Albedo Neutron Research Articles

Influence of environmental parameters on secondary cosmic ray neutrons at high-altitude research stations at Jungfraujoch, Switzerland, and Zugspitze, Germany

Neutrons of secondary cosmic radiation (CR) are produced when primary cosmic radiation interacts with the nuclei in the Earth's atmosphere. The secondary neutron spectra in the atmosphere do not include many thermal and epithermal neutrons at energies below several eV. In contrast, close to the Earth's surface many more of those neutrons are present, due to albedo neutrons backscattered from the ground. The number of albedo neutrons is mainly determined by the environment, i.e. the material in the environment (characteristics of the underground and the environment (building, topology of landscape)). If the environment (buildings, underground) is constant with time then the variation of the albedo neutron fluence is dependent on the soil moisture and snow cover.To investigate snow cover effect in detail, in June 2016 and September 2018 two measurement campaigns were carried out at the High Altitude Research Station Jungfraujoch, Switzerland. During these campaigns the energy distributions of secondary CR neutrons were measured by means of a mobile extended range Bonner sphere spectrometer (ERBSS) at two different positions with different environmental conditions: under the cupola of the astronomical observatory in the Sphinx building at an altitude of 3585 m a.s.l., and below the shelter roof of the research station at 3466 m a.s.l.In addition, since 2004 the energy spectra of neutrons from secondary CR have been continuously measured at the Environmental Research Station (UFS Schneefernerhaus; 2650 m a.s.l.) close to the summit of the Zugspitze mountain, Germany. To measure the neutron spectra in the energy range from a few meV up to several GeV, a stationary ERBSS has been used.The chosen measurement positions allow quantification of environmental conditions which affect the neutron spectral distribution in the whole neutron energy range up to several GeV. With this spectral information, it is also possible to derive detailed information about the neutron ambient dose equivalent (H*(10)) at these altitudes and geomagnetic latitudes.The ERBSS measurements at Jungfraujoch presented here show that snowpack in the surrounding area does not affect the fluence rate of secondary neutrons significantly. However, the influence of topography of the chosen measurement locations on secondary CR neutrons was observed.

Earth's Van Allen Radiation Belts: From Discovery to the Van Allen Probes Era

AbstractDiscovery of the Earth's Van Allen radiation belts by instruments flown on Explorer 1 in 1958 was the first major discovery of the Space Age. The observation of distinct inner and outer zones of trapped megaelectron volt (MeV) particles, primarily protons at low altitude and electrons at high altitude, led to early models for source and loss mechanisms including Cosmic Ray Albedo Neutron Decay for inner zone protons, radial diffusion for outer zone electrons and loss to the atmosphere due to pitch angle scattering. This scattering lowers the mirror altitude for particles in their bounce motion parallel to the Earth's magnetic field until they suffer collisional loss. A view of the belts as quasi‐static inner and outer zones of energetic particles with different sources was modified by observations made during the Solar Cycle 22 maximum in solar activity over 1989–1991. The dynamic variability of outer zone electrons was measured by the Combined Radiation Release and Effects Satellite launched in July 1990. This variability is caused by distinct types of heliospheric structure that vary with the solar cycle. The launch of the twin Van Allen Probes in August 2012 has provided much longer and more comprehensive measurements during the declining phase of Solar Cycle 24. Roughly half of moderate geomagnetic storms, determined by intensity of the ring current carried mostly by protons at hundreds of kiloelectron volts, produce an increase in trapped relativistic electron flux in the outer zone. Mechanisms for accelerating electrons of hundreds of electron volts stored in the tail region of the magnetosphere to MeVenergies in the trapping region are described in this review: prompt and diffusive radial transport and local acceleration driven by magnetospheric waves. Such waves also produce pitch angle scattering loss, as does outward radial transport, enhanced when the magnetosphere is compressed. While quasilinear simulations have been used to successfully reproduce many essential features of the radiation belt particle dynamics, nonlinear wave‐particle interactions are found to be potentially important for causing more rapid particle acceleration or precipitation. The findings on the fundamental physics of the Van Allen radiation belts potentially provide insights into understanding energetic particle dynamics at other magnetized planets in the solar system, exoplanets throughout the universe, and in astrophysical and laboratory plasmas. Computational radiation belt models have improved dramatically, particularly in the Van Allen Probes era, and assimilative forecasting of the state of the radiation belts has become more feasible. Moreover, machine learning techniques have been developed to specify and predict the state of the Van Allen radiation belts. Given the potential Space Weather impact of radiation belt variability on technological systems, these new radiation belt models are expected to play a critical role in our technological society in the future as much as meteorological models do today.

