Neutron detector simultaneously measures fluence and dose equivalent

Neutron detector acts as both an area monitoring instrument and a criticality dosimeter by simultaneously measuring dose equivalent and fluence. The fluence is determined by activation of six foils one inch below the surface of the moderator. Dose equivalent is determined from activation of three interlocked foils at the center of the moderator

The stability of the terrestrial planets with a more massive 'Earth'

Although the long-term numerical integrations of planetary orbits indicate that our planetary system is dynamically stable at least +/- 4 Gyr, the dynamics of our Solar system includes both chaotic and stable motions: the large planets exhibit remarkable stability on gigayear time-scales, while the subsystem of the terrestrial planets is weakly chaotic with a maximum Lyapunov exponent reaching the value of 1/5 Myr(-1). In this paper the dynamics of the Sun-Venus-Earth-Mars-Jupiter-Saturn model is studied, where the mass of Earth was magnified via a mass factor kappa(E). The resulting systems dominated by a massive Earth may serve also as models for exoplanetary systems that are similar to ours. This work is a continuation of our previous study, where the same model was used and the masses of the inner planets were uniformly magnified. That model was found to be substantially stable against the mass growth. Our simulations were undertaken for more than 100 different values of kappa(E) for a time of 20 Myr, and in some cases for 100 Myr. A major result was the appearance of an instability window at kappa(E)approximate to 5, where Mars escaped. This new result has important implications for theories of the planetary system formation process and mechanism. It is shown that with increasing kappa(E) the system splits into two, well-separated subsystems: one consists of the inner planets, and the other consists of the outer planets. According to the results, the model becomes more stable as kappa(E) increases and only when kappa(E) >= 540 does Mars escape, on a Myr time-scale. We found an interesting protection mechanism for Venus. These results give insights also into the stability of the habitable zone of exoplanetary systems, which harbour planets with relatively small eccentricities and inclinations

Where are the Uranus Trojans?

The area of stable motion for fictitious Trojan asteroids around Uranus' equilateral equilibrium points is investigated with respect to the inclination of the asteroid's orbit to determine the size of the regions and their shape. For this task we used the results of extensive numerical integrations of orbits for a grid of initial conditions around the points L4 and L5, and analyzed the stability of the individual orbits. Our basic dynamical model was the Outer Solar System (Jupiter, Saturn, Uranus and Neptune). We integrated the equations of motion of fictitious Trojans in the vicinity of the stable equilibrium points for selected orbits up to the age of the Solar system of 5 billion years. One experiment has been undertaken for cuts through the Lagrange points for fixed values of the inclinations, while the semimajor axes were varied. The extension of the stable region with respect to the initial semimajor axis lies between 19.05 < a < 19.3 AU but depends on the initial inclination. In another run the inclination of the asteroids' orbit was varied in the range 0 < i < 60 and the semimajor axes were fixed. It turned out that only four 'windows' of stable orbits survive: these are the orbits for the initial inclinations 0 < i < 7, 9 < i < 13, 31 < i < 36 and 38 < i < 50. We postulate the existence of at least some Trojans around the Uranus Lagrange points for the stability window at small and also high inclinations.Comment: 15 pages, 12 figures, submitted to CMD

Extrasolar Trojan Planets close to Habitable Zones

We investigate the stability regions of hypothetical terrestrial planets around the Lagrangian equilibrium points L4 and L5 in some specific extrasolar planetary systems. The problem of their stability can be treated in the framework of the restricted three body problem where the host star and a massive Jupiter-like planet are the primary bodies and the terrestrial planet is regarded as being massless. From these theoretical investigations one cannot determine the extension of the stable zones around the equilibrium points. Using numerical experiments we determined their largeness for three test systems chosen from the table of the know extrasolar planets, where a giant planet is moving close to the so-called habitable zone around the host star in low eccentric orbits. The results show the dependence of the size and structure of this region, which shrinks significantly with the eccentricity of the known gas giant.Comment: 4 pages, 4 figures, submitted to A&

Dynamical Stability and Habitability of Gamma Cephei Binary-Planetary System

It has been suggested that the long-lived residual radial velocity variations observed in the precision radial velocity measurements of the primary of Gamma Cephei (HR8974, HD222404, HIP116727) are likely due to a Jupiter-like planet around this star (Hatzes et al, 2003). In this paper, the orbital dynamics of this plant is studied and also the possibility of the existence of a hypothetical Earth-like planet in the habitable zone of its central star is discussed. Simulations, which have been carried out for different values of the eccentricity and semimajor axis of the binary, as well as the orbital inclination of its Jupiter-like planet, expand on previous studies of this system and indicate that, for the values of the binary eccentricity smaller than 0.5, and for all values of the orbital inclination of the Jupiter-like planet ranging from 0 to 40 degrees, the orbit of this planet is stable. For larger values of the binary eccentricity, the system becomes gradually unstable. Integrations also indicate that, within this range of orbital parameters, a hypothetical Earth-like planet can have a long-term stable orbit only at distances of 0.3 to 0.8 AU from the primary star. The habitable zone of the primary, at a range of approximately 3.1 to 3.8 AU, is, however, unstable.Comment: 25 pages, 7 figures, 3 tables, submitted for publicatio

A study of the stability regions in the planetary system HD 74156 - Can it host earthlike planets in habitable zones?

