Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Nuclear level density”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Cosmogenic records in Antarctic meteorites

Aliquot samples of 29 Antarctic L and H chondrites are analyzed for their nuclear track records and Mn-53 activities. The track density in the analyzed samples ranges from 10 to the 4th to approximately 6 x 10 to the 6th per sq cm. A significant finding is the observation of track-rich grains in a set of four L3 chondrites (ALHA 77215, 77216, 77217, and 77252), suspected of belonging to the same fall based on petrographic observations. An additional sample, ALHA 78105, an L6 chondrite, also has track-rich grains. Mn-53 activity is at near saturation level in approximately 65 percent of the analyzed samples, suggesting exposure ages of greater than 10 m.y. in these cases. Very few H chondrites from the 7-m.y. exposure age peak are apparently sampled among the ones investigated in this study. Approximately 6 percent and 4 percent, respectively, of the Antarctic H and L chondrites analyzed thus far for their cosmogenic records have precompaction irradiation features. A combined analysis of Mn-53 and nuclear track data makes it possible to confirm or rule out the proposed pairing of several sets of Antarctic meteorites and to estimate the preatmospheric sizes of some of these meteorites. The results suggest that most of the small Antarctic meteorites (less than 1 kg) have suffered high (greater than 95 percent) ablation mass-loss.

Goswami, J. N.↗
NASA NTRS1984

A search at the millijansky level for milli-arcsecond cores in a complete sample of radio galaxies

A complete sample of 26 extended radio galaxies was observed at 2.29 GHz with the Mark III VLBI system. The fringe spacing was about 3 milli-arcsec, and the detection limit was about 2 millijanskys. Half of the galaxies were found to possess milli-arcsec radio cores. In all but three sources, the nuclear flux density was less than 0.04 of the total flux density. Galaxies with high optical luminosity (less than -21.2) were more likely than less luminous galaxies to contain a detectable milliparcsec radio core (69 percent vs. 20 percent). For objects with arcsec cores, 80 percent were found to have a milli-arcsec core, even though the milli-arcsec object did not always contribute the greater part of the arcsec flux density.

Wehrle, A. E.↗
NASA NTRS1975

A preliminary systems-engineering study of an advanced nuclear-electrolytic hydrogen-production facility

An advanced nuclear-electrolytic hydrogen-production facility concept was synthesized at a conceptual level with the objective of minimizing estimated hydrogen-production costs. The concept is a closely-integrated, fully-dedicated (only hydrogen energy is produced) system whose components and subsystems are predicted on ''1985 technology.'' The principal components are: (1) a high-temperature gas-cooled reactor (HTGR) operating a helium-Brayton/ammonia-Rankine binary cycle with a helium reactor-core exit temperature of 980 C, (2) acyclic d-c generators, (3) high-pressure, high-current-density electrolyzers based on solid-polymer electrolyte technology. Based on an assumed 3,000 MWt HTGR the facility is capable of producing 8.7 million std cu m/day of hydrogen at pipeline conditions, 6,900 kPa. Coproduct oxygen is also available at pipeline conditions at one-half this volume. It has further been shown that the incorporation of advanced technology provides an overall efficiency of about 43 percent, as compared with 25 percent for a contemporary nuclear-electric plant powering close-coupled contemporary industrial electrolyzers.

Escher, W. J. D.↗
NASA NTRS1987

Megawatt level electric propulsion perspectives

For long range space missions, deliverable payload fraction is an inverse exponential function of the propellant exhaust velocity or specific impulse of the propulsion system. The exhaust velocity of chemical systems are limited by their combustion chemistry and heat transfer to a few km/s. Nuclear rockets may achieve double this range, but are still heat transfer limited and ponderous to develop. Various electric propulsion systems can achieve exhaust velocities in the 10 km/s range, at considerably lower thrust densities, but require an external electrical power source. A general overview is provided of the currently available electric propulsion systems from the perspective of their characteristics as a terminal load for space nuclear systems. A summary of the available electric propulsion options is shown and generally characterized in the power vs. exhaust velocity plot. There are 3 general classes of electric thruster devices: neutral gas heaters, plasma devices, and space charge limited electrostatic or ion thrusters.