Modeling the Quasi‐Trapped Electron Fluxes From Cosmic Ray Albedo Neutron Decay (CRAND)

AbstractRecently, cosmic ray albedo neutron decay (CRAND) has been identified as the main source of relativistic electrons measured at the inner edge of inner radiation belt. Here we introduce a drift‐source model that includes azimuthal drift and a CRAND electron source to simulate the quasi‐trapped electron distribution measured by the DEMETER satellite during 20–30 April 2010. The simulated longitude distribution of quasi‐trapped electron fluxes at the inner edge of inner radiation belt successfully reproduces the DEMETER observations, confirming CRAND as the main source for these electrons. Furthermore, a comparison of the energy spectrum and the L distribution of the quasi‐trapped relativistic electrons between simulations and observations further suggests that CRAND is likely the dominant source for 300–700‐keV quasi‐trapped electrons at L < 2 and L ≈ 3.

Cosmic Ray Albedo Neutron Decay (CRAND) as a Source of Inner Belt Electrons: Energy Spectrum Study

AbstractCosmic Ray Albedo Neutron Decay (CRAND) has been recently confirmed as a source of energetic electrons at the inner edge of the inner belt by the Colorado Student Space Weather Experiment (CSSWE) mission. Here we use observations from the Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) mission, to investigate the CRAND contribution to inner belt electrons quantitatively over a broad energy range (~100–800 keV). Spectral fitting analysis supports the conclusion that CRAND is the most important electron source at the inner edge of the inner belt. For the first time, we show that CRAND is the dominant source of >250‐keV quasitrapped electrons throughout the inner belt and slot region during quiet times. We suggest that additional sources for <250‐keV electrons exist, perhaps from inward transport. In contrast, dynamics of electrons in the inner belt and slot region is dominated by injections during active times.

Thermal neutron albedo and flux for different geometries neutron guide

Abstract This paper presents a study on thermal neutron reflection properties of neutron guide for cylinder, spindle, elliptic and parabolic geometries using 241Am-Be neutron source (5.2 Ci) and BF3 detector, whereas neutron guide is important instrument for transportation of neutrons. To this goal, the required inner and outer radii of neutron guide have been calculated to achieve the highest guided thermal neutron flux based on MCNPX Monte Carlo code. The maximum flux of cylinder geometry with a length 50 cm has been obtained at an inner radius 9 cm and an outer radius 21 cm. Also, the maximum value of thermal neutron albedo is 0.46 ± 0.001 at 12 cm thickness of parabolic guide.

Experimental Evidence of Ground Albedo Neutron Impact on Soft Error Rate for Nanoscale Devices

This paper demonstrates the experimental evidence of ground albedo neutron impact on the soft error rate (SER) for nanoscale devices. The SER of a 45-nm technology was measured according to an experimental protocol using a californium sealed source and several scenes based on material blocks. High-density polyethylene and concrete materials were considered to investigate the intrinsic role in albedo neutron productions and their effect on devices. The results show the impact on the spectrum concern mainly energies below 5 MeV. Devices are characterized by a sensitivity which varies according to the presence or not of the material block. Simulations using GEANT4 and MUSCA SEP3 tool were performed to extend analyses. A final part is devoted to investigate the impact of ground albedo neutrons on SER by considering realistic terrestrial neutron field.

