Heavy Absorber Research Articles

Performance Evaluation of a New Transport Operator in SCONE Monte Carlo Code

A novel transport operator, called “HELL”, has been developed and integrated into the SCONE Monte Carlo code. This alternative approach combines two commonly used tracking methods: surface-tracking and deltatracking. The unique aspect of this operator is its flexibility, allowing users to assign these tracking methods to different geometry universes according to their specific requirements. The methodology of HELL and its implementation in SCONE is presented and detailed. The performance and efficiency of the HELL have been evaluated through its application in two different cases. The first case involved a core model featuring involute surfaces, while the second case focused on a Pressurized Water Reactor (PWR) application. The results demonstrated that HELL effectively eliminates the limitations typically associated with surface-tracking in complex geometries and delta-tracking in materials with localized heavy absorbers. This makes it a valuable tool in nuclear physics simulations and computations. The HELL method can significantly reduce the calculation time required for such scenarios, and can be widely applied to Monte Carlo modelling in reactor physics.

Arsenic and Lead Determination in D&C Red No. 6 Lakes and D&C Red No. 7 Lakes Containing Barium Sulfate Using X-Ray Fluorescence Spectrometry.

Color additives requiring batch certification by the U.S. Food and Drug Administration have Code of Federal Regulations (CFR) specification limits for certain elements and are usually analyzed by x-ray fluorescence spectrometry (XRF). However, analysis of some color additives presents difficulties. An XRF method was developed for quickly determining whether barium sulfate-containing color additives certifiable as D&C Red No. 6 lakes and D&C Red No. 7 lakes meet the CFR specifications for arsenic (As) and lead (Pb). Difficulties in preparing XRF standards and analyzing As and Pb in matrices with the heavy x-ray absorber barium (Ba) were overcome by first preparing As- and Pb-fortified cellulose, then blending color additive samples with fortified and unfortified cellulose to produce XRF calibration materials. Satisfactory compensation for changes in intensity caused by Ba absorption was achieved by measuring varying concentrations of As and Pb at several concentrations of Ba. Test samples of barium sulfate-containing D&C Red No. 6 lakes and D&C Red No. 7 lakes were analyzed by the XRF method and by an inductively coupled plasma-mass spectrometry (ICP-MS) method. The ICP-MS method poses some difficulties and is time consuming. In contrast, the XRF method requires very little sample preparation, is nondestructive, uses calibrations that are stable for long periods of time, and offers acceptable determination limits (1 mg/kg As, 4 mg/kg Pb) which are less than the CFR specification limits (3 mg/kg As, 20 mg/kg Pb). The new XRF method is applicable for use in routine batch certification.

Woodcock tracking with arbitrary sampling cross section using negative weights

The paper presents a variant of the Woodcock free flight distance sampling algorithm. Instead of a majorant cross section of the whole system, an arbitrarily chosen cross section can be used for sampling the free flight distance. As the sampling cross section is permitted to be smaller than the maximum of the cross sections, the novel algorithm may cause particle weights to become negative. This technique circumvents the major drawback of conventional Woodcock sampling when a localized heavy absorber implies much more frequent path sampling than required thereby rendering the calculation ineffective. Theoretical derivation is shown for heterogeneous medium. A one dimensional analytical and numerical model is presented for basic optimization study of the free sampling parameters and an applied case illustration is shown using a GPU-based radiotherapy Monte Carlo code.

First indication of LPM effect in LHCf, an LHC experiment

The Large Hadron Collider forward (LHCf) experiment is dedicated to the measurement of very forward neutral particle production in the high energy hadron-hadron collisions at LHC. The aim of the experiment is to improve the cosmic ray air shower development models and its setup gives an important opportunity to directly measure the Landau Pomeranchunk Migdal (LPM) effect in heavy absorber. This work presents the analysis for LPM effect on data taken in 2010 and 2013 at √ s = 7 TeV and √ s NN = 5.02 TeV respectively. We study the interactions of gamma, mainly produced by π 0 decay, in one of the calorimeter pairs of LHCf. This is composed by 16 Tungsten layers as absorbers and 16 plastic scintillators for energy measurements (Arm2). We use three parameters to describe the mean shower profile with respect the photon mean energy. The results are compared with Epics MonteCarlo simulation with LPM active and inactive models, shows a first evidence of LPM effect.

Beam test results for a tungsten-cerium fluoride sampling calorimeter with wavelength-shifting fiber readout

A sampling calorimeter using cerium fluoride scintillating crystals as active material, interleaved with heavy absorber plates, and read out by wavelength-shifting (WLS) fibers is being studied as a calorimeter option for detectors at the upgraded High-Luminosity LHC (HL-LHC) collider at CERN. A prototype has been exposed to electron beams of different energies at the INFN Frascati (Italy) Beam Test Facility. This paper presents results from the studies performed on the prototype, such as signal amplitudes, light yield and energy resolution.

