Production in alpha-Nucleus Collisions from 200 to 800 MeV per Nucleon

peer reviewe

Heavy Ion Carcinogenesis and Human Space Exploration

Prior to the human exploration of Mars or long duration stays on the Earth s moon, the risk of cancer and other diseases from space radiation must be accurately estimated and mitigated. Space radiation, comprised of energetic protons and heavy nuclei, has been show to produce distinct biological damage compared to radiation on Earth, leading to large uncertainties in the projection of cancer and other health risks, while obscuring evaluation of the effectiveness of possible countermeasures. Here, we describe how research in cancer radiobiology can support human missions to Mars and other planets

Differential fragmentation cross sections for 7.3 GeV nitrogen ions incident on protons

Differential cross sections dd for the inclusive reaction N14 + pZ + anything (for 3Z6) have been measured at six laboratory production angles (\u3c5°) for 7.3 GeV nitrogen ions interacting in liquid hydrogen. The angular distributions for C, B, and Be fragments decrease sharply with increasing angle, as expected for this type of peripheral reaction. The corresponding transverse momentum (pt) distributions for these fragments can be represented by Gaussian functions of pt. The Li distribution appears to be non-Gaussian, suggesting one (or more) different production mechanisms. The dependence of the widths of the momentum distributions on fragment mass is not consistent with theoretical predictions, and shows some evidence for an quot;effective number of nucleons which determine the fragmentation spectrum of the nitrogen nucleus. Integration of the angular distributions gives partial production cross sections which are consistent with results at higher energy. This energy-independent behavior implies that limiting fragmentation is applicable down to energies of 0.5 GeV/nucleon. NUCLEAR REACTIONS Relativistic heavy ions; fragmentation of 7.3 GeV nitrogen on protons. © 1979 The American Physical Society