Engineering topics

Wahlen, M.

Publications and source records attributed to Wahlen, M..

4 records

NASA NTRS1989

Carbon-14 in methane sources and in atmospheric methane - The contribution from fossil carbon

Measurements of carbon-14 in small samples of methane from major biogenic sources, from biomass burning, and in clean air samples from both the Northern and Southern hemispheres reveal that methane from ruminants contains contemporary carbon, whereas that from wetlands, peat bogs, rice fields, and tundra, is somewhat depleted in carbon-14. Atmospheric (C-14)H4 seems to have increased from 1986 to 1987, and levels at the end of 1987 were 123.3 + or - 0.8 percent modern carbon in the Northern Hemisphere and 120.0 + or - 0.7 percent modern carbon in the Southern Hemisphere.

Wahlen, M.↗

NASA NTRS1973

Depth profile of Mn-53 in the lunar surface

Measurements of cosmic-ray produced Mn-53 are reported for a series of lunar surface samples down to a depth of 416 g/sq cm. These results clearly illustrate the decrease in activity with depth as the incident galactic cosmic rays are absorbed. Below 60 g/sq cm the production rate decreases exponentially with a mean length of about 220 g/sq cm. These results indicate that, at the Apollo 15 site, the lunar regolith has been unmixed, on a meter scale, for the last 5 m.y. The neutron activation technique for Mn-53, which allowed samples smaller than 200 mg to be used for these measurements, is described.

Imamura, M.↗

NASA NTRS1973

Co-60 in lunar samples.

Results obtained for Co-60 in lunar soils and rocks of different depths are discussed. These results are compared to a production calculation based on the work of Lingenfelter et al. (1972). The measurement of Co-60 activities can give information about the present-day equilibrium neutron flux in the lunar regolith. The most important quantity which can be derived from these data is the absolute present-day lunar neutron production rate.

Wahlen, M.↗

NASA NTRS1972

Cosmogenic nuclides in football-sized rocks.

The activity of long- and short-lived isotopes in a series of samples from a vertical column through the center of rock 14321 was measured. Rock 14321 is a 9 kg fragmental rock whose orientation was photographically documented on the lunar surface. Also investigated was a sample from the lower portion of rock 14310, where, in order to study target effects, two different density fractions (mineral separates) were analyzed. A few nuclides in a sample from the comprehensive fines 14259 were measured. This material has been collected largely from the top centimeter of the lunar soil. The study of the deep samples of 14321 and 14310 provided values for the activity of isotopes at points where only effects produced by galactic cosmic rays are significant.

Wahlen, M.↗