Jahn, Robert G.↗
NASA NTRS2000

Electrostatics of Granular Material (EGM): Space Station Experiment

Aggregates were observed to form very suddenly in a lab-contained dust cloud, transforming (within seconds) an opaque monodispersed cloud into a clear volume containing rapidly-settling, long hair-like aggregates. The implications of such a "phase change" led to a series of experiments progressing from the lab, to KC-135, followed by micro-g flights on USML-1 and USML-2, and now EGM slated for Space Station. We attribute the sudden "collapse" of a cloud to the effect of dipoles. This has significant ramifications for all types of cloud systems, and additionally implicates dipoles in the processes of cohesion and adhesion of granular matter. Notably, there is the inference that like-charged grains need not necessarily repel if they are close enough together: attraction or repulsion depends on intergranular distance (the dipole being more powerful at short range), and the D/M ratio for each grain, where D is the dipole moment and M is the net charge. We discovered that these ideas about dipoles, the likely pervasiveness of them in granular material, the significance of the D/M ratio, and the idea of mixed charges on individual grains resulting from tribological processes --are not universally recognized in electrostatics, granular material studies, and aerosol science, despite some early seminal work in the literature, and despite commercial applications of dipoles in such modern uses as "Krazy Glue", housecleaning dust cloths, and photocopying. The overarching goal of EGM is to empirically prove that (triboelectrically) charged dielectric grains of material have dipole moments that provide an "always attractive" intergranular force as a result of both positive and negative charges residing on the surfaces of individual grains. Microgravity is required for this experiment because sand grains can be suspended as a cloud for protracted periods, the grains are free to rotate to express their electrostatic character, and Coulombic forces are unmasked. Suspended grains will be "interrogated" by applied electrical fields. In one module, grains will be immersed in an inhomogeneous electric field and allowed to be attracted towards or repelled from the central electrode of the module: part of the grain's speed will be a function of its net charge (monopole), part will be a function of the dipole. Observed grain position vs. time will provide a curve that can be deconvolved into the dipole and monopole forces responsible, since both have distinctive radial dependencies. In a second approach, the inhomogeneous field will be alternated at low frequency (e.g., every 5-10 seconds) so that the grains are alternately attracted and repelled from the center of the field. The resulting "zigzag" grain motion will gradually drift inwards, then suddenly change to a unidirectional inward path when a critical radial distance is encountered (a sort of "Coulombic event horizon") at which the dipole strength supersedes the monopole strength --thus proving the presence of a dipole, while also quantifying the D/M ratio. In a second module, an homogeneous electric field eliminates dipole effects (both Coulombic and induced) to provide calibration of the monopole and to more readily evaluate net charge statistical variance. In both modules, the e-fields will be exponentially step-ramped in voltage during the experiment, so that the field "nominalizes" grain speed while spreading the response time --effectively forcing each grain to "wait its turn" to be measured. In addition to rigorously quantifying M, D, and the D/M ratio for many hundreds of grains, the experiment will also observe gross electrometric and RF discharge phenomena associated with grain activity. The parameter space will encompass grain charging levels (via intentional triboelectrification), grain size, cloud density, and material type. Results will prove or disprove the dipole hypothesis. In either case, light will be shed on the role of electrostatic forces in governing granular systems. Knowledge so gained can be applied to natural clouds such as protostellar and protoplanetary dust and debris systems, planetary rings, planetary dust palls and aerosols created by volcanic, impact, aeolian, firestorm, or nuclear winter processes. The data are also directly applicable to adhesion, cohesion, transport, dispersion, and collection of granular materials in industrial, agricultural, pharmaceutical applications, and in fields as diverse as dust contamination of space suits on Mars and crop spraying on Earth.

