Differential Albedo Research Articles

Use of Landsat data to determination of the dynamics of land-use change and differential albedo

Use of Landsat data to determination of the dynamics of land-use change and differential albedo

The amplitude and maximum of daily pavement surface temperature increase linearly with solar absorption

Pavement surface temperature is critical to the pavement design and to the development of cool pavements. There have been numerical models and empirical models to predict the pavement surface temperature, but the theoretical correlation about critical parameters such as solar irradiation, albedo, and thermal inertia is unclear. This study presents a theoretical model to predict the pavement surface temperature and validates the model against experimental data. Eight concrete samples were prepared and painted with differential albedo to investigate the influence of the albedo on the pavement surface temperature. The samples were exposed in an open space for 10 continuous days and their temperatures were recorded. It is found that the amplitude (one half of maximum minus minimum) and maximum of the daily pavement surface temperature increase linearly with the pavement surface solar absorption and the daily zenith solar irradiation.

Shading boards with smaller lower-surface thermal emissivity perform better cooling effect

Roadway embankments over permafrost stratum are susceptible to thawing damage. Installing shading boards on the embankment side slope reflects solar irradiance back to the sky and thus has been deemed as a roadbed cooling technique. Research on the cooling effect of shading boards has centered on the temperature evolution of the roadbed under the board and on the optimum design of the board. Few researches, however, have been dedicated to understand the heat balance between the board and the embankment and to adapt the board's thermal properties to maximize the cooling effect. This study models the heat flux balance between the board and the embankment side slope and validates the model with measured data logged from an in situ shading board experiment. The validation of the model reveals that shading boards with smaller lower-surface thermal emissivity perform stronger cooling effect. Further outdoor experiments are expected to paint the shading board upper surface with differential albedo to understand the influence of board albedo on the cooling effect.

Spatial distribution of reflected gamma rays by Monte Carlo simulation

In nuclear facilities, the reflection of gamma rays of the walls and metals constitutes an unknown origin of radiation. These reflected gamma rays must be estimated and determined. This study concerns reflected gamma rays on metal slabs. We evaluated the spatial distribution of the reflected gamma rays spectra by using the Monte Carlo method. An appropriate estimator for the double differential albedo is used to determine the energy spectra and the angular distribution of reflected gamma rays by slabs of iron and aluminium. We took into the account the principal interactions of gamma rays with matter: photoelectric, coherent scattering (Rayleigh), incoherent scattering (Compton) and pair creation. The Klein–Nishina differential cross section was used to select direction and energy of scattered photons after each Compton scattering. The obtained spectra show peaks at 0.511∗MeV for higher source energy. The Results are in good agreement with those obtained by the TRIPOLI code [J.C. Nimal et al., TRIPOLI02: Programme de Monte Carlo Polycinśetique à Trois dimensions, CEA Rapport, Commissariat à l’Energie Atomique. [1]].

Simulation of medical electron linac bremsstrahlung beam transport in typical shielding materials

The Monte Carlo N-particle code MCNP version 4C3 was used to investigate the backscattering and transmission of high-energy photons in concrete, iron and lead at deep penetration. A typical bremsstrahlung beam from a 24 MV linac was used, and the transmission up to 15 mean-free paths was studied. Broad beam slab geometry was used. Estimates of the transmission in terms of absorbed dose to tissue ratio and air kerma ratio were performed for the primary and secondary components of the transmitted beam in the three materials. The tissue dose and air kerma buildup factors were calculated and fitted to Berger's equation. Finally, the differential dose albedo values for common reflected angles were determined.

Calculation of Double Energy Angle Differential Neutron Albedos for Radiation Shielding Applications

Void radiation shielding problems can be dealt with albedo concept which is an alternative to the complex bringing into operation of the “exact” transport method calculations (SN, Monte Carlo). Up to here, differential albedos are used for single reflections from walls in the NARCISSE-3 propagation albedo code developped at CEA and used for project calculations. For taking into account the neutron multiple reflections on lacunar medium walls, double energy-angle differential albedos are needed. TRIPOLI-4 neutral particle transport Monte Carlo code in three dimensional geometries, has been chosen to implement a double differential albedo calculus routine and therefore to generate albedo data for different kinds of medium. The surfacic estimator, which could be used, is not enough efficient because all neutrons do not contribute to the result. A new estimator is carried out. At each collision site, during the neutron history simulation, it allows to compute the probability of the neutron to go through the medium and to come through the reflection surface in the direction and at the energy considered. This estimator is about hundred times more efficient than the surfacic estimator.