A Variable Partial Covering Model for the Seyfert 1 Galaxy MCG −6–30–15

Abstract We propose a simple spectral model for the Seyfert 1 Galaxy MCG $-$ 6–30–15 that can explain most of the 1–40 keV spectral variation by a change of the partial covering fraction, similar to that proposed by Miller, Turner, and Reeves (2008, A&A, 483, 437). Our spectral model is composed of three continuum components: (1) a direct power-law component, (2) a heavily absorbed power-law component by mildly ionized intervening matter, and (3) a cold-disk reflection component far from the black hole with a moderate solid-angle ($ \Omega/$ 2$ \pi$$ \simeq$ 0.3) accompanying a narrow fluorescent iron line. The first two components are affected by the surrounding thin highly ionized absorber with $ N_{\rm H}$$ \simeq$ 10$ ^{23.4}$ cm$ ^{-2}$ and log $ \xi$$ \simeq$ 3.4. The heavy absorber in the second component is fragmented into many clouds, each of which is composed of radial zones with different ionization states and different column densities, a main body ($ N_{\rm H}$$ \simeq$ 10$ ^{24.2}$ cm$ ^{-2}$ , log $ \xi$$ \simeq$ 1.6), an envelope ($ N_{\rm H}$$ \simeq$ 10$ ^{22.1}$ cm$ ^{-2}$ , log $ \xi$$ \simeq$ 1.9), and presumably a completely opaque core. Not only the intrinsic spectral shape of the X-ray source but also these parameters of the ionized absorbers are unchanged at all. The central X-ray source extends moderately, and its luminosity is not significantly variable. The observed flux and spectral variations are mostly explained by the variation of the geometrical partial covering fraction of the central source ranging from 0 (uncovered) to $ \sim\ $ 0.63 by the intervening ionized clouds in the line of sight. The ionized iron K-edge of the heavily absorbed component explains most of the seemingly broad line-like features, a well-known spectral characteristic of MCG $-$ 6–30–15. The direct component and the absorbed one are negatively correlated, and their variations cancel out each other, so that the fractional spectral variation becomes the minimum at the iron-energy band; thus, another observational characteristic of MCG $-$ 6–30–15 is explained.

Experimental studies of beta positron implantation profiles in condensed matter

AbstractThe results of the new measurements of the linear absorption coefficient for positrons emitted from 22Na and 68Ge\68Ga sources are presented. As a result, improvements were made to the well‐known Gleason et al. (G. I. Gleason et al., Nucleonics 8, 12 (1951) [1]) formula giving the value of the mass absorption coefficient. It was shown that this coefficient depended not only on the maximum energy of emitted positrons but also on the atomic number the implanted absorber and exhibited an oscillatory dependence on atomic number for heavy absorbers. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A new efficient absorption liquid to treat exhaust air loaded with toluene

Volatile organic components (VOC) in the air entail health and environmental concerns. A possibility to treat industrial polluted air loaded with VOCs is absorption. In case of hydrophobic components such as toluene, poor solubility in water requires to use a specific heavy absorbent. A detailed comparison and evaluation of different kinds of organic absorbent was undertaken in purpose of toluene absorption. Four chemical classes were tested (i) polyethylene glycols, (ii) phthalates (iii) adipates and (iv) silicon oil. Experiments were performed to check gas–liquid partitioning and viscosity. Diffusion coefficients were calculated. Results showed that di(2-ethylhexyl)adipate best suits the requirements to be used as an industrial absorbent.

Analysis and improvements of the DP N acceleration technique for the method of characteristics in unstructured meshes

Algebraic preconditioners, renumbering techniques and a two-level algebraic multigrid method have been implemented to speed up the Krylov iterations of the DP N equations used for the acceleration of the method of characteristics in unstructured meshes. These algorithms were customized to take advantage of the cell-based structure of the DP N equations. Moreover, two techniques to speed up the solution of the multigroup eigenvalue MOC equations have been implemented. A solution of the multigroup eigenvalue DP N equation has been developed to provide a first guess for the external transport iterations. Next, a multigroup DP N acceleration method has been developed to accelerate the thermal iterations. This latter development has been particularly useful because our standard multigroup rebalancing acceleration was counterproductive in the presence of heavy absorbents. All these acceleration techniques have been incorporated in the spectral code APOLLO2. Numerical examples and comparisons are given for the 6-group eigenvalue Atrium benchmark problem. Our best calculation, an initialized ILU0-preconditioned DP 1 scheme with thermal acceleration, was 7.7 times faster that the free iteration calculation, while the total number of transport iterations was divided by 17.