Marshall, J.↗
NASA NTRS2016

IC 751: A New Changing Look AGN Discovered by NuSTAR

We present results of five Nuclear Spectroscopic Telescope Array (NuSTAR) observations of the type 2 active galactic nucleus (AGN) in IC 751, three of which were performed simultaneously with XMM-Newton or Swift/ X-Ray Telescope. We find that the nuclear X-ray source underwent a clear transition from a Compton-thick (NH approx. = 2 x10(exp 24)/sq cm) to a Compton-thin ( N(sub H) approx. = 4 x10(exp 23)/sq cm) state on timescales of < or approx.3 months, which makes IC 751 the first changing look AGN discovered by NuSTAR. Changes of the line of sight column density at the approx.2 (sigma) level are also found on a timescale of approx. 48 hr (delta N(sub H approx. 10(exp 23)/sq cm). From the lack of spectral variability on timescales of approx.100 ks, we infer that the varying absorber is located beyond the emission-weighted average radius of the broad-line region (BLR), and could therefore be related either to the external part of the BLR or a clumpy molecular torus. By adopting a physical torus X-ray spectral model, we are able to disentangle the column density of the non-varying absorber (N(sub H) approx. 3.8 x10(exp 23)/sq cm) from that of the varying clouds [N(sub H) approx. (1- 150) x 10(exp 22)/sq cm], and to constrain that of the material responsible for the reprocessed X-ray radiation (N(sub H approx. 6 x 10(exp 24)/sq cm).24 -2). We find evidence of significant intrinsic X-ray variability, with the flux varying by a factor of five on timescales of a few months in the 2-10 and 10-50 keV band.

indivdual: Seyfert↗
NASA NTRS1979

Simplified model of a volumetric direct nuclear pumped He-3-Ar laser

A physical model for the volumetric nuclear pumped He-3-Ar laser is described and the source terms arising from the He-3(n, p)H-3 reaction as well as the rate equations are given. Steady state solutions are derived for the densities of the species vs the fraction of argon. The dominant pumping mechanism is found to be collisional radiative recombination of the argon atomic ions and subsequent cascading into the upper laser level. The reactions following recombination are described and an expression is derived for the difference in densities of the argon 3d and 4p levels. Comparison with experiments shows good agreement.

Harries, W. L.↗
NASA NTRS2004

The Far-Infrared Spectrum of Arp 220

ISO/LWS grating observations of the ultraluminous infrared galaxy Arp 220 shows absorption in molecular lines of OH, H 2 0 , CH, NH, and "3, well as in the [0 I] 63 pm line and emission in the [C 111 158 pm line. We have modeled the continuum and the emission/absorption of all observed features by means of a non-local radiative transfer code. The continuum from 25 to 1300 pm is modeled AS A WARM (106 K) NUCLEAR REGION THAT IS OPTICALLY THICK IN THE FAR-INFRARED, attenuated by an extended region (size 2") that is heated mainly through absorption of nuclear infrared radiation. The molecular absorption in the nuclear region is characterized by high excitation due to the high infrared radiation density. The OH column densities are high toward the nucleus and the extended region (about 2 x 10 sup 17 cm sup-2). The H2O column density is also high toward the nucleus (2 - 10 x 1017 cm-2) and lower in the extended region. The column densities in a halo that accounts for the absorption by the lowest lying levels are similar to what are found in the diffuse clouds toward the star forming regions in the Sgr B2 molecular cloud complex near the Galactic Center. Most notable are the high column densities found for NH and NH3 toward the nucleus, with values of about 1.5 x 10supl6 cmsup-2 and about 3 x 10supl6 cmsup-2, respectively, whereas the NH2 column density is lower than about 2 x 10sup15 cmsup-2. A combination of PDRs in the extended region and hot cores with enhanced H20 photodissociation and a possible shock contribution in the nuclei may explain the relative column densities of OH and H20, whereas the nitrogen chemistry may be strongly affected by cosmic ray ionization. The [C II] 158 pm line is well reproduced by our models and its "deficit" relative to the CII/FIR ratio in normal and starburst galaxies is suggested to be mainly a consequence of the dominant non-PDR component of far- infrared radiation, ALTHOUGH OUR MODELS ALONE CANNOT RULE OUT EXTINCTION EFFECTS IN THE NUCLEI.

Gonzalez-Alfonso, Eduardo↗
NASA NTRS1979

Stark-profile calculations for Lyman-series lines of one-electron ions in dense plasmas

The frequency distributions of the first six Lyman lines of hydrogenlike carbon, oxygen, neon, magnesium, aluminum, and silicon ions broadened by the local fields of both ions and electrons are calculated for dense plasmas. The electron collisions are treated by an impact theory allowing (approximately) for level splittings caused by the ion fields, finite duration of the collisions, and screening of the electron fields. These calculations are fully quantum mechanical and include the full Coulomb interaction. Ion effects are calculated in the quasistatic, linear-Stark-effect approximation, using distribution functions of Hooper and Tighe which include correlation and shielding effects. Theoretical uncertainties from the various approximations are estimated, and the scaling of the profiles with density, temperature, and nuclear charge is discussed. A correction for the effects caused by low-frequency field fluctuations is suggested.

