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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.

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At least 19 records

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NASA NTRS2005

Going to the Bottom of the Explosion that Formed Cas A

The purpose of this INTEGRAL AO 1 proposal was to observe the gamma-ray lines at 1157 keV, as well as 68 keV and 78 keV of the (44)Ti decay chain from the youngest known galactic supernova remnant Cas A. The radioactive decay of (44)Ti in Cas A was first detected by COMPTEL in the 1157 keV line and later confirmed in the lower energy lines using BeppoSAX data. Despite the second confirming measurement, the flux value still has a considerable error, due to a low signal over background ratio and the poor definition of the continuum background in the range of 70 - 100 keV above the line energies. In addition to improving this flux measurement, INTEGRAL has the unique capability, in principle, to measure the line width of the emission. This type of measurement can further constrain supernova explosion models. Unfortunately, the INTEGRAL instrumental background, especially in the SPI spectrometer, turned out to be significantly higher than estimated at the time of proposal submission before launch. This, and to a smaller extent the reduced effective exposure time of about 1.5 Ms compared to requested 2.5 Ms, has precluded us from reaching the sensitivity necessary for this measurement. Studies of the background variability with the goal of improving background modeling are ongoing, and additional 2.5 Ms observing time has just been approved for the next observing cycle.

Oberlack, Uwe↗

NASA NTRS2012

Development of a Quasi-monoenergetic 6 MeV Gamma Facility at NASA Goddard Space Flight Center

The 6 MeV Gamma Facility has been developed at NASA Goddard Space Flight Center (GSFC) to allow in-house characterization and testing of a wide range of gamma-ray instruments such as pixelated CdZnTe detectors for planetary science and Compton and pair-production imaging telescopes for astrophysics. The 6 MeV Gamma Facility utilizes a circulating flow of water irradiated by 14 MeV neutrons to produce gamma rays via neutron capture on oxygen (O-16(n,p)N-16 yields O-16* yields O-16 + gamma). The facility provides a low cost, in-house source of 2.742, 6.129 and 7.117 MeV gamma rays, near the lower energy range of most accelerators and well above the 2.614 MeV line from the Th-228 decay chain, the highest energy gamma ray available from a natural radionuclide. The 7.13 s half-life of the N-16 decay allows the water to be irradiated on one side of a large granite block and pumped to the opposite side to decay. Separating the irradiation and decay regions allows for shielding material, the granite block, to be placed between them, thus reducing the low-energy gamma-ray continuum. Comparison between high purity germanium (HPGe) spectra from the facility and a manufactured source, Pu-238/C-13, shows that the low-energy continuum from the facility is reduced by a factor approx. 30 and the gamma-ray rate is approx.100 times higher at 6.129 MeV.

NASA↗

NASA NTRS1969

Daughter growth in freshly separated Ra-226, Ac-227 and U-232

Report provides computer-calculated curves and tables for the daughter buildup of Ra-226, Ac-227 and U-232 chains. Data are presented as a function of time beginning with pure samples of each parent. The information may be of interest to those using decay chains as isotopic alpha sources or neutron sources.

Basile, L. J.↗

NASA NTRS1994

Evidence for Ni-56 yields Co-56 yields Fe-56 decay in type Ia supernovae

In the prevailing picture of Type Ia supernovae (SN Ia), their explosive burning produces Ni-56, and the radioactive decay chain Ni-56 yields Co-56 yields Fe-56 powers the subsequent emission. We test a central feature of this theory by measuring the relative strengths of a (Co III) emission feature near 5900 A and a (Fe III) emission feature near 4700 A. We measure 38 spectra from 13 SN Ia ranging from 48 to 310 days after maximum light. When we compare the observations with a simple multilevel calculation, we find that the observed Fe/Co flux ratio evolves as expected when the Fe-56/Co-56 abundance ratio follows from Ni-56 yields Co-56 yields Fe-56 decay. From this agreement, we conclude that the cobalt and iron atoms we observe through SN Ia emission lines are produced by the radioactive decay of Ni-56, just as predicted by a wide range of models for SN Ia explosions.

