We examine a sample of 2301 gamma-ray bursts, detected by Konus-Wind in the triggered mode between 1994 and 2017 and localized by the interplanetary network (IPN), for evidence of gravitational ...lensing. We utilize all the available gamma-ray burst (GRB) data: time histories, localizations, and energy spectra. We employ common IPN techniques to find and quantify similarities in the light curves of 2,646,150 burst pairs, and for the pairs with significant similarities, we examine their IPN localizations to determine whether they are consistent with a common origin. For pairs that are consistent, we derive and compare energy spectra, and compute a figure of merit that allows us to compare and rank burst pairs. We conduct both a blind search, between all possible burst pairs, and a targeted search, between pairs in which one burst has both a spectroscopic redshift and an identification of an intervening system, as measured by one or more lower spectroscopic redshifts. We identify six pairs in the blind search that could be taken as evidence for lensing, but none are compelling enough to claim a detection with good confidence. No candidates were detected in the targeted search. For our GRB sample, we set an upper limit to the optical depth to lensing of 0.0033, which is comparable to that of optical sources. We conclude that proposed scenarios in which a large fraction of the GRB population is lensed are extremely unlikely.
A rapid, paper microfluidic- and smartphone-based protocol was developed for the extraction and direct fluorescent identification of the nucleic acids of SalmonellaTyphimurium from field and clinical ...samples. Initially, liquid samples (10% diluted) from fresh poultry packaging were loaded on the paper chips and were lysed with Tris-EDTA (TE) buffer. Nucleic acids from the lysed samples were eluted through the paper channel with TE buffer and the paper channel was excised into three pieces for the further polymerase chain reaction (PCR) assay. The extraction efficiency was determined by measuring fluorescence reflectance with either a benchtop optical detection system (consisting of an LED light source, a pair of optical fibers, and a miniature spectrophotometer, all built on micro-positioning stages) or a smartphone-based fluorescent microscope (in-house fabricated). The limit of detection of SalmonellaTyphimurium in 10% poultry packaging liquid with cellulose paper was 10 super(3) CFU mL super(-1), while that extracted with nitrocellulose paper was 10 super(4) CFU mL super(-1) (as determined by both PCR and fluorescence reflectance). Cellulose channels proved more appropriate for measuring low and very high concentrations of pathogen DNA, while nitrocellulose proved better for analysing the mid-range concentrations. We observed that DNA migrated through nitrocellulose at a faster rate and further than through cellulose due to charge-charge repulsion between nitrocellulose and DNA (both negatively charged), thus contributing to consistent and efficient extraction. We tested the efficiency of Salmonellaextraction from 10% poultry packaging liquid, 10% whole blood, and 10% fecal samples, and obtained comparable extraction efficiency, as confirmed by smartphone-based direct fluorescent detection. This protocol is suitable for the direct detection of total bacteria count in a dirty sample (when specificity is not necessary) as well as determining extraction efficiency. This protocol is compatible with PCR, to provide specific information about the type of pathogen present in sample.
•LEND/LRO instrument neutron counting data sets have been analyzed to create high resolution maps of epithermal neutron flux at polar regions of the Moon.•The conversion from epithermal neutron flux ...to the H/H2O abundances is presented based on the simple subsurface models.•The polar lunar maps (poleward 70S/70N) of homogeneous hydrogen distribution are derived and discussed.
We present a method of conversion of the lunar neutron counting rate measured by the Lunar Reconnaissance Orbiter (LRO) Lunar Exploration Neutron Detector (LEND) instrument collimated neutron detectors, to water equivalent hydrogen (WEH) in the top ∼1m layer of lunar regolith. Polar maps of the Moon's inferred hydrogen abundance are presented and discussed.
The presence of hydrated phases in the soil and near‐surface bedrock of Gale Crater is thought to be direct evidence for water‐rock interaction in the crater in the ancient past. Layered sediments ...over the Gale Crater floor are thought to have formed in past epochs due to sediment transport, accumulation, and cementation through interaction with fluids, and the observed strata of water‐bearing minerals record the history of these episodes. The first data analysis of the Dynamic Albedo of Neutrons (DAN) investigation on board the Curiosity rover is presented for 154 individual points of active mode measurements along 1900 m of the traverse over the first 361 Martian solar days in Gale crater. It is found that a model of constant water content within subsurface should be rejected for practically all tested points, whereas a two‐layer model with different water contents in each layer is supported by the data. A so‐called direct two‐layer model (water content increasing with depth) yields acceptable fits for odometry ranges between 0 and 455 m and beyond 638 m. The mean water (H2O) abundances of the top and bottom layers vary from 1.5 to 1.7 wt % and from 2.2 to 3.3 wt %, respectively, while at some tested spots the water content is estimated to be as high as ~5 wt %. The data for odometry range 455–638 m support an inverse two‐layer model (water content decreasing with depth), with an estimated mean water abundance of 2.1 ± 0.1 wt % and 1.4 ± 0.04 wt % in the top and bottom layers, respectively.
