Hydrogen has been inferred to occur in enhanced concentrations within permanently shadowed regions and, hence, the coldest areas of the lunar poles. The Lunar Crater Observation and Sensing Satellite ...(LCROSS) mission was designed to detect hydrogen-bearing volatiles directly. Neutron flux measurements of the Moon's south polar region from the Lunar Exploration Neutron Detector (LEND) on the Lunar Reconnaissance Orbiter (LRO) spacecraft were used to select the optimal impact site for LCROSS. LEND data show several regions where the epithermal neutron flux from the surface is suppressed, which is indicative of enhanced hydrogen content. These regions are not spatially coincident with permanently shadowed regions of the Moon. The LCROSS impact site inside the Cabeus crater demonstrates the highest hydrogen concentration in the lunar south polar region, corresponding to an estimated content of 0.5 to 4.0% water ice by weight, depending on the thickness of any overlying dry regolith layer. The distribution of hydrogen across the region is consistent with buried water ice from cometary impacts, hydrogen implantation from the solar wind, and/or other as yet unknown sources.
•HEND/Odyssey data were used to study the spacecraft neutron background.•Neutron dose equivalent rate during mars odyssey cruise to mars was estimated.•Cruise observations have been extrapolated to ...the different periods of solar cycle.
In April 2001, Mars Odyssey spacecraft with the High Energy Neutron Detector (HEND) onboard was launched to Mars. HEND/Odyssey was switched on measurement mode for most of transit to Mars to monitor variations of spacecraft background and solar activity. Although HEND/Odyssey was originally designed to measure Martian neutron albedo and to search for Martian subsurface water/water ice, its measurements during cruise phase to Mars are applicable to evaluate spacecraft ambient radiation background. The biological impact of the neutron component of this radiation background should be understood, as it must be taken into account in planning future human missions to Mars. We have modeled the spacecraft neutron spectral density and compared it with HEND measurements to estimate neutron dose equivalent rates during Odyssey cruise phase, which occurred during the maximum period of solar cycle 23. We find that the Odyssey ambient neutron environment during May – September 2001 yields 10.6 ± 2.0 μSv per day in the energy range from 0 to 15 MeV, and about 29 μSv per day when extrapolated to the 0–1000 MeV energy range during solar quiet time (intervals without Solar Particle Events, SPEs). We have also extrapolated HEND/Odyssey measurements to different periods of solar cycle and find that during solar minimum (maximum of GCR flux), the neutron dose equivalent rate during cruise to Mars could be as high as 52 μSv per day with the same shielding. These values are in good agreement with results reported for a similar measurement made with an instrument aboard the Mars Science Laboratory during its cruise to Mars in 2011–2012.
Light-emitting devices of modern photonics are based on the semiconductor structures containing layers with various physical parameters. To preserve initial parameters during focused ion beam (FIB) ...lithography, it is necessary to take into account the processes of radiation defect formation. Radiation-induced defects in target play role of nonradiative recombination centers leading to photoluminescence (PL) quenching. In our work, the FIB impact on the photoluminescence were examined using PL spectroscopy of milled Al
0.18
Ga
0.82
As/GaAs double heterostructure. In order to exclude photoexcited carriers losses in emitter layer, an experiment with subbarrier photoexcitation was organized. Finally, we compare our experimental findings with theoretical data proposed by stopping and range of ions in matter (SRIM) calculation.
Variants of the
gene have been associated with a number of primary cardiac conditions, including left ventricular noncompaction cardiomyopathy (LVNC). Most cases of
-related diseases are associated ...with such variant types as missense substitutions and in-frame indels. Thus, truncating variants in
(
tv) and associated mechanism of haploinsufficiency are usually considered not pathogenic in these disorders. However, recent large-scale studies demonstrated evidence of the significance of
tv for LVNC and gave rise to an assumption that haploinsufficiency may be the causal mechanism for LVNC. In this article, we present a family with isolated LVNC and a heterozygous splice variant of the
gene, analyze possible consequences of this variant and conclude that not all variants that are predicted truncating really act through haploinsufficiency. This study can highlight the importance of a precise assessment of
splicing variants and their participation in the development of LVNC.