Different methods of correcting the readings of the DVGN-01 albedo neutron dosimeter placed behind the IBR-2M protection

The paper presents the results of correction of readings of DVBN-01 albedo dosimeters behind IBR-2M protection, the Neutron Physics Laboratory of the Joint Institute for Nuclear Research (JINR), Dubna, byvarious methods. The neutron spectra were measured at two points behind the IBR-2M protection in the experimental halls, and measurements were carried out with the spherical albedo system at these points. The correction coefficients for DVGN-01 were calculated from the measured spectra based on the data of the spherical albedo system. A good agreement of the coefficients calculated by different methods is shown, which indicates the reliability of the obtained values for the correction coefficients. Based on the results of this work and the data obtained in the other investigations, the values of correction factors recommended for use in individual radiation control (IRC) in the FLNP were obtained.

Efficiency of Individual Targeting of a Three-Dimensional ITER Neutron Source in Monte Carlo Reactor Calculations

The extension of the known source angular biasing technique by individual targeting for each of the source neutrons on a given arbitrary rectangular target on the reactor first wall, indicating the area of interest in the problem, is considered in search of the possibilities to reduce the time of Monte Carlo calculation for bulky ITER models. The technique is tested in the source unit of the 3D code BLANK implementing the direct Monte Carlo method. A simple cylindrical model of ITER with a rectangular generatrix and a thickness of the side wall of the shielding material (80% stainless steel + 20% H2O) of 50 cm is calculated. The rectangular target matches the input hole of the equatorial port (2 × 2 m). The model calculations showed that the application of the technique did not result in a noticeable reduction of statistical uncertainty for the total neutron flux and its energy components in the first wall zone in the entire range of the targeting probability owing to the prevailing contributions of albedo neutrons. The error at the back surface of the model side wall was ~0.75 of the reference uncertainty (without targeting) in a targeting probability range of 0.2–0.4, which corresponds to a potential gain in computation time of up to ~2 times. These results yielded general empirical conclusions: the neutron flux estimated using this technique is unbiased, and a certain gain in the computer time, as compared to the calculation without targeting, is possible. The technique is expected to be more efficient in calculation of the neutron flux functionals in the depth of the shielding compositions, where the contribution of albedo neutrons from the first wall is insignificant, and the result is mainly determined by the intensity of the leading group of source neutrons. Since the considered technique is universal, it can be implemented as a useful option in any Monte Carlo code.

Saturn's Innermost Radiation Belt Throughout and Inward of the D‐Ring

AbstractCassini discovered Saturn's innermost radiation belt during the end of its mission. The belt is populated with relativistic protons, probably up to the trapping limit of ≈20 GeV. It extends from Saturn's dense atmosphere into and throughout the D‐ring. The A–C rings separate this belt entirely from the previously known radiation belts, suggesting that the innermost radiation belt is populated entirely via cosmic ray albedo neutron decay. We find that the proton pitch angle distributions are consistent with being shaped by losses to the D‐ring and the upper atmosphere rather than, for example, wave‐particle interactions. This supports that the main loss process of this new radiation belt is energy loss in neutral material, different from Saturn's other radiation belts. This property constrains the overall scale height of Saturn's exosphere to <700 km and the average D‐ring water molecule column density to being about 1 order of magnitude below the Enceladus gas torus.

Calculation of thermal neutron albedo for mono-material and bi-material reflectors

Thermal neutron albedo has been investigated for different thicknesses of mono-material and bi-material reflectors. An equation has been obtained for a bi-material reflector by considering the neutron diffusion equation. The bi-material reflector consists of binary combinations of water, graphite, lead, and polyethylene. An experimental measurement of thermal neutron albedo has also been conducted for mono-material and bi-material reflectors by using a 241Am–Be (5.2 Ci) neutron source and a BF3 detector. The maximum value of thermal neutron albedo was obtained for a polyethylene–water combination (0.95 ± 0.02).