Neutron-diffraction study of the magnetic structure of GdB 2 C 2

There are two purposes in this study. One is to see the performance of our powder neutron diffractometer, HERMES, for a very heavy neutron absorber, GdB2C2. The other is to see the magnetic structure of GdB2C2 as a compound of the tetragonal RB2C2 family, in which antiferroquadrupolar and magnetic interactions compete. We choose GdB2C2 to clarify the purely magnetic interaction in this system because the Gd ion has no quadrupolar moment. We obtained diffraction data using reflection geometry and concluded that the magnetic interaction is antiferromagnetic in the c plane and ferromagnetic along the c axis.

Merits of using barium as a heavy absorber in major element analysis of rock samples by X-ray fluorescence: new data on ASK-1 and ASK-2 reference samples

It has been demonstrated that XRF analysis of fused discs doped with Ba instead of La can give acceptable results for major element analysis of silicate rock samples, which are comparable to those obtained from La-doped fused discs. Replicate analysis of reference samples using Ba-doped fused discs indicated an analytical precision of approximately 1% and an accuracy of better than 3% for most of the elements. Another advantage of using Ba as a heavy absorber was that it allows simultaneous determination of Na along with other major elements on the same disc. Sodium levels determined by this method are in good agreement with the results of XRF analysis using pressed powder pellets. However, with Ba-doped discs there could be some difficulty in the determination of Ti and Mn as Ba Lα1 and Lτ2 lines are in close proximity to Ti and Mn Kα lines, respectively, causing enhancement of the background signals of Ti and Mn. This can be avoided by carefully selecting suitable background angles. New major elemental analytical data are provided for the Norwegian reference samples ASK-1 (larvikite) and ASK-2 (schist) as the recommended values for these are not available in the literature.

Comparison of a rigid and a dynamic structure absorber model

Rayleigh's model for porous material is based on a rigid frame consisting of parallel tubes. In order to extend the model to consider the structure-borne sound transmitted through the skeleton of an absorbent, a model derived by Zwikker and Kosten was used. This model introduces a dynamic structure matrix while leaving the basic concept of Rayleigh's model untouched. The theoretical results show that in the case of heavy absorbers (density > 100 kg/m3) or thick absorbers (thickness > 0.5 m) the structure takes over the main contribution of the transmission. Resonance phenomena are obtained for the case of absorbers of finite thickness. The use of absorbing material in double partition walls in theory and practice shows only a minor influence of the transmission loss caused by structure borne sound. Only if very heavy or thick layers of absorbents are used the structure-borne sound transmitted through the frame may exceed the sound conducted by the enclosed air. For all other cases Rayleigh's model is sufficient to determine the transmission loss.

Application of X-Ray-Fluorescence Spectrometry to the Analysis of Ta-Nb-Sn Slags and Associated By-Products

This paper describes the development of an accurate, precise, and rapid analytical procedure using x-ray-fluorescence spectrometry for the determination of Nb, Ta, Mg, Al, Si, P, K, Ca, Ti, Mn, Fe, Zr, and Sn in a wide variety of materials resulting from the processing of Ta-Nb-Sn slags to produce Ta-Nb oxides. The method involves evaporation of all the liquids to dryness, a 1:8 fusion of the solid materials with a flux consisting of Na-Li tetraborate and Na2CO3, and the addition of La oxide as a heavy absorber. With the use of a computer program, residual matrix effects are corrected for by influence-factor calculations.

An X-ray fluorescence spectrometric method for the determination of major and minor elements in ferromanganese nodules

Sample preparation and X-ray fluorescence analytical methods are described for determining the major-and minor-element composition of ferromanganese nodules. Major elements are determined on lithium tetraborate glass beads with added La heavy absorber and minor elements are determined on wax-supported powder briquettes, with matrix corrections derived from the major-element analyses. Salt corrections are applied by determining Cl contents on separate subsamples. Standards are prepared from Specpure ® oxides and a well-characterized aluminosilicate reference standard. Samples and standards are analyzed by a fully-automated wavelength-dispersive emission spectrometer, utilizing a Rh target X-ray tube for both major and minor elements. Precision is ±4% (CV) for most elements and a little higher for low-sensitivity analytes or those in low concentration. Accuracy, from comparison with reference nodule and Fe-ore samples, is satisfactory.