The subsurface chlorine depth distribution at Gale crater has been studied using measurements from the Alpha Particle X‐ray Spectrometer (APXS) and Dynamic Albedo of Neutrons (DAN) instruments ...onboard NASA's Curiosity Mars rover. These measurements have been acquired at or near ∼30 drill holes made by Curiosity along its 30 km drive. APXS measured a ∼15 micron surface layer of bedrock and shallow depth of ∼5 cm of drill tailings. DAN is sensitive to the bulk (∼50 cm depth) chlorine abundance and that of other neutron absorbing elements. Joint analysis of APXS and DAN data shows that the chlorine distribution at Gale crater consists of two components: surficial chlorine with concentrations >1 wt.%, possibly controlled by aeolian deposition of Cl‐rich dust and surface alteration, and subsurface chlorine with concentrations <1 wt.%, likely a result of groundwater activity in the past.
Plain Language Summary
The Curiosity rover has been exploring layered sediments enriched with hydrated mineral phases which were formed in past epochs due to the interaction with fluids in Gale crater, Mars. Curiosity carries 10 science instruments to conduct remote and contact measurements and has already made ∼30 drill holes along its 30 km drive, testing samples of Martian soils and rocks. One of Curiosity's science tasks is to measure the elemental composition of the Martian surface and chlorine is considered here as an important chemical component that could tell us what has occurred on Mars in the past. Several instruments aboard Curiosity are capable of estimating the concentration of chlorine and we selected two of them (Dynamic Albedo of Neutrons and Alpha Particle X‐ray Spectrometer) to evaluate how chlorine is distributed with depth using data acquired at drill locations. We found that the chlorine distribution at Gale crater consists of two components: surficial chlorine with concentration >1%, possibly controlled by wind‐driven deposition of Cl‐rich dust and surface alteration, and subsurface chlorine with concentration <1%, likely a result of groundwater activity in the past.
Key Points
A correlation between Alpha Particle X‐ray Spectrometer drill tailings and Dynamic Albedo of Neutrons measurements of subsurface chlorine was found
Chlorine depth distribution consists of surficial chlorine (>1 wt.%) and bulk chlorine (<1 wt.%) components
The surficial Cl is controlled by Aeolian deposition and surface alteration, and bulk Cl is a result of groundwater activity
This article presents a description of the experiment on the Joint Institute for Nuclear Research (JINR) Phasotron proton beam for a laboratory model of a space instrument for the gamma spectrometry ...of celestial bodies based on the method of tagged charged particles of galactic cosmic rays. One feature of the experiment is the use of a p-type high-purity germanium semiconductor detector as part of the model.
Diagenetic silica enrichment in fracture‐associated halos that crosscut lacustrine and unconformably overlying aeolian sedimentary bedrock is observed on the lower north slope of Aeolis Mons in Gale ...crater, Mars. The diagenetic silica enrichment is colocated with detrital silica enrichment observed in the lacustrine bedrock yet extends into a considerably younger, unconformably draping aeolian sandstone, implying that diagenetic silica enrichment postdates the detrital silica enrichment. A causal connection between the detrital and diagenetic silica enrichment implies that water was present in the subsurface of Gale crater long after deposition of the lacustrine sediments and that it mobilized detrital amorphous silica and precipitated it along fractures in the overlying bedrock. Although absolute timing is uncertain, the observed diagenesis likely represents some of the most recent groundwater activity in Gale crater and suggests that the timescale of potential habitability extended considerably beyond the time that the lacustrine sediments of Aeolis Mons were deposited.
Key Points
Silica‐rich diagenetic halos penetrate lacustrine and unconformably draping aeolian bedrock in Gale crater, Mars
Colocation of diagenetic and detrital silica suggests aqueous remobilization of detrital silica
Presence of diagenetic halos in the unconformably draping aeolian bedrock suggests late‐stage groundwater activity in Gale crater
The ion-beam etching of AlGaAs/GaAs heterostructures gives rise to radiation defects and, as a result, leads to photoluminescence quenching. Annealing at 620°C in an atmosphere of As almost ...completely restores the quantum efficiency of photoluminescence in the case of radiation-induced defects lying at a distance of up to 150 nm from the heterointerface.