Response functions for detectors in cosmic ray neutron sensing

Cosmic-Ray Neutron Sensing (CRNS) is a novel technique for determining environmental water content by measuring albedo neutrons in the epithermal to fast energy range with moderated neutron detectors. We have investigated the response function of stationary and mobile neutron detectors typically used for environmental research in order to improve the model accuracy for neutron transport studies. Monte Carlo simulations have been performed in order to analyze the detection probability in terms of energy-dependent response and angular sensitivity for different variants of CRNS detectors and converter gases. Our results reveal the sensor’s response to neutron energies from 0.1 eV to 106 eV and highest sensitivity to vertical fluxes. The detector efficiency shows good agreement with reference data from the structurally similar Bonner Spheres. The relative probability of neutrons contributing to the overall integrated signal is especially important in regions with non-uniform albedo fluxes, such as complex terrain or heterogeneous distribution of hydrogen pools.

Measuring spent fuel assembly multiplication in borated water with a passive neutron albedo reactivity instrument

The performance of a passive neutron albedo reactivity (PNAR) instrument to measure neutron multiplication of spent nuclear fuel in borated water is investigated as part of an integrated non-destructive assay safeguards system. To measure the PNAR Ratio, which is proportional to the neutron multiplication, the total neutron count rate is measured in high- and low-multiplying environments by the PNAR instrument. The integrated system also contains a load cell and a passive gamma emission tomograph, and as such meets all the recommendations of the IAEA’s recent ASTOR Experts Group report. A virtual spent fuel library for VVER-440 fuel was used in conjunction with MCNP simulations of the PNAR instrument to estimate the measurement uncertainties from (1) variation in the water boron content, (2) assembly positioning in the detector and (3) counting statistics. The estimated aggregate measurement uncertainty on the PNAR Ratio measurement is 0.008, to put this uncertainty in context, the difference in the PNAR Ratio between a fully irradiated assembly and this same assembly when fissile isotopes only absorb neutrons, but do not emit neutrons, is 0.106, a 13-sigma effect. The 1-sigma variation of 0.008 in the PNAR Ratio is estimated to correspond to a 3.2 GWd/tU change in assembly burnup.

A Study of Background Conditions for Sphinx—The Satellite-Borne Gamma-Ray Burst Polarimeter

SPHiNX is a proposed satellite-borne gamma-ray burst polarimeter operating in the energy range 50–500 keV. The mission aims to probe the fundamental mechanism responsible for gamma-ray burst prompt emission through polarisation measurements. Optimising the signal-to-background ratio for SPHiNX is an important task during the design phase. The Geant4 Monte Carlo toolkit is used in this work. From the simulation, the total background outside the South Atlantic Anomaly (SAA) is about 323 counts/s, which is dominated by the cosmic X-ray background and albedo gamma rays, which contribute ∼60% and ∼35% of the total background, respectively. The background from albedo neutrons and primary and secondary cosmic rays is negligible. The delayed background induced by the SAA-trapped protons is about 190 counts/s when SPHiNX operates in orbit for one year. The resulting total background level of ∼513 counts/s allows the polarisation of ∼50 GRBs with minimum detectable polarisation less than 30% to be determined during the two-year mission lifetime.

Observed diurnal variations in Mars Science Laboratory Dynamic Albedo of Neutrons passive mode data

The Mars Science Laboratory Dynamic Albedo of Neutrons (DAN) experiment measures the martian neutron leakage flux in order to estimate the amount of water equivalent hydrogen present in the shallow regolith. When DAN is operating in passive mode, it is sensitive to neutrons produced through the interactions of galactic cosmic rays (GCR) with the regolith and atmosphere and neutrons produced by the rover’s Multi-Mission Radioisotope Thermoelectric Generator (MMRTG). During the mission, DAN passive mode data were collected over the full diurnal cycle at the locations known as Rocknest (sols 60–100) and John Klein (sols 166–272). A weak, but unexpected, diurnal variation was observed in the neutron count rates reported at these locations. We investigate different hypotheses that could be causing these observed variations. These hypotheses are variations in subsurface temperature, atmospheric pressure, the exchange of water vapor between the atmosphere and regolith, and instrumental effects on the neutron count rates. Our investigation suggests the most likely factors contributing to the observed diurnal variations in DAN passive data are instrumental effects and time-variable preferential shielding of alpha particles, with other environmental effects only having small contributions.