Kuchner, Marc J.↗

NASA NTRS1971

Improved neutron activation prediction code system development

Two integrated neutron activation prediction code systems have been developed by modifying and integrating existing computer programs to perform the necessary computations to determine neutron induced activation gamma ray doses and dose rates in complex geometries. Each of the two systems is comprised of three computational modules. The first program module computes the spatial and energy distribution of the neutron flux from an input source and prepares input data for the second program which performs the reaction rate, decay chain and activation gamma source calculations. A third module then accepts input prepared by the second program to compute the cumulative gamma doses and/or dose rates at specified detector locations in complex, three-dimensional geometries.

Saqui, R. M.↗

NASA NTRS1981

Adaptation of the TH Epsilon Mu formalism for the analysis of the equivalence principle in the presence of the weak and electroweak interaction

The TH epsilon mu formalism, used in analyzing equivalence principle experiments of metric and nonmetric gravity theories, is adapted to the description of the electroweak interaction using the Weinberg-Salam unified SU(2) x U(1) model. The use of the TH epsilon mu formalism is thereby extended to the weak interactions, showing how the gravitational field affects W sub mu (+ or -1) and Z sub mu (0) boson propagation and the rates of interactions mediated by them. The possibility of a similar extension to the strong interactions via SU(5) grand unified theories is briefly discussed. Also, using the effects of the potentials on the baryon and lepton wave functions, the effects of gravity on transition mediated in high-A atoms which are electromagnetically forbidden. Three possible experiments to test the equivalence principle in the presence of the weak interactions, which are technologically feasible, are then briefly outline: (1) K-capture by the FE nucleus (counting the emitted X-ray); (2) forbidden absorption transitions in high-A atoms' vapor; and (3) counting the relative Beta-decay rates in a suitable alpha-beta decay chain, assuming the strong interactions obey the equivalence principle.

Fennelly, A. J.↗

NASA NTRS1982

Supernovae, young remnants, and nucleosynthesis

Chemical abundance data from extragalactic supernovae and from supernova remnants (SNR) less than 1000 yrs old are employed to show that nuclear burning beyond helium synthesis actually occurs. Supernova (SN) are classified into types I or II, having no hydrogen lines or featuring hydrogen lines, respectively. The SN I's have been observed as having a preponderance of Fe lines, and emitting from a source at around 12,000 K with a center continuum of approximately 10 AU. Decay chains which could account for detected luminosities and spectra are presented, noting a good fit of Fe II spectrum with observed SN spectra. SNR pass through younger and older stages, going from the outpouring of material to diffusion in the interstellar medium. Expanding flocculi from young SNR show oxygen abundances as well as lines from sulfur, calcium, and argon, with a corresponding necessity of an explosive source of 15 solar masses.

Kirshner, R. P.↗

NASA NTRS1987

Prospects for gamma-ray line observations of individual supernovae

The gamma-ray line emission from individual type I and type II supernovae are studied using numerical simulations and photon propagation codes to predict the flux levels and line shapes. For both types, the gamma ray lines with the highest flux from an individual event are the 0.847 and 1.238 MeV lines from the Ni-56 to Co-56 to Fe-56 decay chain. For type I supernovae, the 0.847 MeV line peaks at about 70 days after event onset. The historical record indicates an approximate discovery rate of once in 10 years for balloon-borne instruments, once in two to three years for the Gamma-Ray Observatory, and once in one to two years for a proposed space mission. The 0.847 MeV line flux from type II supernovae peaks at about 600 days after event onset at a low level which restricts observations to the events in the Galaxy and its nearest neighbors. The expected line shape is narrower than for type I supernovae.

Gehrels, Neil↗

NASA NTRS1989

Signatures of particle acceleration at SN 1987A

At least eight experiments are currently monitoring SN 1987A for photons or neutrinos with energies in the TeV range or higher. Observation of such signals would indicate that the supernova is the site of acceleration of charged particles to even higher energies. The way that the acceleration might occur is discussed, and the prospects for detection of such signals in light of current limits on power in the supernova from sources other than the nickel-cobalt-iron decay chain are evaluated. It is pointed out that signals of particle acceleration may show up in continuum MeV gamma rays as well as in the 100 MeV range.

