Development of Neutron Intensity Monitors

The crystal structure of Li(ND4)SO4 was analysed by neutron diffraction method. The crystal is a partially deuterated Li(NH4)SO4 and one of the ferroelectric materials with hydrogen atoms. The crystal is orthorhombic at room temperature with lattice parameters of a=5.2773(5) Å, b=9.124(2) Å, c=8.772(1) Å and Z=4. Neutron intensity data were collected on the Four-Circle Diffractometer (FCD) at HANARO in Korea Atomic Energy Research Institute. The structure was refined by full-matrix least-square to final R value of 0.049 for 745 observed reflections by neutron diffraction. All atomic positions of four hydrogen atoms at NH4 and the occupation factors of D and H were refined. From these results we obtained the average chemical structure of this sample, LiND3.05H0.95SO4. Five years later, neutron intensity data were collected and analysed once more with same crystal. The crystal is orthorhombic but with different lattice parameters, or hexagonal. We will report and discuss these results in this presentation.

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A reevaluation of the atmospheric pressure dependence of secondary cosmic-ray neutrons in the context of Cosmic-Ray Neutron Sensing

10.5194/egusphere-egu21-10602 ◽

2021 ◽

Author(s):

Jannis Weimar ◽

Paul Schattan ◽

Martin Schrön ◽

Markus Köhli ◽

Rebecca Gugerli ◽

...

Keyword(s):

Cosmic Rays ◽

Hydrogen Content ◽

Atmospheric Pressure ◽

Cosmic Ray ◽

Galactic Cosmic Rays ◽

Atmospheric Air ◽

Neutron Intensity ◽

The Earth ◽

Wide Range ◽

Primary Cosmic Rays

Secondary cosmic-ray neutrons may be effectively used as a proxy for environmental hydrogen content at the hectare scale. These neutrons are generated mostly in the upper layers of the atmosphere within particle showers induced by galactic cosmic rays and other secondary particles. Below 15 km altitude their intensity declines as primary cosmic rays become less abundant and the generated neutrons are attenuated by the atmospheric air. At the earth surface, the intensity of secondary cosmic-ray neutrons heavily depends on their attenuation within the atmosphere, i.e. the amount of air the neutrons and their precursors pass through. Local atmospheric pressure measurements present an effective means to account for the varying neutron attenuation potential of the atmospheric air column above the neutron sensor. Pressure variations possess the second largest impact on the above-ground epithermal neutron intensity. Thus, using epithermal neutrons to infer environmental hydrogen content requires precise knowledge on how to correct for atmospheric pressure changes.We conducted several short-term field experiments in saturated environments and at different altitudes, i.e. different pressure states to observe the neutron intensity pressure relation over a wide range of pressure values. Moreover, we used long-term measurements above glaciers in order to monitor the local dependence of neutron intensities and pressure in a pressure range typically found in Cosmic-Ray Neutron Sensing. The results are presented along with a broad Monte Carlo simulation campaign using MCNP 6. In these simulations, primary cosmic rays are released above the earth atmosphere at different cut-off rigidities capturing the whole evolution of cosmic-ray neutrons from generation to attenuation and annihilation. The simulated and experimentally derived pressure relation of cosmic-ray neutrons is compared to those of similar studies and assessed in the light of an appropriate atmospheric pressure correction for Cosmic-Ray Neutron Sensing.

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Geomagnetic activity and diurnal variation of cosmic ray neutron intensity

Proceedings of the Indian Academy of Sciences - Section A ◽

10.1007/bf03047467 ◽

1965 ◽

Vol 62 (3) ◽

pp. 139-144

Author(s):

D. S. R. Murty ◽

Y. Nagabhushanam ◽

K. Ramanuja Rao

Keyword(s):

Diurnal Variation ◽

Geomagnetic Activity ◽

Cosmic Ray ◽

Neutron Intensity

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Investigating temporal field sampling strategies for site-specific calibration of three soil moisture–neutron intensity parameterisation methods

Hydrology and Earth System Sciences ◽

10.5194/hess-19-3203-2015 ◽

2015 ◽

Vol 19 (7) ◽

pp. 3203-3216 ◽

Cited By ~ 17

Author(s):

J. Iwema ◽

R. Rosolem ◽

R. Baatz ◽

T. Wagener ◽

H. R. Bogena

Keyword(s):