Using numerical methods we thoroughly investigate the dynamical stability in the region between the two planets found in HD 74156. The two planets with minimum masses 1.56 M_JUP (HD 74156b) and 7.5 M_JUP (HD 74156c), semimajor axes 0.276 AU and 3.47 AU move on quite eccentric orbits (e=0.649 and 0.395). There is a region between 0.7 and 1.4 AU which may host additional planets which we checked via numerical integrations using different dynamical models. Besides the orbital evolution of several thousands of massless regarded planets in a three-dimensional restricted 4-body problem (host star, two planets + massless bodies) we also have undertaken test computation for the orbital evolution for fictive planets with masses of 0.1, 0.3 and 1 M_JUP in the region between HD74156b and HD74156c. For direct numerical integrations up to 10^7 years we used the Lie-integrator, a method with adaptive stepsize; additionally we used the Fast Lyapunov Indicators as tool for detecting chaotic motion in this region. We emphasize the important role of the inner resonances (with the outer planet) and the outer resonances (with the inner planet) with test bodies located inside the resonances. In these two "resonance" regions almost no orbits survive. The region between the 1:5 outer resonance (0.8 AU) and the 5:1 inner resonance (1.3 AU), just in the right position for habitability, is also very unstable probably due to three-body-resonances acting there. Our results do not strictly "forbid" planets to move there, but the existence of a planet on a stable orbit between 0.8 and 1.3 AU is unlikely.Comment: submitted to A&A, 4 pages, 5 figure

Planets in habitable zones: A study of the binary Gamma Cephei

The recently discovered planetary system in the binary GamCep was studied concerning its dynamical evolution. We confirm that the orbital parameters found by the observers are in a stable configuration. The primary aim of this study was to find stable planetary orbits in a habitable region in this system, which consists of a double star (a=21.36 AU) and a relatively close (a=2.15 AU) massive (1.7 Mjup sin i) planet. We did straightforward numerical integrations of the equations of motion in different dynamical models and determined the stability regions for a fictitious massless planet in the interval of the semimajor axis 0.5 AU < a < 1.85 AU around the more massive primary. To confirm the results we used the Fast Lyapunov Indicators (FLI) in separate computations, which are a common tool for determining the chaoticity of an orbit. Both results are in good agreement and unveiled a small island of stable motions close to 1 AU up to an inclination of about 15 deg (which corresponds to the 3:1 mean motion resonance between the two planets). Additionally we computed the orbits of earthlike planets (up to 90 earthmasses) in the small stable island and found out, that there exists a small window of stable orbits on the inner edge of the habitable zone in GamCep even for massive planets.Comment: 4 pages, 5 figures, changed 2 references made minor changes due to referees advic

An overview of airborne radioactive emissions at Los Alamos National Laboratory

Strict control is essential over any emissions of radioactivity in the ventilation exhaust from facilities where radioactive materials may become airborne. At Los Alamos National Laboratory there are 87 stacks exhausting ventilation air to the environment from operations with a potential for radioactive emissions. These stacks cover the diverse operations at all Laboratory facilities where radioactive materials are handled and require continuous sampling/monitoring to detect levels of contamination. An overview is presented of the operations, associated ventilation exhaust cleanup systems, and analysis of the emissions. In keeping with the as-low-as-reasonably-achievable concept, emissions of radionuclides are reduced whenever practicable. A specific example describing the reduction of emissions from the linear accelerator beam stop area at the Los Alamos Meson Physics Facility during 1985 by a factor of 8 over previous emissions is presented

The Development of a Universally Accepted Sacral Fracture Classification: A Survey of AOSpine and AOTrauma Members.

Study Design Survey study. Objective To determine the global perspective on controversial aspects of sacral fracture classifications. Methods While developing the AOSpine Sacral Injury Classification System, a survey was sent to all members of AOSpine and AOTrauma. The survey asked four yes-or-no questions to help determine the best way to handle controversial aspects of sacral fractures in future classifications. Chi-square tests were initially used to compare surgeons\u27 answers to the four key questions of the survey, and then the data was modeled through multivariable logistic regression analysis. Results A total of 474 surgeons answered all questions in the survey. Overall 86.9% of respondents felt that the proposed hierarchical nature of injuries was appropriate, and 77.8% of respondents agreed that that the risk of neurologic injury is highest in a vertical fracture through the foramen. Almost 80% of respondents felt that the separation of injuries based on the integrity of L5-S1 facet was appropriate, and 83.8% of surgeons agreed that a nondisplaced sacral U fracture is a clinically relevant entity. Conclusion This study determines the global perspective on controversial areas in the injury patterns of sacral fractures and demonstrates that the development of a comprehensive and universally accepted sacral classification is possible