Gaisser, T. K.↗

NASA NTRS1989

Minimum length Pb/SCIN detector for efficient cosmic ray identification

A study was made of the performance of a minimal length cosmic ray shower detector that would be light enough for space flight and would provide efficient identification of positions and protons. Cosmic ray positions are mainly produced in the decay chain of: Pion yields Muon yields Positron and they provide a measure of the matter density traversed by primary protons. Present positron flux measurements are consistent with the Leaky Box and Halo models for sources of cosmic rays. Abundant protons in the space environment are a significant source of background that would wash out the positron signal. Protons and positrons produced very distictive showers of particles when they enter matter; many studies have been published on their behavior on large calorimeter detectors. The challenge is to determine the minimal material necessary (minimal calorimeter depth) for positive particles identification. The primary instrument for the investigation is the Monte Carlo code GEANT, a library of programs from CERN that can be used to model experimental geometry, detector responses and particle interaction processes. The use of the Monte Carlo approach is crucial since statistical fluctuations in shower shape are significant. Studies conducted during the 1988 summer program showed that straightforward approaches to the problem achieved 85 to 90 percent correct identification, but left a residue of 10 to 15 percent misidentified particles. This percentage improved to a few percent when multiple shower-cut criteria were applied to the data. This summer, the same study was extended to employ several physical and statistical methods of identifying response of the calorimeter and the efficiency of the optimal shower cuts to off-normal incidence particle was determined.

Snyder, H. David↗

NASA NTRS2019

Impact Shocking of a Zircon-Sanidine Mixture and Investigations of Pb Mobility

The purpose of this project is to explore the mobility, mixing, and possible clumping of Pb isotopes during laboratory impact shock experiments. Impact events are a common planetary occurrence and their effect on istotope systematics and subsequent geochronology is not fully understood. By artificially shocking mixtures of zircon and sanidine and investigating the sample products, it may be possible to understand if and how Pb is mobilized during impact shock. Isotopes of Pb are the final daughter products of the decay chains of 238U, 235U and 232Th and therefore understanding how mobile the daughter product is during impact events could have consequences for dating impact events. These investigations will also reveal if Pb isotopes can be mixed between minerals

Szumila, I.↗

NASA NTRS2019

Impact Shocking of a Zircon-Sanidine Mixture and Investigations of Pb Mobility

Szumila, I.↗

NASA NTRS1998

Rossi X-Ray Timing Explorer Guest Investigator Program

Rossi X-ray Timing Explorer (RXTE) observations of the bright supernova remnant Cas A have revealed a hard power law component above 10 keV in addition to two thermal components inferred from ASCA measurements of the many line centroids from low-Z elements. The power law can be shown to be consistent with synchrotron emission from radio to hard x-rays by electrons of up to 4 x 10(exp 13) eV. Measurement of the 1157 keV line by CGRO (Compton Gamma Ray Observatory) from SC-44 in the chain of decay of Ti-44 predicts that the two Ti-44 lines at 68 and 78 keV should appear at the CGRO intensity. RXTE has placed upper limits on such lines that are marginally consistent with the CGRO measurement. Implications of these results on sites for cosmic ray acceleration and nucleosynthesis are discussed.

Lingenfelter, Richard E.↗

NASA NTRS1982

A Markov chain model for reliability growth and decay

A mathematical model is developed to describe a complex system undergoing a sequence of trials in which there is interaction between the internal states of the system and the outcomes of the trials. For example, the model might describe a system undergoing testing that is redesigned after each failure. The basic assumptions for the model are that the state of the system after a trial depends probabilistically only on the state before the trial and on the outcome of the trial and that the outcome of a trial depends probabilistically only on the state of the system before the trial. It is shown that under these basic assumptions, the successive states form a Markov chain and the successive states and outcomes jointly form a Markov chain. General results are obtained for the transition probabilities, steady-state distributions, etc. A special case studied in detail describes a system that has two possible state ('repaired' and 'unrepaired') undergoing trials that have three possible outcomes ('inherent failure', 'assignable-cause' 'failure' and 'success'). For this model, the reliability function is computed explicitly and an optimal repair policy is obtained.