Remote Sensing ◽

Soil Moisture ◽

Satellite Remote Sensing ◽

Cosmic Ray ◽

Sampling Strategies ◽

Site Specific ◽

Neutron Intensity ◽

Soil Wetness ◽

Semi Arid

Abstract. The Cosmic-Ray Neutron Sensor (CRNS) can provide soil moisture information at scales relevant to hydrometeorological modelling applications. Site-specific calibration is needed to translate CRNS neutron intensities into sensor footprint average soil moisture contents. We investigated temporal sampling strategies for calibration of three CRNS parameterisations (modified N0, HMF, and COSMIC) by assessing the effects of the number of sampling days and soil wetness conditions on the performance of the calibration results while investigating actual neutron intensity measurements, for three sites with distinct climate and land use: a semi-arid site, a temperate grassland, and a temperate forest. When calibrated with 1 year of data, both COSMIC and the modified N0 method performed better than HMF. The performance of COSMIC was remarkably good at the semi-arid site in the USA, while the N0mod performed best at the two temperate sites in Germany. The successful performance of COSMIC at all three sites can be attributed to the benefits of explicitly resolving individual soil layers (which is not accounted for in the other two parameterisations). To better calibrate these parameterisations, we recommend in situ soil sampled to be collected on more than a single day. However, little improvement is observed for sampling on more than 6 days. At the semi-arid site, the N0mod method was calibrated better under site-specific average wetness conditions, whereas HMF and COSMIC were calibrated better under drier conditions. Average soil wetness condition gave better calibration results at the two humid sites. The calibration results for the HMF method were better when calibrated with combinations of days with similar soil wetness conditions, opposed to N0mod and COSMIC, which profited from using days with distinct wetness conditions. Errors in actual neutron intensities were translated to average errors specifically to each site. At the semi-arid site, these errors were below the typical measurement uncertainties from in situ point-scale sensors and satellite remote sensing products. Nevertheless, at the two humid sites, reduction in uncertainty with increasing sampling days only reached typical errors associated with satellite remote sensing products. The outcomes of this study can be used by researchers as a CRNS calibration strategy guideline.

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Error estimation for soil moisture measurements with cosmic-ray neutron sensing and implications for rover surveys

10.5194/egusphere-egu2020-8488 ◽

2020 ◽

Author(s):

Jannis Jakobi ◽

Johan Alexander Huisman ◽

Martin Schrön ◽

Justus Fiedler ◽

Cosimo Brogi ◽

...

Keyword(s):

Soil Moisture ◽

Measurement Uncertainty ◽

Survey Design ◽

Time Windows ◽

Inverse Correlation ◽

Cosmic Ray ◽

Environmental Water ◽

Neutron Measurement ◽

Neutron Intensity ◽

Computationally Intensive

The cosmic ray neutron (CRN) probe is a non-invasive device to measure soil moisture at the field scale. This instrument relies on the inverse correlation between aboveground epithermal neutron intensity (1eV &#8211; 100 keV) and environmental water content. The measurement uncertainty of the neutron detector follows Poisson statistics and thus decreases with decreasing neutron intensity, which corresponds to increasing soil moisture. In order to reduce measurement uncertainty (e.g. < 0.03 m3/m3), the neutron count rate is often aggregated over large time windows (e.g. 12h or 24h). To enable shorter aggregation intervals, the measurement uncertainty can be reduced either by using more efficient detectors or by using arrays of detectors, as in the case of CRN rover applications. Depending on soil moisture and driving speed, aggregation of neutron counts may also be necessary to obtain sufficiently accurate soil moisture estimates in rover applications. To date, signal aggregation has not been investigated sufficiently with respect to the optimisation of temporal (stationary probes) and spatial (roving applications) resolution. In this work, we present an easy-to-use method for uncertainty quantification of soil moisture observations from CRN sensors based on Gaussian error propagation theory. We have estimated the uncertainty using a third order Taylor expansion and compared the result with a more computationally intensive Monte Carlo approach and found excellent agreement. Furthermore, we used our method to quantify the dependence of soil moisture uncertainty on CRN rover survey design and on selected aggregation time. We anticipate that the new approach helps to quantify cosmic ray neutron measurement uncertainty. In particular, it is anticipated that the strategic planning and evaluation of CRN rover surveys based on uncertainty requirements can be improved considerably.

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