Gamma Ray Albedo Data Generated by the Invariant Embedding Method

The energy-and-angle dependent doubly differential γ-ray albedos for homogeneous semi-infinite medium have been calculated for water, ordinary concrete, soil, heavy concrete, iron, tin and lead. The procedure of calculation employed in the present paper is the invariant embedding method which is being developed to solve neutral particle transport problems in homogeneous one dimensional medium. The calculated γ-ray albedos are stored in the data base. One can easily obtain from this data base the various kinds of albedos (number, dose, energy, etc.) with a simple interface program. The accuracy of the calculated γ-ray albedos is ascertained by comparing with the Monte Carlo calculations (MCNP4A and EGS4).

Data for the Chilton-Huddleston Photon-Albedo Approximations

Empirical parameters for two differential gamma-ray albedo formulas, originally proposed by Chilton and Huddleston, are presented for water, concrete, iron, and lead for 12 photon energies ranging from 0.1 to 10 MeV and for reflected doses based on the ambient dose equivalent, the effective dose equivalent, and the exposure. The parameters were obtained by fitting the albedo formulas to MCNP-calculated albedo values over the complete ranges of incident and reflected directions.

Determination of the Double Angular and Energy Differential Gamma-Ray Albedo for Iron Material by Using the Monte Carlo Method

The Monte Carlo method can be used to compute the gamma-ray backscattering albedo. This method was used by Raso to compute the angular differential albedo. Raso’s results have been used by Chilton ...

Measurements of Backscattered Neutrons and Secondary Gamma-Rays from Stainless Steel and Limestone Concrete for 14-MeV Source Neutrons

Simultaneous measurements of fast neutron and prompt γ-ray albedos were performed by nominal 14-MeV neutrons for the type 304 SS and the limestone concrete. Both neutrons and γ-rays were detected by an NE-213 scintillator with the aid of the n-γ discrimination circuit. The time-of-flight method was used to obtain neutron spectra, whereas the unfolding method was applied to analyze γ-ray pulse-height data of the scintillator. The measured data were compared with those calculated by the MCNP code with the ENDF/B-IV data. The calculation reproduced the measured secondary γ-ray differential albedo data well for both materials. For neutrons, apparent disagreement was seen in the albedo data of the 304 SS between the calculation and the experiment. This was due to some inaccuracies in the chromium cross sections in the ENDF/B-IV. The agreement of the neutron data was better for the limestone concrete than for the 304 SS.

Measurements of backscattered neutrons and secondary gamma-rays from stainless steel and limestone concrete for 14-MeV source neutrons.

Simultaneous measurements of fast neutron and prompt γ-ray albedos were performed by nominal 14-MeV neutrons for the type 304 SS and the limestone concrete. Both neutrons and γ-rays were detected by an NE-213 scintillator with the aid of the n-γ discrimination circuit. The time-of-flight method was used to obtain neutron spectra, whereas the unfolding method was applied to analyze γ-ray pulse-height data of the scintillator. The measured data were compared with those calculated by the MCNP code with the ENDF/B-IV data. The calculation reproduced the measured secondary γ-ray differential albedo data well for both materials. For neutrons, apparent disagreement was seen in the albedo data of the 304 SS between the calculation and the experiment. This was due to some inaccuracies in the chromium cross sections in the ENDF/B-IV. The agreement of the neutron data was better for the limestone concrete than for the 304 SS.

Formation of x-ray spectra in close binary systems. Reflection effects

The reflection of the x rays emitted by a compact source from the atmosphere of a normal star is considered. An equation that describes Compton scattering by electrons is derived. Analytic expressions are obtained for the differential, integrated, and spherical albedos, and also for the spectrum of the reflected radiation. The influence of the corona of the normal star on the spectrum of the reflected radiation is investigated.

Applicability of Neutron-Gamma-Ray-Coupled Albedo Monte Carlo Method to Streaming Analysis in Fusion Reactors

The neutron-gamma-ray-coupled albedo Monte Carlo (AMC) method has been developed and implemented in MORSE-I. The energy- and angle-dependent differential albedo data, which include secondary gamma ...