Griem, H. R.↗
NASA NTRS1978

The spectrum of cosmic electrons with energies between 6 and 100 GeV

Final results are reported concerning the spectrum of 6-100-GeV cosmic-ray electrons observed during a balloon exposure of approximately 3500 sq m-s-sr at an average depth of 4.8 g/sq cm. The spectral intensity of primary cosmic-ray electrons is found to have a power-law dependence on electron energy with an index of 3.4 + or - 0.1; the ground-level spectrum of secondary cosmic-ray electrons is also shown to be a power-law spectrum, but with an index of 2.9 + or - 0.1. The observed spectrum, which is significantly steeper than the nuclear spectrum, is interpreted as a fully steepened one reflecting an equilibrium between injection and energy loss. It is suggested that the confinement volume for cosmic rays extends beyond the galactic disk and includes a halo of reduced gas density where the Compton-synchrotron mechanism operates but the probability of nuclear interactions is small.

Meegan, C. A.↗
NASA NTRS2001

Our Sun IV: The Standard Model and Helioseismology: Consequences of Uncertainties in Input Physics and in Observed Solar Parameters

Helioseismic frequency observations provide an extremely accurate window into the solar interior; frequencies from the Michaelson Doppler Imager (MDI) on the Solar and Heliospheric Observatory (SOHO) spacecraft, enable the adiabatic sound speed and adiabatic index to be inferred with an accuracy of a few parts in 10(exp 4) and the density with an accuracy of a few parts in 10(exp 3). This has become a Serious challenge to theoretical models of the Sun. Therefore, we have undertaken a self-consistent, systematic study of the sources of uncertainties in the standard solar models. We found that the largest effect on the interior structure arises from the observational uncertainties in the photospheric abundances of the elements, which affect the sound speed profile at the level of 3 parts in 10(exp 3). The estimated 4% uncertainty in the OPAL opacities could lead to effects of 1 part in 10(exp 3); the approximately 5%, uncertainty in the basic pp nuclear reaction rate would have a similar effect, as would uncertainties of approximately 15% in the diffusion constants for the gravitational settling of helium. The approximately 50% uncertainties in diffusion constants for the heavier elements would have nearly as large an effect. Different observational methods for determining the solar radius yield results differing by as much as 7 parts in 10(exp 4); we found that this leads to uncertainties of a few parts in 10(exp 3) in the sound speed int the solar convective envelope, but has negligible effect on the interior. Our reference standard solar model yielded a convective envelope position of 0.7135 solar radius, in excellent agreement with the observed value of 0.713 +/- 0.001 solar radius and was significantly affected only by Z/X, the pp rate, and the uncertainties in helium diffusion constants. Our reference model also yielded envelope helium abundance of 0.2424, in good agreement with the approximate range of 0.24 to 0.25 inferred from helioseismic observations; only extreme Z/X values yielded envelope helium abundance outside this range. We found that other current uncertainties, namely, in the solar age and luminosity, in nuclear rates other than the pp reaction, in the low-temperature molecular opacities, and in the low-density equation of state, have no significant effect on the quantities that can be inferred from helioseismic observations. The predicted pre-main-sequence lithium depletion is uncertain by a factor of 2. The predicted neutrino capture rate is uncertain by approximately 30% for the Cl-27 experiment and by approximately 3% for Ga-71 experiments, while the B-8 neutrino flux is uncertain by approximately 30%.

Boothroyd, Arnold I.↗
NASA NTRS1998

"2001: A Space Odyssey" Revisited--The Feasibility of 24 Hour Commuter Flights to the Moon Using NTR Propulsion with LUNOX Afterburners