Key Points
First analysis of active neutron data from DAN instrument on board MSL roverEstimations of water distribution along MSL rover traverse by DAN instrumentEstimations of chlorine abundance along MSL rover traverse by DAN instrument
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.
The description of Dynamic Albedo of Neutrons (DAN) experiment is presented, as a part of the NASA’s Mars Science Laboratory mission onboard the mars rover Curiosity. The instrument DAN includes ...Pulsing Neutron Generator (PNG) producing pulses of 14.1 MeV neutrons for irradiation of subsurface material below the rover, and Detectors and Electronics (DE) unit, which operates the instrument itself and measures the die-away time profiles of epithermal and thermal neutrons following each neutron pulse. It is shown that the DAN investigation will measure a content of hydrogen along the path of the MSL rover, and it will also provide information about a depth distribution of hydrogen at 10–20 regions selected for the detailed studies and sampling analysis.
Data gathered with the Dynamic Albedo of Neutron (DAN) instrument onboard rover Curiosity were analyzed for variations in subsurface neutron flux and tested for possible correlation with local ...geological context. A special DAN observation campaign was executed, in which 18 adjacent DAN active measurements were acquired every 0.75–1.0 m to search for the variations of subsurface hydrogen content along a 15 m traverse across geologic contacts between the Sheepbed and Gillespie Lake members of the Yellowknife Bay formation. It was found that several subunits in Sheepbed and Gillespie Lake could be characterized with different depth distributions of water‐equivalent hydrogen (WEH) and different chlorine‐equivalent abundance responsible for the distribution of neutron absorption elements. The variations of the average WEH at the top 60 cm of the subsurface are estimated at up to 2–3%. Chlorine‐equivalent neutron absorption abundances ranged within 0.8–1.5%. The largest difference in WEH and chlorine‐equivalent neutron absorption distribution is found between Sheepbed and Gillespie Lake.
Key Points
DAN special campaign in Yellowknife Bay
DAN local measurements of water and chlorine abundance
Correlation of DAN measurements and geological context
Results are presented for the LEND instrument onboard LRO for the detection of local spots of suppression and excess of epithermal neutron emission at the lunar poles. Twelve local Neutron ...Suppression Regions (NSRs) and Neutron Excess Regions (NERs) are detected. It is shown using the data from the LOLA and Diviner instruments that six NSRs have the empirical property “less local irradiation and lower temperature – fewer local neutrons.” These NSRs may be identified with spots of water‐ice rich permafrost on the Moon. It is shown that detected NSRs are include in both permanently shadowed and illuminated areas, and they are not coincident with Permanently Shadowed Regions (PSRs) at the bottom of polar craters, as has been commonly expected before LEND presented neutron data with high spatial resolution.
Key Points
Neutron suppression regions and neutron excess regions discovered
Empirical law
Water‐ice rich permafrost spots may be identified with these regions on the Moon
Understanding the long‐term radiation environment at the surface of Mars allows us to estimate the exposure for future robotic and crewed missions. Typically, the radiation environment includes ...charged particles (i.e., protons and heavier ions) and neutral particles (i.e., gamma rays and secondary neutrons). Previous studies used in‐situ measurements, models, or both to determine the characteristics of the radiation at Mars. For example, the Mars Science Laboratory instrument, the Radiation Assessment Detector (RAD), has provided invaluable in‐situ data since landing in 2012. However, the RAD instrument is only sensitive to neutrons with energies > ∼6 MeV and therefore misses what is expected to be a substantial flux of lower‐energy neutrons. To address this gap, we have developed an approach to derive the surface neutron spectrum using the MSL RAD data augmented by orbital data from the High Energy Neutron Detector (HEND) onboard Mars Odyssey (neutron energy < ∼10 MeV). Using a power law fit, we determine neutron flux spectra that reproduce the measurements recorded by both RAD and HEND. Our approach involves a series of Monte Carlo simulations to develop a set of atmospheric transmission functions that enables us to convert the on‐orbit HEND data to their corresponding surface neutron flux spectra. The combined RAD—HEND data present a unique opportunity to obtain a complete picture of the surface neutron environment.
Plain Language Summary
Unlike Earth, Mars does not possess an intrinsic magnetic field or a thick atmosphere to shield it from hostile space radiation. In this paper, we provide a methodology to predict how many neutrons will be present on the surface of Mars. We found that the number of neutrons on the surface varies with the Martian seasons and the Solar activity. Knowing the neutron environment allows us to determine the risks to future Mars crewed and robotic missions from neutron exposure.
Key Points
Martian surface neutron flux can be estimated from Radiation Assessment Detector and High Energy Neutron Detector data
Atmospheric variations are crucial in determining the neutron flux spectral shape and changes at the Martian surface. The neutrons' response to atmospheric density depends on the neutron's energy
Ambient dose equivalent rates from neutrons at the surface of Mars are on the order of 120–180 μSv/d
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