Radiation Measured for Chinese Satellite SJ‐10 Space Mission

AbstractsSpace biological effects are mainly a result of space radiation particles with high linear energy transfer (LET); therefore, accurate measurement of high LET space radiation is vital. The radiation in low Earth orbits is composed mainly of high‐energy galactic cosmic rays (GCRs), solar energetic particles, particles of radiation belts, the South Atlantic Anomaly, and the albedo neutrons and protons scattered from the Earth's atmosphere. CR‐39 plastic nuclear track detectors sensitive to high LET are the best passive detectors to measure space radiation. The LET method that employs CR‐39 can measure all the radiation LET spectra and quantities. CR‐39 detectors can also record the incident directions and coordinates of GCR heavy ions that pass through both CR‐39 and biosamples, and the impact parameter, the distance between the particle's incident point and the seed's spore, can then be determined. The radiation characteristics and impact parameter of GCR heavy ions are especially beneficial for in‐depth research regarding space radiation biological effects. The payload returnable satellite SJ‐10 provided an excellent opportunity to investigate space radiation biological effects with CR‐39 detectors. The space bio‐effects experiment was successfully conducted on board the SJ‐10 satellite. This paper introduces space radiation in low Earth orbits and the LET method in radiation‐related research and presents the results of nuclear tracks and biosamples hitting distributions of GCR heavy ions, the radiation LET spectra, and the quantities measured for the SJ‐10 space mission. The SJ‐10 bio‐experiment indicated that radiation may produce significant bio‐effects.

Experimental and theoretical study of BF 3 detector response for thermal neutrons in reflecting materials

Abstract Experimental measurements of the response of BF 3 detector to a 3 Ci Am–Be neutron source for three different reflecting materials, i.e., aluminum, wood, and Perspex of varying thicknesses have been carried out. The varying contribution of wall effect to the response due to change in active volume of the detector has also been determined experimentally. Then, a Monte Carlo code has been developed for the calculation of the neutron response function of the BF 3 detector using source biasing and importance sampling. This code simulates the BF 3 detector response exposed to the neutron field in a three-dimensional source, detector, and reflecting medium configurations. The results of simulation have been compared with the corresponding experimental measurements and are found to be in good agreement. The experimental neutron albedo measurements for various values of Perspex thickness show saturating behavior, and results agree very well with the data obtained by Monte Carlo simulation.

Response assessment of a new albedo neutron dosimeter

The use of thermoluminescent dosimeters (TLDs) by personnel who work in radiation-rich environments is required by law. However, many professionals prefer to use Electronic Personal Dosimeters (EPDs), which provide dose estimation in real time. This preference may lead to a generalized use of the EPD instead of using the required TLD, as the use of both types at once can be uncomfortable and impractical. In an effort to avoid this scenario, a gamma/neutron dosimeter composed of a TLD and an EPD is being developed. In this paper, the results obtained from the studies performed in order to develop the neutron albedo dosimeter to be incorporated in the TLD[Formula: see text]EPD dosimeter are presented. Monte Carlo simulations using the state-of-the-art Monte Carlo N-Particle Transport (MCNPX) code were used to calculate the response of the albedo dosimeter. The thermal neutron detectors under consideration for use in the proposed dosimeter are the EJ-426 and the EJ-420. Both detectors employ a lithium compoundenriched to 95% [Formula: see text]Li dispersed in a ZnS:(Ag) matrix. The tomographic phantom Korean Typical Man-2 was used in the simulations to calculate the fraction of radiation backscattered by a human body in different radiation field conditions. From these results, it was concluded that both dosimeters are fit to be used as albedo dosimeters.