The prospects for "24 hour" commuter flights to the Moon, similar to that portrayed in 2001: A Space Odyssey but on a more Spartan scale, are examined using two near term, "high leverage" technologies--liquid oxygen (LOX)-augmented nuclear thermal rocket (NTR) propulsion and "lunar-derived" oxygen (LUNOX) production. Ironrich volcanic glass, or "orange soil," discovered during the Apollo 17 mission to Taurus-Littrow, has produced a 4% oxygen yield in recent NASA experiments using hydrogen reduction. LUNOX development and utilization would eliminate the need to transport oxygen supplies from Earth and is expected to dramatically reduce the size, cost and complexity of space transportation systems. The LOX-augmented NTR concept (LANTR) exploits the high performance capability of the conventional liquid hydrogen (LH2)-cooled NTR and the mission leverage provided by LUNOX in a unique way, LANTR utilizes the large divergent section of its nozzle as an "afterburner" into which oxygen is injected and supersonically combusted with nuclear preheated hydrogen emerging front the engine's choked sonic throat--essentially "scramjet propulsion in reverse." By varying the oxygen-to-hydrogen mixture ratio, the LANTR engine can operate over a wide range of thrust and specific impulse (Isp) values while the reactor core power level remains relatively constant. The thrust augmentation feature of LANTR means that "big engine" performance can be obtained using smaller, more affordable, easier to test NTR engines. The use of high-density LOX in place of low-density LH2 also reduces hydrogen mass and tank volume resulting in smaller space vehicles. An implementation strategy and evolutionary lunar mission architecture is outlined which requires only Shuttle C or "in-line" Shuttle-derived launch vehicles, and utilizes conventional NTR-powered lunar transfer vehicles (LTVs), operating in an "expendable mode" initially, to maximize delivered surface payload on each mission. The increased payload is dedicated to installing "modular" LUNOX production units with the intent of supplying LUNOX to lunar landing vehicles (LLVS) and then LTVs at the earliest possible opportunity. Once LUNOX becomes available in low lunar orbit (LLO), monopropellant NTRs would be outfitted with an oxygen propellant module, feed system and afterburner nozzle for "bipropellant" operation. Transition to a "reusable" mission architecture now occurs with smaller, LANTR-powered LTVs delivering approximately 400% more payload on each piloted round trip mission than earlier expendable "all LH2" NTR systems. As initial lunar outposts grow to eventual lunar settlements and LUNOX production capacity increases, the LANTR concept can enable a rapid "commuter" shuttle capable of 24 hour "one way" trips to and from the Moon, A vast deposit of"iron-rich" volcanic glass beads identified at just one candidate site--located at the southeastern edge of Mare Serenitatis--could supply, sufficient LUNOX to support daily commuter flights to the Moon for the next 9000 years!

Borowski, Stanley K.↗
NASA NTRS2003

2001: A Space Odyssey Revisited: The Feasibility of 24 Hour Commuter Flights to the Moon Using NTR Propulsion with LUNOX Afterburners

The prospects for 24 hour commuter flights to the Moon, similar to that portrayed in 2001: A Space Odyssey but on a more Spartan scale, are examined using two near term, high leverage technologies: liquid oxygen (LOX)-augmented nuclear thermal rocket (NTR) propulsion and lunar-derived oxygen (LUNOX) production. Iron-rich volcanic glass, or orange soil, discovered during the Apollo 17 mission to Taurus-Littrow, has produced a 4 percent oxygen yield in recent NASA experiments using hydrogen reduction. LUNOX development and utilization would eliminate the need to transport oxygen supplies from Earth and is expected to dramatically reduce the size, cost and complexity of space transportation systems. The LOX-augmented NTR concept (LANTR) exploits the high performance capability of the conventional liquid hydrogen (LH2)-cooled NTR and the mission leverage provided by LUNOX in a unique way. LANTR utilizes the large divergent section of its nozzle as an afterburner into which oxygen is injected and supersonically combusted with nuclear preheated hydrogen emerging from the engine's choked sonic throat, essentially scramjet propulsion in reverse. By varying the oxygen-to-hydrogen mixture ratio, the LANTR engine can operate over a wide range of thrust and specific impulse (Isp) values while the reactor core power level remains relatively constant. The thrust augmentation feature of LANTR means that big engine performance can be obtained using smaller, more affordable, easier to test NTR engines. The use of high-density LOX in place of low density LH2 also reduces hydrogen mass and tank volume resulting in smaller space vehicles. An implementation strategy and evolutionary lunar mission architecture is outlined which requires only Shuttle C or in-line Shuttle-derived launch vehicles, and utilizes conventional NTR-powered lunar transfer vehicles (LTVs), operating in an expendable mode initially, to maximize delivered surface payload on each mission. The increased payload is dedicated to installing modular LUNOX production units with the intent of supplying LUNOX to lunar landing vehicles (LLVs) and then LTVs at the earliest possible opportunity. Once LUNOX becomes available in low lunar orbit (LLO), monopropellant NTRs would be outfitted with an oxygen propellant module, feed system and afterburner nozzle for bipropellant operation. Transition to a reusable mission architecture now occurs with smaller, LANTR-powered LTVs delivering ~400% more payload on each piloted round trip mission than earlier expendable all LH2 NTR systems. As initial lunar outposts grow to eventual lunar settlements and LUNOX production capacity increases, the LANTR concept can enable a rapid commuter shuttle capable of 24 hour one way trips to and from the Moon. A vast deposit of iron-rich volcanic glass beads identified at just one candidate site located at the southeastern edge of Mare Serenitatis could supply sufficient LUNOX to support daily commuter flights to the Moon for the next 9000 years!