New Efficient Albedo Monte Carlo Method for Neutron Streaming Analyses

An efficient albedo Monte Carlo method newly developed has been studied by analyzing two types of experiments on neutron streaming. The method is characterized by employing the energy-angle dependent doubly differential albedos for slab, which can be calculated in a short computer time with a one-dimensional transport theory, such as the Sn method and more efficient invariant imbedding method. This paper describes the features of the present albedo Monte Carlo method, including fundamental formulas. In the analyses of the neutron streaming experiments, the calculated results agreed with the measured data within a factor of 2 for a benchmark experiment at the YAYOI reactor and within a factor of 3 for an SNR sodium duct mock-up experiment. It is concluded that the present albedo Monte Carlo method is practical and applicable to the reactor shielding analysis concerning radiation streaming.

Calculation of neutron albedos for slab with invariant imbedding method.

The albedo data are important for use in solving the radiation streaming problem with albedo techniques, such as albedo Monte Carlo and albedo-Sn methods. This paper describes a method for calculating the energy-angle dependent doubly differential albedos for slab geomery with one-dimensional transport theory, based on the invariant imbedding method as well as the Sn method. Neutron albedo data calculated by the invariant imbedding method, are compared with those calculated by the Sn method and with the experimental data. It is found that the invariant imbedding method can be used to calculate the albedo data for a semi-infinitely thick slab several dozens of times faster than when using the Sn method. The calculated results have excellent agreement with the measured values.

New efficient albedo Monte Carlo method for neutron streaming analyses.

An efficient albedo Monte Carlo method newly developed has been studied by analyzing two types of experiments on neutron streaming. The method is characterized by employing the energy-angle dependent doubly differential albedos for slab, which can be calculated in a short computer time with a one-dimensional transport theory, such as the Sn method and more efficient invariant imbedding method. This paper describes the features of the present albedo Monte Carlo method, including fundamental formulas. In the analyses of the neutron streaming experiments, the calculated results agreed with the measured data within a factor of 2 for a benchmark experiment at the YAYOI reactor and within a factor of 3 for an SNR sodium duct mock-up experiment. It is concluded that the present albedo Monte Carlo method is practical and applicable to the reactor shielding analysis concerning radiation streaming.

Probing of the earth's surface and the atmosphere with an airborne laser spectrometer

Differential albedo and absorption measurements indicate the feasibility of remote detection of minerals, soil moisture, oil-spills and atmospheric trace gases. Laboratory measurements and results from several flight campaigns with a coherent CW CO 2 laser sensor are reported.

Applicability of albedo-Sn transport method to analysis of radiation shielding problem.

Albedo-Sn method was developed to predict the angular flux near the coupling boundary in the bootstrap method, using the energy-and-angle dependent double differential albedo boundary condition. In order to verify the applicability of the method to the reactor shielding design, two types of shielding problem have been analyzed. First, the neutron skyshine dose rates measured at the YAYOI reactor in University of Tokyo are predicted within an accuracy of 20%. It is also found that the neutron spectrum in the air-over-ground is much affected by albedo reflection from the ground and is reproduced well by the albedo-Sn method. Second, as for the neutron streaming through a sodium pipe chase-way, the albedo-Sn calculation saves a computer time and gives the results which agree with those by the reference Sn calculation.

Development of albedo-Sn transport method to analyze radiation shielding problem.

In order to reduce the error and the computer time of the Sn calculation, the albedo-Sn method has been developed considering the albedo boundary treated with the energy-and-angle dependent doubly differential albedos which can be calculated with the one-dimensional transport theory. In this paper, fundamental formulas are described which express the albedo boundary source and flux convergence acceleration with pointwise rebalancing technique. Test calculations were performed for the model which consists of sodium region surrounded by concrete shield. As a result, the present albedo-Sn method could evaluate the neutron flux near the albedo boundary with a good accuracy and with less computer time. The width of overlapping area required for the Sn calculation with the boot-strap method is also discussed.

Application of proportional response photon counter in the measurement of the energy albedo of backscattered photons

A proportional response photon counter the detection efficiency of which is proportional to the energy of the interacting photon has been used in the measurement of the differential energy albedo of backscattered photons. The application of this counter eliminated the need to use tedious efficiency corrections such as required when conventional counting systems are used. Moreover, the results obtained are more accurate than the results existing in the literature. The differential albedo has been measured for five different elements (aluminium, concrete, iron, tin and lead) for 662 KeV photons at angular steps of 10°. The total albedo has been calculated from the measured differential albedo by numerical integration. The present values, when compared with the theoretical and available experimental results, show better agreement with the theoretical values.