The variations of neutron component of lunar radiation background from LEND/LRO observations

Litvak, M.; Митрофанов, И. Г.; Санин, А. Б.; Bakhtin, B. N.; Bodnarik, J.; Boynton, W. V.; Chin, G.; Evans, L. G.; Harshman, K.; Livengood, T. A.; Malakhov, A.; Мокроусов, М. И.; McClanahan, T. P.; Sagdeev, R. Z.; Starr, R.

doi:10.1016/j.pss.2016.01.006

Cited by 16 publications

(10 citation statements)

References 37 publications

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“…Between these two cases, Teodoro et al (2014) favor a condition with greater background and nearzero signal in collimation. They did not derive an optimal description of CSETN performance, so it is not clear how to compare their result to the intermediate description of spacecraft background and collimated signal derived here and by Litvak et al (2016) in independent analysis.…”

Section: Estimates For Collimated Component Of Csetn Detected Signalmentioning

confidence: 91%

“…4 and Table2is 2 greater than the published Litvak et al estimate, translating to 97.5% confidence that the background actually has some value greater than 2.42 cps. The estimate byLitvak et al (2012a) for background count rates at the Moon included an assumed 7% decrease in spacecraft-sourced neutron background due to fuel consumption that is probably incorrect according to more recent work byLitvak et al (2016). Compensating for this erroneous correction brings the background ofLitvak et al (2012a) up to 2.60 cps, while the more recent work byLitvak et al (2016) estimates 2.74±0.09 cps, similar to the value from Eke…”

mentioning

confidence: 88%

“…et al (2012). For internal consistency, we stand by the value we have derived from the operational data, since no single one of the determinations by Litvak et al (2016), Eke et al (2012) or ourselves is clearly preferable to another. The distinction is less than one uncertainty unit using our estimate for uncertainty, less than 2 using the estimate from Litvak et al (2016).…”

Section: Analysis Of Lend Csetn Detectormentioning

confidence: 99%

“…Data acquired at the Moon during the first (roughly) two and a half years of the LRO mission demonstrate the actual performance of the LEND instrument in action at the Moon, responding to the combined lunar neutron flux and background. This work tests background estimates in three of LEND's detector systems that were determined from cruise-phase measurements en route to the Moon (Litvak et al 2012a) and uses a method independent from a recent determination of background detection rates by Litvak et al (2016). The present method also explores similarities and differences between measurements of neutron flux by LEND and by the earlier Lunar Prospector (LP) neutron detectors (Feldman et al 1999).…”

Section: Introductionmentioning

confidence: 99%

“…This effort differs from Litvak et al (2012b), which compares the first 1.3 years of LEND data to LP mapped neutron flux measurements, by using substantially more LEND data and by quantitatively investigating the relative contribution of neutrons from different populations in each LEND detector. Litvak et al (2016) also investigated LEND detector background, using orbital phase profiles rather than complete two-dimensional maps and using only data from LEND detectors rather than LP. Eke et al (2012) modeled the performance of one LEND detector system, the CSETN collimated detector, comparing the data stream of individual one-second integrations by LEND against latitude-longitude maps compiled from LP.…”

Section: Introductionmentioning

confidence: 99%

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Background and lunar neutron populations detected by LEND and average concentration of near-surface hydrogen near the Moon's poles

Livengood

Митрофанов

Chin

et al. 2018

Planetary and Space Science

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Neutron flux measurements by the Lunar Exploration Neutron Detector (LEND) on the Lunar Reconnaissance Orbiter (LRO) enable quantifying hydrogen-bearing volatiles in the lunar surface from orbit. Accurately determining hydrogen abundance requires discriminating between the instrument background detection rate and the population of lunar-sourced neutrons that are sensitive to surficial hydrogen. We have investigated the detection rate for lunar and non-lunar (spacecraft-sourced) neutrons in LEND by modeling maps of measured count rate in three LEND detector systems using linear combinations of maps compiled from LEND detectors and from the Lunar Prospector Neutron Spectrometer. We find that 30% of the global-average 24.926±0.020 neutron counts per second (cps) detected by the LEND STN3 thermal-energy neutron sensor are lunar-sourced neutrons in the thermal energy range (E<0.4 eV), 65% are lunar-sourced neutrons in the epithermal and fast energy range (E>0.4 eV), and 5% are from spacecraft-sourced background signal. In the SETN epithermal neutron detector, 90% of the 10.622±0.002 neutron detections per second are consistent with a lunar source of epithermal and fast neutrons combined (E>0.4 eV), with 3% due to lunar-sourced thermal neutron leakage into the detector (E<0.4 eV), and background signal accounting for 7% of total detections. Background signal due to spacecraft-derived neutrons is substantial in the CSETN collimated detector system, accounting for 57% of the global average detection rate of 5.082±0.001 cps, greater than the 48% estimated from cruise-phase data. Lunar-sourced epithermal and fast neutrons account for 43% of detected neutrons, including neutrons in collimation as well as neutrons that penetrate the collimator wall to reach the detector. We estimate a lower limit of 17% of lunar-sourced neutrons detected by CSETN are epithermal neutrons in collimation (0.37 cps), with an upper limit estimate of 54±11% of lunar-sourced neutrons received in collimation, or 1.2±0.2 cps global average. The pole-to-equator contrast ratio in epithermal and high-energy epithermal neutron flux indicates that the average concentration of hydrogen in the polar regolith above 80° north or south latitude is ~105 ppmw (parts per million by weight), or 0.095±0.01 wt% water-equivalent hydrogen. Above 88° north or south, the concentration increases to ~140 ppmw, or 0.13±0.02 wt% water-equivalent hydrogen. The similar pattern of neutron flux suppression at both poles suggests that hydrogen concentration generally increases nearer the pole and is not closely associated with a specific feature such as Shackleton Crater at the lunar south pole that has no northern counterpart. Epithermal neutron flux decreases with increasing latitude outside the polar regions, consistent with surface hydration that increases with latitude if that hydration extends to ~13-40 cm into the surface.

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Section: Estimates For Collimated Component Of Csetn Detected Signalmentioning

confidence: 91%

mentioning

confidence: 88%