Borowski, Stanley↗
NASA NTRS2001

"2001: A Space Odyssey" Revisited: The Feasibility of 24 Hour Commuter Flights to the Moon Using NTR Propulsion with LUNOX Afterburners

The prospects for "24 hour" commuter flights to the Moon. similar to that portrayed in 2001: A Space Odyssey but on a more Spartan scale. are examined using two near term. "high leverage" technologies-liquid oxygen (LOX)-augmented nuclear thermal rocket (NTR) propulsion and "lunar-derived" oxygen (LUNOX) production. Iron-rich volcanic glass. or "orange soil," discovered during the Apollo 17 mission to Taurus-Littrow. has produced a 4% oxygen yield in recent NASA experiments using hydrogen reduction. LUNOX development and utilization would eliminate the need to transport oxygen supplies from Earth and is expected to dramatically reduce the size, cost and complexity of space transportation systems. The LOX-augmented NTR concept (LANTR) exploits the high performance capability of the conventional liquid hydrogen (LH2)-cooled NTR and the mission leverage provided by LUNOX in a unique way. LANTR utilizes the large divergent section of its nozzle as an "afterburner" into which oxygen is injected and supersonically combusted with nuclear preheated hydrogen emerging from the engine's choked sonic throat-essentially "scramjet propulsion in reverse." By varying the oxygen-to-hydrogen mixture ratio, the LANTR engine can operate over a wide range of thrust and specific impulse (Isp) values while the reactor core power level remains relatively constant. The thrust augmentation feature of LANTR means that "big engine" performance can be obtained using smaller. more affordable. easier to test NTR engines. The use of high-density LOX in place of low-density LH2 also reduces hydrogen mass and tank volume resulting in smaller space vehicles. An implementation strategy and evolutionary lunar mission architecture is outlined which requires only Shuttle C or "in-line" Shuttle-derived launch vehicles, and utilizes conventional NTR-powered lunar transfer vehicles (LTVs), operating in an "expendable mode" initially, to maximize delivered surface payload on each mission. The increased payload is dedicated to installing "modular" LUNOX production units with the intent of supplying LUNOX to lunar landing vehicles (LLVs) and then LTVs at the earliest possible opportunity. Once LUNOX becomes available in low lunar orbit (LLO), monopropellant NTRs would be outfitted with an oxygen propellant module, feed system and afterburner nozzle for "bipropellant" operation. Transition to a "reusable" mission architecture now occurs with smaller, LANTR-powered LTVs delivering approximately 400% more payload on each piloted round trip mission than earlier expendable "all LH2" NTR systems. As initial lunar outposts grow to eventual lunar settlements and LUNOX production capacity increases, the LANTR concept can enable a rapid "commuter" shuttle capable of 24 hour "one way" trips to and from the Moon. A vast deposit of "iron-rich" volcanic glass beads identified at just one candidate site - located at the southeastern edge of Mare Serenitatis - could supply sufficient LUNOX to support daily commuter flights to the Moon for the next 9000 years'.

Borowski, Stanley K.↗
NASA NTRS2004

Using the Moon and Mars as Giant Detectors for Strange Quark Nuggets

On the Earth, the detectability of small seismic signals is limited by pervasive seismic background noise, caused primarily by interactions of the atmosphere and oceans with the solid surface. Mars, with a very thin atmosphere and no ocean is expected to have a noise level at least an order of magnitude lower than the Earth, and the airless Moon is even quieter still. These pristine low-vibration environments are ideal for searching for nuggets of "strange quark matter." Strange quark matter was postulated by Edward Witten [Phys. Rev. D30, 272, 1984] as the lowest possible energy state of matter. It would be made of up, down, and strange quarks, instead of protons and neutrons made only of up and down quarks. It would have nuclear densities, and hence be difficult to detect. Micron-sized nuggets would weigh in the ton range. As suggested by de Rujula and Glashow [Nature 312 (5996): 734, 1984], a massive strange quark nugget can generate a trail of seismic waves, as it traverses a celestial body. We discuss the mission concept for deploying a network of sensitive seismometers on Mars and on the Moon for such a search.