This paper is Part II of a double‐paper series that presents the abundance of water and chlorine along with other neutron‐absorbing elements in the shallow subsurface of Gale crater based on ...measurements by the Dynamic Albedo of Neutron (DAN) instrument onboard NASA's Curiosity rover. Initial results were represented as pixels on map data products from both DAN active and passive measurements made along the 27‐km traverse of the rover, corresponding to the mission period from landing on the martian surface in August 2012 through December 2021. In Part II, the contents of water and chlorine along with other neutron absorbers are studied separately for distinct geological regions along the traverse. Mean values and sample variances of these values are presented for each region. Water‐equivalent hydrogen (WEH) measurements show variability within the Jura member of the Murray formation and increase within the Carolyn Shoemaker formation. A large fraction of stratigraphic units (e.g., Bradbury, Sheepbed, Pahrump Hills and others) have mean WEH values between 2 and 3 wt.%, while units in the second part of the traverse (Jura, Knockfarrill Hill, Glasgow, Pontours) have mean values of WEH above 3 wt.%. The mean absorption‐equivalent chlorine value has no large variations for all tested geologic units; it is equal to around 1% for all of them.
Plain Language Summary
The Dynamic Albedo of Neutrons instrument installed on NASA's Curiosity rover provides measurements of hydrogen (as an indicator of water) and other neutron‐absorbing elements (primarily chlorine) in the shallow subsurface of Gale crater on Mars. The initial data set for this study consists of pixel data products obtained from the instrument measurements taken over the rover's traverse of 27 km from August 2012 to December 2021. The data has been analyzed for distinct geological members defined by the Mars Science Laboratory team, allowing independent examination of various geological locations. The Jura, Knockfarrill Hill, and Pontours members exhibit mean water estimation values above 3 wt.%, while the majority of stratigraphic units, such as Bradbury and Sheepbed, have mean water values ranging between 2 and 3 wt.%. Measurements of water reveal differentiation in the Jura member of the Murray formation. The highest water values, reaching up to 4 wt.%, are observed in locations of the Carolyn Shoemaker formation. For other neutron‐absorbing elements, the mean value is roughly 1 wt.% for all geological units tested and does not vary significantly.
Key Points
The Dynamic Albedo of Neutron (DAN) data was analyzed for the period of time from August 2012 to December 2021, for almost 27 km of the MSL traverse
15 distinct MSL geological regions were examined using the DAN data
The DAN data recognized the presence of two subregions within the Jura member of the Murray formation based on Water‐equivalent hydrogen concentration
We use measurements from the Lunar Exploration Neutron Detector (LEND) collimated sensors during more than one year of the mapping phase of NASA's Lunar Reconnaissance Orbiter (LRO) mission to make ...estimates of the epithermal neutron flux within known large Permanently Shadowed Regions (PSRs). These are compared with the local neutron background measured outside PSRs in sunlit regions. Individual and collective analyses of PSR properties have been performed. Only three large PSRs, Shoemaker and Cabeus in the south and Rozhdestvensky U in the north, have been found to manifest significant neutron suppression. All other PSRs have much smaller suppression, only a few percent, if at all. Some even display an excess of neutron emission in comparison to the sunlit vicinity around them. Testing PSRs collectively, we have not found any average suppression for them. Only the group of 18 large PSRs, with area >200 km2, show a marginal effect of small average suppression, ∼2%, with low statistical confidence. A ∼2% suppression corresponds to ∼125 ppm of hydrogen taking into account the global neutron suppression near the lunar poles and assuming a homogeneous H distribution in depth in the regolith. This means that all PSRs, except those in Shoemaker, Cabeus and Rozhdestvensky U craters, do not contain any significant amount of hydrogen in comparison with sunlit areas around them at the same latitude.
Key Points
Latest LEND measurements of neutron fluxes from the Moon are presented
Comparison of neutron flux within large PSRs and in sunlit regions is discussed
Only three large PSRs manifest significant neutron suppression
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