Measurement of electrons from albedo neutron decay and neutron density in near-Earth space

The Galaxy is filled with cosmic-ray particles, mostly protons with kinetic energies greater than hundreds of megaelectronvolts. Around Earth, trapped energetic protons, electrons and other particles circulate at altitudes from about 500 to 40,000 kilometres in the Van Allen radiation belts. Soon after these radiation belts were discovered six decades ago, it was recognized that the main source of inner-belt protons (with kinetic energies of tens to hundreds of megaelectronvolts) is cosmic-ray albedo neutron decay (CRAND). In this process, cosmic rays that reach the upper atmosphere interact with neutral atoms to produce albedo neutrons, which, being prone to β-decay, are a possible source of geomagnetically trapped protons and electrons. These protons would retain most of the kinetic energy of the neutrons, while the electrons would have lower energies, mostly less than one megaelectronvolt. The viability of CRAND as an electron source has, however, been uncertain, because measurements have shown that the electron intensity in the inner Van Allen belt can vary greatly, while the neutron-decay rate should be almost constant. Here we report measurements of relativistic electrons near the inner edge of the inner radiation belt. We demonstrate that the main source of these electrons is indeed CRAND, and that this process also contributes to electrons in the inner belt elsewhere. Furthermore, measurement of the intensity of electrons generated by CRAND provides an experimental determination of the neutron density in near-Earth space-2 × 10-9 per cubic centimetre-confirming theoretical estimates.

Results from the dynamic albedo of neutrons (DAN) passive mode experiment: Yellowknife Bay to Amargosa Valley (Sols 201–753)

The Mars Science Laboratory (Curiosity rover) Dynamic Albedo of Neutrons (DAN) experiment detects neutrons for the purpose of searching for hydrogen in the shallow subsurface of Mars. DAN has two modes of operation, active and passive. In passive mode, the instrument detects neutrons produced by Galactic Cosmic Ray interactions in the atmosphere and regolith and by the rover's Multi-Mission Radioisotope Thermoelectric Generator. DAN passive data from Yellowknife Bay to Amargosa Valley (sols 201 through 753) are presented and analyzed here. Water equivalent hydrogen (WEH) estimates from this portion of Curiosity's traverse range from 0.0 wt. % up to 15.3 wt. %. Typical uncertainties on these WEH estimates are ∼0.5 wt. % but in some cases can be as high as ∼4.0 wt. % depending on the specific circumstances of a given measurement. Here we also present a new way of reporting results from the passive mode of the experiment, the DAN passive geochemical index (DPGI). This index is sensitive to some key geochemical variations, but it does not require assumptions about the abundances of high thermal neutron absorption cross section elements, which are needed to estimate WEH. DPGI variations in this section of the traverse indicate that the shallow regolith composition is changing on both the local (∼meters) and regional (∼100 s of meters) scales. This variability is thought to be representative of the diverse composition of source regions for sediments within the crater floor. Kolmogorov-Smirnov Tests on the populations of WEH estimates and DPGI values demonstrate there are statistically significant differences between nearly all of the geologic units investigated along the rover's traverse. We also present updated previous DAN passive results from Bradbury Landing to John Klein that make use of revised DAN active mode results for calibration, however, no qualitative changes in the interpretations made in Tate et al. (2015b) are incurred.

Investigation of reflection properties of applied reflectors for thermal neutrons by considering the albedo and spectral shift

In this paper, thermal neutrons reflection coefficient has been measured experimentally for water, graphite, polyethylene, and lead reflectors at average incident angle 56∘ by using 241Am-Be neutron source (5.2 Ci) and BF3 detector. Based on obtaining experimental data from different thicknesses for four reflectors, the maximum saturation value of the thermal neutron albedo is for polyethylene reflector and the minimum value of spectral shift is for lead reflector. The best reflector is a compromise included both high albedo and low spectral shift which causes to increase the safety of reactor. The measured value for thermal neutron albedo is 0.95 ± 0.03 at about 8 cm reflector thickness. Also, there is suitable agreement achieved between the experimental values and simulation results by using MCNPX Monte Carlo code.