Chui, Talso↗
NASA NTRS1992

Near Earth asteroid orbit perturbation and fragmentation

Collisions by near earth asteroids or the nuclei of comets pose varying levels of threat to man. A relatively small object, approximately 100 meter diameter, which might be found on an impact trajectory with a populated region of the Earth, could potentially be diverted from an Earth impacting trajectory by mass driver rocket systems. For larger bodies, such systems would appear to be beyond current technology. For any size object, nuclear explosions appear to be more efficient, using either the prompt blow-off from neutron radiation, the impulse from ejecta of near-surface explosion for deflection, or as a fragmenting charge. Practical deflections of bodies with diameters of 0.1, 1, and 10 km require interception, years to decades prior to earth encounter, with explosions a few kilotons, megatons, or gigatons, respectively, of equivalent TNT energy to achieve orbital velocity changes or destruction to a level where fragments are dispersed to harmless spatial densities.

Ahrens, Thomas J.↗
NASA NTRS1991

Molecular clouds in starburst galaxy nuclei

New CO observations of a complete sample of starburst galaxies are presented in order to determine the range of molecular gas masses and star-formation efficiencies that characterize these systems. The properties of the galaxies in the sample are given, and the H-alpha and R-band CCD images for six of the galaxies are shown. The novel feature of this study is that the galaxies in this study are infrared selected as opposed to optically selected. They exhibit levels of nuclear star formation activity which are comparable to the starburst galaxies M82 and NGC 253. A subset of galaxies with unusually narrow CO line widths, high star-formation efficiencies, and compact 10-micron distributions is revealed. It is proposed that, if gas distributions in these galaxies are also compact, as the narrow linewidths suggest, the high yields of massive stars per unit mass of molecular gas may be attributed to a star-formation mechanism which becomes more efficient as the gas density increases.

Young, Judith S.↗
NASA NTRS2005

The Far-Infrared Spectrum of Arp 220

ISO/LWS grating observations of the ultraluminous infrared galaxy Arp 220 shows absorption in molecular lines of OH, H(sub 2)O, CH, NH, and NH(sub 3), as well as in the [O I] 63 micron line and emission in the [C II] 158 micron line. We have modeled the continuum and the emission/absorption of all observed features by means of a non-local radiative transfer code. The continuum from 25 to 1300 microns is modeled as a warm (106 K) nuclear region that is optically thick in the far-infrared, attenuated by an extended region (size 2") that is heated mainly through absorption of nuclear infrared radiation. The molecular absorption in the nuclear region is characterized by high excitation due to the high infrared radiation density. The OH column densities are high toward the nucleus (2 - 6 x 10(exp 17) cm(exp -2)) and the extended region (approximately 2 x 10(exp 17) cm(exp -2)). The H(sub 2)O column density is also high toward the nucleus (2 - 10 x 10(exp 17) cm(exp -2)) and lower in the extended region. The column densities in a halo that accounts for the absorption by the lowest lying levels are similar to what are found in the diffuse clouds toward the star forming regions in the Sgr B2 molecular cloud complex near the Galactic Center. Most notable are the high column densities found for NH and NH(sub 3) toward the nucleus, with values of approximately 1.5 x 10(exp 16) cm(exp -2) and approximately 3 x 10(exp 16) cm(exp -2), respectively, whereas the NH(sub 2) column density is lower than approximately 2 x 10(exp 15) cm(exp -2). A combination of PDRs in the extended region and hot cores with enhanced H(sub 2)O photodissociation and a possible shock contribution in the nuclei may explain the relative column densities of OH and H(sub 2)O, whereas the nitrogen chemistry may be strongly affected by cosmic ray ionization. The [C II] 158 micron line is well reproduced by our models and its deficit relative to the CII/FIR ratio in normal and starburst galaxies is suggested to be mainly a consequence of the dominant non-PDR component of far-infrared radiation, although our models alone cannot rule out extinction effects in the nuclei.

Gonzalez-Alfonso, Eduardo↗