Engineering topics

Evans, Larry

Publications and source records attributed to Evans, Larry.

3 records

NASA NTRS2013

Subsurface In Situ Elemental Composition Measurements with PING

This paper describes the Probing In situ with Neutron and Gamma rays (PING) instrument, that can measure the subsurface elemental composition in situ for any rocky body in the solar system without the need for digging into the surface. PING consists of a Pulsed Neutron Generator (PNG), a gamma ray spectrometer and neutron detectors. Subsurface elements are stimulated by high-energy neutrons to emit gamma rays at characteristic energies. This paper will show how the detection of these gamma rays results in a measurement of elemental composition. Examples of the basalt to granite ratios for aluminum and silicon abundance are provided.

Parsons, Ann↗

NASA NTRS2011

Correlation of LEND and Diviner Data

Correlated results from the Lunar Reconnaissance Orbiter's (LRO) Lunar Exploration Neutron Detector (LEND) and Lunar Orbiting Laser Altimeter (LOLA) suggest insolation effects influence the spatial distribution of Lunar H poleward of 60deg latitude. Diviner results indicate an insolation induced thermal contrast between pole-facing and equator-facing slopes of crater walls. Our research shows that the contrasting thermal conditions observed in pole-facing vs equator-facing slopes and epithermal neutron rates from LEND are positively correlated. Numerical transformations of LOLA topography facilitated a systematic decomposition of LEND epithermal maps as a function of insolation effects. The results suggest a significantly positive local epithermal contrast in these regions. Comparing pole-facing and equator-facing slopes, we find that the pole-facing slopes show epithermal neutron suppression ranging from -0.005 to 0.02 cps relative to the equator-facing slopes .. We further investigate insolation effects on epithermal neutrons by comparing the predicted insolation contrast derived from the 3-D LOLA topography model with the LEND results. We also investigate and discuss the possibility of slope mass wasting effects being correlated with our insolation-effect hypothesis

McClanahan, Tim↗

NASA NTRS1997

Comparison Between Predictions & Observations of Induced Radioactive Background in Interplanetary Missions

Radioactivity induced in detector materials and their immediate surroundings is the major source of discrete-line, gamma-ray background and an important source of continuum background in the performance of remote-sensing, gamma-ray spectroscopy of planetary bodies. In interplanetary space the dominant sources of particles are cosmic rays and their secondaries arising from interactions with the spacecraft and the surface of the target body. In addition, certain future gamma-ray astronomy missions, such as INTEGRAL, are to be located so as to perform their observations in interplanetary space rather than in the traditional low earth orbits. Such location removes contributions from the earth's atmosphere and inner radiation belt at the expense of increased exposure to cosmic rays and solar particle events. Accurate prediction of the activation of key materials by cosmic rays is of the utmost importance for detector design and data interpretation.

Dyer, Clivea↗