An Experimental and Theoretical Study of Neutron Leakage and Transport in a Fast Neutron Moderator and Flight-Path Arrangement

Drüke, V.; Schaal, H.

doi:10.13182/nse91-a23854

Cited by 3 publications

(1 citation statement)

References 6 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…One possible explanation for the enhanced neutron emission could be surface or near-surface roughness, of the sort seen by radar measurements out to twice the crater radius [Stickle et al, 2015]. While previous neutron transport simulations for planetary surfaces have assumed emission from a flat surface [Lawrence et al, 2006], it has been shown that the neutron leakage flux can be enhanced for non-flat surfaces [Drüke and Schaal , 1991]. If such roughness leads to the increase in emitted neutron flux required to fit the observed LPNS count rate profiles, then the neutron count rate could actually be sensitive to the physical condition of the lunar surface, making it complementary to the radar and thermal infrared data sets [Bandfield et al, 2011;Ghent et al, 2015].…”

Section: Improvements To the Simple Modelmentioning

confidence: 99%

The effect of craters on the lunar neutron flux

et al. 2015

View full text Add to dashboard Cite

The variation of remotely sensed neutron count rates is measured as a function of cratercentric distance using data from the Lunar Prospector Neutron Spectrometer. The count rate, stacked over many craters, peaks over the crater center, has a minimum near the crater rim, and at larger distances, it increases to a mean value that is up to 1% lower than the mean count rate observed over the crater. A simple model is presented, based upon an analytical topographical profile for the stacked craters fitted to data from the Lunar Orbiter Laser Altimeter. The effect of topography coupled with neutron beaming from the surface largely reproduces the observed count rate profiles. However, a model that better fits the observations can be found by including the additional freedom to increase the neutron emissivity of the crater area by ∼0.35% relative to the unperturbed surface. It is unclear what might give rise to this effect, but it may relate to additional surface roughness in the vicinities of craters. The amplitude of the crater-related signal in the neutron count rate is small, but not too small to demand consideration when inferring water-equivalent hydrogen (WEH) weight percentages in polar permanently shaded regions (PSRs). If the small crater-wide count rate excess is concentrated into a much smaller PSR, then it can lead to a large bias in the inferred WEH weight percentage. For instance, it may increase the inferred WEH for Cabeus crater at the Moon's south pole from ∼1% to ∼4%.

show abstract