Simulation of mask scattering effects in masked ion beam lithography

A new simulation program has been developed for modeling masked ion beam lithography and has been used to study the impact of mask scattering on resist profile shape. The model uses analytical calculations to find the energy deposition in the resist. The program output is the development contour in the resist for any specified time, mask, resist, or beam parameters. The program has been applied to a study of the mask membranes and absorber patterns used in masked ion beam lithography. The applications are to membrane support scattering, absorber layer scattering, tapered absorbers, and technological evaluation. The membrane scattering of the beam is found to have a minimum divergence of ≊0.3°. It is also possible to achieve inverse contrast in the ion beam mask, for thin absorbers. This same effect causes the effective bias of a tapered absorber to be approximately 75% of the taper width. Also, relatively high angled tapers can be tolerated for heavy absorbers within certain limitations. Finally, using optimistic assumptions, the channeling approach to masked ion beam lithography appears limited to a minimum feature size of about 0.25 μm.

Application of Instrumentation for Materials Analysis in Refractory Industry

Methods have been developed for analysis of alumino-silicate and magnesia-chrome materials by X-ray fluorescence by fusing the materials into a glass disc and then analyzing the components by irradiating with X-rays. Lithium tetraborate has been used for alumino-silicates, and sodium hexametaphosphate along with lithium metaborate has been used for chrome-magnesia materials. Addition of La2O3 as a heavy absorber has been eliminated in both cases by using programmes for inter-elemental corrections by the computer. Calibration lines made from available standards have been made and their standard deviation and coeficient of determinations are mentioned. To cope with the changes in refractory technology, thermal analysis equipment have been used to solve problems related to change in thermal applications. DTA and TGA have been used extensively and some specific applications have been mentioned. The use of GC, GC/MS and HPLC are also becoming common to characterize health and safety related problems.

Monte-Carlo simulation of electromagnetic cascades in dense media

An extended three-dimensional simulation of electromagnetic cascades in heavy absorbers has been carried out up to 300 GeV. The results are compared in the central region with electromagnetic cascades induced by the FNAL electron beam and the consequences on multiple Coulomb scattering are considered. At ultra-high energy (106 GeV), predictions on cascade behaviour taking the Landau-Pomeranchuk-Migdal effect into account are presented.

Development of EDXRF techniques for the quantitative multielement analysis of urban dust samples

The investigation and monitoring of suspended particulate matter in air require accurate and sensitive multielement analysis of large numbers of samples. In the work described, airborne particles and settled urban dusts were examined by energy dispersive X-ray fluorescence spectrometry with secondary-target excitation. The practical requirements of trace-element determinations in dusts are reasonably satisfied by two techniques. Deposition of fine particles (under 3.5μm) on Nucleopore membrane filters provides thin-film samples, for which absorption and particle-size effects are usually negligible. Calibration is achieved by sputtering of certified NBS standard glasses onto membrane filters. In the destructive “fusion and direct solidification” technique, sample inhomogeneities and particle-size effects are eliminated by fusing the sample with lithium borate in a Pt/Au alloy crucible. La2O3 or WO3, added as heavy absorbers, can reduce the interelement-effects of the thick specimens to a certain extent. A newly developed computer program, based on a modified mathematical expression for the intensity, compensates for absorption and secondary fluorescence effects. It is demonstrated that for some trace elements the background can be easily predicted as a linear function of the incomplete charge-collection of the Si(Li) detector. An intermethod comparison with atomic-absorption results is presented; the results are verified with the NBS Fly Ash standard reference material.

Some Applications of a Computer-Controlled X-Ray Spectrometer in a Steel Research Laboratory

The U. S. Steel Research x-ray spectrometric laboratory performs between 7,000 and 10,000 analytical determinations each month for alloying elements in all types of steels and raw -materials. The spectrometer is automatically controlled by a DEC PDP 8/1 minicomputer utilizing vari ations of software packages provided by Siemens Corporation. As many as 256 individual analytical measurements can be sequentially performed. The minimal interelemental effects encountered in low-alloy steel analyses are corrected in a separate program written in FOCAL language. Correction coefficients for the program were established by multiple linear regression analyses.Stainless and multialloy steels are analyzed with a two-part control and correction program. The control program controls all functions of the spectrometer automatically and stores parabolic calibration coefficients. Following a sequential determination of the alloying elements control is switched to a correction program written in FOCAL. The correction program prints a tabular listing of the elements determined, followed by a listing of the corrected concentrations of elements adjusted for interelemental effects. Orthogonal polynomial analyses were performed to determine σ values for all constituents determined.For analysis of raw materials, the samples are fused prior to analysis by use of a flux and heavy absorber technique that essentially eliminates interelement effects and permits linear calibrations up to 100 percent. Samples are ground and pelletized after fusion for better reproducibility. Single sets of calibration standards are used regardless of raw materials mineralogical history. Synthetic standards can be produced for ranges where no calibration standards exist.

Note on the use of a heavy absorber for matrix control in quantitative modal analysis by X-ray diffraction

Note on the use of a heavy absorber for matrix control in quantitative modal analysis by X-ray diffraction