Siegrist, K.↗

NASA NTRS1996

Chain Dynamics in a Dilute Magnetorheological Fluid

The structure, formation, and dynamics of dilute, mono-dispersive ferrofluid emulsions in an external magnetic field have been investigated using dynamic light scattering techniques. In the absence of the magnetic field, the emulsion particles are randomly distributed and behave like hard spheres in Brownian motion. An applied magnetic field induces a magnetic dipole moment in each particle. Dipolar interactions between particles align them into chains where correlation functions show two decay processes. The short-time decay shows the motion of straight chains as a whole where the apparent chain length increases with the applied magnetic field and the particle volume fraction. Good scaling results are obtained showing that the apparent chain length grows with time following a power law with exponent of 0.6 and depends on the applied field, particle volume fraction, and diffusion constant of the particles. The long-time decay in the correlation function shows oscillation when the chains reach a certain length with time and stiffness with threshold field This result shows that chains not only fluctuate, but move in a periodic motion with a frequency of 364 Hz at lambda = 15. It may suggest the existence of phonons. This work is the first step in the understanding of the structure formation, especially chain coarsening mechanism, of magnetorheological (MR) fluids at higher volume fractions.

Liu, Jing↗

NASA NTRS1987

First polymer in space identified in Comet Halley

The heavy-ion mass spectrum obtained in the inner coma of Comet Halley with the PICCA instrument on the Giotto spacecraft has been examined. Short polymer chains of polyoxymethylene and their decay products are identified as the source for the spectrum with six mass peaks between about 45 and 120 atomic mass units. The properties of polyoxymethylene are consistent with many of the unexpected observations in the coma.

Huebner, W. F.↗

NASA NTRS1998

Time-Resolved O3 Chemical Chain Reaction Kinetics Via High-Resolution IR Laser Absorption Methods

Excimer laser photolysis in combination with time-resolved IR laser absorption detection of OH radicals has been used to study O3/OH(v = 0)/HO2 chain reaction kinetics at 298 K, (i.e.,(k(sub 1) is OH + 03 yields H02 + 02 and (k(sub 2) is H02 + 03 yields OH + 202). From time-resolved detection of OH radicals with high-resolution near IR laser absorption methods, the chain induction kinetics have been measured at up to an order of magnitude higher ozone concentrations ([03] less than or equal to 10(exp 17) molecules/cu cm) than accessible in previous studies. This greater dynamic range permits the full evolution of the chain induction, propagation, and termination process to be temporally isolated and measured in real time. An exact solution for time-dependent OH evolution under pseudo- first-order chain reaction conditions is presented, which correctly predicts new kinetic signatures not included in previous OH + 03 kinetic analyses. Specifically, the solutions predict an initial exponential loss (chain "induction") of the OH radical to a steady-state level ([OH](sub ss)), with this fast initial decay determined by the sum of both chain rate constants, k(sub ind) = k(sub 1) + k(sub 2). By monitoring the chain induction feature, this sum of the rate constants is determined to be k(sub ind) = 8.4(8) x 10(exp -14) cu cm/molecule/s for room temperature reagents. This is significantly higher than the values currently recommended for use in atmospheric models, but in excellent agreement with previous results from Ravishankara et al.

Kulcke, Axel↗

NASA NTRS1985

A remark about pointed bubbles

The polymer expansion is a formal algebraic identity between a partition function and logarithm in statistical physics problems. The expansion gives a systematic method to control the free energy or to establish exponential tree-graph decay of connected correlations. Here, the convergence properties of the polymer expansion are analyzed in connection with three practical examples, including: intersecting bonds in chemical polymer chains; a connected closed hypersurface built from the (d-1)-faces of the d-dimensional unit cubes; and the set of Feynamn diagrams in the perturbation series of the Euclidean field theory partition function Z. The example of connected polymer chains is generalized to apply to other lattice models, including n-state Ising models at high temperature; short range lattice gases at high temperature; and weak coupling lattice field and gauge theories.

Garabedian, P. R.↗